<pre>Network Working Group                                          A. Robert
Request for Comments: 2351                                          SITA
Category: Informational                                         May 1998


              <span class="h1">Mapping of Airline Reservation, Ticketing,</span>
                     <span class="h1">and Messaging Traffic over IP</span>

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

Security Disclaimer:

   This document fails to adequately address security concerns.  The
   protocol itself does not include any security mechanisms.  The
   document notes that traffic can be authenticated based on external
   mechanisms that use static identifiers or what are apparently clear-
   text passwords, neither of which provide sound security.  The
   document notes in general terms that traffic can be secured using
   IPSEC, but leaves this form of sound security strictly optional.

Abstract

   This memo specifies a protocol for the encapsulation of the airline
   specific protocol over IP.

Table of Conents

   1. INTRODUCTION                                                    2
   2. TERMINOLOGY &amp; ACRONYMS                                          4
   3. LAYERING                                                        7
   4. TRAFFIC IDENTIFICATION                                          7
   5. TCP PORT ALLOCATION                                             8
   6. MATIP SESSION ESTABLISHMENT                                     8
   7. OVERALL PACKET FORMAT FOR TYPE A &amp; TYPE B                       9
   8. MATIP FORMAT FOR TYPE A CONVERSATIONAL TRAFFIC                 10
    8.1 Control Packet Format                                        10
     8.1.1 Session Open format (SO)                                  10
     8.1.2 Open Confirm format (OC)                                  12
     8.1.3 Session Close (SC)                                        14
    8.2 Data Packet Format                                           14



<span class="grey">Robert                       Informational                      [Page 1]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-2" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


   9. MATIP FORMAT FOR TYPE A HOST-TO-HOST TRAFFIC                   15
    9. 1 Control Packet Format                                       15
     9.1.1 Session Open format (SO)                                  15
     9.1.2 Open Confirm format (OC)                                  17
     9.1.3 Session Close (SC)                                        17
    9.2 Data Packet Format                                           18
   10. MATIP FORMAT FOR TYPE B TRAFFIC                               19
    10.1 Control packet format                                       19
     10.1.1 Session Open format (SO)                                 19
     10.1.2 Open confirm format (OC)                                 20
     10.1.3 Session Close (SC)                                       21
    10.2 Data packet format                                          21
   11. SECURITY CONSIDERATIONS                                       22
   12. AUTHOR'S ADDRESS                                              22
   13. FULL COPYRIGHT STATEMENT                                      23

<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>. Introduction</span>

   The airline community has been using a worldwide data network for
   over 40 years, with two main types of traffic:

    Transactional traffic

      This is used typically for communication between an airline office
      or travel agency and a central computer system for seat
      reservations and ticket issuing. A dumb terminal or a PC accesses
      the central system (IBM or UNISYS) through a data network.

      This traffic is also called TYPE A and is based on real-time
      query/response with limited protection, high priority and can be
      discarded. The user can access only one predetermined central
      computer system. In case of no response (data loss), the user can
      duplicate the request.

    Messaging

      This is an e-mail application where real-time is not needed.
      However a high level of protection is required. The addressing
      scheme uses an international format defined by IATA and contains
      the city and airline codes.

      This traffic is also called TYPE B and is transmitted with a high
      level of protection, multi-addressing and 4 levels of priority.

   The detailed formats for TYPE A and TYPE B messages are defined in
   the IATA standards.





<span class="grey">Robert                       Informational                      [Page 2]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-3" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


   At the bottom level, synchronous protocols have been built since
   1960's and well before the OSI and SNA standards.

   At present, there is a big number of legacy equipment installed in
   thousands of airline offices around the world. Many airlines do not
   have immediate plans to replace their terminals with more modern
   equipment using open standards. They are in search of more economical
   ways for connecting these terminals to the present reservation
   system.

   Most airlines are willing to migrate from airline specific protocols
   to standardized protocols in order to benefit from the lower cost of
   new technologies, but the migration has been slow done to the
   following factors:

   - Applications have not been migrated.
   - Dumb terminals using airline protocols P1024B (IBM ALC) or P1024C
     (UNISYS UTS) are still numerous.

   There are currently many different proprietary solutions based on
   gateways available to take advantage of low cast networking, but they
   are not scalable and cannot interact.

