1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561 1562 1563 1564 1565 1566 1567 1568 1569 1570 1571 1572 1573 1574 1575 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620 1621 1622 1623 1624 1625 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636 1637 1638 1639 1640 1641 1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653 1654 1655 1656 1657 1658 1659 1660 1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695 1696 1697 1698 1699 1700 1701 1702 1703 1704 1705 1706 1707 1708 1709 1710 1711 1712 1713 1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 1725 1726 1727 1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759 1760 1761 1762 1763 1764 1765 1766 1767 1768 1769 1770 1771 1772 1773 1774 1775 1776 1777 1778 1779 1780 1781 1782 1783 1784 1785 1786 1787 1788 1789 1790 1791 1792 1793 1794 1795 1796 1797 1798 1799 1800 1801 1802 1803 1804 1805 1806 1807 1808 1809 1810 1811 1812 1813 1814 1815 1816 1817 1818 1819 1820 1821 1822 1823 1824 1825 1826 1827 1828 1829 1830 1831 1832 1833 1834 1835 1836 1837 1838 1839 1840 1841 1842 1843 1844 1845 1846 1847 1848 1849 1850 1851 1852 1853 1854 1855 1856 1857 1858 1859 1860 1861 1862 1863 1864 1865 1866 1867 1868 1869 1870 1871 1872 1873 1874 1875 1876 1877 1878 1879 1880 1881 1882 1883 1884 1885 1886 1887 1888 1889 1890 1891 1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034 2035 2036 2037 2038 2039 2040 2041 2042 2043 2044 2045 2046 2047 2048 2049 2050 2051 2052 2053 2054 2055 2056 2057 2058 2059 2060 2061 2062 2063 2064 2065 2066 2067 2068 2069 2070 2071 2072 2073 2074 2075 2076 2077 2078 2079 2080 2081 2082 2083 2084 2085 2086 2087 2088 2089 2090 2091 2092 2093 2094 2095 2096 2097 2098 2099 2100 2101 2102 2103 2104 2105 2106 2107 2108 2109 2110 2111 2112 2113 2114 2115 2116 2117 2118 2119 2120 2121 2122 2123 2124 2125 2126 2127 2128 2129 2130 2131 2132 2133 2134 2135 2136 2137 2138 2139 2140 2141 2142 2143 2144 2145 2146 2147 2148 2149 2150 2151 2152 2153 2154 2155 2156 2157 2158 2159 2160 2161 2162 2163 2164 2165 2166 2167 2168 2169 2170 2171 2172 2173 2174 2175 2176 2177 2178 2179 2180 2181 2182 2183 2184 2185 2186 2187 2188 2189 2190 2191 2192 2193 2194 2195 2196 2197 2198 2199 2200 2201 2202 2203 2204 2205 2206 2207 2208 2209 2210 2211 2212 2213 2214 2215 2216 2217 2218 2219 2220 2221 2222 2223 2224 2225 2226 2227 2228 2229 2230 2231 2232 2233 2234 2235 2236 2237 2238 2239 2240 2241 2242 2243 2244 2245 2246 2247 2248 2249 2250 2251 2252 2253 2254 2255 2256 2257 2258 2259 2260 2261 2262 2263 2264 2265 2266 2267 2268 2269 2270 2271 2272 2273 2274 2275 2276 2277 2278 2279 2280 2281 2282 2283 2284 2285 2286 2287 2288 2289 2290 2291 2292 2293 2294 2295 2296 2297 2298 2299 2300 2301 2302 2303 2304 2305 2306 2307 2308 2309 2310 2311 2312 2313 2314 2315 2316 2317 2318 2319 2320 2321 2322 2323 2324 2325 2326 2327 2328 2329 2330 2331 2332 2333 2334 2335 2336 2337 2338 2339 2340 2341 2342 2343 2344 2345 2346 2347 2348 2349 2350 2351 2352 2353 2354 2355 2356 2357 2358 2359 2360 2361 2362 2363 2364 2365 2366 2367 2368 2369 2370 2371 2372 2373 2374 2375 2376 2377 2378 2379 2380 2381 2382 2383 2384 2385 2386 2387 2388 2389 2390 2391 2392 2393 2394 2395 2396 2397 2398 2399 2400 2401 2402 2403 2404 2405 2406 2407 2408 2409 2410 2411 2412 2413 2414 2415 2416 2417 2418 2419 2420 2421 2422 2423 2424 2425 2426 2427 2428 2429 2430 2431 2432 2433 2434 2435 2436 2437 2438 2439 2440 2441 2442 2443 2444 2445 2446 2447 2448 2449 2450 2451 2452 2453 2454 2455 2456 2457 2458 2459 2460 2461 2462 2463 2464 2465 2466 2467 2468 2469 2470 2471 2472 2473 2474 2475 2476 2477 2478 2479 2480 2481 2482 2483 2484 2485 2486 2487 2488 2489 2490 2491 2492 2493 2494 2495 2496 2497 2498 2499 2500 2501 2502 2503 2504 2505 2506 2507 2508 2509 2510 2511 2512 2513 2514 2515 2516 2517 2518 2519 2520 2521 2522 2523 2524 2525 2526 2527 2528 2529 2530 2531 2532 2533 2534 2535 2536 2537 2538 2539 2540 2541 2542 2543 2544 2545 2546 2547 2548 2549 2550 2551 2552 2553 2554 2555 2556 2557 2558 2559 2560 2561 2562 2563 2564 2565 2566 2567 2568 2569 2570 2571 2572 2573 2574 2575 2576 2577 2578 2579 2580 2581 2582 2583 2584 2585 2586 2587 2588 2589 2590 2591 2592 2593 2594 2595 2596 2597 2598 2599 2600 2601 2602 2603 2604 2605 2606 2607 2608 2609 2610 2611 2612 2613 2614 2615 2616 2617 2618 2619 2620 2621 2622 2623 2624 2625 2626 2627 2628 2629 2630 2631 2632 2633 2634 2635 2636 2637 2638 2639 2640 2641 2642 2643 2644 2645 2646 2647 2648 2649 2650 2651 2652 2653 2654 2655 2656 2657 2658 2659 2660 2661 2662 2663 2664 2665 2666 2667 2668 2669 2670 2671 2672 2673 2674 2675 2676 2677 2678 2679 2680 2681 2682 2683 2684 2685 2686 2687 2688 2689 2690 2691 2692 2693 2694 2695 2696 2697 2698 2699 2700 2701 2702 2703 2704 2705 2706 2707 2708 2709 2710 2711 2712 2713 2714 2715 2716 2717 2718 2719 2720 2721 2722 2723 2724 2725 2726 2727 2728 2729 2730 2731 2732 2733 2734 2735 2736 2737 2738 2739 2740 2741 2742 2743 2744 2745 2746 2747 2748 2749 2750 2751 2752 2753 2754 2755 2756 2757 2758 2759 2760 2761 2762 2763 2764 2765 2766 2767 2768 2769 2770 2771 2772 2773 2774 2775 2776 2777 2778 2779 2780 2781 2782 2783 2784 2785 2786 2787 2788 2789 2790 2791 2792 2793 2794 2795 2796 2797 2798 2799 2800 2801 2802 2803 2804 2805 2806 2807 2808 2809 2810 2811 2812 2813 2814 2815 2816 2817 2818 2819 2820 2821 2822 2823 2824 2825 2826 2827 2828 2829 2830 2831 2832 2833 2834 2835 2836 2837 2838 2839 2840 2841 2842 2843 2844 2845 2846 2847 2848 2849 2850 2851 2852 2853 2854 2855 2856 2857 2858 2859 2860 2861 2862 2863 2864 2865 2866 2867 2868 2869 2870 2871 2872 2873 2874 2875 2876 2877 2878 2879 2880 2881 2882 2883 2884 2885 2886 2887 2888 2889 2890 2891 2892 2893 2894 2895 2896 2897 2898 2899 2900 2901 2902 2903 2904 2905 2906 2907 2908 2909 2910 2911 2912 2913 2914 2915 2916 2917 2918 2919 2920 2921 2922 2923 2924 2925 2926 2927 2928 2929 2930 2931 2932 2933 2934 2935 2936 2937 2938 2939 2940 2941 2942 2943 2944 2945 2946 2947 2948 2949 2950 2951 2952 2953 2954 2955 2956 2957 2958 2959 2960 2961 2962 2963 2964 2965 2966 2967 2968 2969 2970 2971 2972 2973 2974 2975 2976 2977 2978 2979 2980 2981 2982 2983 2984 2985 2986 2987 2988 2989 2990 2991 2992 2993 2994 2995 2996 2997 2998 2999 3000 3001 3002 3003 3004 3005 3006 3007 3008 3009 3010 3011 3012 3013 3014 3015 3016 3017 3018 3019 3020 3021 3022 3023 3024 3025 3026 3027 3028 3029 3030 3031 3032 3033 3034 3035 3036 3037 3038 3039 3040 3041 3042 3043 3044 3045 3046 3047 3048 3049 3050 3051 3052 3053 3054 3055 3056 3057 3058 3059 3060 3061 3062 3063 3064 3065 3066 3067 3068 3069 3070 3071 3072 3073 3074 3075 3076 3077 3078 3079 3080 3081 3082 3083 3084 3085 3086 3087 3088 3089 3090 3091 3092 3093 3094 3095 3096 3097 3098 3099 3100 3101 3102 3103 3104 3105 3106 3107 3108 3109 3110 3111 3112 3113 3114 3115 3116 3117 3118 3119 3120 3121 3122 3123 3124 3125 3126 3127 3128 3129 3130 3131 3132 3133 3134 3135 3136 3137 3138 3139 3140 3141 3142 3143 3144 3145 3146 3147 3148 3149 3150 3151 3152 3153 3154 3155 3156 3157 3158 3159 3160 3161 3162 3163 3164 3165 3166 3167 3168 3169 3170 3171 3172 3173 3174 3175 3176 3177 3178 3179 3180 3181 3182 3183 3184 3185 3186 3187 3188 3189 3190 3191 3192 3193 3194 3195 3196 3197 3198 3199 3200 3201 3202 3203 3204 3205 3206 3207 3208 3209 3210 3211 3212 3213 3214 3215 3216 3217 3218 3219 3220 3221 3222 3223 3224 3225 3226 3227 3228 3229 3230 3231 3232 3233 3234 3235 3236 3237 3238 3239 3240 3241 3242 3243 3244 3245 3246 3247 3248 3249 3250 3251 3252 3253 3254 3255 3256 3257 3258 3259 3260 3261 3262 3263 3264 3265 3266 3267 3268 3269 3270 3271 3272 3273 3274 3275 3276 3277 3278 3279 3280 3281 3282 3283 3284 3285 3286 3287 3288 3289 3290 3291 3292 3293 3294 3295 3296 3297 3298 3299 3300 3301 3302 3303 3304 3305 3306 3307 3308 3309 3310 3311 3312 3313 3314 3315 3316 3317 3318 3319 3320 3321 3322 3323 3324 3325 3326 3327 3328 3329 3330 3331 3332 3333 3334 3335 3336 3337 3338 3339 3340 3341 3342 3343 3344 3345 3346 3347 3348 3349 3350 3351 3352 3353 3354 3355 3356 3357 3358 3359 3360 3361 3362 3363 3364 3365 3366 3367 3368 3369 3370 3371 3372 3373 3374 3375 3376 3377 3378 3379 3380 3381 3382 3383 3384 3385 3386 3387 3388 3389 3390 3391 3392 3393 3394 3395 3396 3397 3398 3399 3400 3401 3402 3403 3404 3405 3406 3407 3408 3409 3410 3411 3412 3413 3414 3415 3416 3417 3418 3419 3420 3421 3422 3423 3424 3425 3426 3427 3428 3429 3430 3431 3432 3433 3434 3435 3436 3437 3438 3439 3440 3441 3442 3443 3444 3445 3446 3447 3448 3449 3450 3451 3452 3453 3454 3455 3456 3457 3458 3459 3460 3461 3462 3463 3464 3465 3466 3467 3468 3469 3470 3471 3472 3473 3474 3475 3476 3477 3478 3479 3480 3481 3482 3483 3484 3485 3486 3487 3488 3489 3490 3491 3492 3493 3494 3495 3496 3497 3498 3499 3500 3501 3502 3503 3504 3505 3506 3507 3508 3509 3510 3511 3512 3513 3514 3515 3516 3517 3518 3519 3520 3521 3522 3523 3524 3525 3526 3527 3528 3529 3530 3531 3532 3533 3534 3535 3536 3537 3538 3539 3540 3541 3542 3543 3544 3545 3546 3547 3548 3549 3550 3551 3552 3553 3554 3555 3556 3557 3558 3559 3560 3561 3562 3563 3564 3565 3566 3567 3568 3569 3570 3571 3572 3573 3574 3575 3576 3577 3578 3579 3580 3581 3582 3583 3584 3585 3586 3587 3588 3589 3590 3591 3592 3593 3594 3595 3596 3597 3598 3599 3600 3601 3602 3603 3604 3605 3606 3607 3608 3609 3610 3611 3612 3613 3614 3615 3616 3617 3618 3619 3620 3621 3622 3623 3624 3625 3626 3627 3628 3629 3630 3631 3632 3633 3634 3635 3636 3637 3638 3639 3640 3641 3642 3643 3644 3645 3646 3647 3648 3649 3650 3651 3652 3653 3654 3655 3656 3657 3658 3659 3660 3661 3662 3663 3664 3665 3666 3667 3668 3669 3670 3671 3672 3673 3674 3675 3676 3677 3678 3679 3680 3681 3682 3683 3684 3685 3686 3687 3688 3689 3690 3691 3692 3693 3694 3695 3696 3697 3698 3699 3700 3701 3702 3703 3704 3705 3706 3707 3708 3709 3710 3711 3712 3713 3714 3715 3716 3717 3718 3719 3720 3721 3722 3723 3724 3725 3726 3727 3728 3729 3730 3731 3732 3733 3734 3735 3736 3737 3738 3739 3740 3741 3742 3743 3744 3745 3746 3747 3748 3749 3750 3751 3752 3753 3754 3755 3756 3757 3758 3759 3760 3761 3762 3763 3764 3765 3766 3767 3768 3769 3770 3771 3772 3773 3774 3775 3776 3777 3778 3779 3780 3781 3782 3783 3784 3785 3786 3787 3788 3789 3790 3791 3792 3793 3794 3795 3796 3797 3798 3799 3800 3801 3802 3803 3804 3805 3806 3807 3808 3809 3810 3811
|
Network Working Group W. Edmond
Request for Comments: 1221 BBN
Updates: RFC 907 April 1991
Host Access Protocol (HAP) Specification - Version 2
Status of this Memo
This memo describes the Host Access Protocol implemented in the
Terrestrial Wideband Network (TWBNET). It obsoletes most but not all
of RFC 907. This memo provides information for the Internet
community. It does not specify an Internet standard. Distribution
of this memo is unlimited.
