LMP-WDM: Link Management Protocol (LMP) for Dense Wavelength Division Multiplexing (DWDM) Optical Line Systems
How a router and the DWDM line equipment next to it exchange link properties and fault reports over LMP.
Fredette, A., Ed. and J. Lang, Ed., "Link Management Protocol (LMP) for Dense Wavelength Division Multiplexing (DWDM) Optical Line Systems", RFC 4209, DOI 10.17487/RFC4209, October 2005, <https://www.rfc-editor.org/info/rfc4209>.
@misc{rfc4209,
series = {Request for Comments},
number = 4209,
howpublished = {RFC 4209},
publisher = {RFC Editor},
doi = {10.17487/RFC4209},
url = {https://www.rfc-editor.org/info/rfc4209},
author = {A. Fredette and J. Lang},
title = {{Link Management Protocol (LMP) for Dense Wavelength Division Multiplexing (DWDM) Optical Line Systems}},
pagetotal = 16,
year = 2005,
month = oct,
} RFC text
Contents
Network Working Group A. Fredette, Ed.
Request for Comments: 4209 Hatteras Networks
Category: Standards Track J. Lang, Ed.
Sonos Inc.
October 2005
Link Management Protocol (LMP) for
Dense Wavelength Division Multiplexing (DWDM) Optical Line Systems
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
The Link Management Protocol (LMP) is defined to manage traffic
engineering (TE) links. In its present form, LMP focuses on peer
nodes, i.e., nodes that peer in signaling and/or routing. This
document proposes extensions to LMP to allow it to be used between a
peer node and an adjacent optical line system (OLS). These
extensions are intended to satisfy the "Optical Link Interface
Requirements" described in a companion document.
1. Introduction
Networks are being developed with routers, switches, optical cross-
connects (OXCs), dense wavelength division multiplexing (DWDM)
optical line systems (OLSes), and add-drop multiplexors (ADMs) that
use a common control plane (e.g., Generalized MPLS (GMPLS)) to
dynamically provision resources and to provide network survivability
using protection and restoration techniques.
The Link Management Protocol (LMP) is being developed as part of the
GMPLS protocol suite to manage traffic engineering (TE) links
[RFC4204]. In its present form, LMP focuses on peer nodes, i.e.,
nodes that peer in signaling and/or routing (e.g., OXC-to-OXC, as
illustrated in Figure 1). In this document, extensions to LMP are
proposed to allow it to be used between a peer node and an adjacent
optical line system (OLS). These extensions are intended to satisfy
the "Optical Link Interface Requirements" described in [OLI]. It is
assumed that the reader is familiar with LMP, as defined in
[RFC4204].
+------+ +------+ +------+ +------+
| | ----- | | | | ----- | |
| OXC1 | ----- | OLS1 | ===== | OLS2 | ----- | OXC2 |
| | ----- | | | | ----- | |
+------+ +------+ +------+ +------+
^ ^
| |
+---------------------LMP---------------------+
Figure 1: LMP Model
Consider two peer nodes (e.g., two OXCs) interconnected by a
wavelength-multiplexed link, i.e., a DWDM optical link (see Figure 1
above). Information about the configuration of this link and its
current state is known by the two OLSes (OLS1 and OLS2). Allowing
them to communicate this information to the corresponding peer nodes
(OXC1 and OXC2) via LMP can improve network usability by reducing
required manual configuration and by enhancing fault detection and
recovery.
Information about the state of LSPs using the DWDM optical link is
known by the peer nodes (OXC1 and OXC2), and allowing them to
communicate this information to the corresponding OLSes (OLS1 and
OLS2) is useful for alarm management and link monitoring. Alarm
management is important because the administrative state of an LSP,
known to the peer nodes (e.g., via the Admin Status object of GMPLS
signaling [RFC3471]), can be used to suppress spurious alarm
reporting from the OLSes.
The model for extending LMP to OLSes is shown in Figure 2.
+------+ +------+ +------+ +------+
| | ----- | | | | ----- | |
| OXC1 | ----- | OLS1 | ===== | OLS2 | ----- | OXC2 |
| | ----- | | | | ----- | |
+------+ +------+ +------+ +------+
^ ^ ^ ^ ^ ^
| | | | | |
| +-----LMP-----+ +-----LMP-----+ |
| |
+----------------------LMP-----------------------+
Figure 2: Extended LMP Model
In this model, a peer node may have LMP sessions with adjacent OLSes,
as well as adjacent peer nodes. In Figure 2, for example, the OXC1-
OXC2 LMP session can be used to build traffic-engineering (TE) links
for GMPLS signaling and routing, as described in [RFC4204]. The
OXC1-OLS1 and the OXC2-OLS2 LMP sessions are used to exchange
information about the configuration of the DWDM optical link and its
current state and information about the state of LSPs using that
link.
