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<pre>Internet Engineering Task Force (IETF) H. Long
Request for Comments: 8625 M. Ye, Ed.
Category: Standards Track Huawei Technologies Co., Ltd.
ISSN: 2070-1721 G. Mirsky, Ed.
ZTE
A. D'Alessandro
Telecom Italia S.p.A
H. Shah
Ciena
August 2019
<span class="h1">Ethernet Traffic Parameters with Availability Information</span>
Abstract
A packet-switching network may contain links with variable bandwidths
(e.g., copper and radio). The bandwidth of such links is sensitive
to the external environment (e.g., climate). Availability is
typically used to describe these links when doing network planning.
This document introduces an optional Bandwidth Availability TLV in
RSVP-TE signaling. This extension can be used to set up a GMPLS
Label Switched Path (LSP) in conjunction with the Ethernet
SENDER_TSPEC object.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in <a href="./rfc7841#section-2">Section 2 of RFC 7841</a>.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
<a href="https://www.rfc-editor.org/info/rfc8625">https://www.rfc-editor.org/info/rfc8625</a>.
<span class="grey">Long, et al. Standards Track [Page 1]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-2" ></span>
<span class="grey"><a href="./rfc8625">RFC 8625</a> Availability Extension to RSVP-TE August 2019</span>
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a> and the IETF Trust's Legal
Provisions Relating to IETF Documents
(<a href="https://trustee.ietf.org/license-info">https://trustee.ietf.org/license-info</a>) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
<a href="#section-1">1</a>. Introduction ....................................................<a href="#page-3">3</a>
<a href="#section-1.1">1.1</a>. Conventions Used in This Document ..........................<a href="#page-4">4</a>
<a href="#section-2">2</a>. Overview ........................................................<a href="#page-4">4</a>
<a href="#section-3">3</a>. Extension to RSVP-TE Signaling ..................................<a href="#page-5">5</a>
<a href="#section-3.1">3.1</a>. Bandwidth Availability TLV .................................<a href="#page-5">5</a>
<a href="#section-3.2">3.2</a>. Signaling Process ..........................................<a href="#page-6">6</a>
<a href="#section-4">4</a>. Security Considerations .........................................<a href="#page-7">7</a>
<a href="#section-5">5</a>. IANA Considerations .............................................<a href="#page-8">8</a>
<a href="#section-6">6</a>. References ......................................................<a href="#page-8">8</a>
<a href="#section-6.1">6.1</a>. Normative References .......................................<a href="#page-8">8</a>
<a href="#section-6.2">6.2</a>. Informative References .....................................<a href="#page-9">9</a>
<a href="#appendix-A">Appendix A</a>. Bandwidth Availability Example .......................<a href="#page-11">11</a>
Acknowledgments ...................................................<a href="#page-13">13</a>
Authors' Addresses ................................................<a href="#page-13">13</a>
<span class="grey">Long, et al. Standards Track [Page 2]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-3" ></span>
<span class="grey"><a href="./rfc8625">RFC 8625</a> Availability Extension to RSVP-TE August 2019</span>
<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>. Introduction</span>
The RSVP-TE specification [<a href="./rfc3209" title=""RSVP-TE: Extensions to RSVP for LSP Tunnels"">RFC3209</a>] and GMPLS extensions [<a href="./rfc3473" title=""Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation Protocol- Traffic Engineering (RSVP-TE) Extensions"">RFC3473</a>]
specify the signaling message, including the bandwidth request for
setting up an LSP in a packet-switching network.
Some data communication technologies allow a seamless change of the
maximum physical bandwidth through a set of known discrete values.
The parameter availability [<a href="#ref-G.827" title=""Availability performance parameters and objectives for end-to-end international constant bit-rate digital paths"">G.827</a>] [<a href="#ref-F.1703" title=""Availability objectives for real digital fixed wireless links used in 27 500 km hypothetical reference paths and connections"">F.1703</a>] [<a href="#ref-P.530" title=""Propagation data and prediction methods required for the design of terrestrial line-of-sight systems"">P.530</a>] is often used to
describe the link capacity during network planning. The availability
is based on a time scale, which is a proportion of the operating time
that the requested bandwidth is ensured. A more detailed example of
bandwidth availability can be found in <a href="#appendix-A">Appendix A</a>. Assigning
different bandwidth availability classes to different types of
services over links with variable discrete bandwidth provides for a
more efficient planning of link capacity. To set up an LSP across
these links, bandwidth availability information is required for the
nodes to verify bandwidth satisfaction and make a bandwidth
reservation. The bandwidth availability information should be
inherited from the bandwidth availability requirements of the
services expected to be carried on the LSP. For example, voice
service usually needs 99.999% bandwidth availability, while non-real-
time services may adequately perform at 99.99% or 99.9% bandwidth
availability. Since different service types may need different
availability guarantees, multiple <availability, bandwidth> pairs may
be required when signaling.