Preface
This memo specifies the Host Access Protocol (HAP). HAP is a Network
layer (OSI Layer 3 lower) access protocol that was first implemented
about a decade ago for the DARPA/DCA sponsored Wideband Packet
Satellite Network (WBNET), the precursor of the current Terrestrial
Wideband Network (TWBNET). This version of the specification
obsoletes references [1] and [2] in addition to most of RFC 907.
HAP is a developmental protocol, and will be revised as new
capabilities are added and unused features are eliminated or revised.
One reason that HAP is being revised now is that, unlike the original
WBNET's satellite channel, the TWBNET's T1 fiber links are not a
broadcast medium. This has prompted some changes to the protocol
that will permit greater efficiency in a mesh topology network.
Another cause of revision is the need to make HAP able to support a
variety of OSI layer 3 upper protocols, such as DECNET Phase V, ST,
and CLNP, where before only Internet Protocol (IP) was used.
Appendix B describes how backward compatibility with the older IP-
only version of HAP is achieved. A third cause of protocol changes
is the desire to simplify interaction between ST2 protocol (RFC 1190)
agents and the TWBNET. This has mainly affected the way certain
setup errors are handled. These changes are expected to be backward
compatible. Appendix A describes two capabilities that may be added
to HAP in the future.
One of the protocol enhancements, "Group Streams", described in
reference [2] has been eliminated. There are no known applications
that use the feature. As described in Appendix A, a new mechanism,
to be called "shared streams", capable of providing equivalent
capabilities will be implemented if needed. Changes in [2] that have
been retained include various query/reply control messages that
permit a host to determine what resources it owns (mostly useful for
Edmond [Page 1]
RFC 1221 HAP2 April 1991
cleanup following a host reboot or crash).
This document assumes the reader is familiar with DoD internetworking
terminology.
1. Introduction
The Host Access Protocol (HAP) is a network layer protocol (as is
X.25). ("Network layer" here means ISO layer 3 lower, the protocol
layer below the DoD Internet Protocol (IP) layer [3] and above any
link layer protocol.) HAP defines the different types of host-to-
network control messages and host-to-host data messages that may be
exchanged over the access link connecting a host and the network
packet switch node. The protocol establishes formats for these
messages, and describes procedures for determining when each type of
message should be transmitted and what it means when one is received.
HAP has been implemented in the wide-area network called the
Terrestrial Wideband Network (TWBNET) [5] and in the routers and
other hosts that connect to TWBNET. The packet switch nodes that
compose the TWBNET are called Wideband Packet Switches (WPS).
Both the precursor to HAP, the Host/SATNET Protocol [6], used in the
Atlantic Packet Satellite Network (SATNET) and the Mobile Access
Terminal Network (MATNET [7]), and HAP, used in the original Wideband
Satellite Network (WBNET) [8], were originally designed to provide
efficient access to the single satellite channel each network used to
connect all sites. The HAP protocol designers reflected some of the
peculiarities of the single satellite channel environment in the HAP
protocol itself. The current Terrestrial Wideband Network (TWBNET)
utilizes T1-speed fiber connections between sites. Future networks
and TWBNET may use a combination of terrestrial connections and
satellite connections, and may have more than one of each. The HAP
protocol has been changed to accommodate these extensions.
Section 2 presents an overview of HAP. Details of HAP formats and
message exchange procedures are contained in Sections 3 through 10.
Further explanation of some of the topics addressed in this HAP
specification can be found in reference [1].
Any protocol employed to provide sufficiently reliable message
exchange over the Host-WPS link is assumed to be transparent to the
protocol defined in this document. Examples of such link-level
protocols are ARPANET 1822 local and distant host [9], ARPANET VDH
protocol [9], and HDLC.
Edmond [Page 2]
RFC 1221 HAP2 April 1991
2. Overview
HAP can be characterized as a full duplex, nonreliable protocol with
an optional flow control mechanism. HAP messages flow simultaneously
in both directions between the WPS and the host. Transmission is
nonreliable in the sense that the protocol does not provide any
guarantee of error-free sequenced delivery. If error-free delivery
on the host's access link is required, it must be provided by the
link layer protocol below HAP. (Use of link layer protocols for this
purpose is not within the scope of this document.) HAP's flow
control mechanism operates independently in each direction, but the
choice to enable flow control or not applies to both directions
together.
HAP supports host-to-host communication in two modes corresponding to
the two types of HAP data messages, datagram messages and stream
messages. Each type of message can be up to 2048 octets in length.
The basic transmission service in the network is datagram service.
Datagrams are variable length, unsequenced, independent, and delivery
is not guaranteed. The HAP header of each datagram determines the
processing of the message.
On this datagram service base a "stream" service is built. Stream
service provides network bandwidth guarantees, but requires explicit
setup and teardown operations to allocate and deallocate network
resources. Stream traffic is best suited for continuous media
traffic, but may also be used to obtain the lowest possible network
delay. Host streams are established by a setup message exchange
between the host and the network prior to the commencement of data
flow. Although established host streams can have their
characteristics modified by subsequent setup messages while they are
in use, the fixed allocation properties of streams relative to
datagrams impose rather strict requirements on the source of the
traffic using the stream. Stream traffic arrivals must match the
stream allocation both in interarrival time and message size if
reasonable efficiency is to be achieved. The characteristics and use
of datagrams and streams are described in detail in Sections 3 and 4
of this document.
Both datagram and stream transmission in the network use logical
addressing. Each host on the network is assigned a permanent 16-bit
logical address which is independent of the physical port on the WPS
to which it is attached. These 16-bit logical addresses are present
in all Host-to-WPS and WPS-to-Host data messages.
HAP supports multicast addressing via "groups". Multicast addressing
is provided primarily to support the multi-destination delivery
required for conferencing applications. Group addresses are
Edmond [Page 3]
RFC 1221 HAP2 April 1991
dynamically created and deleted by the use of setup messages
exchanged between a host and the WPS. Membership in a group may be
any arbitrary subset of the network hosts. A message addressed to a
group address is delivered to all hosts that are members of that
group, except the sender. Once a multicast address has been created,
any member host may use that address, not just the creator.
Although HAP does not guarantee error-free delivery, error control is
an important aspect of the protocol design. HAP error control is
concerned with both local transfers between a host and its local WPS
and transfers through the network to the destination(s). The WPS
offers users a choice of network error protection options based on
the network's ability to selectively send messages over its
transmission media at different forward error correction (FEC) rates.
These FEC options are referred to as reliability levels. Four
reliability levels (low, medium-low, medium-high, and high) are
available. The precise error rate provided by each reliability level
is not specified.
Various checksum and CRC mechanisms are employed in the network to
provide an error detection capability. A host has an opportunity
when sending a message to indicate whether the message should be
delivered to its destination or discarded if a data error is detected
by the network. Each message received by a host from the network
will have a flag indicating whether or not an error was detected in
that particular message. A host can decide on a per-message basis
whether or not it wants to accept or discard transmissions containing
data errors.
For connection of a host and WPS in close proximity, error rates due
to external noise or hardware failures on the access circuit may
reasonably be expected to be much smaller than the best network trunk
circuit error rates. Thus for this case, little is gained by using
error detection and retransmission on the access circuit. A 16-bit
header checksum is provided, however, to ensure that WPSen do not act
on incorrect control information. For relatively long distances or
noisy connections, retransmissions over the access circuit may be
required to optimize performance for both low and high reliability
traffic. It is expected that link layer error control procedures
(such as HDLC with retransmission) will be used for this purpose, but
use of a reliable link layer protocol is not within the scope of this
document.
Each datagram message submitted to the WPS by a host is marked as
being in one of three priority classes, from priority 2 (highest)
through priority 0 (lowest). The priority class is used by the WPS
for arbitrating contention for scarce network resources (e.g., link
bandwidth). That is, if the network cannot deliver all of the
Edmond [Page 4]
RFC 1221 HAP2 April 1991
offered messages, high priority messages will be delivered in
preference to low priority messages. Priority level affects the
order of access to intersite link bandwidth and the order of message
delivery at the destination WPS.
Each stream message also has three priority classes, from priority 2
(highest) through priority 0 (lowest). In addition, streams
themselves have three precedence classes, from precedence 2 (highest)
through precedence 0. A stream of higher precedence can preempt a
stream of lower precedence at setup time. Stream message priority
provides a mechanism for a low-bandwidth host to receive a high-
bandwidth stream and selectively discard messages marked as less
important by the sender. Stream message priority does not affect the
order of delivery of stream messages between the source and the
destination.
Datagram and stream messages being presented to the WPS by a host may
not be accepted for a number of reasons: priority too low,
destination dead, lack of buffers in the source WPS, etc. The host
faces a similar situation with respect to handling messages from the
WPS. To permit the receiver of a message to inform the sender of the
local disposition of its message, an acceptance/refusal (A/R)
mechanism is implemented. The mechanism is the external
manifestation of the WPS's (or host's) internal flow and congestion
control algorithm. If A/Rs are enabled, an explicit or implicit
acceptance or refusal for each message is returned to the host by the
WPS (and conversely). This allows the host (or WPS) to retry refused
messages at its discretion and can provide information useful for
optimizing the sending of subsequent messages when the reason for
refusals is also provided. The A/R mechanism can be disabled to
provide a "pure discard" interface. The host's choice to use the A/R
mechanism or not does not limit its ability to send and receive
messages to any other hosts.
While the A/R mechanism allows control of individual message
transfers, it does not facilitate regulation of priority flows. Such
regulation is handled by passing advisory status information (GOPRI)
across the Host-WPS interface indicating which priorities are
currently being accepted. As long as this information, relative to
the change in priority status, is passed frequently, the sender can
avoid originating messages which are sure to be refused.
HAP defines both data messages (datagram messages and stream
messages) and link control messages. Data messages are used to send
information between hosts on the network. Link control messages are
exchanged between a host and the WPS to manage the local access link.
Allocation of network resources, such as streams and groups, is
Edmond [Page 5]
RFC 1221 HAP2 April 1991
accomplished via an exchange of datagram messages, called Setups,
between the user host and an agent inside the WPS called the "Service
Agent." Setups are used to reserve, allocate, modify, free, and
deallocate network resources. Each allocated resource has a unique
identifier which, when placed in an appropriate field in a message
header, allows that message to use the resource. E.g., after an
exchange of Setups to create a group address, a message may be sent
to the group by placing the group address in the destination field of
that message. The Service Agent also permits a host to inquire about
resources it owns.
Every HAP message consists of an integral number of 16-bit words
(i.e., an even number of octets). The first several words of the
message always contain control information and are referred to as the
message header. The first word of the message header identifies the
type of message which follows. The second word of the message header
is a checksum which covers all header information. Any message whose
received header checksum does not match the checksum computed on the
received header information must be discarded. The format of the
rest of the header depends on the specific message type.
The formats and use of the individual message types are detailed in
the following sections. A common format description is used for this
purpose. Words in a message are numbered starting at zero (i.e.,
zero is the first word of a message header). Bits within a word are
numbered from zero (most significant) to fifteen (least significant).