   In the future, TCP/IP will be more commonly used as a common
   transport means for traffic types because:

   - TCP/IP is the standard protocol of UNIX based applications
   - TCP/IP stacks are inexpensive
   - TCP/IP is used on intranets.

   The purpose of this RFC is to define the mapping of the airline
   traffic types over TCP/IP. The airlines implementing it in their
   systems should have a TCP/IP stack to enable the traffic exchange
   below:

















<span class="grey">Robert                       Informational                      [Page 3]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-4" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


     !----!          (            )
     !    !----------(            )
     !----!          (            )
     Type B HOST     (   NETWORK  )
                     (            )
                     (            )            !---o
     !----!          (            )--------! D !---o Type A stations
     !----!----------(            )            !---o
     !----!          (            )
     TYPE A HOST           !
                           !
                           !
                           !
                        --------
                       !       !
                        --------
                      Network Messaging System


      (D) : Gateway TYPE A router

   The different airline traffic flows concerned by this RFC are:

     - TYPE A Host / Terminal
     - TYPE A Host / TYPE A host
     - TYPE B Host / Network messaging System

   In the case of dumb terminals, a conversion is required on the
   terminal side in order to have an IP connection between the host and
   the router. However, the IP connection is directly between the
   central airline host and the intelligent workstation if the latter
   has a direct connection to the network, a TCP/IP stack and a terminal
   emulation

<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>. Terminology &amp; Acronyms</span>

   ALC
   Airline Line Control: IBM airline specific protocol (see P1024B)

   ASCII
   American Standard Code for Information Interchange

   ASCU
   Agent Set Control Unit: Cluster at the user side.

   AX.25
   Airline X.25: Airline application of the X.25 OSI model (published by
   IATA)



<span class="grey">Robert                       Informational                      [Page 4]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-5" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


   BAUDOT
   Alphabet defined in ITU-T Number 5. BAUDOT uses 5 bits. Padded BAUDOT
   uses 7 bits with the Most significant bit (bit 7) for the parity and
   the bit 6 equal to 1.

   BATAP
   Type B Application to Application Protocol. Protocol to secure the
   TYPE B traffic. It was specified by SITA and is now published by IATA
   (SCR Vol. 3)

   EBCDIC
   Extended Binary Coded Decimal Interchange Code

   Flow ID Traffic
   Flow identifier used in host to host traffic  to differentiate
   traffic flow types.

   HLD
   High Level Designator: Indicates the entry or exit point of a block
   in the network.

   IA
   Interchange Address: ASCU identifier in P1024B protocol.

   IATA
   International Air Transport Association

   IP
   Internet Protocol

   IPARS
   International Program Airline Reservation System: IPARS code is used
   in ALC

   HTH
   Host to Host (traffic).

   LSB
   Least Significant Bit

   MATIP
   Mapping of Airline Traffic over Internet Protocol

   MSB
   Most Significant Bit

   OC
   Open Confirm (MATIP command)



<span class="grey">Robert                       Informational                      [Page 5]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-6" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


   OSI
   Open Standard Interface

   P1024B
   SITA implementation of the ALC, the IBM airlines specific protocol.
   It uses 6-bit padded characters (IPARS) and IA/ TA for physical
   addressing.

   P1024C
   SITA implementation of the UTS, the UNISYS terminal protocol. It uses
   7-bit (ASCII) characters and RID/ SID for physical addressing.

   RFU
   Reserved for Future Use

   RID
   Remote Identifier: ASCU identifier in P1024C protocol.

   SC
   Session Close (MATIP command)

   SCR
   System and Communication Reference. (IATA document)

   SID
   Station Identifier: Terminal identifier in P1024C protocol.

   SITA
   Societe International de Telecommunications Aeronautiques

   SO
   Session Open (MATIP command)

   TA
   Terminal Address: Terminal identifier in P1024B protocol.

   TCP
   Transport Control Protocol

   TYPE A Traffic
   Interactive traffic or host to host

   TYPE B Traffic
   Messaging traffic in IATA compliant format with high level of
   reliability

   UTS
   Universal Terminal System by Unisys: (see P1024C)



<span class="grey">Robert                       Informational                      [Page 6]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-7" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>. LAYERING</span>

   MATIP is an end to end protocol. Its purpose is to have a mapping
   standard between the TCP layer and the airline application without
   any routing element.