The latter type of LMP sessions is discussed in this document. It is
important to note that a peer node may have LMP sessions with one or
more OLSes and an OLS may have LMP sessions with one or more peer
nodes.
Although there are many similarities between an LMP session between
two peer nodes and an LMP session between a peer node and an OLS,
there are some differences as well. The former type of LMP session
is used to provide the basis for GMPLS signaling and routing. The
latter type of LMP session is used to augment knowledge about the
links between peer nodes.
A peer node maintains its peer node-to-OLS LMP sessions and its peer
node-to-peer node LMP sessions independently. This means that it
MUST be possible for LMP sessions to come up in any order. In
particular, it MUST be possible for a peer node-to-peer node LMP
session to come up in the absence of any peer node-to-OLS LMP
sessions, and vice versa.
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
The reader is assumed to be familiar with the terminology in
[RFC4204].
DWDM: Dense wavelength division multiplexing
OLS: Optical line system
Opaque:
A device is called X-opaque if it examines or modifies the X
aspect of the signal while forwarding an incoming signal from
input to output.
OXC: Optical cross-connect
Transparent:
As defined in [RFC4204], a device is called X-transparent if it
forwards incoming signals from input to output without examining
or modifying the X aspect of the signal. For example, a Frame
Relay switch is network-layer transparent; an all-optical switch
is electrically transparent.
1.2. Scope of LMP-WDM Protocol
This document focuses on extensions required for use with opaque
OLSes. In particular, this document is intended for use with OLSes
having SONET, SDH, and Ethernet user ports.
At the time of this writing, work is ongoing in the area of fully
transparent wavelength routing; however, it is premature to identify
the necessary information to be exchanged between a peer node and an
OLS in this context. Nevertheless, the protocol described in this
document provides the necessary framework in which to exchange
additional information that is deemed appropriate.
2. LMP Extensions for Optical Line Systems
LMP currently consists of four main procedures, of which the first
two are mandatory and the last two are optional:
1. Control channel management
2. Link property correlation
3. Link verification
4. Fault management
All four functions are supported in LMP-WDM.
2.1. Control Channel Management
As in [RFC4204], we do not specify the exact implementation of the
control channel; it could be, for example, a separate wavelength,
fiber, Ethernet link, an IP tunnel routed over a separate management
network, a multi-hop IP network, or the overhead bytes of a data
link.
The control channel management for a peer node-to-OLS link is the
same as for a peer node-to-peer node link, as described in [RFC4204].
To distinguish between a peer node-to-OLS LMP session and a peer
node-to-peer node LMP session, a new LMP-WDM CONFIG object is defined
(C-Type = 2). The format of the CONFIG object is as follows:
Class = 6
o C-Type = 2, LMP-WDM_CONFIG
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|W|O| (Reserved) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Reserved field should be sent as zero and ignored on receipt.
WDM: 1 bit
This bit indicates support for the LMP-WDM extensions defined
in this document.
OLS: 1 bit
If set, this bit indicates that the sender is an optical line
system (OLS). If clear, this bit indicates that the sender is
a peer node.
The LMP-WDM extensions are designed for peer node-to-OLS LMP
sessions. The OLS bit allows a node to identify itself as an OLS or
a peer node. This is used to detect misconfiguration of a peer
node-to-OLS LMP session between two peer nodes or a peer node-to-peer
node LMP session between a peer node and an OLS.
If the node does not support the LMP-WDM extensions, it MUST reply to
the Config message with a ConfigNack message.
If a peer node that is configured to run LMP-WDM receives a Config
message with the OLS bit clear in LMP-WDM_CONFIG object, it MUST
reply to the Config message with a ConfigNack message.
2.2. Link Verification
The Test procedure used with OLSes is the same as described in
[RFC4204]. The VerifyTransportMechanism (included in the BeginVerify
and BeginVerifyAck messages) is used to allow nodes to negotiate a
link verification method and is essential for line systems that have
access to overhead bytes rather than the payload. The VerifyId
(provided by the remote node in the BeginVerifyAck message and used
in all subsequent Test messages) is used to differentiate Test
messages from different LMP Link Verification procedures. In
addition to the Test procedure described in [RFC4204], the trace
monitoring function of [RFC4207] may be used for link verification
when the OLS user ports are SONET or SDH.