The notation used to identify a particular field location is:
<WORD#>{-<WORD#>} [ <BIT#>{-<BIT#>} ] <description>
where optional elements in {} are used to specify the (inclusive)
upper limit of a range. The reader should refer to these field
identifiers for precise field size specifications. Fields which are
common to several message types are defined in the first section
which uses them. Only the name of the field will usually appear in
the descriptions in subsequent sections.
Link-level protocols used to support HAP can differ in the order in
which they transmit the bits constituting HAP messages. The words of
the message are transmitted from word 0 to word N.
3. Datagram Messages
Datagrams are one of the two message types provided by HAP, as
described in the previous section. Because network resources are not
reserved in advance for datagram traffic, delivery of datagram
traffic is subject to greater delivery delays and delay variance than
stream traffic, and is subject to flow and congestion controls.
Edmond [Page 6]
RFC 1221 HAP2 April 1991
Datagram priority determines which packets are delivered or discarded
when network resources do not permit handling all of the presented
traffic. It is expected that datagram messages will be used to
support the majority of computer-to-computer and terminal-to-computer
traffic which is bursty in nature.
The format of datagram messages and the purpose of each of the header
control fields is described in Figure 1.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
0 | 0|LB|GOPRI| 0 | F| MESSAGE NUMBER |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
1 | HEADER CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
2 | A/R |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
3 | 0|IL| D| E| PRI | TTL | RLY | RLEN |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
4 | DESTINATION HOST ADDRESS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
5 | SOURCE HOST ADDRESS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
6 | PROTOCOL ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| |
7-N : DATA :
| |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
DATAGRAM MESSAGE
Figure 1
0[0] Message Class. This bit identifies the message as a
data message or a control message.
0 = Data Message
1 = Control Message
0[1] Loopback indicator. This bit allows the sender of a
message to determine if its own messages are being
looped back. The host and the WPS each use different
settings of this bit for their transmissions. If a
message arrives with the loopback bit set equal to its
Edmond [Page 7]
RFC 1221 HAP2 April 1991
outgoing value, then the message has been looped.
0 = Sent by Host
1 = Sent by WPS
0[2-3] Go-Priority. In WPS-to-Host messages, this field
provides advisory information concerning the lowest
priority currently being accepted by the WPS. The host
may optionally choose to provide similar priority
information to the WPS.
0 = Low Priority
1 = Medium Priority
2 = High Priority
3 = (Reserved.)
0[4-6] Reserved. Must be zero.
0[7] Reserved. Must be zero. Formerly used for WPS
diagnostic purposes.
0[8-15] Message Number. This field contains the identification
of the message used by the acceptance/refusal (A/R)
mechanism (when enabled). If the message number is
zero, A/R is disabled for this specific message. See
Section 5 for a detailed description of the A/R
mechanism.
1[0-15] Header Checksum. The checksum is the 2's-complement of
the 2's-complement sum of words 0-6 (excluding the
checksum word itself).
2[0-15] Piggybacked A/R. This field may contain an
acceptance/refusal word providing A/R status on traffic
flowing in the opposite direction. Its inclusion may
eliminate the need for a separate A/R control message
(see Section 5). A value of zero for this word is used
to indicate that no piggybacked A/R information is
present.
3[0] Data Message Type. This bit identifies whether the
message is a datagram message or a stream message.
0 = Datagram Message
1 = Stream Message
3[1] IL flag. Obsolete. Must be zero. (See Appendix B.)
Edmond [Page 8]
RFC 1221 HAP2 April 1991
3[2] Discard Flag. This flag allows a source host to
instruct the network (including the destination host)
what to do with the message when data errors are
detected (assuming the header checksum is correct).
0 = Discard message if data errors detected.
1 = Don't discard message if data errors detected.
The value of this flag, set by the source host, is
passed on to the destination host.
3[3] Data Error Flag. This flag is used in conjunction with
the Discard Flag to indicate to the destination host
whether any data errors have been detected in the
message prior to transmission over the destination's
WPS-to-Host access link. It is used only if Discard
Flag = 1. It should be set to zero by the source host.
0 = No Data Errors Detected
1 = Data Errors Detected
3[4-5] Priority. The source host uses this field to specify
the priority with which the message should be handled
within the network.
0 = Low Priority
1 = Medium Priority
2 = High Priority
3 = (Reserved.)
The priority of each message is passed to the
destination host by the destination WPS.
3[6-7] Time-to-Live Designator. The source host uses this
field to specify the maximum time that a message should
be allowed to exist within the network before being
deleted. Elapsed time begins when the message has been
received by the WPS from the source host (or is sent by
a WPS agent) and is last checked when the message is
queued for transmission out the I/O interface to the
destination host. If a message is multicast, each copy
is treated separately.
0 = 1 seconds
1 = 2 seconds
2 = 5 seconds
3 = 10 seconds
Edmond [Page 9]
RFC 1221 HAP2 April 1991
3[8-9] Reliability. The source host uses this field to
specify the basic bit error rate requirement for the
data portion of this message. The source WPS uses this
field to determine the trunk circuit transmission
parameters and forward error correction level required
to provide that bit error rate.
0 = Low Reliability
1 = Medium-Low Reliability
2 = Medium-High Reliability
3 = High Reliability
3[10-15] Reliability Length. The source host uses this field to
specify a portion of the user data which should be
transmitted at the highest reliability level (lowest
bit error rate). Both the HAP message header words and
the first 2*<Reliability Length> octets of user data
will be transmitted at high reliability while the
remainder of the user data will be transmitted at
whatever reliability level is specified in field 3[8-
9]. The reliability length mechanism gives the user
the ability to transmit private header information
(e.g., IP and TCP headers) at a higher reliability
level than the remainder of the data.
4[0-15] Destination Host Address. This field contains the
network logical address of the destination host.
5[0-15] Source Host Address. This field contains the network
logical address of the source host.
6[0-15] Protocol ID. This field specifies the next higher
level protocol. Protocol identifiers are assigned
administratively, except 0 which is reserved, and are
not part of this specification. See reference [10].
7-N Data. This field contains up to 16,384 bits (2048
octets) of user data, and must be an even number of
octets.
4. Stream Messages
Stream messages are the second message type provided by HAP, as
described in Section 2. Streams provide guaranteed bandwidth between
the source and destination(s), and provide the minimum delivery delay
and delay variance available in the network. Streams are suitable
for volatile traffic, such as speech, and for support of high duty
cycle applications that require throughput guarantees.
Edmond [Page 10]
RFC 1221 HAP2 April 1991
Streams must be created before stream messages can flow from host to
host. The protocol to accomplish stream creation is described in
Section 6.1. Once established, a stream is allocated specific
network resources, such as bandwidth. Within the bounds of its
stream allocation, a host is permitted considerable flexibility in
how it may use the stream. Although the time to live, reliability,
and reliability length of each stream message is fixed at stream
setup time, the destination logical address can vary from stream
message to stream message.
A host can, therefore, multiplex a variety of logical flows onto a
single stream, as long as the stream was set up to reach all the
destination hosts. The format of stream messages is described in
Figure 2.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
0 | 0|LB|GOPRI| 0 | MESSAGE NUMBER |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
1 | HEADER CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
2 | A/R |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
3 | 1|IL| D| E| PRI | HOST STREAM ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
4 | DESTINATION HOST ADDRESS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
5 | SOURCE HOST ADDRESS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
6 | PROTOCOL ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| |
7-N : DATA :
| |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
STREAM MESSAGE
Figure 2
0[0] Message Class = 0 (Data Message).
0[1] Loopback indicator.
0[2-3] Go-Priority.
Edmond [Page 11]
RFC 1221 HAP2 April 1991
0[4-7] Reserved.
0[8-15] Message Number. This field serves the same purpose as
the message number field in the datagram message.
Moreover, a single message number sequence is used for
both datagram and stream messages (see Section 5).
1[0-15] Header Checksum. (See datagram checksum for
description.)
2[0-15] Piggybacked A/R.
3[0] Data Message Type = 1 (Stream).
3[1] IL flag. Obsolete. Must be zero.
3[2] Discard Flag.
3[3] Data Error Flag.
3[4-5] Stream message priority. Note that all stream messages
have priority over any datagram message. Priority will
not affect the order of stream message delivery.
0 = Low priority
1 = Medium priority
2 = High priority
3 = Reserved
3[6-15] Stream ID. The WPS uses this field to identify the
preallocated network resources (bandwidth allocations,
queues, buffers, etc.) to use for delivery of the
message. Streams and their identifying numbers (stream
IDs) are established by an explicit Create Stream
request (see Section 6.1).
4[0-15] Destination Host Address.
5[0-15] Source Host Address.
6[0-15] Protocol ID.
7-N Data. This field contains up to 16,384 bits (2048
octets) of user data, and must be an even number of
octets.
Edmond [Page 12]
RFC 1221 HAP2 April 1991
5. Flow Control Messages
The WPS supports an acceptance/refusal (A/R) mechanism in each
direction on the host access link. The A/R mechanism is enabled for
the link by the host by setting a bit in the Restart Complete control
message (see Section 8). Each datagram and stream message contains
an 8-bit message number used to identify the message for flow control
purposes. When the A/R mechanism is enabled, the message number is
incremented modulo 256 in successive messages, skipping over message
number zero (zero indicates that A/R's are disabled for that
message). Up to 127 messages may be outstanding (awaiting acceptance
or refusal) in each direction. If the receiver of a message is
unable to accept the message, a refusal indication containing the
message number of the refused message and the reason for the refusal
is returned. The refusal indication may be piggybacked on data
messages in the opposite direction over the link or may be sent in a
separate control message in the absence of reverse data traffic.
Acceptance indications are returned in a similar manner, either
piggybacked on data messages or in a separate control message. An
acceptance is returned by the receiver to indicate that the
identified message was received from the host access link and was not
refused. Acceptance indications returned by the WPS are not an end-
to-end acknowledgement and do not imply any guarantee of delivery to
the destination host(s), or even any assurance that the message will
not be intentionally discarded by the network. They are sent
primarily to facilitate buffer management in the host.
To reduce the number of A/R messages exchanged, a single A/R
indication can be returned for multiple (lower numbered) previously
unacknowledged messages. Explicit acceptance of message number N
implies implicit acceptance of outstanding messages with numbers N-1,
N-2, etc., according to the definition of acceptance outlined above.
Analogous interpretation of the refusal message number allows the
receiver of a group of messages to reject them as a group when they
all are being refused for the same reason. As a further efficiency
measure, HAP permits aggregation of any mix of A/R indications into a
single A/R control message. Such a message might be used, for
example, to reject a group of messages where the refusal code on each
is different.
In some circumstances the overhead associated with processing A/R
messages may prove unattractive. For these cases, it is possible to
disable the A/R mechanism and operate the HAP interface in a purely
discard mode. The ability to effect this on a link basis has already
been noted (see Sections 2 and 8). In addition, messages with
sequence number zero are taken as messages for which the A/R
mechanism is selectively disabled. To permit critical feedback, even
Edmond [Page 13]
RFC 1221 HAP2 April 1991
when operating in discard mode, HAP defines an "Unnumbered Response"
control message. Flow control information, and other information
which cannot be sent as an A/R indication, is sent in an Unnumbered
Response control message. The format of this type of message is
illustrated in Figure 5.
The format shown in Figure 3 is used both for A/R indications that
are piggybacked on data messages (word 2), and for aggregated A/R
information in A/R control messages. The format of A/R control
messages is shown in Figure 4.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|AR| REFUSAL CODE | A/R MESSAGE NUMBER |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
ACCEPTANCE/REFUSAL WORD
Figure 3
[0] Acceptance/Refusal Type. This field identifies whether
A/R information is an acceptance or a refusal.
0 = Acceptance
1 = Refusal
[1-7] Refusal Code. When the Acceptance/Refusal Type = 1,
this field gives the Refusal Code.
0 = Priority not being accepted
1 = Source WPS congestion
2 = Destination WPS congestion
3 = Destination host dead
4 = Destination WPS dead
5 = Illegal destination host address
6 = Destination host access not allowed
7 = Illegal source host address
8 = Message lost in access link
9 = Invalid stream ID
10 = Illegal source host for stream ID
11 = Message length too long
12 = Stream message too early
13 = Illegal control message type
14 = Illegal refusal code in A/R
15 = Can't implement loop
Edmond [Page 14]
RFC 1221 HAP2 April 1991
16 = Destination host congestion
17 = Delivery refused
18 = Odd byte length packet (not allowed)
19 = Invalid stream time-to-live value
20 = "Reliability length" exceeds message length
[8-15] A/R Message Number. This field contains the number of
the message to which this acceptance/refusal refers.
It also applies to all outstanding messages with
earlier numbers. Note that this field can never be
zero since a message number of zero implies that the
A/R mechanism is disabled.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
0 | 1|LB|GOPRI| 0 | LENGTH | 1 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
1 | HEADER CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| |
2-N : A/R's :
| |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
ACCEPTANCE/REFUSAL MESSAGE
Figure 4
0[0] Message Class = 1 (Control Message).
0[1] Loopback indicator.
0[2-3] Go-Priority.
0[4-7] Reserved.
0[8-11] Message Length. This field contains the total length
of this message in words (N+1).