     +-------------------------------+
     |Airline TYPE A | Airline TYPE B|
     |               |   Application |
     |               |---------------|
     | Application   |   BATAP       |
     +-------------------------------+
     |   MATIP A     |   MATIP B     |
     +-------------------------------+
     |            T.C.P              |
     +-------------------------------+
     |             I.P               |
     +-------------------------------+
     |            MEDIA              |
     +-------------------------------+

<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>. TRAFFIC IDENTIFICATION</span>

   In TYPE A conversational traffic, the airline host application
   recognizes the ASCU due to 4 bytes (H1, H2, A1, A2). These bytes are
   assigned by the host and are unique per ASCU. Thus, a host can
   dynamically recognize the ASCU independent of IP address.

   H1 H2 A1 A2 bytes follow one of the three cases below:

     - A1,A2 only are used and H1H2 is set to 0000.
     - H1,H2 identify the session and A1A2 the ASCU inside the session.
     - H1,H2,A1,A2 identify the ASCU.

   The first two cases are fully compatible with the AX.25 mapping where
   H1H2 may be equivalent to the HLD of the concentrator, i.e., 2 bytes
   hexadecimal. The third rule allows more flexibility but is not
   compatible with AX.25.

   In TYPE A host to host traffic the identification field is also
   present and is equal to 3 bytes H1 H2 Flow ID (optional). H1H2 are
   reserved for remote host identification (independently of the IP
   address) and must be allocated bilaterally.

   In Type B traffic, identification of End Systems may be carried out
   by the use of HLDs, or directly by the pair of IP addresses.





<span class="grey">Robert                       Informational                      [Page 7]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-8" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>. TCP PORT ALLOCATION</span>

   IANA (Internet Assigned Numbers Authority) has allocated the
   following ports for MATIP TYPE A and TYPE B traffic:
     MATIP Type A TCP port = 350
     MATIP Type B TCP port = 351

   Therefore the traffic type A or B is selected according to the TCP
   port.

<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>. MATIP SESSION ESTABLISHMENT</span>

   Prior to any exchange between two applications, a single MATIP
   session is established above the TCP connection in order to identify
   the traffic characteristic such as:

     - Subtype of traffic for TYPE A (Type A host to host or Type A
       conversational )
     - Multiplexing used (for Type A)
     - Data header
     - Character set

   A separate session and TCP connection must be established for each
   set of parameters (e.g., P1024B, P1024C traffic between two points
   needs two separate sessions).

   The establishment of a MATIP session can be initiated by either side.
   No keep-alive mechanism is defined at MATIP level. Session time out
   relies on the TCP time-out parameters.

   There are three commands defined to manage the MATIP session:

   - Session Open (SO) to open a session.
   - Open Confirm (OC) to confirm the SO command.
   - Session close (SC) to close the current session.

   A MATIP session can be up only if the associated TCP connection is
   up.  However it is not mandatory to close the TCP connection when
   closing the associated MATIP session.

   Typical exchange is:

                      TCP session establishment

             Session Open ---------&gt;
                            &lt;-----------   Open confirm
                          data exchange
             ----------------------&gt;



<span class="grey">Robert                       Informational                      [Page 8]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-9" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


                             &lt;-------------------------
                             .
                             .
                             .
    Session Close -----------------&gt;
                             .
                             .
                             .
                              &lt;-------------------------   Session Open
   Open confirm -------------------&gt;
                        data exchange
                               &lt;-------------------------
             ----------------------&gt;

   The Session Open command may contain configuration elements. An
   Session Open command received on a session already opened (i.e., same
   IP address and port number) will automatically clear the associated
   configuration and a new configuration will be set up according to the
   information contained in the new open session command.

   As illustrated above, the open and close commands are symmetrical.

   For type A conversational traffic, the SO and OC commands contain
   information for the identification of the ASCUs and the session.
   ASCUs are identified within a session by two or 4 bytes. A flag is
   set to indicate if the ASCU is identified by 4 bytes (H1H2A1A2) or by
   2 bytes (A1A2). In the latter case, H1H2 is reserved for session
   identification.

   The SO command is sent to open the MATIP session. In Type A
   conversational it may contains the list of ASCUs configured in this
   session.