In a combined LMP and LMP-WDM context, there is an interplay between
the data links being managed by peer node-to-peer node LMP sessions
and peer node-to-OLS LMP sessions. For example, in Figure 2, the
OXC1-OLS1 LMP session manages the data links between OXC1 and OLS1,
and the OXC2-OLS2 LMP session manages the data links between OXC2 and
OLS2. However, the OXC1-OXC2 LMP session manages the data links
between OXC1 and OXC2, which are actually a concatenation of the data
links between OXC1 and OLS1, the DWDM span between OLS1 and OLS2, and
the data links between OXC2 and OLS2. It is these concatenated links
that comprise the TE links that are advertised in the GMPLS TE link
state database.
The implication of this is that when the data links between OXC1 and
OXC2 are being verified, using the LMP link verification procedure,
OLS1 and OLS2 need to make themselves transparent with respect to
these concatenated data links. The coordination of verification of
OXC1-OLS1 and OXC2-OLS2 data links to ensure this transparency is the
responsibility of the peer nodes, OXC1 and OXC2.
It is also necessary for these peer nodes to understand the mappings
between the data links of the peer node - OLS LMP session and the
concatenated data links of the peer node - peer node LMP session.
2.3. Link Summarization
As in [RFC4204], the LinkSummary message is used to synchronize the
Interface_Ids and correlate the properties of the TE link. (Note
that the term "TE link" originated from routing/signaling
applications of LMP, and this concept does not necessarily apply to
an OLS. However, the term is used in this document to remain
consistent with LMP terminology.) The LinkSummary message includes
one or more DATA_LINK objects. The contents of the DATA_LINK object
consist of a series of variable-length data items called Data Link
sub-objects describing the capabilities of the data links.
In this document, several additional Data Link sub-objects are
defined to describe additional link characteristics. The link
characteristics are, in general, those needed by the CSPF to select
the path for a particular LSP. These link characteristics describe
the specified peer node-to-OLS data link, as well as the associated
DWDM span between the two OLSes.
The format of the Data Link sub-objects follows the format described
in [RFC4204] and is shown below for readability:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---------------//--------------+
| Type | Length | (Sub-object contents) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---------------//--------------+
Type: 8 bits
The Type indicates the type of contents of the sub-object.
Length: 8 bits
The Length field contains the total length of the sub-object in
bytes, including the Type and Length fields. The Length MUST
be at least 4, and MUST be a multiple of 4.
The following link characteristics are exchanged on a per data link
basis.
2.3.1. Link Group ID
The main purpose of the Link Group ID is to reduce control traffic
during failures that affect many data links. A local ID may be
assigned to a group of data links. This ID can be used to reduce the
control traffic in the event of a failure by enabling a single
ChannelStatus message with the LINK GROUP CHANNEL_STATUS object (see
Section 2.4.1) to be used for a group of data links instead of
individual ChannelStatus messages for each data link. A data link
may be a member of multiple groups. This is achieved by including
multiple Link Group ID sub-objects in the LinkSummary message.
The Link Group ID feature allows Link Groups to be assigned based on
the types of fault correlation and aggregation supported by a given
OLS. From a practical perspective, the Link Group ID is used to map
(or group) data links into "failable entities" known primarily to the
OLS. If one of those failable entities fails, all associated data
links are failed and the peer node is notified with a single message.
For example, an OLS could create a Link Group for each laser in the
OLS. The data links associated with each laser would then each be
assigned the Link Group ID for that laser. If a laser fails, the OLS
would then report a single failure affecting all of the data links
with a Link Group ID of the failed laser. The peer node that
receives the single failure notification then knows which data links
are affected. Similarly, an OLS could create a Link Group ID for a
fiber, to report a failure affecting all of the data links associated
with that fiber if a loss-of-signal (LOS) is detected for that fiber.
The format of the Link Group ID sub-object (Type = 3, Length = 8) is
as follows:
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 | (Reserved) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Group ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Reserved field should be sent as zero and ignored on receipt.
Link Group ID: 32 bits
Link Group ID 0xFFFFFFFF is reserved and indicates all data
links in a TE link. All data links are members of Link Group
0xFFFFFFFF by default.
2.3.2. Shared Risk Link Group (SRLG) Identifier
This identifies the SRLGs of which the data link is a member. This
information may be configured on an OLS by the user and used for
diverse path computation (see [RFC4202]).