If the bandwidth availability requirement is not specified in the
signaling message, the bandwidth will likely be reserved as the
highest bandwidth availability. Suppose, for example, the bandwidth
with 99.999% availability of a link is 100 Mbps, and the bandwidth
with 99.99% availability is 200 Mbps. When a video application makes
a request for 120 Mbps without a bandwidth availability requirement,
the system will consider the request as 120 Mbps with 99.999%
bandwidth availability, while the available bandwidth with 99.999%
bandwidth availability is only 100 Mbps. Therefore, the LSP path
cannot be set up. However, the video application doesn't need
99.999% bandwidth availability; 99.99% bandwidth availability is
enough. In this case, the LSP could be set up if the bandwidth
availability is also specified in the signaling message.
To fulfill an LSP setup by signaling in these scenarios, this
document specifies a Bandwidth Availability TLV. The Bandwidth
Availability TLV can be applicable to any kind of physical link with
variable discrete bandwidth, such as microwave or DSL. Multiple
Bandwidth Availability TLVs, together with multiple Ethernet
<span class="grey">Long, et al. Standards Track [Page 3]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-4" ></span>
<span class="grey"><a href="./rfc8625">RFC 8625</a> Availability Extension to RSVP-TE August 2019</span>
Bandwidth Profile TLVs, can be carried by the Ethernet SENDER_TSPEC
object [<a href="./rfc6003" title=""Ethernet Traffic Parameters"">RFC6003</a>]. Since the Ethernet FLOWSPEC object has the same
format as the Ethernet SENDER_TSPEC object [<a href="./rfc6003" title=""Ethernet Traffic Parameters"">RFC6003</a>], the Bandwidth
Availability TLV can also be carried by the Ethernet FLOWSPEC object.
<span class="h3"><a class="selflink" id="section-1.1" href="#section-1.1">1.1</a>. Conventions Used in This Document</span>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
<a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a> [<a href="./rfc2119" title=""Key words for use in RFCs to Indicate Requirement Levels"">RFC2119</a>] [<a href="./rfc8174" title=""Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words"">RFC8174</a>] when, and only when, they appear in all
capitals, as shown here.
The following acronyms are used in this document:
RSVP-TE Resource Reservation Protocol - Traffic Engineering
LSP Label Switched Path
SNR Signal-to-Noise Ratio
TLV Type-Length-Value
LSA Link State Advertisement
QAM Quadrature Amplitude Modulation
QPSK Quadrature Phase Shift Keying
<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>. Overview</span>
A tunnel in a packet-switching network may span one or more links in
a network. To set up an LSP, a node may collect link information
that is advertised in a routing message (e.g., an OSPF TE LSA
message) by network nodes to obtain network topology information, and
it can then calculate an LSP route based on the network topology.
The calculated LSP route is signaled using a PATH/RESV message to set
up the LSP.
If a network contains one or more links with variable discrete
bandwidths, a <bandwidth, availability> requirement list should be
specified for an LSP at setup. Each <bandwidth, availability> pair
in the list means the listed bandwidth with specified availability is
required. The list can be derived from the results of service
planning for the LSP.
<span class="grey">Long, et al. Standards Track [Page 4]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-5" ></span>
<span class="grey"><a href="./rfc8625">RFC 8625</a> Availability Extension to RSVP-TE August 2019</span>
A node that has link(s) with variable discrete bandwidth attached
should contain a <bandwidth, availability> information list in its
OSPF TE LSA messages. The list provides the mapping between the link
nominal bandwidth and its availability level. This information can
then be used for path calculation by the node(s). The routing
extension for availability can be found in [<a href="./rfc8330" title=""OSPF Traffic Engineering (OSPF-TE) Link Availability Extension for Links with Variable Discrete Bandwidth"">RFC8330</a>].
When a node initiates a PATH/RESV signaling to set up an LSP, the
PATH message should carry the <bandwidth, availability> requirement
list as a bandwidth request. Intermediate node(s) will allocate the
bandwidth resources for each availability requirement from the
remaining bandwidth with the corresponding availability. An error
message may be returned if any <bandwidth, availability> request
cannot be satisfied.