   The OC command confirms the SO command. It can refuse or accept it,
   totally or conditionally. In Type A, it contains the list of the
   ASCUs either rejected or configured in the session.

<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>. OVERALL PACKET FORMAT FOR TYPE A &amp; TYPE B</span>

   The first 4 bytes of the MATIP header follow the following rules.

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0|0|0|0|0| Ver |C|     Cmd     |            length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





<span class="grey">Robert                       Informational                      [Page 9]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-10" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


   Ver
   The `Ver' (Version) field represents the version of the MATIP. It
   must contain the value 001 otherwise the packet is considered as
   invalid.

   C
   Identifies a CONTROL packet.
     When set to 1, the packet is a Control packet
     When set to 0, the packet is a Data packet

   Cmd
   This field identifies the control command if the flag C is set to 1.

   Length
   This field indicates the number of bytes of the whole packet, header
   included.

   Notes : Fields identified as optional (Opt) are not transmitted if
   not used.

<span class="h2"><a class="selflink" id="section-8" href="#section-8">8</a>. MATIP FORMAT FOR TYPE A CONVERSATIONAL TRAFFIC</span>

<span class="h2"><a class="selflink" id="section-8" href="#section-8">8</a>. 1 Control Packet Format</span>

   There are 3 control packets to open or close the session at the MATIP
   level.

<span class="h4"><a class="selflink" id="section-8.1.1" href="#section-8.1.1">8.1.1</a> Session Open format (SO)</span>

   To be able to identify the session and before sending any data
   packets, a Session Open command is sent. It can be initiated by
   either side. In case of collision, the open session from the side
   having the lower IP address is ignored.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |0|0|0|0|0| Ver |1|1 1 1 1 1 1 0|           length              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |0 0|0 1|0| CD  | STYP  |0 0 0 0|       RFU     |MPX|HDR| PRES. |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      H1       |      H2       |           RFU                 |
      |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Reserved    |              RFU              | Nbr of ASCUs  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Nbr of ASCUs |        ASCU list (opt)                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




<span class="grey">Robert                       Informational                     [Page 10]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-11" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


   RFU
   Reserved for future use. Must be set to zero.

   CD
   This field specifies the Coding
      000 : 5 bits (padded baudot)
      010 : 6 bits (IPARS)
      100 : 7 bits (ASCII)
      110 : 8 bits (EBCDIC)
      xx1 : R.F.U

   STYP
   This is the traffic subtype (type being TYPE A).
      0001 : TYPE A Conversational

   MPX
   This flag specifies the multiplexing used within the TCP session.
   Possible values are:
      00 : Group of ASCU with 4 bytes identification per ASCU (H1H2A1A2)
      01 : Group of ASCUs with 2 bytes identification per ASCU (A1A2)
      10 : single ASCU inside the TCP session.


   HDR
   This field specifies which part of the airline's specific address is
   placed ahead of the message texts transmitted over the session.
   Possible values are:
      00 : ASCU header = H1+H2+A1+A2
      01 : ASCU Header = A1+A2
      10 : No Header
      11 : Not used

   The MPX and HDR must be coherent. When ASCUs are multiplexed, the data
   must contain the ASCU identification. The table below summarizes the
   allowed combinations:

       +--------------------------+
       |       MPX | 00 | 01 | 10 |
       +--------------------------+
       | HDR       |              |
       | 00        | Y  | Y  | Y  |
       | 01        | N  | Y  | Y  |
       | 10        | N  | N  | Y  |
       +--------------------------+







<span class="grey">Robert                       Informational                     [Page 11]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-12" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


   PRES
   This field indicates the presentation format
      0001 : P1024B presentation
      0010 : P1024C presentation
      0011 : 3270 presentation


   H1 H2
   These fields can logically identify the session if MPX is not equal to
   00. When this field is not used, it must be set to 0. If used in
   session (MPX &lt;&gt; 0) with HDR=00, H1H2 in data packet must have the same
   value as set in SO command.

   Nbr of ASCUs
   Nbr_of_ASCUs field is mandatory and gives the number of ASCUs per
   session. A 0 (zero) value means unknown. In this case the ASCU list is
   not present in the `Open Session' command and must be sent by the
   other end in the `Open Confirm' command.