The format of the SRLG sub-object (Type = 4, Length = (N+1)*4 where N
is the number of SRLG values) is as follows:
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 | (Reserved) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRLG value #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRLG value #2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ... //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRLG value #(N-1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRLG value #N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Reserved field should be sent as zero and ignored on receipt.
Shared Risk Link Group Value: 32 bits
See [RFC4202]. List as many SRLGs as apply.
2.3.3. Bit Error Rate (BER) Estimate
This object provides an estimate of the BER for the data link.
The Bit Error Rate (BER) is the proportion of bits that have errors
relative to the total number of bits received in a transmission,
usually expressed as ten to a negative power. For example, a
transmission might have a BER of "10 to the minus 13", meaning that,
out of every 10,000,000,000,000 bits transmitted, one bit may be in
error. The BER is an indication of overall signal quality.
The format of the BER Estimate sub-object (Type = 5; Length = 4) is
as follows:
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 | BER | (Reserved) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Reserved field should be sent as zero and ignored on receipt.
BER: 8 bits
The exponent from the BER representation described above. That
is, if the BER is 10 to the minus X, the BER field is set to X.
2.3.4. Optical Protection
This indicates whether the link is protected by the OLS. This
information can be used as a measure of link capability. It may be
advertised by routing and used by signaling as a selection criterion,
as described in [RFC3471].
The format of the Optical Protection sub-object (Type = 6; Length =
4) is as follows:
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 | (Reserved) | Link Flags|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Reserved field should be sent as zero and ignored on receipt.
Link Flags: 6 bits
Encoding for Link Flags is defined in Section 7 of [RFC3471].
2.3.5. Total Span Length
This indicates the total distance of fiber in the OLS. This may be
used as a routing metric or to estimate delay.
The format of the Total Span Length sub-object (Type = 7, Length = 8)
is as follows:
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 | (Reserved) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Span Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Reserved field should be sent as zero and ignored on receipt.
Span Length: 32 bits
This value represents the total length of the WDM span in
meters, expressed as an unsigned (long) integer.
2.3.6. Administrative Group (Color)
The administrative group (or Color) to which the data link belongs.
The format of the Administrative Group sub-object (Type = 8, Length =
8) is as follows:
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 | (Reserved) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Administrative Group |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Reserved field should be sent as zero and ignored on receipt.
Administrative Group: 32 bits
A 32-bit value, as defined in [RFC3630].
2.4. Fault Management
The Fault Management procedure used between a peer and an OLS follows
the procedures described in [RFC4204]; some further extensions are
defined in this section. The information learned from the OLS-peer
fault management procedures may be used to trigger peer-peer LMP
fault management, or may be used to trigger GMPLS signaling/routing
procedures directly.
Fault management consists of three major functions:
1. Fault Detection
2. Fault Localization
3. Fault Notification
The fault detection mechanisms are the responsibility of the
individual nodes and are not specified as part of this protocol.
Fault detection mechanisms may include a Bit Error Rate (BER)
exceeding a threshold, and loss-of-signal (LOS) and SONET/SDH-level
errors. It is the responsibility of the OLS to translate these
failures into (Signal) OK, Signal Failure (SF), or Signal Degrade
(SD), as described in [RFC4204].
That is, an OLS uses the messages defined in the LMP fault
localization procedures (ChannelStatus, ChannelStatusAck,
ChannelStatusRequest, and ChannelStatusResponse messages) to inform
the adjacent peer node of failures it has detected, in order to
initiate the LMP fault localization procedures between peer nodes,
but it does not participate in those procedures.
The OLS may also execute its own fault localization process to allow
it to determine the location of the fault along the DWDM span. For
example, the OLS may be able to pinpoint the fault to a particular
amplifier in a span of thousands of kilometers in length.
To report data link failures and recovery conditions, LMP-WDM uses
the ChannelStatus, ChannelStatusAck, ChannelStatusRequest, and
ChannelStatusResponse messages defined in [RFC4204].
Each data link is identified by an Interface_ID. In addition, a Link
Group ID may be assigned to a group of data links (see Section
2.3.1). The Link Group ID may be used to reduce the control traffic
by providing channel status information for a group of data links. A
new LINK GROUP CHANNEL_STATUS object is defined below for this
purpose. This object may be used in place of the CHANNEL_STATUS
objects described in [RFC4204] in the ChannelStatus message.
2.4.1. LINK_GROUP CHANNEL_STATUS Object
The LINK_GROUP CHANNEL_STATUS object is used to indicate the status
of the data links belonging to a particular Link Group. The
correlation of data links to Group ID is made with the Link Group ID
sub-object of the DATA_LINK object.
