Link Management Protocol (LMP) for Dense Wavelength Division Multiplexing (DWDM) Optical Line Systems
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- rfc-6898 — Link Management Protocol Behavior Negotiation and Configuration Modifications
Extracted elements (21)
Admin status of an LSP known to peer nodes (via the Admin Status object of GMPLS signaling) can be communicated to OLSes to suppress spurious alarm reporting, motivating the peer node-to-OLS LMP session for alarm management.
An OLS uses LMP fault localization messages (ChannelStatus, ChannelStatusAck, etc.) to inform adjacent peer nodes of detected failures in order to initiate LMP fault localization between peer nodes, but does not itself participate in the peer-to-peer fault localization procedure.
LMP is extended to operate between a peer node (e.g., OXC) and an adjacent optical line system (OLS), not just between peer nodes. This allows the OLS to communicate link configuration and state to peer nodes, reducing manual configuration and enhancing fault detection and recovery.
Peer node-to-OLS LMP sessions are maintained independently from peer node-to-peer node LMP sessions. It MUST be possible for LMP sessions to come up in any order, including a peer node-to-peer node session without any peer node-to-OLS sessions.
The Link Group ID is designed to reduce control traffic during failures affecting many data links. A single ChannelStatus message with a LINK GROUP CHANNEL_STATUS object can cover an entire group rather than requiring individual messages per data link.
The TE link between two peer nodes is a concatenation of the peer node-to-OLS data links and the DWDM span between OLSes. Peer nodes must understand the mappings between these sub-links to properly coordinate verification.
When verifying data links between peer nodes (e.g., OXC1-OXC2) using LMP link verification, the OLSes (OLS1 and OLS2) must be made transparent with respect to the concatenated data links. Coordination of this transparency is the responsibility of the peer nodes.
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 configured to run LMP-WDM receives a Config message with the OLS bit clear in the LMP-WDM_CONFIG object, it MUST reply with a ConfigNack message, detecting misconfiguration.
A new LMP-WDM CONFIG object (Class = 6, C-Type = 2) is defined to distinguish peer node-to-OLS LMP sessions from peer node-to-peer node sessions. It contains a WDM bit (support for LMP-WDM extensions) and an OLS bit (sender is OLS if set, peer node if clear).
Data Link sub-objects are variable-length items within the DATA_LINK object of LinkSummary messages. Each has an 8-bit Type, 8-bit Length (minimum 4, multiple of 4), and variable contents describing link characteristics for CSPF path selection.
The Administrative Group sub-object (Type = 8, Length = 8) carries a 32-bit administrative group (color) value as defined in RFC 3630, indicating the administrative group to which the data link belongs.
The LINK_GROUP CHANNEL_STATUS object (Class = 13, C-Type = 4) reports channel status for all data links in a Link Group using one 32-bit Link Group ID and one 32-bit Channel Status field (with A and D bits) per group entry. It is non-negotiable.
The Link Group ID sub-object (Type = 3, Length = 8) assigns a 32-bit local ID to a group of data links. Link Group ID 0xFFFFFFFF is reserved and indicates all data links in a TE link; all data links are members of this group by default.
The Optical Protection sub-object (Type = 6, Length = 4) carries a 6-bit Link Flags field indicating whether and how the OLS protects the link, encoded as defined in RFC 3471 Section 7.
The SRLG sub-object (Type = 4, Length = (N+1)*4) carries N 32-bit Shared Risk Link Group values identifying the SRLGs of which the data link is a member, used for diverse path computation.
The Total Span Length sub-object (Type = 7, Length = 8) carries a 32-bit unsigned integer representing the total WDM span length in meters, usable as a routing metric or propagation delay estimate.
This document registers new LMP assignments under IANA namespaces defined in RFC 4204: CONFIG C-Type 2 (LMP-WDM_CONFIG), CHANNEL_STATUS C-Type 4 (LINK_GROUP), and DATA_LINK sub-object Types 3–8 (Link_GroupId, SRLG, BER_Estimate, Optical_Protection, Total_Span_Length, Administrative_Group).
LMP message security uses IPsec as described in RFC 4204. This document only defines new LMP objects carried in existing LMP messages and introduces no additional security considerations beyond those in RFC 4204.
The BER Estimate sub-object (Type = 5, Length = 4) contains an 8-bit BER field encoding the negative exponent X such that BER = 10^(-X), providing an overall signal quality estimate for the data link.
The LMP-WDM_CONFIG object is a 32-bit field with bit W (WDM support) and bit O (OLS identity) in the most significant positions, followed by a Reserved field sent as zero and ignored on receipt.