<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>. Extension to RSVP-TE Signaling</span>
<span class="h3"><a class="selflink" id="section-3.1" href="#section-3.1">3.1</a>. Bandwidth Availability TLV</span>
A Bandwidth Availability TLV is defined as a TLV of the Ethernet
SENDER_TSPEC object [<a href="./rfc6003" title=""Ethernet Traffic Parameters"">RFC6003</a>] in this document. The Ethernet
SENDER_TSPEC object MAY include more than one Bandwidth Availability
TLV. The Bandwidth Availability TLV has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Index | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Availability |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Bandwidth Availability TLV
Type (2 octets): 4
Length (2 octets): 0x0C. Indicates the length in bytes of the whole
TLV, including the Type and Length fields. In this case, the length
is 12 bytes.
Index (1 octet): When the Bandwidth Availability TLV is included, the
Ethernet Bandwidth Profile TLV MUST also be included. If there are
multiple bandwidth requirements present (in multiple Ethernet
Bandwidth Profile TLVs) and they have different availability
requirements, multiple Bandwidth Availability TLVs MUST be carried.
In such a case, the Bandwidth Availability TLV has a one-to-one
<span class="grey">Long, et al. Standards Track [Page 5]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-6" ></span>
<span class="grey"><a href="./rfc8625">RFC 8625</a> Availability Extension to RSVP-TE August 2019</span>
correspondence with the Ethernet Bandwidth Profile TLV as both have
the same value in the Index field. If all the bandwidth requirements
in the Ethernet Bandwidth Profile TLV have the same availability
requirement, one Bandwidth Availability TLV SHOULD be carried. In
this case, the Index field is set to 0.
Reserved (3 octets): These bits SHOULD be set to zero when sent and
MUST be ignored when received.
Availability (4 octets): A 32-bit floating-point number in binary
interchange format [<a href="#ref-IEEE754" title=""IEEE Standard for Floating-Point Arithmetic"">IEEE754</a>] describes the decimal value of the
availability requirement for this bandwidth request. The value MUST
be less than 1 and is usually expressed as one of the following
values: 0.99, 0.999, 0.9999, or 0.99999. The IEEE floating-point
number is used here to align with [<a href="./rfc8330" title=""OSPF Traffic Engineering (OSPF-TE) Link Availability Extension for Links with Variable Discrete Bandwidth"">RFC8330</a>]. When representing
values higher than 0.999999, the floating-point number starts to
introduce errors to intended precision. However, in reality, 0.99999
is normally considered the highest availability value (which results
in 5 minutes of outage in a year) in a telecom network. Therefore,
the use of a floating-point number for availability is acceptable.
<span class="h3"><a class="selflink" id="section-3.2" href="#section-3.2">3.2</a>. Signaling Process</span>
The source node initiates a PATH message, which may carry a number of
bandwidth requests, including one or more Ethernet Bandwidth Profile
TLVs and one or more Bandwidth Availability TLVs. Each Ethernet
Bandwidth Profile TLV corresponds to an availability parameter in the
associated Bandwidth Availability TLV.
When the intermediate and destination nodes receive the PATH message,
the nodes compare the requested bandwidth under each availability
level in the SENDER_TSPEC objects, with the remaining link bandwidth
resources under a corresponding availability level on a local link,
to check if they can meet the bandwidth requirements.
o When all <bandwidth, availability> requirement requests can be
satisfied (that is, the requested bandwidth under each
availability parameter is smaller than or equal to the remaining
bandwidth under the corresponding availability parameter on its
local link), the node SHOULD reserve the bandwidth resources from
each remaining sub-bandwidth portion on its local link to set up
this LSP. Optionally, a higher availability bandwidth can be
allocated to a lower availability request when the lower
availability bandwidth cannot satisfy the request.
<span class="grey">Long, et al. Standards Track [Page 6]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-7" ></span>
<span class="grey"><a href="./rfc8625">RFC 8625</a> Availability Extension to RSVP-TE August 2019</span>
o When at least one <bandwidth, availability> requirement request
cannot be satisfied, the node SHOULD generate a PathErr message
with the error code "Admission Control Error" and the error value
"Requested Bandwidth Unavailable" (see [<a href="./rfc2205" title=""Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification"">RFC2205</a>]).