   ASCU LIST
   Contains the list of identifier for each ASCU. If MPX=00 it has a
   length of four bytes (H1H2A1A2) for each ASCU, otherwise it is two
   bytes (A1A2).

<span class="h4"><a class="selflink" id="section-8.1.2" href="#section-8.1.2">8.1.2</a> Open Confirm format (OC)</span>

   The OC (Open Confirm) command is a response to an SO (Session Open)
   command and is used to either refuse the session or accept it
   conditionally upon checking hte configuration of each ASCU.

   In case of acceptance, the OC indicates the number and the address of
   the rejected ASCUs, if any. Alternatively, it indicates the list of
   ASCUs configured for that MATIP session if the list provided by the
   SO command was correct or the number of ASCUs configured in the
   session was unknown (n. of ASCU equals 0).

<span class="h5"><a class="selflink" id="section-8.1.2.1" href="#section-8.1.2.1">8.1.2.1</a> Refuse the connection</span>

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0|0|0|0|0| Ver |1|1 1 1 1 1 0 1|0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     cause     |
     +-+-+-+-+-+-+-+-+

   Cause
   This field indicates the reason for the MATIP session refusal:



<span class="grey">Robert                       Informational                     [Page 12]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-13" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


       0 0 0 0 0 0 0 1 : No Traffic Type matching between Sender &amp;
           Recipient
       0 0 0 0 0 0 1 0 : Information in SO header incoherent

       1 0 0 0 0 1 0 0
           up to       : Application dependent
       1 1 1 1 1 1 1 1

       Other values reserved.

<span class="h5"><a class="selflink" id="section-8.1.2.2" href="#section-8.1.2.2">8.1.2.2</a> Accept the connection</span>

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0|0|0|0|0| Ver |1|1 1 1 1 1 0 1|            length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 R 0 0 0 0 0| Nbr of ASCUs  |Nbr of ASCU(opt|  ASCU LIST    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   R
   Flag indicating an error in the ASCU configuration provided in the SO
   command.

   NBR of ASCUs
   If the MPX value is equal to 00 in the SO command, this field is two
   bytes long. Otherwise, it is one byte.
   If the R flag is set, the Nbr_of_ASCUs field represents the number of
   ASCUs in error. Otherwise, it indicates the number of ASCUs configured
   for that MATIP session.

   Notes: The length of this field is either one or two bytes. In the SO
   command, the length is always two bytes. This discrepancy comes from
   backward compatibility with AX25 (see chapter 4). In the SO command,
   it is possible to use a free byte defined in the AX25 call user data.
   Unfortunately, there is no such free byte in the AX25 clear user
   data.

   ASCU LIST
   Depending on the R flag, this field indicates the list of ASCUs  (A1A2
   or H1H2A1A2) either in error or within the session.






<span class="grey">Robert                       Informational                     [Page 13]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-14" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


<span class="h4"><a class="selflink" id="section-8.1.3" href="#section-8.1.3">8.1.3</a> Session Close (SC)</span>

   The SC (Session Close) command is used to close an existing MATIP
   session.

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0|0|0|0|0| Ver |1|1 1 1 1 1 0 0|0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Close  Cause  |
     +-+-+-+-+-+-+-+-+

   Close Cause
   Indicates the reason for the session closure:

       0 0 0 0 0 0 0 0 : Normal Close

       1 0 0 0 0 1 0 0
            up to      : Application dependent
       1 1 1 1 1 1 1 1

       Other values reserved.

<span class="h3"><a class="selflink" id="section-8.2" href="#section-8.2">8.2</a> Data Packet Format</span>


     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0|0|0|0|0| Ver |0|0 0 0 0 0 0 0|          length               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         ID (optional)                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                         Payload                               |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   ID
   This field is optional and has a different length and format
   according to the value of HDR, PRES indicated during the session
   establishment.








<span class="grey">Robert                       Informational                     [Page 14]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-15" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


     +------------------------------+-------------------------------+
     |HDR |  PRES = P1024B and 3270 |     PRES = P1024C             |
     +------------------------------+-------------------------------+
     |00  |ID = 4 bytes H1-H2-A1-A2 | ID = 5 bytes H1-H2-A1-0x01-A2 |
     +------------------------------+-------------------------------+
     |01  |ID = 2 bytes A1-A2       | ID = 3 bytes A1-0x01-A2       |
     +------------------------------+-------------------------------+
     |10  |ID = 0 bytes             | ID = 0 bytes                  |
     +------------------------------+-------------------------------+

   H1, H2 value must match the value given in the SO command if MPX is
   different from 0.