0[12-15] Control Message Type = 1 (Acceptance/Refusal).
1[0-15] Header Checksum. The checksum is the 2's-complement of
the 2's-complement sum of words 0-N (excluding the
checksum word itself).
Edmond [Page 15]
RFC 1221 HAP2 April 1991
2[0-15] Acceptance/Refusal Word.
3-N Additional Acceptance/Refusal Words (optional).
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
0 | 1|LB|GOPRI| 0 | RES-CODE | 5 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
1 | HEADER CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
2 | RESPONSE INFO |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
3 | RESPONSE INFO |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
UNNUMBERED RESPONSE
Figure 5
0[0] Message Class = 1 (Control Message).
0[1] Loopback indicator.
0[2-3] Go-Priority.
0[4-7] Reserved.
0[8-11] Response Code.
3 = Destination unreachable
5 = Illegal destination host address
7 = Illegal source host address
9 = Nonexistent stream ID
10 = Illegal stream ID
13 = Protocol violation
15 = Can't implement loop
0[12-15] Control Message Type = 5 (Unnumbered Response).
1[0-15] Header Checksum. The checksum is the 2's-complement of
the 2's-complement sum of words 0-3 (excluding the
checksum word itself).
2[0-15] Response Information. If Response Code is:
Edmond [Page 16]
RFC 1221 HAP2 April 1991
3: Destination Host Address
5: Destination Host Address
7: Source Host Address
9: Stream ID (right justified)
10: Stream ID (right justified)
13: Word 0 of offending message
15: Word 0 of Loopback Request message
3[0-15] Response Information. If Response Code is:
3,5,7, or 9: Undefined
10: Source Host Address
13: Word 3 of offending message, or 0 if no word 3
15: Word 2 of Loopback Request message
6. The Service Agent
Allocation of network resources, such as streams and groups, is
accomplished via an exchange of datagram messages, called Setup
messages, between the user host and the Service Agent (network
address zero). Setup operations include reserving, allocating,
modifying, freeing, and deallocating resources. The Service Agent
causes the requested action to be carried out and serves as the
intermediary between the user and the rest of the network. In the
process of implementing the requested action, various network data
bases are updated to reflect the current state of the referenced
resource. The Service Agent also permits a host to inquire about
resources it owns using Information Request and Information Reply
messages.
A setup interaction initiated by a host involves a 3-way exchange
where: (1) the requesting host sends a Setup Request to the Service
Agent, (2) the Service Agent returns a Setup Reply to the requesting
host, and (3) the requesting host returns a Setup Acknowledgment to
the Service Agent. This procedure is used to ensure reliable
transmission of Setup Requests and Replies. In order to allow more
than one Setup Request message from a host to be outstanding, each
Request is assigned a unique Request ID. The associated Reply and
subsequent Acknowledgment are identified by the Request ID that they
contain. The requesting host should receive a reply to a setup
request within 3 seconds. The actual delay will depend on the nature
of the request and the topology of the network. For simple networks,
the delay will often be less than one second. The requesting host
should respond to a Reply with a Setup Acknowledgment within one
second.
Setup exchanges initiated by the Service Agent involve a two-way
exchange where: (1) the Service Agent sends a Notification to
Edmond [Page 17]
RFC 1221 HAP2 April 1991
affected hosts, and (2) the hosts return a Setup Acknowledgment to
the Service Agent. Notifications are used to inform a host of
changes in the status of a network resource. In order to allow more
than one Notification to be outstanding, each is assigned a unique
Notification ID. The Setup Acknowledgment returned by the notified
host to the Service Agent must contain the Notification ID. The host
should respond within one second.
An information query is initiated by a host and involves a two-way
exchange where: (1) the host sends an Information Request message to
the Service Agent, and (2) the Service Agent sends back an
Information Reply. There is no acknowledgment mechanism, since this
request does not change any resource allocation. Furthermore, if
there is an error in the request, only one response will be sent by
the WPS, and the WPS will make no effort to check for or retransmit
lost responses. It is the responsibility of the host to wait a
certain amount of time and then determine that an unanswered
information request has been lost and to resend it. (The time
necessary to answer such a request is usually much less than one
second.) The WPS will return the message ID of the information
request in the information reply message.
The general format of all Service Agent messages is:
<DATAGRAM MESSAGE HEADER>
<SERVICE AGENT HEADER>
<MESSAGE BODY>
The Protocol ID field in the datagram message header must be
HAP_PROTO_SETUP (1) (see Appendix C) for messages sent to the Service
Agent and will be HAP_PROTO_SETUP in messages received from the
Service Agent. The Service Agent does not recognize or support use
of other higher level protocols (e.g., IP), in setup messages, and
will discard messages containing such headers.
Illustrations of message formats below show only the Service Agent
Header header and message body and do not include the datagram
message header. As a reminder that the datagram header is not
included, word offsets are prefixed with an "S".
The format of the Service Agent Header is illustrated in Figure 6.
The body of the message will depend on the particular message type.
Stream Request and Reply messages are described in Section 6.1.
Group Request and Reply messages are described in Section 6.2. The
format of Notifications is described in Section 6.3, and Setup
Acknowledgments are described in Section 6.4. Information Request
and Reply messages are described in Section 6.5.
Edmond [Page 18]
RFC 1221 HAP2 April 1991
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | MESSAGE TYPE | CODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | MESSAGE ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
SERVICE AGENT HEADER
Figure 6
S0[0-7] Message Type. This field determines the type of
message.
0 = Setup Acknowledgment
1 = Setup Request
2 = Setup Reply
3 = Notification
4 = Information Request
5 = Information Reply
S0[8-15] Code. For Setup Requests, this field identifies the
request type.
1 = Create group (multicast) address
2 = Delete group address
3 = Join group
4 = Leave group
5 = Create stream
6 = Delete stream
7 = Change stream
8 = Create shared stream
9 = Delete all streams owned by this host
10 = Add member to group
11 = Remove member from group
For Setup Replies, this field provides the Reply Code.
Some of the Reply Codes can be returned to any setup
request and others are request specific.
0 = Group or stream created
1 = Group or stream deleted
2 = Host added to group
3 = Host deleted from group
4 = Stream changed
Edmond [Page 19]
RFC 1221 HAP2 April 1991
5 = (Reserved)
6 = Request type invalid or unsupported
7 = (Reserved)
8 = Network trouble
9 = Bad group key
10 = Group address/stream ID nonexistent
11 = Not member of group/not creator of stream
12 = Stream precedence not being accepted
13 = (Reserved)
14 = (Reserved)
15 = (Reserved)
16 = Unable to add all the new hosts
17 = Insufficient network resources
18 = Requested bandwidth too large
19 = (Reserved)
20 = (Reserved)
21 = Maximum messages per interval too small
22 = Reply lost in network
23 = Illegal priority or precedence value
24 = Invalid address provided
For Notifications, this field contains the Notification
Type. (See Section 6.3.)
For Setup Acknowledgments, this field contains the
Acknowledgment Type. (See Section 6.4.)
For Information Requests, this field contains the
request type. (See Section 6.5.)
For Information Replies, this field contains the reply
type. (See Section 6.5.)
S1[0-15] Checksum. The checksum is the 2's-complement of the
2's-complement sum of the words in the Service Agent
Header (excluding the checksum word itself) and the
message body. Messages received with bad checksums
must be discarded.
S2[0-15] Message ID. This field is assigned by the host to
uniquely identify outstanding requests (Request ID) and
by the Service Agent to uniquely identify outstanding
notifications (Notification ID).
6.1. Stream Setup Messages
Streams provide a means of reserving network resources for the
delivery of traffic at a specified maximum throughput to a specified
Edmond [Page 20]
RFC 1221 HAP2 April 1991
list of recipients. Traffic sent via a stream has priority over all
non-stream traffic, and is delivered with the minimum end-to-end
delay possible. Hosts use streams to support applications that have
predictable traffic loads (such as packet voice or video or other
continuous media traffic) or that require minimum transmission delay
and lowest delay variance. Streams are typically used for traffic
flows of moderate to long duration, where the cost of performing a
stream Setup is acceptable.
Streams must be set up before stream data messages can flow. The
stream setup messages, each of which has a Request and a Reply, are
Create Stream, Delete Stream, Change Stream, and Delete All Streams.
(Create Shared Stream Request is a planned future addition to the
protocol.) The use of these messages is illustrated in the scenario
of exchanges between a host and the Service Agent shown in Figure 7
where the host establishes a stream, sends some data, modifies the
stream characteristics, sends some more data, and finally closes down
the stream. Not illustrated, but implicit in this scenario, are the
optional A/R indications associated with each of the stream Setup
messages.
Service Other
Host Agent hosts
Create Stream Request ---------->
Create Stream Reply <----------
Reply Acknowledgment ---------->
Stream Messages --------------------->
: :
Change Stream Request ---------->
Change Stream Reply <----------
Reply Acknowledgment ---------->
Stream Messages --------------------->
: :
Delete Stream Request ---------->
Delete Stream Reply <----------
Reply Acknowledgment ---------->
STREAM EXAMPLE
Figure 7
Streams have eight characteristic properties which are selected at
stream setup time. These properties are: (1) data words per time
interval, (2) time interval, (3) reliability, (4) reliability length,
(5) precedence, (6) maximum messages per interval, (7) the list of
recipients, and (8) the set of other streams with which this stream
shares resources. To establish a stream, the host sends the Create
Edmond [Page 21]
RFC 1221 HAP2 April 1991
Stream Request message (Figure 8) to the Service Agent. After the
network has processed the Create Stream Request, the Service Agent
will reply with a Create Stream Reply message (Figure 9). If the
reply code in the Create Stream Reply indicates that the stream has
been created successfully, the host may proceed to transmit stream
data messages after sending a Reply Acknowledgment.
During the lifetime of a stream, the host which created it may decide
that some of its characteristic properties should be modified. All
but one of the properties can be modified using the Change Stream
Request message (Figure 10). The one property that cannot be changed
is whether or not the stream is willing to share its resources with
other streams. After the network has processed the Change Stream
Request, the Service Agent will respond by sending a Change Stream
Reply (Figure 11) to the host. A host requesting a reduced channel
allocation should decrease its sending rate immediately without
waiting for receipt of the Change Stream Reply. A host requesting an
increased allocation should not proceed to transmit according to the
new set of parameters without first having received a Reply Code
indicating that the requested change has taken effect.
When the host no longer needs the stream it created, it should first
stop sending traffic via the stream and then send the Service Agent a
Delete Stream Request message (Figure 12). After the network has
processed the Delete Stream Request, the Service Agent will respond
by sending a Delete Stream Reply (Figure 13) to the host.
If the host has crashed or restarted, it may no longer know what
streams it owns. The host may use an Information Request (see
Section 6.5) to determine what streams it owns, or the host may use a
Delete All Streams Request (Figure 14) to discard whatever stream
resources it may own. The format for the Delete All Streams Reply is
shown in Figure 15.
Note that streams, like all other resources allocated by the Service
Agent, may be reclaimed by the network if unused. Currently, if no
traffic is sent to a stream in a 6 minute interval, and if the owner
of the steam is down or unreachable, the stream may be deleted.
Edmond [Page 22]
RFC 1221 HAP2 April 1991
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 1 | 5 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | SETUP CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | REQUEST ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S3 | MAX MES | PRE | INT | RLY | RLEN |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S4 | DATA WORDS PER INTERVAL |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S5 | INTERVAL |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S6 | 0 | ADDRESS LIST LENGTH |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| |
S7-SN : DESTINATION ADDRESS LIST :
| |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
CREATE STREAM REQUEST
Figure 8
S0[0-7] Setup Type = 1 (Request).
S0[8-15] Request Type = 5 (Create Stream).
S1[0-15] Setup Checksum. (See setup header description.)
S2[0-15] Request ID.
S3[0-3] Maximum Messages Per Interval (1-15). This field
specifies the maximum number of stream messages the
host will deliver to the WPS in any single stream
interval.
S3[4-5] Precedence. This field specifies the precedence of the
stream. When there are insufficient network resources
to support all the requested streams, requests for
higher precedence streams will preempt existing lower
precedence streams, and requests for streams with
insufficient precedence will be rejected. Medium
precedence is recommended as the default choice.
Edmond [Page 23]
RFC 1221 HAP2 April 1991
0 = Low Precedence
1 = Medium Precedence
2 = High Precedence
S3[6-7] Interval. This field specifies the interval, in
multiples of 21.22 milliseconds. (For backward
compatibility only. New applications should use 3.
Use of this field to specify an interval is being
phased out.)
0 = 21.22 milliseconds
1 = 42.44 milliseconds
2 = 84.88 milliseconds
3 = use interval in word S5
S3[8-9] Reliability. This field specifies the basic bit-error
rate requirement for the data portion of all messages
in the stream. The exact error rate obtained by each
choice is not specified.
0 = Low Reliability
1 = Medium-Low Reliability
2 = Medium-High Reliability
3 = High Reliability
S3[10-15] Reliability Length. This field specifies how many
words beyond the stream message header should be
transmitted at maximum reliability for all messages in
the host stream.