The format of the LINK_GROUP CHANNEL_STATUS object is as follows
(Class = 13, C-Type = 4):
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Group ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|D| Channel Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| : |
// : //
| : |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Group ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|D| Channel Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Link Group ID: 32 bits
The Link Group ID 0xFFFFFFFF is reserved and indicates all data
links in a TE link. All data links are members of the Link
Group 0xFFFFFFFF by default.
Channel Status: 32 bits
The values for the Channel Status field are defined in
[RFC4204].
This object is non-negotiable.
3. Security Considerations
LMP message security uses IPsec, as described in [RFC4204]. This
document only defines new LMP objects that are carried in existing
LMP messages. As such, this document introduces no other new
security considerations not covered in [RFC4204].
4. IANA Considerations
LMP [RFC4204] defines the following name spaces and the ways in which
IANA can make assignments to these namespaces:
- LMP Message Type
- LMP Object Class
- LMP Object Class type (C-Type) unique within the Object Class
- LMP Sub-object Class type (Type) unique within the Object Class
This memo introduces the following new assignments:
LMP Object Class Types:
o under CONFIG class name (as defined in [RFC4204])
- LMP-WDM_CONFIG (C-Type = 2)
o under CHANNEL_STATUS class name (as defined in [RFC4204])
- LINK_GROUP (C-Type = 4)
LMP Sub-Object Class names:
o under DATA_LINK Class name (as defined in [RFC4204])
- Link_GroupId (sub-object Type = 3)
- SRLG (sub-object Type = 4)
- BER_Estimate (sub-object Type = 5)
- Optical_Protection (sub-object Type = 6)
- Total_Span_Length (sub-object Type = 7)
- Administrative_Group (sub-object Type = 8)
5. Contributors
The authors would like to acknowledge Osama S. Aboul-Magd, Stuart
Brorson, Sudheer Dharanikota, John Drake, David Drysdale, W. L.
Edwards, Adrian Farrel, Andre Fredette, Rohit Goyal, Hirokazu
Ishimatsu, Monika Jaeger, Ram Krishnan, Jonathan P. Lang, Raghu
Mannam, Eric Mannie, Dimitri Papadimitriou, Jagan Shantigram, Ed
Snyder, George Swallow, Gopala Tumuluri, Yong Xue, Lucy Yong, and
John Yu.
6. References
6.1. Normative References
[RFC4202] Kompella, K., Ed., and Y. Rekhter, Ed., "Routing
Extensions in Support of Generalized Multi-Protocol Label
Switching (GMPLS)", RFC 4202, September 2005.
[RFC4204] Lang, J., Ed., "The Link Management Protocol (LMP)", RFC
4204, September 2005.
[RFC4207] Lang, J., and D. Papadimitriou, "Synchronous Optical
Network (SONET)/Synchronous Digital Hierarchy (SDH)
Encoding for Link Management Protocol (LMP) Test
Messages", RFC 4207, September 2005.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3471] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Functional Description", RFC 3471,
January 2003.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic
Engineering (TE) Extensions to OSPF Version 2", RFC 3630,
September 2003.
6.2. Informative References
[OLI] Fredette, A., Editor, "Optical Link Interface
Requirements", Work in Progress.
Editors' Addresses
Andre Fredette
Hatteras Networks
P.O. Box 110025
Research Triangle Park
NC 27709-0025, USA
EMail: Afredette@HatterasNetworks.com
Jonathan P. Lang
Sonos, Inc.
223 E. De La Guerra St.
Santa Barbara, CA 93101
EMail: jplang@ieee.org
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§1Why the Line System Joins the Conversation
Networks are being developed with routers, switches, optical cross-connects (OXCs), dense wavelength division multiplexing (DWDM) optical line systems (OLSes) and add-drop multiplexors (ADMs) that use a common control plane, such as Generalized MPLS (GMPLS), to provision resources dynamically and to provide network survivability with protection and restoration techniques.
The Link Management Protocol (LMP) is being developed as part of the GMPLS protocol suite to manage traffic engineering (TE) links. In its present form LMP focuses on peer nodes, meaning nodes that peer in signaling or routing, such as two OXCs. This document proposes extensions to LMP so it can be used between a peer node and an adjacent OLS, and the extensions are intended to satisfy the Optical Link Interface Requirements described in a companion document. The reader is assumed to be familiar with LMP as defined in the base specification.
Figure 1 of the RFC shows two peer nodes interconnected by a wavelength-multiplexed link, a DWDM optical link, with an OLS on each side of the span. Information about the configuration of this link and its current state is known by the two OLSes. Letting them communicate that information to the corresponding peer nodes over LMP can improve network usability by reducing the required manual configuration and by enhancing fault detection and recovery.
