Operating Virtual Concatenation (VCAT) and the Link Capacity Adjustment Scheme (LCAS) with Generalized Multi-Protocol Label Switching (GMPLS)
updates
- rfc-4606 — Generalized Multi-Protocol Label Switching (GMPLS) Extensions for Synchronous Optical Network (SONET) and Synchronous Digital Hierarchy (SDH) Control
Extracted elements (27)
RFC 4606 restricts virtual concatenation components within a single LSP to travel over the same component link due to label-to-link binding, making diversely routed VCG members impossible with one LSP. Multiple control plane LSPs are therefore required to support diversely routed VCG member sets.
The VCG ID is explicitly separated from the VCAT Call ID to support member-sharing scenarios. This allows one or more calls (with accompanying LSPs) to be moved between VCGs without tearing down the server-layer connections.
Section 5.2 states 'This field MUST be set to 2' for the Type field of the VCAT TLV, but the diagram in the same section shows 'Type = 4' and the IANA assignment in Section 7.1 also assigns value 4 to the VCAT TLV. The normative text value of 2 appears to contradict the diagram and IANA registry.
For non-LCAS-capable interfaces, removing one component of the VCG will result in failure detection of the member at the endpoint and failure of the whole group. Dynamic member removal without management intervention requires LCAS-capable interfaces.
RFC 4606 is updated by this document. Section 4 describes single-member-set VCG procedures for informational purposes only; RFC 4606 remains normative for that case. In any conflict between Section 4 of this document and RFC 4606, RFC 4606 takes precedence.
Any failure in call or LSP establishment MUST be treated as a failure of the VCG as a whole and MAY trigger deletion of all calls and LSPs associated with the VCG.
Before modifying VCG bandwidth, a Notify message MUST be sent for each existing VCAT call with Action=2 and Number of Members set to the anticipated post-change count. If an error occurs, the number of members MUST be reverted and the reverted value MUST be re-signaled.
GMPLS mechanisms for the operation of VCAT are REQUIRED for both the case where LCAS is available and the case where it is not. The GMPLS procedures for the two cases SHOULD be identical.
GMPLS signaling for LCAS-capable interfaces MUST support all VCG member configuration scenarios (fixed co-routed, fixed diversely routed, fixed member sharing, dynamic co-routed, dynamic diversely routed, dynamic member sharing) with no loss of traffic.
GMPLS signaling for non-LCAS-capable interfaces MUST support only the fixed scenarios (fixed co-routed, fixed diversely routed, fixed member sharing).
GMPLS signaling MUST carry on behalf of the VCAT endpoints: the type of the member signal, the total number of members in the VCG, and identification of the VCG and its associated members.
The Number of Members field MUST indicate the total number of members in the VCG (not just the call) and MUST be updated over the life of the VCG to reflect the current number of members.
The Signal Type field in the VCAT TLV MUST never change over the lifetime of a VCG. The LCR field MUST NOT change over the life of a VCG. The VCG ID MUST NOT change over the lifetime of a VCG but MAY change over the lifetime of a call.
To associate an existing VCAT call with a new VCG, a Notify message MUST be sent with CALL_ATTRIBUTES containing a VCAT TLV with Action=1, and Number of Members MUST equal the sum of all LSPs associated with the VCG. The sender MUST be prepared to receive an error response.
To establish a VCAT call with no VCG association (for pre-establishment), a CALL_ATTRIBUTES object with the VCAT TLV MUST be included in the Notify message with the Action field set to 0.
To remove the association between a call and a VCG, a Notify message MUST be sent with a VCAT TLV where Action is set to 3. When the association between a VCG and all existing calls has been removed, the VCG is considered torn down.
To set up a new VCAT call and VCG simultaneously, a CALL_ATTRIBUTES object containing the VCAT TLV MUST be included in the Notify message with the Action field set to 1. LSPs MUST then be added until the member count reaches the value specified in the TLV.
VCAT-layer calls and related LSPs MUST follow the procedures defined in RFC 4974, with the addition of a CALL_ATTRIBUTES object containing the VCAT TLV. A call MUST NOT contain members used in more than one VCG.
The Action field (8 bits) in the VCAT TLV indicates the relationship between the call and the VCG: 0=No VCG ID (pre-establishment), 1=New VCG for Call, 2=Modification of Number of Members, 3=Remove VCG from Call.
The LCR (LCAS Required) field (2 bits) in the VCAT TLV indicates LCAS capability requirements: 0=LCAS required, 1=LCAS desired, 2=LCAS not supported. This field MUST NOT change over the life of a VCG.
The Signal Type field (16 bits) in the VCAT TLV identifies the elementary signal carried by all VCG members. Defined values include: 1=VT1.5 SPE/VC-11, 2=VT2 SPE/VC-12, 3=STS-1 SPE/VC-3, 4=STS-3c SPE/VC-4, 11=ODU1, 12=ODU2, 13=ODU3, 21=T1, 22=E1, 23=E3, 24=T3. Signal types can never be mixed in a VCG.
IANA assigned Call Attributes TLV value 4 for the VCAT TLV in the 'Call Attributes TLV' section of the 'RSVP PARAMETERS' registry. New allocations require IETF Review.
IANA assigned RSVP Error Code 39 ('VCAT Call Management') with seven error values (1–7) covering: VCG signal type not supported, LCAS option not supported, max VCGs exceeded, max VCG members exceeded, LSP type incompatible, unknown LCR value, unknown/unsupported ACTION.
IANA created the 'VCAT Elementary Signal' registry (range 0–65535, value 0 Reserved) to track elementary signal types as defined in Section 5.2, initially populated with 11 signal type values. New allocations require IETF Review.
IANA created the 'VCAT VCG Operation Actions' registry (range 0–255) to track VCAT TLV Action field values as defined in Section 5.2, initially populated with values 0–3. New allocations require IETF Review.
This document introduces no new signaling messages and does not change control-plane adjacency relationships. However, intercepted call information for diversely routed VCG members may reveal to an attacker that these LSPs belong to the same VCAT group via different routes, indicating the VCG is designed for increased reliability.
The CALL_ATTRIBUTES VCAT TLV is 12 octets: Type (16 bits, value 4), Length (16 bits, value 12), Signal Type (16 bits), Number of Members (16 bits), LCR (2 bits), Reserved (6 bits), Action (8 bits), VCG ID (16 bits).