S4[0-15] Data words per interval. This field specifies the
maximum number of 16-bit words of this stream's data
the network will need to carry during each interval,
not counting HAP stream message header words. The
stream data may be carried in however many messages (up
to MAX MES) in each interval the host chooses.
S5[0-15] Interval (125 microsecond units). This field specifies
the time interval over which the <data words per
interval> data in <max mes> messages will be sent. For
backward compatibility, an interval of 0 selects an
interval of 169.76 milliseconds. This field is ignored
unless the INT field is 3.
S6[0-7] Reserved. Must be zero.
S6[8-15] Destination address list length. This field specifies
the number of entries in the Destination Address List
Edmond [Page 24]
RFC 1221 HAP2 April 1991
field. Allowed values are 1-8.
S7-SN Destination address list. This list must specify, at
least indirectly, all the intended recipients of this
stream's traffic. At least one destination address
must be supplied. Any valid network address,
specifically including group addresses, may be used
(except the Service Agent's address, 0). Messages sent
in the stream are not limited to using the HAP
addresses listed. E.g., if the list consists of only
group address G, and host A is a member of G, a stream
message may be sent to A, which was not in the list.
Caution: Group membership is only evaluated at setup time. Changes
in group membership do not cause the stream to be modified.
Caution: Stream creation involves allocation of specific network
resources along specific routes for delivery of that traffic. A
stream message sent to hosts other than those specified via Setup
will probably be undeliverable. A stream message to a group address
that has gained new members since the stream's last Setup may be
undeliverable to the new members.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 2 | REPLY CODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | SETUP CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | REQUEST ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S3 | 0 | STREAM ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S4 | 0 | ADDRESS LIST LENGTH |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| |
S5-SN : ADDRESS LIST :
| |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
CREATE STREAM REPLY
Figure 9
S0[0-7] Setup Type = 2 (Reply).
Edmond [Page 25]
RFC 1221 HAP2 April 1991
S0[8-15] Reply Code. Any reply other than "Stream created"
means the stream was not created.
0 = Stream created
8 = Network trouble
12 = Stream precedence not being accepted
17 = Insufficient network resources
18 = Requested bandwidth too large
21 = Max. messages per interval too small
22 = Reply lost in network
23 = Illegal precedence value
24 = Invalid destination address in list
S1[0-15] Setup Checksum. (See setup header description.)
S2[0-15] Request ID.
S3[0-5] Reserved. Must be zero.
S3[6-15] Stream ID. This field contains a stream ID assigned by
the network. It must be included in all stream data
messages sent by the host to allow the WPS to associate
the message with stored stream characteristics and the
resources reserved for that stream's traffic.
S4[0-5] Reserved. Must be zero.
S4[6-15] Address list length. The number of entries in the
Address List field.
S5-SN Address list. This contains the destination addresses
from the Create Stream Request that were invalid or
unreachable. Unreachable destinations are listed as a
group if every member of the group was unreachable, or
individually otherwise; i.e., group addresses are
expanded and the unreachable members are included in
the list. The list of unreachable destinations will be
truncated, if needed, to limit this Reply to a single,
maximum length HAP message.
Edmond [Page 26]
RFC 1221 HAP2 April 1991
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 1 | 7 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | SETUP CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | REQUEST ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S3 | 0 | STREAM ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S4 | MAX MES | PRE | INT | RLY | RLEN |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S5 | DATA WORDS PER INTERVAL |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S6 | INTERVAL |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S7 | 0 | ADDRESS LIST LENGTH |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| |
S8-SN : DESTINATION ADDRESS LIST :
| |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
CHANGE STREAM REQUEST
Figure 10
S0[0-7] Setup Type = 1 (Request).
S0[8-15] Request Type = 7 (Change Stream).
S1[0-15] Setup Checksum. (See setup header description.)
S2[0-15] Request ID.
S3[0-5] Reserved. Must be zero.
S3[6-15] Stream ID.
S4[0-3] New Maximum Messages Per Interval.
S4[4-5] New Precedence.
S4[6-7] New Interval selection.
S4[8-9] New Reliability.
Edmond [Page 27]
RFC 1221 HAP2 April 1991
S4[10-15] New Reliability Length.
S5[0-15] New Data Words Per Interval.
S6[0-15] New Interval (ignored unless INT = 3).
S7[0-7] Reserved. Must be zero.
S7[8-15] Destination Address List length. This field specifies
the number of entries in the new Destination Address
List. Allowed values are 0-8. Use zero (indicating no
addresses in the list) to avoid changing the list of
recipient hosts.
S8-SN New Destination Address List. The new, complete, list
of recipient hosts. Membership of group addresses is
evaluated at setup execution time. Subsequent changes
in group membership do not cause the stream to be
modified. Note that using the same destination address
list in the Change Stream Request as was used in the
Create Stream Request can result in a change in the
list of recipient hosts if membership in a group has
changed.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 2 | REPLY CODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | SETUP CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | REQUEST ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S3 | 0 | ADDRESS LIST LENGTH |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| |
S4-SN : ADDRESS LIST :
| |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
CHANGE STREAM REPLY
Figure 11
S0[0-7] Setup Type = 2 (Reply).
Edmond [Page 28]
RFC 1221 HAP2 April 1991
S0[8-15] Reply Code. The number in parentheses indicates the
processing phase at the time of the error (see Caution
below). Phase zero and phase one errors leave the
stream unchanged; errors from later phases may leave
the stream partially modified.
4 = Stream changed
8 = (1) Network trouble
10 = (0) Stream ID nonexistent
11 = (0) Not creator of stream
12 = (0) Stream precedence not being accepted
16 = (3) Unable to add all the new recipients
17 = (2) Insufficient network resources
18 = (2) Requested bandwidth too large
21 = (0) Maximum messages per interval too small
22 = (2) Reply lost in network
23 = (0) Illegal precedence value
24 = (0) Invalid destination address in list
S1[0-15] Setup Checksum. (See setup header description.)
S2[0-15] Request ID.
S3[0-5] Reserved. Must be zero.
S3[6-15] Address list length. This field specifies the number
of addresses in the Address List.
S4-SN Address list. This contains the destination addresses
from the Change Stream Request that were invalid (phase
0 errors) or unreachable (phase 3 errors). Unreachable
destinations are listed as a group if every member of
the group was unreachable, or individually otherwise;
i.e., group addresses are expanded and the unreachable
members are included in the list. The list of
unreachable destinations will be truncated, if needed,
to limit this Reply to a single, maximum length HAP
message.
Caution: The Change Stream Reply will indicate failure if any
aspect of the requested changes did not occur. However, the
stream may have been partially modified. Processing is performed
in the following phases:
0: check for invalid requests;
1: drop former recipients that are not in the latest list;
2: increase or decrease the stream's bandwidth allocation
(decreases are normally successful); then
3: extend the stream to any new recipients.
Edmond [Page 29]
RFC 1221 HAP2 April 1991
If phase 2 fails, phase 3 is not performed, the Reply Code will
indicate an error and the stream parameters will be unchanged.
If phase 3 fails, the Address List will contain the destinations,
if any, from the latest list that the stream does not reach.
Phase 1 only fails if the stream has been suspended (see
Notifications) or the WPS is experiencing network connectivity
problems.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 1 | 6 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | SETUP CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | REQUEST ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S3 | 0 | STREAM ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
DELETE STREAM REQUEST
Figure 12
S0[0-7] Setup Type = 1 (Request).
S0[8-15] Request Type = 6 (Delete Stream).
S1[0-15] Setup Checksum. (See setup header description.)
S2[0-15] Request ID.
S3[0-5] Reserved. Must be zero.
S3[6-15] Stream ID.
Edmond [Page 30]
RFC 1221 HAP2 April 1991
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 2 | REPLY CODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | SETUP CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | REQUEST ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
DELETE STREAM REPLY
Figure 13
S0[0-7] Setup Type = 2 (Reply).
S0[8-15] Reply Code. If the request was valid, the Service
Agent will have marked the stream for deletion even if
the stream resources have not actually been deleted
yet.
1 = Stream deleted
10 = Stream ID nonexistent
11 = Not creator of stream
S1[0-15] Setup Checksum. (See setup header description.)
S2[0-15] Request ID.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 1 | 9 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | SETUP CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | REQUEST ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
DELETE ALL STREAMS REQUEST
Figure 14
S0[0-7] Setup Type = 1 (Request).
S0[8-15] Request Type = 9 (Delete All Streams).
Edmond [Page 31]
RFC 1221 HAP2 April 1991
S1[0-15] Setup Checksum. (See setup header description.)
S2[0-15] Request ID.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 2 | REPLY CODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | SETUP CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | REQUEST ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
DELETE ALL STREAMS REPLY
Figure 15
S0[0-7] Setup Type = 2 (Reply).
S0[8-15] Reply Code. The Service Agent will have marked all of
the host's streams for deletion, even if the stream
resources have not actually been deleted yet.
1 = Streams deleted
S1[0-15] Setup Checksum. (See setup header description.)
S2[0-15] Request ID.
6.2. Group Setup Messages
Group (multicast) addressing allows a host to send the same message
to N different hosts without having to send N copies of the message.
The network duplicates the message as required. In addition to
reducing the burden on the originating host, multicasting reduces the
load on the network because the network no longer has to carry the
duplicates along the common portions of the paths between the source
and destinations. Multicasting is particularly recommended for
multi-site conferencing and distributed simulations.
Group addresses are dynamically created and deleted via setup
messages exchanged between the hosts and the Service Agent.
Membership in a group may be any arbitrary subset of the network
hosts. A datagram message or stream message addressed to a group is
delivered to all hosts that are members of that group (exception:
stream messages sent to a group address that includes hosts the
Edmond [Page 32]
RFC 1221 HAP2 April 1991
stream was not set up to reach). The group setup messages, each of
which has a Request and a Reply, are Create Group, Delete Group, Join
Group, Leave Group, Add Group Member, and Remove Group Member.
Figure 16 shows a typical use of group setup messages. The figure
illustrates a scenario of exchanges between three hosts and the
Service Agent. In the scenario one host, Host A, creates a group
which is joined by hosts B and C. The hosts then exchange some data
messages using the group address. Note that multicast messages are
not returned to their originator. Hosts A and C then leave the
group, and Host B decides to delete the group. As in the scenario in
Section 6.1, A/R indications have been omitted for clarity.
Part of the group creation procedure involves the Service Agent
returning to the creating host a 48-bit key along with the 16-bit
group address. The creating host must pass the key along with the
group address to other hosts that want to join the group. These
other hosts must supply the key along with the group address in their
Join Group Requests. The key is used by the network to authenticate
these operations and thereby minimize the probability that unwanted
hosts will deliberately or inadvertently become members of the group.
The procedure used by a host to distribute the group address and key
is not within the scope of HAP.
In the figure below, the network Service Agent is pictured as a
single entity for simplicity.
Edmond [Page 33]
RFC 1221 HAP2 April 1991
Service Host Host Host
Agent A B C
Create Group Request |<-------|
Create Group Reply |------->|
Reply Acknowledgment |<-------|
: :
Distribute Group Adr & Key |---->|
Distribute Group Adr & Key |---------->|
: :
Join Group Request (C) |<-------------------|
Join Group Reply |------------------->|
Reply Acknowledgment |<-------------------|
Join Group Request (B) |<-------------|
Join Group Reply |------------->|
Reply Acknowledgment |<-------------|
: :
Data Message 1 (A to B and C) |---->|---->|
Data Message 2 (B to A and C) |<----|---->|
Data Message 3 (C to A and B) |<----|<----|
: :
Leave Group Request (C) |<-------------------|
Leave Group Reply |------------------->|
Reply Acknowledgment |<-------------------|
Leave Group Request (A) |<-------|
Leave Group Reply |------->|
Reply Acknowledgment |<-------|
Delete Group Request |<-------------|
Delete Group Reply |------------->|
Reply Acknowledgment |<-------------|
GROUP EXAMPLE
Figure 16
An alternative method of adding and removing group members is the use
of Add Group Member and Remove Group Member. These setup requests
allow hosts that are already members of the group to add or delete
other hosts.
The Setup requests Join Group, Leave Group, Add Group Member, Remove
Group Member, and Delete Group are authenticated using the 48-bit
key. Leave Group and Remove Group Member will remove a host from the
group membership list but will not alter the existence of the group.
Delete Group expunges all knowledge of the group from the network.
HAP permits any host with the proper key to delete the group at any
time. Thus, group addresses can be deleted even if the host which
originally created the group has left the group or has crashed.
Moreover, groups may exist for which there are currently no members
Edmond [Page 34]
RFC 1221 HAP2 April 1991
because each member has executed a Leave while none has executed a
Delete. It is the responsibility of the hosts to coordinate and
manage the use of group addresses.
Note that group addresses, like all other resources allocated by the
network, may be reclaimed by the network if unused for too long.
Currently, if no traffic is sent to the group address in a 6 minute
interval, the network may delete the group and notify all members
that the group no longer exists.
The Create Group Request (Figure 17) is used to establish a multicast
address. After the network has processed the Create Group Request,
the Service Agent will respond by sending a Create Group Reply
(Figure 18) to the host.