The information runs the other way too. The state of the label switched paths (LSPs) that use the link is known by the peer nodes, and passing it to the OLSes is useful for alarm management and link monitoring. Alarm management matters because the administrative state of an LSP, known to the peer nodes for example through the Admin Status object of GMPLS signaling, can be used to suppress spurious alarm reporting from the OLSes.
Figure 2 shows the extended model. A peer node may have LMP sessions with adjacent OLSes as well as with adjacent peer nodes. The peer-to-peer session between OXC1 and OXC2 is used to build the TE links used for GMPLS signaling and routing, while the OXC1-to-OLS1 and OXC2-to-OLS2 sessions are used to exchange information about the configuration of the DWDM optical link, its current state, and the state of the LSPs using that link. A peer node may have LMP sessions with one or more OLSes, and an OLS may have LMP sessions with one or more peer nodes.
A peer node maintains its peer-to-OLS sessions and its peer-to-peer sessions independently. It MUST therefore be possible for LMP sessions to come up in any order, in particular for a peer-to-peer session to come up in the absence of any peer-to-OLS sessions, and the other way round.
Two kinds of device work together on a long optical link: routers at the ends, and the line equipment that carries the light between them. This RFC lets them exchange link information using the protocol the routers already use with each other.
- LMP sessionPeer node to adjacent OLS: link configuration, current state and LSP information.
- LMP sessionPeer node to the OLS on the other side of the DWDM span.
- LMP sessionPeer to peer: builds the TE links used for GMPLS signaling and routing.
| Session | Peer node to peer node | Peer node to OLS |
|---|---|---|
| Purpose | Provides the basis for GMPLS signaling and routing | Augments knowledge about the links between peer nodes |
| Data links managed | The concatenated links: peer to OLS, the DWDM span, and OLS to peer | The data links between the peer node and the OLS |
| Information carried | TE link properties and interface identifiers | The configuration of the DWDM link, its current state, and the state of the LSPs using it |
§1.2Scope: Opaque Line Systems
The RFC defines the vocabulary it uses. DWDM is dense wavelength division multiplexing and an OLS is an optical line system. A device is called X-opaque if it examines or modifies the X aspect of the signal while forwarding an incoming signal from input to output. A device is called X-transparent if it forwards incoming signals from input to output without examining or modifying that aspect of the signal. A Frame Relay switch is network-layer transparent, and an all-optical switch is electrically transparent.
This document focuses on the extensions required for use with opaque OLSes, and is intended for OLSes having SONET, SDH and Ethernet user ports.
At the time of writing, work was ongoing in the area of fully transparent wavelength routing. The RFC calls it premature to identify the information that would have to be exchanged between a peer node and an OLS in that context. The protocol described in the document nevertheless provides the framework in which additional information can be exchanged later if it is judged appropriate.
This RFC covers line equipment that examines or changes the signal as it forwards it. Equipment that passes signals through untouched is left for later work, although the protocol leaves room to add it.
§2.1Control Channel Management and the CONFIG Object
LMP consists of four main procedures, of which the first two are mandatory and the last two are optional: control channel management, link property correlation, link verification and fault management. All four functions are supported in LMP-WDM.
The RFC does not specify the exact implementation of the control channel. It could be, for example, a separate wavelength, a fiber, an Ethernet link, an IP tunnel routed over a separate management network, a multi-hop IP network, or the overhead bytes of a data link. Control channel management for a peer node-to-OLS link is the same as for a peer node-to-peer node link.
To tell a peer node-to-OLS session from a peer node-to-peer node session, the RFC defines a new LMP-WDM CONFIG object, with Class 6 and C-Type 2. The object carries two bits and a reserved field. The WDM bit indicates support for the LMP-WDM extensions defined in the document. The OLS bit says whether the sender is an optical line system, when it is set, or a peer node, when it is clear. The reserved field should be sent as zero and ignored on receipt.
The OLS bit allows a node to identify itself as an OLS or a peer node, which is used to detect the misconfiguration of a peer node-to-OLS session between two peer nodes, or of a peer node-to-peer node session between a peer node and an OLS. If a node does not support the LMP-WDM extensions, it MUST reply to the Config message with a ConfigNack message. If a peer node that is configured to run LMP-WDM receives a Config message with the OLS bit clear, it MUST also reply with a ConfigNack message.