   Payload
   payload begins with the terminal identification:
      - One byte Terminal identifier (TA) in P1024B
      - Two bytes SID/DID Terminal identifier in P1024C.

<span class="h2"><a class="selflink" id="section-9" href="#section-9">9</a>. MATIP FORMAT FOR TYPE A HOST-TO-HOST TRAFFIC</span>

<span class="h2"><a class="selflink" id="section-9" href="#section-9">9</a>. 1 Control Packet Format</span>

   There are 3 control packets to open or close the session at the MATIP
   level.

<span class="h4"><a class="selflink" id="section-9.1.1" href="#section-9.1.1">9.1.1</a> Session Open format (SO)</span>

   To be able to identify the session and before sending any data
   packet, a Session Open command is sent. It can be initiated by either
   side. In case of collision, the open session from the side having the
   lower IP address is ignored.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0|0|0|0|0| Ver |1|1 1 1 1 1 1 0|     length                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0|0 1|0| CD  | STYP  |0 0 0 0|       RFU     |MPX|HDR|0 0 0 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      H1       |      H2       |           RFU                 |
     |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Flow ID(opt)|
     +-+-+-+-+-+-+-+-+

   RFU
   Reserved for future use. Must be set to zero.





<span class="grey">Robert                       Informational                     [Page 15]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-16" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


   CD
   This field specifies the Coding, as defined in <a href="#section-8.1.1.1">section 8.1.1.1</a>.

   STYP
   This is the traffic subtype (type being Type A).
   0010 : TYPE A IATA Host to Host
   1000 : SITA Host to Host

   MPX
   This flag specifies the multiplexing used within the MATIP session in
   TYPE A SITA host to host. Possible values are:

   00 : irrelevant
   01 : multiple flow inside the TCP connection
   10 : single flow inside the TCP connection

   HDR
   This field specifies which part of the airline's specific address is
   placed ahead of the message text transmitted over the session.
   Possible values are:

   00 : used in TYPE A SITA Host to Host Header = H1+H2+Flow ID
   01 : used in TYPE A SITA Host to Host Header = Flow ID
   10 : No Header (default for IATA host to Host)
   11 : Not used

   The MPX and HDR must be coherent. When flow are multiplexed, the data
   must contain the flow identification. The table below summarizes the
   possible combinations:

         +---------------------+
         |       MPX | 01 | 10 |
         +---------------------+
         | HDR       |    |    |
         | 00        | Y  | Y  |
         | 01        | Y  | Y  |
         | 10        | N  | Y  |
         +---------------------+

   H1 H2
   These fields can be used to identify the session. When this field is
   not used, it must be set to 0. If HDR=00, H1H2 in data packet must
   have the same value as set in SO command.

   Flow ID
   This field is optional and indicates the Flow ID (range 3F - 4F Hex).





<span class="grey">Robert                       Informational                     [Page 16]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-17" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


<span class="h4"><a class="selflink" id="section-9.1.2" href="#section-9.1.2">9.1.2</a> Open Confirm format (OC)</span>

   The OC (Open Confirm) command is a response to an SO (Session Open)
   command and is used to either refuse the session or accept it.

<span class="h5"><a class="selflink" id="section-9.1.2.1" href="#section-9.1.2.1">9.1.2.1</a> Refuse the connection</span>

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0|0|0|0|0| Ver |1|1 1 1 1 1 0 1|0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     cause     |
     +-+-+-+-+-+-+-+-+

   Cause
   This field indicates the reason for the MATIP session refusal

       0 0 0 0 0 0 0 1 : No Traffic Type matching between Sender &amp;
            Recipient
       0 0 0 0 0 0 1 0 : Information in SO header incoherent

       1 0 0 0 0 1 0 0
            up to      : Application dependent
       1 1 1 1 1 1 1 1

       Other values reserved.