A host may become a member of a group, once it knows the group
address and the 48-bit key, by sending the Service Agent the Join
Group Request message (Figure 19). The Service Agent will respond to
the Join Group Request with a Join Group Reply (Figure 20). The host
which creates a group automatically becomes a member of that group
without any need for an explicit Join Group Request.
A member host may add another host to the group by sending the
Service Agent the Add Group Member Request message (Figure 21). The
Service Agent will respond with an Add Group Member Reply (Figure
22).
At any time after becoming a member of a group, a host may choose to
drop out of the group. To do this, the host sends the Service Agent
a Leave Group Request (Figure 23). The Service Agent will respond
with a Leave Group Reply (Figure 24).
One member host may expel another member of the group by sending the
Service Agent the Remove Group Member Request message (Figure 25).
The Service Agent will respond with a Remove Group Member Reply
(Figure 26).
A host can delete an existing group via a Delete Group Request
(Figure 27). The Service Agent will respond with a Delete Group
Reply (Figure 28). The Service Agent will also send the other
members of the group, if any, a notification that the group has been
deleted (see Section 6.3).
Edmond [Page 35]
RFC 1221 HAP2 April 1991
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 1 | 1 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | SETUP CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | REQUEST ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
CREATE GROUP REQUEST
Figure 17
S0[0-7] Setup Type = 1 (Request).
S0[8-15] Request Type = 1 (Create Group).
S1[0-15] Setup Checksum. (See setup header description.)
S2[0-15] Request ID.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 2 | REPLY CODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | SETUP CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | REQUEST ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S3 | GROUP ADDRESS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S4 | KEY |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S5 | KEY |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S6 | KEY |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
CREATE GROUP REPLY
Figure 18
S0[0-7] Setup Type = 2 (Reply).
Edmond [Page 36]
RFC 1221 HAP2 April 1991
S0[8-15] Reply Code.
0 = Group created
8 = Network trouble
17 = Insufficient network resources
22 = Reply lost in network
S1[0-15] Setup Checksum. (See setup header description.)
S2[0-15] Request ID.
S3[0-15] Group Address. This field contains the 16-bit
multicast address that any group member may use to
reach the other group members. Multicast addresses are
dynamically assigned by the network.
S4-S6 Key. This field contains a 48-bit key assigned by the
network which is associated with the group address. It
must be provided for subsequent Join Group, Leave
Group, Add Group Member, Remove Group Member, and
Delete Group requests which reference the group
address.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 1 | 3 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | SETUP CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | REQUEST ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S3 | GROUP ADDRESS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S4 | KEY |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S5 | KEY |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S6 | KEY |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S7 | 0 | MGP |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
JOIN GROUP REQUEST
Figure 19
Edmond [Page 37]
RFC 1221 HAP2 April 1991
S0[0-7] Setup Type = 1 (Request).
S0[8-15] Request Type = 3 (Join Group).
S1[0-15] Setup Checksum. (See setup header description.)
S2[0-15] Request ID.
S3[0-15] Group Address. This is the group that the host wishes
to join. Upon successfully joining the group, the host
may send messages to the group and will receive
messages sent to the group when those messages have a
priority of MGP or higher.
S4-S6 Key. This is the key associated with the group
address.
S7[0-13] Reserved. Must be zero.
S7[14-15] Minimum group message priority. The host will not
receive messages sent to the group that have a message
priority less than MGP. Send another Join Group
Request message to change the minimum priority.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 2 | REPLY CODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | SETUP CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | REQUEST ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
JOIN GROUP REPLY
Figure 20
S0[0-7] Setup Type = 2 (Reply).
S0[8-15] Reply Code.
2 = Host added to group
9 = Bad key
10 = Group address nonexistent
17 = Insufficient network resources
Edmond [Page 38]
RFC 1221 HAP2 April 1991
S1[0-15] Setup Checksum. (See setup header description.)
S2[0-15] Request ID.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 1 | 10 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | SETUP CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | REQUEST ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S3 | GROUP ADDRESS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S4 | KEY |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S5 | KEY |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S6 | KEY |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S7 | HOST ADDRESS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
ADD GROUP MEMBER REQUEST
Figure 21
S0[0-7] Setup Type = 1 (Request).
S0[8-15] Request Type = 3 (Join Group).
S1[0-15] Setup Checksum. (See setup header description.)
S2[0-15] Request ID.
S3[0-15] Group Address. This is the group the host will join.
Upon successfully joining the group, the host may send
messages to the group and will receive messages sent to
the group by other hosts (the initial minimum priority
will be 0).
S4-S6 Key. This is the key associated with the group
address.
S7[0-15] Host address. The network address of the host to add
Edmond [Page 39]
RFC 1221 HAP2 April 1991
to the group.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 2 | REPLY CODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | SETUP CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | REQUEST ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
ADD GROUP MEMBER REPLY
Figure 22
S0[0-7] Setup Type = 2 (Reply).
S0[8-15] Reply Code.
2 = Host added to group (or was already a member)
9 = Bad key
10 = Group address nonexistent
11 = Requestor is not a member of the group
17 = Insufficient network resources
22 = Reply lost in network
24 = Host address was invalid
S1[0-15] Setup Checksum. (See setup header description.)
S2[0-15] Request ID.
Edmond [Page 40]
RFC 1221 HAP2 April 1991
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 1 | 4 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | SETUP CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | REQUEST ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S3 | GROUP ADDRESS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S4 | KEY |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S5 | KEY |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S6 | KEY |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
LEAVE GROUP REQUEST
Figure 23
S0[0-7] Setup Type = 1 (Request).
S0[8-15] Request Type = 4 (Leave Group).
S1[0-15] Setup Checksum. (See setup header description.)
S2[0-15] Request ID.
S3[0-15] Group Address. This is the group that the host wishes
to cease being a member of. After leaving the group,
the host will cease receiving messages sent to the
group and will be unable to send to the group.
S4-S6 Key. This is the key associated with the group
address.
Edmond [Page 41]
RFC 1221 HAP2 April 1991
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 2 | REPLY CODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | SETUP CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | REQUEST ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
LEAVE GROUP REPLY
Figure 24
S0[0-7] Setup Type = 2 (Reply).
S0[8-15] Reply Code.
3 = Host deleted from group
9 = Bad key
10 = Invalid group address
11 = Not member of group
17 = Insufficient network resources
S1[0-15] Setup Checksum. (See setup header description.)
S2[0-15] Request ID.
Edmond [Page 42]
RFC 1221 HAP2 April 1991
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 1 | 11 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | SETUP CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | REQUEST ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S3 | GROUP ADDRESS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S4 | KEY |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S5 | KEY |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S6 | KEY |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S7 | HOST ADDRESS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
REMOVE GROUP MEMBER REQUEST
Figure 25
S0[0-7] Setup Type = 1 (Request).
S0[8-15] Request Type = 4 (Leave Group).
S1[0-15] Setup Checksum. (See setup header description.)
S2[0-15] Request ID.
S3[0-15] Group Address. This is the group from which the host
should be removed. After leaving the group, that host
will cease receiving messages sent to the group and
will be unable to send to the group.
S4-S6 Key. This is the key associated with the group
address.
S7[0-15] Host address. The network address of the host to
remove from the group.
Edmond [Page 43]
RFC 1221 HAP2 April 1991
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 2 | REPLY CODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | SETUP CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | REQUEST ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
REMOVE GROUP MEMBER REPLY
Figure 26
S0[0-7] Setup Type = 2 (Reply).
S0[8-15] Reply Code.
3 = Host deleted from group (or was not a member)
9 = Bad key
10 = Invalid group address
11 = Requestor is not a member of the group
17 = Insufficient network resources
22 = Reply lost in network
24 = Host address was invalid
S1[0-15] Setup Checksum. (See setup header description.)
S2[0-15] Request ID.
Edmond [Page 44]
RFC 1221 HAP2 April 1991
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 1 | 2 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | SETUP CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | REQUEST ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S3 | GROUP ADDRESS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S4 | KEY |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S5 | KEY |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S6 | KEY |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
DELETE GROUP REQUEST
Figure 27
S0[0-7] Setup Type = 1 (Request).
S0[8-15] Request Type = 2 (Delete Group).
S1[0-15] Setup Checksum. (See setup header description.)
S2[0-15] Request ID.
S3[0-15] Group Address. This is the multicast address to
delete. If the group is deleted, the other remaining
members of the group, if any, will be notified of the
group's deletion.
S4-S6 Key.
Edmond [Page 45]
RFC 1221 HAP2 April 1991
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 2 | REPLY CODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | SETUP CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | REQUEST ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
DELETE GROUP REPLY
Figure 28
S0[0-7] Setup Type = 2 (Reply).
S0[8-15] Reply Code.
1 = Group deleted
8 = Network trouble
9 = Bad key
10 = Invalid group address
17 = Insufficient network resources
22 = Reply lost in network
S1[0-15] Setup Checksum. (See setup header description.)
S2[0-15] Request ID.
6.3. Notifications
Notifications are Setup exchanges initiated by the WPS to inform a
host of changes in the status of a network resource. The format of
Notification messages is shown in Figure 29.
Edmond [Page 46]
RFC 1221 HAP2 April 1991
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 3 | CODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | NOTIFICATION ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S3 | NOTIFICATION INFO |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
NOTIFICATION MESSAGE
Figure 29
S0[0-7] Message Type = 3 (Notification).
S0[8-15] Code. This indicates what the Notification signifies.
0 = Stream suspended
1 = Stream resumed
2 = Stream deleted
3 = Group deleted by a host
4 = Group deleted by network
5 = All streams deleted
6 = All groups deleted
7 = Group changed by a host
8 = Group changed by network
S1[0-15] Checksum. (See Service Agent Header description.)
S2[0-15] Notification ID.
S3[0-15] Notification Information.
For notification types 0, 1, and 2, NOTIFICATION INFO
contains the following:
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S3 | 0 | stream ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
For notification types 3, 4, 7, and 8, NOTIFICATION
INFO contains the following:
Edmond [Page 47]
RFC 1221 HAP2 April 1991
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S3 | group address |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
For notification types 5 and 6, which refer to all
streams or groups, NOTIFICATION INFO is zero.
6.4. Setup Acknowledgments
The host must acknowledge receipt of Setup Replies and Notifications
from the Service Agent, as described earlier. The format for the
Setup Acknowledgment message is shown in Figure 30.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 0 | CODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | MESSAGE ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
SETUP ACKNOWLEDGMENT
Figure 30
S0[0-7] Message Type = 0 (Acknowledgment).
S0[8-15] Code. This field indicates the type of acknowledgment.
0 = Reply acknowledgment
1 = Notification acknowledgment
S1[0-15] Checksum. (See Service Agent Header description.)
S2[0-15] Message ID. This is either a Request ID or a
Notification ID.
6.5. Information Request / Reply Messages
The host may obtain information about WPS state and about what
resources the WPS currently has allocated for the host by sending an
Information Request message to the Service Agent. The Information
Reply that is returned will enable the host to determine 1) what
Edmond [Page 48]
RFC 1221 HAP2 April 1991
resources the WPS has allocated to the host, and 2) the current state
of the network and, possibly, certain network parameters. This
allows the host to refrain from trying to use resources it no longer
has, and to regain information it may have lost on its network
resources. This communication also informs the host of the network
state so that it may make priority and routing decisions.
Each Information Request (Figure 31) and Information Reply (Figure
32) message deals with a single type of resource at a time. The
header of the Information Reply message contains the number of
entries within the message, the number of 16-bit words in each entry,
and an instance of the appropriate information structure for each
resource the Information Reply message describes. These information
structures are described in Figures 33 and 34.
Future versions of the HAP protocol may permit queries about network
connectivity, estimated delay to a specified destination address
under specified conditions, etc. This is a section of the protocol
that is likely to expand in the future. Extensions are expected to
be backward compatible provided implementors do not hard code the
size of the returned information entries.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 4 | CODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | MESSAGE ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
INFORMATION REQUEST MESSAGE
Figure 31
S0[0-7] Message type = 4 (Information Request).
S0[8-15] Code. This field identifies the Information Request
Type.
1 = streams owned by host
2 = groups to which the host belongs
S1[0-15] Checksum. (See Service Agent Header description.)
Edmond [Page 49]
RFC 1221 HAP2 April 1991
S2[0-15] Message ID. This field is assigned by the host to
uniquely identify outstanding requests (Request ID).
This ID is copied into Information Replies by the
Service Agent.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S0 | 5 | CODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S1 | CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S2 | MESSAGE ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
S3 | NUMBER OF ENTRIES | WORDS PER ENTRY |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| |
S4-SN : ENTRIES (0 or more) :
| |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
INFORMATION REPLY MESSAGE
Figure 32
S0[0-7] Message type = 5 (Information Reply).
S0[8-15] Code. This field identifies the Information Reply
Type.
1 = streams owned by host
2 = groups to which the host belongs
3 = error in Information Request message
4 = network trouble
5 = access not allowed
S1[0-15] Checksum. (See Service Agent Header description.)