When two devices open a session, each one says whether it is a router-like node or the line equipment. If the two sides are paired wrongly, the device that notices answers with a ConfigNack message.
| Field | Name | Size | Value | Description |
|---|---|---|---|---|
WDM-BIT | WDM | 1 bits | Set to indicate support for the LMP-WDM extensions defined in this document. | |
OLS-BIT | OLS | 1 bits | Set when the sender is an optical line system, clear when the sender is a peer node. | |
RESERVED | Reserved | 30 bits | Should be sent as zero and ignored on receipt. |
§2.2Link Verification Across the Span
The Test procedure used with OLSes is the same as in the base LMP specification. The VerifyTransportMechanism, included in the BeginVerify and BeginVerifyAck messages, allows nodes to negotiate a link verification method, and it is essential for line systems that have access to overhead bytes rather than to the payload. The VerifyId, provided by the remote node in the BeginVerifyAck message and used in all subsequent Test messages, differentiates Test messages from different link verification procedures. In addition to the Test procedure, the trace monitoring function of RFC 4207 may be used for link verification when the OLS user ports are SONET or SDH.
There is an interplay between the data links managed by peer-to-peer sessions and those managed by peer-to-OLS sessions. In the figure of the RFC, the OXC1-to-OLS1 session manages the data links between OXC1 and OLS1, and the OXC2-to-OLS2 session manages the data links between OXC2 and OLS2. The OXC1-to-OXC2 session, however, manages the data links between OXC1 and OXC2, which are actually a concatenation of the data links between OXC1 and OLS1, the DWDM span between OLS1 and OLS2, and the data links between OXC2 and OLS2. It is those concatenated links that comprise the TE links advertised in the GMPLS TE link state database.
The implication is that when the data links between OXC1 and OXC2 are being verified, OLS1 and OLS2 need to make themselves transparent with respect to these concatenated data links. Coordinating the verification of the OXC1-to-OLS1 and OXC2-to-OLS2 data links so that this transparency holds is the responsibility of the peer nodes, OXC1 and OXC2. It is also necessary for those peer nodes to understand the mappings between the data links of the peer node-to-OLS session and the concatenated data links of the peer node-to-peer node session.
To check the whole link, the line equipment on the way has to pass the test signal through without looking at it. The routers at the ends arrange that and keep track of which pieces belong to which path.
§2.3Link Summarization and the New Sub-objects
The LinkSummary message is used to synchronize the Interface_Ids and to correlate the properties of the TE link. It includes one or more DATA_LINK objects, and the contents of a DATA_LINK object consist of a series of variable-length data items called Data Link sub-objects that describe the capabilities of the data links.
This document defines several additional Data Link sub-objects. The link characteristics they describe are, in general, those needed by the CSPF, the function that selects the path for a particular LSP. They describe the specified peer node-to-OLS data link as well as the associated DWDM span between the two OLSes.
Every sub-object starts with a Type field of 8 bits and a Length field of 8 bits. The Length field contains the total length of the sub-object in bytes, including the Type and Length fields, and it MUST be at least 4 and MUST be a multiple of 4. The reserved fields of the sub-objects below should be sent as zero and ignored on receipt.
- Link Group ID, Type 3 and Length 8: a local ID assigned to a group of data links. Its main purpose is to reduce control traffic during failures that affect many data links, by allowing a single ChannelStatus message to cover a group of data links instead of one message for each data link. A data link may be a member of multiple groups, which is done by including multiple Link Group ID sub-objects in the LinkSummary message. The groups map the data links into the failable entities that the OLS knows about, so that if one of those entities fails, all the associated data links are failed and the peer node is notified with a single message. An OLS could create a Link Group for each laser, and one for each fiber, so that a loss of signal on a fiber is reported as one failure affecting all the data links on it. The Link Group ID 0xFFFFFFFF is reserved and indicates all data links in a TE link, and all data links are members of that group by default.
- SRLG, Type 4 and Length (N+1)*4 where N is the number of SRLG values: identifies the shared risk link groups of which the data link is a member. This information may be configured on an OLS by the user and used for diverse path computation.
- BER Estimate, Type 5 and Length 4: an estimate of the bit error rate of the data link. The bit error rate is the proportion of bits that have errors relative to the total number of bits received in a transmission, usually expressed as ten to a negative power. A rate of ten to the minus 13 means that out of every 10,000,000,000,000 bits transmitted, one bit may be in error. The 8-bit field holds the exponent, so a rate of ten to the minus X is sent as the value X. The rate is an indication of overall signal quality.