When two LSPs request bandwidth with the same availability
requirement, the contention MUST be resolved by comparing the node
IDs, where the LSP with the higher node ID is assigned the
reservation. This is consistent with the general contention
resolution mechanism provided in <a href="./rfc3471#section-4.2">Section 4.2 of [RFC3471]</a>.
When a node does not support the Bandwidth Availability TLV, the node
should send a PathErr message with error code "Unknown Attributes
TLV", as specified in [<a href="./rfc5420" title=""Encoding of Attributes for MPLS LSP Establishment Using Resource Reservation Protocol Traffic Engineering (RSVP-TE)"">RFC5420</a>]. An LSP could also be set up in this
case if there's enough bandwidth (note that the availability level of
the reserved bandwidth is unknown). When a node receives Bandwidth
Availability TLVs with a mix of zero and non-zero indexes, the
message MUST be ignored and MUST NOT be propagated. When a node
receives Bandwidth Availability TLVs (non-zero index) with no
matching index value among the Ethernet Bandwidth Profile TLVs, the
message MUST be ignored and MUST NOT be propagated. When a node
receives several <bandwidth, availability> pairs, but there are extra
Ethernet Bandwidth Profile TLVs that do not match the index of any
Bandwidth Availability TLV, the extra Ethernet Bandwidth Profile TLVs
MUST be ignored and MUST NOT be propagated.
<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>. Security Considerations</span>
This document defines a Bandwidth Availability TLV in RSVP-TE
signaling used in GMPLS networks. [<a href="./rfc3945" title=""Generalized Multi-Protocol Label Switching (GMPLS) Architecture"">RFC3945</a>] notes that
authentication in GMPLS systems may use the authentication mechanisms
of the component protocols. [<a href="./rfc5920" title=""Security Framework for MPLS and GMPLS Networks"">RFC5920</a>] provides an overview of
security vulnerabilities and protection mechanisms for the GMPLS
control plane. In particular, <a href="./rfc5920#section-7.1.2">Section 7.1.2 of [RFC5920]</a> discusses
the control-plane protection with RSVP-TE by using general RSVP
security tools, limiting the impact of an attack on control-plane
resources, and using authentication for RSVP messages. Moreover, the
GMPLS network is often considered to be a closed network such that
insertion, modification, or inspection of packets by an outside party
is not possible.
<span class="grey">Long, et al. Standards Track [Page 7]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-8" ></span>
<span class="grey"><a href="./rfc8625">RFC 8625</a> Availability Extension to RSVP-TE August 2019</span>
<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>. IANA Considerations</span>
IANA maintains a registry of GMPLS parameters called the "Generalized
Multi-Protocol Label Switching (GMPLS) Signaling Parameters"
registry. This registry includes the "Ethernet Sender TSpec TLVs/
Ethernet Flowspec TLVs" subregistry that contains the TLV type values
for TLVs carried in the Ethernet SENDER_TSPEC object. This
subregistry has been updated to include the Bandwidth Availability
TLV:
Type Description Reference
---- ---------------------- ---------
4 Bandwidth Availability <a href="./rfc8625">RFC 8625</a>
<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>. References</span>
<span class="h3"><a class="selflink" id="section-6.1" href="#section-6.1">6.1</a>. Normative References</span>
[<a id="ref-IEEE754">IEEE754</a>] IEEE, "IEEE Standard for Floating-Point Arithmetic",
IEEE 754, DOI 10.1109/IEEESTD.2008.4610935.
[<a id="ref-RFC2119">RFC2119</a>] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc2119">RFC 2119</a>,
DOI 10.17487/RFC2119, March 1997,
<<a href="https://www.rfc-editor.org/info/rfc2119">https://www.rfc-editor.org/info/rfc2119</a>>.
[<a id="ref-RFC2205">RFC2205</a>] Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", <a href="./rfc2205">RFC 2205</a>, DOI 10.17487/RFC2205,
September 1997, <<a href="https://www.rfc-editor.org/info/rfc2205">https://www.rfc-editor.org/info/rfc2205</a>>.
[<a id="ref-RFC3209">RFC3209</a>] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", <a href="./rfc3209">RFC 3209</a>, DOI 10.17487/RFC3209, December 2001,
<<a href="https://www.rfc-editor.org/info/rfc3209">https://www.rfc-editor.org/info/rfc3209</a>>.