S2[0-15] Message ID. This field is assigned by the host in the
Information Request message to uniquely identify
outstanding requests. This ID is copied into the
Information Reply message by the Service Agent.
S3[0-7] Number of entries included in the Information Reply
message.
Edmond [Page 50]
RFC 1221 HAP2 April 1991
S3[8-15] Number of 16-bit words per entry.
S4-SN Zero or more instances of either the stream information
or group information structure.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
0 | 0 | STREAM ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
1 | STREAM TYPE OF SERVICE WORD |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
2 | STREAM SIZE (bits per interval) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
3 | STREAM INTERVAL (in units of 0.125 ms.) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
STREAM INFORMATION
Figure 33
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
0 | GROUP ADDRESS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
1 | 0 | MGP |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
GROUP INFORMATION
Figure 34
7. Host Access Link Monitoring
While the access link is operating, statistics on traffic load and
error rate are maintained by the host and WPS. Once a second, the
host and WPS exchange this information via Status messages (Figure
35). This periodic exchange of Status messages permits both ends of
the link to monitor flows in both directions. The WPS also reports
these monitoring statistics to the Network Operations Center (NOC).
If either host or WPS fails to receive Status messages for ten
seconds, the link will be restarted (see Section 8).
Edmond [Page 51]
RFC 1221 HAP2 April 1991
The link restart procedure initializes all internal WPS counts and
statistics for that link to zero. As data and control messages are
processed, counts are updated to reflect the total number of messages
sent, messages received correctly, and messages received with
different classes of errors since the last link restart. Whenever a
Status message arrives, a snapshot is taken of the local WPS counts.
The local receive counts, in conjunction with a sent count contained
in the received Status message, permits the computation of traffic
statistics in the one second update interval assuming that the set of
counts at the time of the previous monitoring report have been saved.
By including in the Status message sent (in the opposite direction)
the receive counts and the received sent count that was used with
them, the transmitting end of the access link as well as the
receiving end can determine the link performance from sender to
receiver.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
0 | 1|LB|GOPRI| 0 | 0 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
1 | HEADER CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
2 | MOST RECENT A/R SENT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
3 | STREAM CAPACITY |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
4 | TIMESTAMP |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
5 | SBU |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
6 | STU |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
7 | RNE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
8 | RWE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
9 | BHC |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
10 | HEI |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
STATUS MESSAGE
Figure 35
Edmond [Page 52]
RFC 1221 HAP2 April 1991
0[0] Message Class = 1 (Control Message).
0[1] Loopback indicator.
0[2-3] Go-Priority.
0[4-11] Reserved. Must be zero.
0[12-15] Control Message Type = 0 (Status).
1[0-15] Header Checksum. The checksum is the 2's-complement of
the 2's-complement sum of words 0-10 (excluding the
checksum word itself).
2[0-15] Most Recent A/R Sent. This field is a duplicate of the
most recent acceptance/refusal word. It is included in
the periodic Status message in case previous
transmissions containing A/R information were lost.
3[0-15] Stream Capacity. When sent by the WPS, this field
indicates how much stream capacity is unused, in units
of data bits per millisecond. There is no guarantee
that a request for a stream of this size will succeed.
Since available capacity depends directly on a variety
of parameters that can be selected by the user, the
value of this field is the maximum capacity that could
be achieved if existing streams were expanded at low
reliability. This field is not meaningful in messages
sent from the host to the WPS and must be set to zero.
4[0-15] Timestamp. This field indicates the time that the
Status message was generated. When sent by a WPS, the
time is in units of seconds since the last link
restart. The host should also timestamp its messages
in units of seconds.
5[0-15] Sent By Us. Count of messages sent by us since the
last link restart (not including this one).
6[0-15] Sent To Us. Count of messages sent to us since the
last link restart. This is the count from word 5 of
the last Status message received.
7[0-15] Received, No Errors. This is the count of messages
received without errors (since the last link restart)
at the time that the last Status message was received.
8[0-15] Received With Errors. This is the count of messages
Edmond [Page 53]
RFC 1221 HAP2 April 1991
received with errors (since the last link restart) at
the time the last Status message was received.
9[0-15] Bad Header Checksums. This is the count of messages
received with bad header checksums (since the last link
restart) at the time the last Status message was
received.
10[0-15] Hardware Error Indication. This is the count of
messages received with hardware CRC errors or hardware
interface error indications (since the last link
restart) at the time the last Status message was
received.
8. Initialization
The Host Access Protocol uses a number of state variables that must
be initialized in order to function properly. These variables are
associated with the send and receive message numbers used by the
acceptance/refusal mechanism and the statistics maintained to support
link monitoring. Link initialization should be carried out when a
machine is initially powered up, when it does a system restart, when
the ON state (see below) times out, when a loopback condition times
out (see Section 9), or whenever the link transitions from non-
operational to operational status.
Initialization is accomplished by the exchange of Restart Request
(RR) and Restart Complete (RC) messages between a host and a WPS.
Either end (or both ends) may send an initial RR, and both ends must
have sent and received an RC message in order to declare the link up.
Because the RC message is a reply (to an RR or RC), receipt of an RC
message by both ends guarantees that the physical link is operating
in both directions. The initialization state diagram that must be
implemented by both WPS and host is shown in Figure 36. Five states
are identified in the state diagram:
OFF Entered upon recognition of a requirement to restart.
The interface in the Host or WPS can recognize this
requirement itself or be forced to restart by receipt
of an RR message from the other end while in the ON
state.
INIT Local state variables have been initialized but no RC
messages have yet been sent or received. If receipt of
an RR initiated the restart, or if an RR has been
received since this restart began, send an RC
(optional, reduces startup time). Otherwise, send an
RR to alert the other end of the restart.
Edmond [Page 54]
RFC 1221 HAP2 April 1991
RR-SNT A request to reinitialize (RR) has been sent to the
other end, but no RR or RC messages have been received.
RC-SNT An RC has been sent to the other end in response to an
RR. The interface is waiting to receive an RC.
ON RC messages have been both sent and received. Local
counters have been zeroed. Data and control messages
can now be exchanged between the WPS and host.
All states have 10-second timeouts (not illustrated) which return the
protocol to the OFF state. The occurrence of any events other than
those indicated in the diagram are ignored.
Edmond [Page 55]
RFC 1221 HAP2 April 1991
.-----.
Any Timeout or ----->| OFF |<----------------------------+
Device Down `--+--' |
| |
| (When I/O Device Up) |
V |
.-------. |
| INIT | |
`---+---' |
| |
(Yes) V (No) |
+---------RR Received?----------+ |
| | |
| Send RR |
| | |
| V |
| .--------. |
Send RC <-----+-------<--------+ RR-SNT | |
| | (Rcv RR) `---+----' |
| | | (Rcv RC) |
V | | |
.--------. | | |
| RC-SNT +--->--+ Send RC |
`----+---' (Rcv RR) | |
(Rcv RC) | | |
| | |
+------->------+-------<--------+ |
| |
Initialize Status Counters |
| |
V |
.-----. Rcv RR or |
Rcv Any +----->| ON +---------------------->------+
Other | `--+--' Fail to Rcv Status message
+---------+ for 10 seconds
HAP LINK RESTART STATE DIAGRAM
Figure 36
The Restart Request control message (Figure 37) is sent by either a
host or a WPS when it wishes to restart a link. The Restart Request
causes all the monitoring statistics reported in the Status Message
to be reset to zero and stops all traffic on the link in both
directions. The Restart Complete message (Figure 38) is sent in
response to a received Restart Request or Restart Complete to
complete link initialization. The Restart Complete carries a field
used by the host to enable or disable the acceptance/refusal
Edmond [Page 56]
RFC 1221 HAP2 April 1991
mechanism for the link being restarted (see Section 5). After the
Restart Complete is processed, traffic may flow on the link.
The allocation and state of network resources (streams and groups)
are separate from the state of the host's access link(s) to the WPS.
The Information Request message (see Section 6.5) may be used by a
host to determine what resources it has. If the "SL" bit is set in
the Restart Complete message from the WPS, and if the host believes
it has resources allocated to it, the host is strongly encouraged to
use an Information Request to verify that it still has its resources.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
0 | 1|LB| 0 |VERSION | 0 | 3 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
1 | HEADER CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
2 | HOST ADDRESS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
3 | LINK NUMBER |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
RESTART REQUEST
Figure 37
0[0] Message Type = 1 (Control Message).
0[1] Loopback indicator.
0[2-4] Reserved. Must be zero.
0[5-7] HAP version number. Use 1. Use of zero invokes
backward compatibility code (see Appendix B).
0[8-11] Reserved. Must be zero.
0[12-15] Control Message Type = 3 (Restart Request).
1[0-15] Header Checksum. The checksum is the 2's-complement of
the 2's-complement sum of words 0-3 (excluding the
checksum word itself).
2[0-15] Host Address. The WPS inserts the primary network
address of the host. The host may insert any of its
Edmond [Page 57]
RFC 1221 HAP2 April 1991
network addresses in this field (hosts may have more
than one logical address per physical port). The WPS
will only bring up the HAP link if the host address is
valid for the port being used.
3[0-15] Link Number. This field contains the sender's
identification of the physical link being used. This
information is used to identify the link when reporting
errors to the Network Operations Center (NOC).
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
0 | 1|LB| 0 |VERSION | 0 |SL|AR| 4 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
1 | HEADER CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
2 | HOST ADDRESS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
3 | LINK NUMBER |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
RESTART COMPLETE
Figure 38
0[0] Message Type = 1 (Control Message).
0[1] Loopback indicator.
0[2-4] Reserved. Must be zero.
0[5-7] HAP version number. Use 1. Use of zero invokes
backward compatibility code (see Appendix B).
0[8-9] Reserved. Must be zero.
0[10] Service loss alert (boolean) (WPS to host only; host
must send zero). If the WPS has any reason to believe
that the resources allocated to the host may not match
what the host believes is allocated, SL is set to one.
If SL is one, a host that believes it owns any resources
is strongly encouraged to use an Information Request to
verify that the resources are still allocated. SL will
be one the first time a link is brought up after a WPS
is restarted, and may be set in other cases.
Edmond [Page 58]
RFC 1221 HAP2 April 1991
0[11] Acceptance/Refusal Control. This bit is used by the
host to enable or disable the acceptance/refusal
mechanism for all traffic on the link.
0 = Disable acceptance/refusal
1 = Enable acceptance/refusal
0[12-15] Control Message Type = 4 (Restart Complete).
1[0-15] Header Checksum. Covers words 0-3.
2[0-15] Host Address.
3[0-15] Link Number.
9. Loopback Control
The Host Access Protocol provides a Loopback Request control message
which can be used by a WPS or a host to request the remote loopback
of its HAP messages. Such requests are usually the result of
operator intervention for purposes of system fault diagnosis. For
clarity in the following discussion, the unit (WPS or host)
requesting the remote loopback is referred to as the "transmitter"
and the unit implementing (or rejecting) the loopback is referred to
as the "receiver".
When the host access link is remotely looped, all HAP messages will
be returned, unmodified, over the access link by the receiver.
(Messages that are too long to be valid HAP messages may be discarded
instead of being returned.) The receiver will not send any of its
own messages to the transmitter while it is implementing the loop.
WPS-generated messages are distinguished from host-generated messages
by means of the Loopback indicator that is in every HAP message
header.
Two types of remote loopback may be requested: loopback at the
receiver's interface hardware and loopback at the receiver's I/O
driver software. HAP does not specify the manner in which the
receiver should implement these loops; additionally, some receivers
may use interface hardware which is incapable of looping the
transmitter's messages, only allowing the receiver to provide
software loops. A receiver may not be able to interpret the
transmitter's messages as it is looping them back. If such
interpretation is possible, however, the receiver will not act on any
of the transmitter's messages other than requests to reinitialize the
WPS-host link (Restart Request (RR) control messages; see Section 8.)
When a receiver initiates a loopback condition in response to a
Edmond [Page 59]
RFC 1221 HAP2 April 1991
loopback request, it makes an implicit promise to maintain the
condition for the duration specified in the Loopback Request message.
However, if an unanticipated condition such as a system restart
occurs in either the transmitter or the receiver, the affected unit
will try to reinitialize the WPS-host link by sending an RR message
to the other unit. If the RR message is recognized by the other
unit, a link initialization sequence can be completed. This will
restore the link to an unlooped condition even if the specified loop
duration has not yet expired. If a receiver cannot interpret a
transmitter's RR messages, and in the absence of operator
intervention at the receiver, the loop will remain in place for its
duration.
HAP does not specify the characteristics of any loopback conditions
that may be locally implemented by a given unit. An example of such
a condition is that obtained when a WPS commands its host interface
to loop back its own messages. If such local loop conditions also
cause the reflection of messages received from the remote unit, the
remote unit will detect the condition via the HAP header Loopback
indicator.