- Optical Protection, Type 6 and Length 4: indicates whether the link is protected by the OLS. The information can be used as a measure of link capability, and it may be advertised by routing and used by signaling as a selection criterion. The encoding of the 6 link flags is defined in the GMPLS signaling specification.
- Total Span Length, Type 7 and Length 8: the total distance of fiber in the OLS, held as a 32-bit unsigned integer that gives the total length of the WDM span in meters. It may be used as a routing metric or to estimate delay.
- Administrative Group, also called Color, Type 8 and Length 8: the administrative group to which the data link belongs, held as a 32-bit value.
Each new sub-object is a small record about one link: which failure group it belongs to, how clean the signal is, whether a backup path exists, and how long the fiber is. The routing function reads these records when it chooses a path.
| Field | Name | Size | Value | Description |
|---|---|---|---|---|
TYPE | Type | 1 byte | 3 | Sub-object type. |
LENGTH | Length | 1 byte | 8 | Total length of the sub-object in bytes, including Type and Length. |
RESERVED | Reserved | 2 bytes | Should be sent as zero and ignored on receipt. | |
GROUP-ID | Link Group ID | 4 bytes | Local ID of a group of data links. The value 0xFFFFFFFF means all data links in a TE link. |
- 3Link_GroupId — Group of data links that fail together, such as one laser or one fiber.
- 4SRLG — The shared risk link groups the data link belongs to.
- 5BER_Estimate — The exponent of the bit error rate, so a rate of ten to the minus X is sent as X.
- 6Optical_Protection — Whether the optical line system protects the link.
- 7Total_Span_Length — Total length of the WDM span in meters, as a 32-bit unsigned integer.
- 8Administrative_Group — The administrative group, or color, the data link belongs to.
§2.4Fault Management and Group Status
The fault management procedure used between a peer and an OLS follows the procedures of the base LMP specification, with some further extensions defined here. The information learned from the OLS-to-peer fault management procedures may be used to trigger peer-to-peer LMP fault management, or may be used to trigger GMPLS signaling and routing procedures directly.
Fault management consists of three major functions: fault detection, fault localization and fault notification. The fault detection mechanisms are the responsibility of the individual nodes and are not specified as part of this protocol. They may include a bit error rate exceeding a threshold, and loss of signal and SONET or SDH level errors. It is the responsibility of the OLS to translate these failures into (Signal) OK, Signal Failure or Signal Degrade.
The OLS uses the messages defined in the LMP fault localization procedures, ChannelStatus, ChannelStatusAck, ChannelStatusRequest and ChannelStatusResponse, to inform the adjacent peer node of failures it has detected, in order to initiate the LMP fault localization procedures between the peer nodes. It does not participate in those procedures itself. The OLS may also run its own fault localization process, so that it can determine the location of a fault along the DWDM span, for example pinpointing the fault to a particular amplifier in a span of thousands of kilometers in length.
Each data link is identified by an Interface_ID, and a Link Group ID may also be assigned to a group of data links. To report the status of a group instead of each link, the RFC defines a new LINK_GROUP CHANNEL_STATUS object, with Class 13 and C-Type 4. It carries a 32-bit Link Group ID, two flag bits shown as A and D in the RFC's diagram, and a 32-bit Channel Status value whose values are defined in the base LMP specification. The object may be used in place of the CHANNEL_STATUS objects in a ChannelStatus message, and it is non-negotiable.
When a laser or a fiber fails, the line equipment sends one message that covers every link affected. The router at the end then starts the fault location procedure, while the line equipment may look for the fault itself.
§3Security Considerations
LMP message security uses IPsec, as described in the base LMP specification. This document only defines new LMP objects that are carried in existing LMP messages, so it introduces no other new security considerations beyond those already covered in the base specification.
The messages are protected in the same way as in the base protocol, so there is nothing new to guard here.
§4IANA Assignments
LMP defines four name spaces and the ways in which IANA can make assignments to them: the LMP Message Type, the LMP Object Class, the LMP Object Class type (C-Type), which is unique within the Object Class, and the LMP Sub-object Class type (Type), which is unique within the Object Class.
This memo introduces the following new assignments. Under the CONFIG class name it allocates LMP-WDM_CONFIG with C-Type 2. Under the CHANNEL_STATUS class name it allocates LINK_GROUP with C-Type 4. Under the DATA_LINK class name it allocates the sub-object types Link_GroupId (3), SRLG (4), BER_Estimate (5), Optical_Protection (6), Total_Span_Length (7) and Administrative_Group (8).
The RFC gives every new object and field a number so that two devices agree on which is which. The numbers are listed in the section itself.