[<a id="ref-RFC3471">RFC3471</a>] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Functional Description",
<a href="./rfc3471">RFC 3471</a>, DOI 10.17487/RFC3471, January 2003,
<<a href="https://www.rfc-editor.org/info/rfc3471">https://www.rfc-editor.org/info/rfc3471</a>>.
<span class="grey">Long, et al. Standards Track [Page 8]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-9" ></span>
<span class="grey"><a href="./rfc8625">RFC 8625</a> Availability Extension to RSVP-TE August 2019</span>
[<a id="ref-RFC3473">RFC3473</a>] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Extensions", <a href="./rfc3473">RFC 3473</a>,
DOI 10.17487/RFC3473, January 2003,
<<a href="https://www.rfc-editor.org/info/rfc3473">https://www.rfc-editor.org/info/rfc3473</a>>.
[<a id="ref-RFC5420">RFC5420</a>] Farrel, A., Ed., Papadimitriou, D., Vasseur, JP., and A.
Ayyangarps, "Encoding of Attributes for MPLS LSP
Establishment Using Resource Reservation Protocol Traffic
Engineering (RSVP-TE)", <a href="./rfc5420">RFC 5420</a>, DOI 10.17487/RFC5420,
February 2009, <<a href="https://www.rfc-editor.org/info/rfc5420">https://www.rfc-editor.org/info/rfc5420</a>>.
[<a id="ref-RFC6003">RFC6003</a>] Papadimitriou, D., "Ethernet Traffic Parameters",
<a href="./rfc6003">RFC 6003</a>, DOI 10.17487/RFC6003, October 2010,
<<a href="https://www.rfc-editor.org/info/rfc6003">https://www.rfc-editor.org/info/rfc6003</a>>.
[<a id="ref-RFC8174">RFC8174</a>] Leiba, B., "Ambiguity of Uppercase vs Lowercase in <a href="./rfc2119">RFC</a>
<a href="./rfc2119">2119</a> Key Words", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc8174">RFC 8174</a>, DOI 10.17487/RFC8174,
May 2017, <<a href="https://www.rfc-editor.org/info/rfc8174">https://www.rfc-editor.org/info/rfc8174</a>>.
<span class="h3"><a class="selflink" id="section-6.2" href="#section-6.2">6.2</a>. Informative References</span>
[<a id="ref-EN-302-217">EN-302-217</a>]
ETSI, "Fixed Radio Systems; Characteristics and
requirements for point-to-point equipment and antennas;
Part 1: Overview and system-independent common
characteristics", ETSI EN 302 217-1, Version 3.1.1, May
2017.
[<a id="ref-F.1703">F.1703</a>] ITU-R, "Availability objectives for real digital fixed
wireless links used in 27 500 km hypothetical reference
paths and connections", ITU-R Recommendation F.1703-0,
January 2005, <<a href="https://www.itu.int/rec/R-REC-F.1703/en">https://www.itu.int/rec/R-REC-F.1703/en</a>>.
[<a id="ref-G.827">G.827</a>] ITU-T, "Availability performance parameters and objectives
for end-to-end international constant bit-rate digital
paths", ITU-T Recommendation G.827, September 2003,
<<a href="https://www.itu.int/rec/T-REC-G.827/en">https://www.itu.int/rec/T-REC-G.827/en</a>>.
[<a id="ref-P.530">P.530</a>] ITU-R, "Propagation data and prediction methods required
for the design of terrestrial line-of-sight systems",
ITU-R Recommendation P.530-17, December 2017,
<<a href="https://www.itu.int/rec/R-REC-P.530/en">https://www.itu.int/rec/R-REC-P.530/en</a>>.
<span class="grey">Long, et al. Standards Track [Page 9]</span></pre>
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[<a id="ref-RFC3945">RFC3945</a>] Mannie, E., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", <a href="./rfc3945">RFC 3945</a>,
DOI 10.17487/RFC3945, October 2004,
<<a href="https://www.rfc-editor.org/info/rfc3945">https://www.rfc-editor.org/info/rfc3945</a>>.
[<a id="ref-RFC5920">RFC5920</a>] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", <a href="./rfc5920">RFC 5920</a>, DOI 10.17487/RFC5920, July 2010,
<<a href="https://www.rfc-editor.org/info/rfc5920">https://www.rfc-editor.org/info/rfc5920</a>>.
[<a id="ref-RFC8330">RFC8330</a>] Long, H., Ye, M., Mirsky, G., D'Alessandro, A., and H.