A specific sequence must be followed for setting up a remote
loopback. It begins after the HAP link has been initialized and a
decision is made to request a remote loop. The transmitter then
sends a Loopback Request message (Figure 39) to the receiver and
waits for either (1) a 10-second timer to expire, (2) a "Can't
implement loop" Unnumbered Response message from the receiver, or (3)
one of its own reflected messages. If event (1) or (2) occurs the
request has failed and the transmitter may, at its option, try again
with a new Loopback Request message. If event (3) occurs, the remote
loopback condition has been established. While waiting for one of
these events, messages from the receiver are processed normally.
Note that RR messages arriving from the receiver during this time
will terminate the loopback request.
When a receiver gets a Loopback Request message, it either implements
the requested loop for the specified duration, or returns a "Can't
implement loop" response without changing the state of the link. The
latter response would be returned, for example, if a receiver is
incapable of implementing a requested hardware loop. A receiver
should initiate reinitialization of the link with an RR message(s)
whenever a loopback condition times out.
There is one asymmetry that is required in the above sequence to
resolve the (unlikely) case where both WPS and host request a remote
loopback at the same time. If a WPS receives a Loopback Request
message from a host while it is itself waiting for an event of type
(1)-(3), it will return a "Can't implement loop" response to the host
Edmond [Page 60]
RFC 1221 HAP2 April 1991
and will continue to wait. A host in the converse situation,
however, will abort its loopback request and will instead act on the
WPS's loopback request.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
0 | 1|LB|GOPRI| 0 | LOOP TYPE | 8 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
1 | HEADER CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
2 | LOOP DURATION |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
LOOPBACK REQUEST
Figure 39
0[0] Message Type = 1 (Control Message).
0[1] Loopback indicator.
0[2-3] Go-Priority.
0[4-7] Reserved. Must be zero.
0[8-11] Loop Type. This field indicates the type of loop that
is being requested as follows:
0 = Undefined
1 = Loop at interface (hardware loop)
2 = Loop at driver (software loop)
3-15 = Undefined
0[12-15] Control Message Type = 8 (Loopback Request).
1[0-15] Header Checksum. The checksum is the 2's-complement of
the 2's-complement sum of words 0-2 (excluding the
checksum word itself).
2[0-15] Loop Duration. The transmitter of a Loopback Request
message uses this field to specify the number of
seconds that the loop is to be maintained by the
receiver.
Edmond [Page 61]
RFC 1221 HAP2 April 1991
10. Other Control Messages
Before a WPS or a host voluntarily disables a WPS-host link, it
should send at least one Link Going Down control message (Figure 40)
over that link. HAP does not define the action(s) that should be
taken by a WPS or a host when such a message is received; informing
the Network Operations Center (NOC) and/or the network users of the
impending event is a typical course of action. Note that each Link
Going Down message only pertains to the WPS-host link that it is sent
over; if a host and a WPS are connected by multiple links, these
links may be selectively disabled.
A No Operation (NOP) control message (Figure 41) may be sent at any
time by a WPS or a host. A NOP message contains up to 32 words of
arbitrary data which are undefined by HAP. NOP messages may be
required in some cases to clear the state of the WPS-host link
hardware.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
0 | 1|LB|GOPRI| 0 | REASON | 7 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
1 | HEADER CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
2 | TIME UNTIL DOWN |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
3 | DOWN DURATION |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
LINK GOING DOWN
Figure 40
0[0] Message Type = 1 (Control Message).
0[1] Loopback indicator.
0[2-3] Go-Priority.
0[4-7] Reserved. Must be zero.
0[8-11] Reason. This field is used by the WPS or the host to
indicate the reason for disabling this WPS-host link as
follows:
Edmond [Page 62]
RFC 1221 HAP2 April 1991
0 = Cancel previous notice, not going down
1 = Unspecified reason
2 = Scheduled PM
3 = Scheduled hardware work
4 = Scheduled software work
5 = Emergency restart
6 = Power outage
7 = Software breakpoint
8 = Hardware failure
9 = Not scheduled up
10 = Last warning: The WPS or host will disable
the link in 10 seconds
11-15 = Undefined
0[12-15] Control Message Type = 7 (Link Going Down).
1[0-15] Header Checksum. The checksum is the 2's-complement of
the 2's-complement sum of words 0-3 (excluding the
checksum word itself).
2[0-15] Time Until Down. This field specifies the amount of
time remaining until the WPS or host disables the link
(in minutes). An entry of zero indicates that there is
less than a minute remaining.
3[0-15] Down Duration. This field specifies the amount of time
that the WPS-host link will be down (in minutes). An
entry of zero indicates that the down duration will be
less than a minute. An entry of -1 (all bits set)
indicates an indefinite down duration.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
0 | 1|LB| 0 | LENGTH | 6 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
1 | HEADER CHECKSUM |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| |
2-N : ARBITRARY DATA :
| |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
NO OPERATION (NOP)
Figure 41
Edmond [Page 63]
RFC 1221 HAP2 April 1991
0[0] Message Type = 1 (Control Message).
0[1] Loopback indicator.
0[2-6] Reserved. Must be zero.
0[7-11] Length. The number of words of arbitrary data.
0[12-15] Control Message Type = 6 (NOP).
1[0-15] Header Checksum. The checksum is the 2's-complement of
the 2's-complement sum of words 0-N (excluding the
checksum word itself).
2-N Arbitrary Data. Up to 32 words of data may be sent.
The data are undefined by HAP.
11. Appendix A -- Future Extensions
The extensions to HAP described below are included to provide
additional context for the understanding of HAP's current
capabilities, as well as suggest how HAP may be enhanced in the
future to provide better support for multi-site conferencing. These
capabilities are not supported by TWBNET.
One change under consideration is the addition of a "conference"
resource, which would own some number of streams and groups and
improve the network's ability to meet the needs of video conference
users. A single request to modify the "conference", such as to add a
new member, would result in modifying all the streams in the
conference to include the new member, modifying the conference's
primary group address to add the new member, etc., in a single
network operation. Such a capability would not only simplify
conference resource management for hosts, but also reduce the number
of network setup operations, permit more nearly "atomic" decisions of
whether a particular conference modification is possible, and reduce
the problem of recovery if modification is not possible.
Another change under consideration is the addition of "shared
streams." This capability would allow hosts to share a single
allocation of network bandwidth (and other resources) wherever the
streams shared a common communication path. Hosts using a shared
stream must be willing to restrict their total transmission rate to
the rate of the shared bandwidth. Multi-site conferences could use
such a capability to avoid allocating full bandwidth for voice data
for all conference members. Instead, bandwidth for, say, four active
voices at once could be allocated and shared, and voice messages
would only be lost when more than four people tried to talk at once.
Edmond [Page 64]
RFC 1221 HAP2 April 1991
The Create Shared Stream Request would use a different request code
than Create Stream Request, and the setup message would likely
contain at least one additional field to identify the set of shared
streams. Change and Delete Stream requests could be used for both
shared and non-shared streams.
12. Appendix B -- Backward compatibility
The WPS will support the use of HAP version 0 by hosts until all
hosts have upgraded to version 1. The WPS determines which HAP
version the host is using by examining the Restart Request and/or
Restart Complete control messages sent by the host to the WPS. If
the host initiates a restart and thus sends both a Restart Request
and a Restart Complete, and if the HAP version numbers in the two
messages differ, the version number in the Restart Complete will
prevail. The WPS will always set the version number to 1. If the
host sends 0 in the version number field, version 0 compatiblity mode
will be invoked.
Version 0 of HAP did not contain the PROTOCOL ID field in the
datagram and stream message headers. Instead, the IL bit in the Type
of Service word was used to indicate the presence or absence of an
Internet Protocol (IP) header (any version number) following the HAP
header. This is the original description of that bit:
3[1] Internet/Local Flag. This flag is set by a source host to
specify to a destination host whether the data portion of
the message contains an Internet Protocol (IP) header [3].
This field is passed transparently by the source and
destination WPSen for traffic between network hosts. This
field is examined by WPS Agents in order to support
Internet operation.
0 = Internet
1 = Local
Conversion Algorithms
Link control messages (e.g., Restart Request) do not require
conversion. Datagram and stream messages sent by or to a host
running HAP version 0 will be converted by the WPS. Message
conversion will probably cause the maximum throughput of hosts using
HAP version 0 to be somewhat lower than that of hosts using HAP
version 1.
HAP version 0 used the IL bit in the HAP Type of Service word to
indicate the presence or absence of an IP header. Version 1 uses the
Protocol ID field. To convert host-to-WPS messages, the IL bit will
Edmond [Page 65]
RFC 1221 HAP2 April 1991
be cleared, and the protocol ID field will be inserted, with the
value indicated:
IL was Destination Protocol ID set to:
------ ------------- ---------------------
0 any HAP_PROTO_IP (0x800)
1 Service Agent HAP_PROTO_SETUP (1)
1 other HAP_PROTO_NONE (0)
To convert WPS-to-host messages, the protocol ID field will be
deleted, and the IL bit will be set by:
IL = (protocol_id was HAP_PROTO_IP) ? 0 : 1;
HAP_PROTO_IP (see Appendix C) will be used for IP "versions" 3
(GG protocol), 4 (IP), and 5 (ST).
The datagram message header fields TTL and PRI have been swapped in
HAP version 0 compared to version 1. The conversion code swaps the
contents of these two fields for hosts running version 0.
The stream message header field TTL in HAP version 0 was replaced by
the PRE field in version 1. Since the only permitted value of TTL
was 1, and it is a valid PRE value, no conversion is necessary.
In HAP version 0, messages between a host and the Service Agent were
allowed to contain Internet Protocol headers. No hosts use that
capability, so no provision will be made to accommodate IP headers in
Setups between hosts and the Service Agent.
In version 0, the Restart Request control message contained a "reason
for restart" field. That field was ignored in all current
implementations and has been eliminated in version 1.
Current implementations expect the WPS to insert an "incarnation
count" in bits 5-10 of the first word of both Restart Request and
Restart Complete messages. This functionality has been replaced by
the "SL" bit in the Restart Complete message in version 1.
Compatibility code will be added if needed, but it is expected that
none will be needed.
13. Appendix C -- HAP Protocol ID Assigned Numbers
This section lists the values of the PROTOCOL ID field. This part of
the specification will be obsolete when a version of the Assigned
Numbers RFC containing HAP protocol ID numbers is issued.
HAP adopts the Ether-type numbers in the 1500-65535 range. Protocol
IDs 256-511 identify ISO protocols. Zero indicates the absence of a
Edmond [Page 66]
RFC 1221 HAP2 April 1991
higher level protocol header. Other protocol IDs are reserved for
future assignment.
Protocol ID Indicates
----------- ---------
0 No higher level protocol
1 For Network Service Agent messages
2-255 Reserved
256-511 ISO protocol identifier + 256
512-1499 Reserved
1500-65535 Identical to Ether-type [10].
HAP PROTOCOL ID NUMBERS
Figure 42
REFERENCES
1. Falk, G., Groff, S., Koolish, R., and W. Milliken, "PSAT
Technical Report", BBN Technical Report No. 4469, Chapter 4, May
1981.
2. Rees, T., Editor, "A Host Access Protocol Specification", BBN
Laboratories, Inc., May 1987. (A revision of RFC 907 that was
distributed to DARPA and the WBNET user community but not
resubmitted as an RFC.)
3. Postel, J., Editor, "Internet Protocol - DARPA Internet Program
Protocol Specification", RFC 791, USC/Information Sciences
Institute, September 1981.
4. Topolcic, C., Editor, "Experimental Internet Stream Protocol,
Version 2 (ST-II)", RFC 1190, Bolt Beranek and Newman, Inc.,
October 1990.
5. Edmond, W., Seo, K., Leib, M., and C. Topolcic, "The DARPA
Wideband Network Dual Bus Protocol", Proceedings of ACM SIGCOMM
'90, pages 79-89, September 24-27, 1990.
6. "Host/SATNET Protocol", Internet Engineering Note (IEN) 192, July
1981.
7. Evenchik, L., McNeill, D., Bressler, R., Owen, A., Rice, Jr., R.,
Trout, G., Pavey, C., Damer, R., Deckelman, F., and T. Hughes,
"MATNET, An Experimental Navy Shipboard Satellite Communications
Network", Proceedings of INFOCOM '82, pages 3-11, March 30 -
April 1, 1982.
Edmond [Page 67]
RFC 1221 HAP2 April 1991
8. Falk, G., Groff, J., Milliken, W., Nodine, M., Blumenthal, S.,
and W. Edmond, "Integration of Voice and Data in the Wideband
Packet Satellite Network", IEEE Journal on Selected Areas in
Communications, Vol. SAC-1, No. 6, December 1983.
9. "Interface Message Processor: Specifications for the
Interconnection of a Host and an IMP", BBN Technical Report No.
1822, October 1980.
10. Reynolds, J., and J. Postel, "Assigned Numbers", RFC 1060,
USC/Information Sciences Institute, March 1990.
Security Considerations
Security issues are not discussed in this memo.
Author's Address
Winston Edmond
Bolt Beranek and Newman, Inc.
Network Technologies Department
10 Moulton Street
Cambridge, Massachusetts 02138
Phone: (617) 873-3000
EMail: wbe@bbn.com
Edmond [Page 68]
|