<span class="h5"><a class="selflink" id="section-9.1.2.2" href="#section-9.1.2.2">9.1.2.2</a> Accept the connection</span>

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0|0|0|0|0| Ver |1|1 1 1 1 1 0 1|0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 0 0 0|
     +-+-+-+-+-+-+-+-+

<span class="h4"><a class="selflink" id="section-9.1.3" href="#section-9.1.3">9.1.3</a> Session Close (SC)</span>

   The SC (Session Close) command is used to close an existing MATIP
   session.









<span class="grey">Robert                       Informational                     [Page 17]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-18" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0|0|0|0|0| Ver |1|1 1 1 1 1 0 0|0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Close  Cause  |
     +-+-+-+-+-+-+-+-+

   Close Cause
   Indicates the reason for the session closure:


       0 0 0 0 0 0 0 0 : Normal Close

       1 0 0 0 0 1 0 0
            up to      : Application dependent
       1 1 1 1 1 1 1 1

       Other values reserved

<span class="h3"><a class="selflink" id="section-9.2" href="#section-9.2">9.2</a> Data Packet Format</span>

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0|0|0|0|0| Ver |0|0 0 0 0 0 0 0|          length               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         ID (optional)                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                         Payload                               |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   ID
   This field is optional and has a different length and format
   according to the value of   HDR indicated during the session
   establishment.

     +-------------------------------+
     |HDR |        I.D.              |
     +-------------------------------+
     |00  |ID = 3 bytes H1-H2 FLOW ID|
     +-------------------------------+
     |01  |ID = FLOW ID              |
     +-------------------------------+
     |10  |ID nor present            |
     +-------------------------------+



<span class="grey">Robert                       Informational                     [Page 18]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-19" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


   Payload packet
   The payload format is relevant to the MATIP layer. It is formatted
   according to the IATA host to host specifications and agreed
   bilaterally by the sender and the receiver.

<span class="h2"><a class="selflink" id="section-10" href="#section-10">10</a>. MATIP FORMAT FOR TYPE B TRAFFIC</span>

<span class="h3"><a class="selflink" id="section-10.1" href="#section-10.1">10.1</a> Control packet format</span>

   There are 3 control packets used to open or close the session at the
   MATIP level for exchanging Type B data

<span class="h4"><a class="selflink" id="section-10.1.1" href="#section-10.1.1">10.1.1</a> Session Open format (SO)</span>

   Before sending any data packets, it is recommended to let the systems
   establishing a session check that they are indeed able to communicate
   (i.e., Both systems agree on the characteristics of the traffic that
   will cross the connection). For this purpose, a two way handshake,
   using the Session commands defined hereafter, is performed
   immediately after the establishment of the TCP level connection.
   Either side can initiate this procedure. In case of collision, the
   open session from the side having the lower IP address is ignored.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0|0|0|0|0| Ver |1|1 1 1 1 1 1 0|            length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0| C D | PROTEC| BFLAG |          Sender HLD           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |       Recipient HLD           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Length
   This field indicates the number of bytes of the whole command, header
   included. The only possible values are equal to 6 bytes or 10 bytes.

   CD
   This field specifies the Coding, as defined in <a href="#section-8.1.1.1">section 8.1.1.1</a>.

   PROTEC
   Identifies the end to end Messaging Responsibility Transfer protocol
   used.
   0010: BATAP
   All other values available.

   BFLAG (X means `do not care'




<span class="grey">Robert                       Informational                     [Page 19]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-20" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


   X X 0 0 means that the fields `Sender HLD, Recipient HLD' do not exist
        in this packet. In this case, the exact length of the packet is 6
        Bytes.

   X X 1 0 means that the `Sender HLD, Recipient HLD' are carried
        respectively in bytes 9,10 and 11,12 of this packet. In this
        case, the exact length of the packet is 10 Bytes.

   0 0 X X means that the connection request has been transmitted from a
   host (Mainframe system)

   0 1 X X means that the connection request has been transmitted from a
   gateway)


   Sender HLD
   HLD of the Type B System sending the Session Open.

   Recipient HLD
   HLD of the Type B system to which session opening is destined.

<span class="h4"><a class="selflink" id="section-10.1.2" href="#section-10.1.2">10.1.2</a> Open confirm format (OC)</span>

   The OC (Open Confirm) command is a response to an SO (Session Open)
   command and is used to either refuse the session or accept it.