Shah, "OSPF Traffic Engineering (OSPF-TE) Link
Availability Extension for Links with Variable Discrete
Bandwidth", <a href="./rfc8330">RFC 8330</a>, DOI 10.17487/RFC8330, February 2018,
<<a href="https://www.rfc-editor.org/info/rfc8330">https://www.rfc-editor.org/info/rfc8330</a>>.
<span class="grey">Long, et al. Standards Track [Page 10]</span></pre>
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<span class="h2"><a class="selflink" id="appendix-A" href="#appendix-A">Appendix A</a>. Bandwidth Availability Example</span>
In mobile backhaul networks, microwave links are very popular for
providing connections of last hops. To maintain link connectivity in
heavy rain conditions, the microwave link may lower the modulation
level since moving to a lower modulation level provides for a lower
SNR requirement. This is called "adaptive modulation" technology
[<a href="#ref-EN-302-217">EN-302-217</a>]. However, a lower modulation level also means a lower
link bandwidth. When a link bandwidth is reduced because of
modulation downshifting, high-priority traffic can be maintained,
while lower-priority traffic is dropped. Similarly, copper links may
change their link bandwidth due to external interference.
Presume that a link has three discrete bandwidth levels:
o The link bandwidth under modulation level 1 (e.g., QPSK) is 100
Mbps.
o The link bandwidth under modulation level 2 (e.g., 16QAM) is 200
Mbps.
o The link bandwidth under modulation level 3 (e.g., 256QAM) is 400
Mbps.
On a sunny day, modulation level 3 can be used to achieve a 400 Mbps
link bandwidth.
Light rain with a X mm/h rate triggers the system to change the
modulation level from level 3 to level 2, with the bandwidth changing
from 400 Mbps to 200 Mbps. The probability of X mm/h rain in the
local area is 52 minutes in a year. Then the dropped 200 Mbps
bandwidth has 99.99% availability.
Heavy rain with a Y(Y>X) mm/h rate triggers the system to change the
modulation level from level 2 to level 1, with the bandwidth changing
from 200 Mbps to 100 Mbps. The probability of Y mm/h rain in the
local area is 26 minutes in a year. Then the dropped 100 Mbps
bandwidth has 99.995% availability.
For the 100 Mbps bandwidth of modulation level 1, only extreme
weather conditions can cause the whole system to be unavailable,
which only happens for 5 minutes in a year. So the 100 Mbps
bandwidth of the modulation level 1 owns the availability of 99.999%.
There are discrete buckets per availability level. Under the worst
weather conditions, there's only 100 Mbps capacity, which is 99.999%
available. It's treated effectively as "always available" since
better availability is not possible. If the weather is bad but not
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the worst possible conditions, modulation level 2 can be used, which
gets an additional 100 Mbps bandwidth (i.e., 200 Mbps total).
Therefore, 100 Mbps is in the 99.999% bucket, and 100 Mbps is in the
99.995% bucket. In clear weather, modulation level 3 can be used to
get 400 Mbps total, but that's only 200 Mbps more than at modulation
level 2, so the 99.99% bucket has that "extra" 200 Mbps, and the
other two buckets still have 100 Mbps each.
Therefore, the maximum bandwidth is 400 Mbps. The sub-bandwidth and
its availability according to the weather conditions are shown as
follows:
Sub-bandwidth (Mbps) Availability
------------------ ------------
200 99.99%
100 99.995%
100 99.999%
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Acknowledgments
The authors would like to thank Deborah Brungard, Khuzema Pithewan,
Lou Berger, Yuji Tochio, Dieter Beller, and Autumn Liu for their
comments on and contributions to the document.
Authors' Addresses
Hao Long
Huawei Technologies Co., Ltd.
No.1899, Xiyuan Avenue, Hi-tech Western District
Chengdu 611731
China
Phone: +86-18615778750
Email: longhao@huawei.com
Min Ye (editor)
Huawei Technologies Co., Ltd.
No.1899, Xiyuan Avenue, Hi-tech Western District
Chengdu 611731
China
Email: amy.yemin@huawei.com
Greg Mirsky (editor)
ZTE
Email: gregimirsky@gmail.com
Alessandro D'Alessandro
Telecom Italia S.p.A
Email: alessandro.dalessandro@telecomitalia.it
Himanshu Shah
Ciena Corp.
3939 North First Street
San Jose, CA 95134
United States of America
Email: hshah@ciena.com
Long, et al. Standards Track [Page 13]
</pre>
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