<span class="h5"><a class="selflink" id="section-10.1.2.1" href="#section-10.1.2.1">10.1.2.1</a> Refuse the connection</span>

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0|0|0|0|0| Ver |1|1 1 1 1 1 0 1|0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0|1|   Cause   |
     +-+-+-+-+-+-+-+-+

   Length of this packet is 5 Bytes.

   Cause
   Indicates the cause of the rejection

       0 0 0 0 0 1 : No Traffic Type matching between Sender &amp; Recipient
       0 0 0 0 1 0 : Information in SO header incoherent
       0 0 0 0 1 1 : Type of Protection mechanism are different
       0 0 0 1 0 0 up to 1 1 1 1 1 1 : R.F.U






<span class="grey">Robert                       Informational                     [Page 20]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-21" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


<span class="h5"><a class="selflink" id="section-10.1.2.2" href="#section-10.1.2.2">10.1.2.2</a> Accept the connection</span>

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0|0|0|0|0| Ver |1|1 1 1 1 1 0 1|0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 0 0 0|
     +-+-+-+-+-+-+-+-+

   Length of this packet is 5 Bytes.

<span class="h4"><a class="selflink" id="section-10.1.3" href="#section-10.1.3">10.1.3</a> Session Close (SC)</span>

   The SC (Session Close) command is used to close an existing MATIP
   session.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0|0|0|0|0| Ver |1|1 1 1 1 1 0 0|0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Close  Cause  |
     +-+-+-+-+-+-+-+-+

   Close Cause
   Indicates the reason for the session closure:
   0 0 0 0 0 0 0 0 : Normal Close
   1 0 0 0 0 1 0 0 up to 1 1 1 1 1 1 1 1 : Application dependent

   Other values reserved

<span class="h3"><a class="selflink" id="section-10.2" href="#section-10.2">10.2</a> Data packet format</span>

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0|0|0|0|0| Ver |0|0 0 0 0 0 0 0|            length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                         Payload                               |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Length
   This field indicates the number of bytes of the whole packet, header
   included.




<span class="grey">Robert                       Informational                     [Page 21]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-22" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


   Payload
   Type B message formatted according to the IATA standard and
   conforming to the rules of the accessed TYPE B service

<span class="h2"><a class="selflink" id="section-11" href="#section-11">11</a>. Security Considerations</span>

   The security is a very sensitive point for airline industry. Security
   for the MATIP users can take place at different levels:

   The ASCU must be defined to enable the session with the host
   application. The control can be achieved in two ways: either the ASCU
   address (H1 H2 A1 A2) is defined at the application level by the
   means of a static configuration, or the ASCU is identified by a User
   ID / password. In most cases, the User ID and Password are verified
   by a dedicated software running in the central host. But they can
   also be checked by the application itself.

   The MATIP sessions being transported over TCP/IP, It can go through a
   firewall. Depending on the firewall level, the control can be
   performed at network (IP addresses) or TCP application layer.

   For higher level of security all compliant implementations MAY
   implement IPSEC ESP for securing control packets.  Replay protection,
   the compulsory cipher suite for IPSEC ESP, and NULL encryption MAY be
   implemented. Optionally, IPSEC AH MAY also be supported.  All
   compliant implementations MAY also implement IPSEC ESP for protection
   of data packets. Replay prevention and integrity protection using
   IPSEC ESP mandated cipher suit MAY be implemented.  NULL encryption
   also MAY be supported. Other IPSEC ESP required ciphers MAY also be
   supported.

<span class="h2"><a class="selflink" id="section-12" href="#section-12">12</a>. Author's Address</span>

   Alain Robert
   S.I.T.A.
   18, rue Paul Lafargue
   92904 PARIS LA DEFENSE 10
   FRANCE

   Phone: 33 1 46411491
   Fax: 33 1 46411277
   EMail: arobert@par1.par.sita.int









<span class="grey">Robert                       Informational                     [Page 22]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-23" ></span>
<span class="grey"><a href="./rfc2351">RFC 2351</a>                         MATIP                          May 1998</span>


<span class="h2"><a class="selflink" id="section-13" href="#section-13">13</a>.  Full Copyright Statement</span>

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
























Robert                       Informational                     [Page 23]
</pre>