Liaison statement
GMPLS Signaling for VCAT/LCAS
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State | Posted |
---|---|
Submitted Date | 2007-09-04 |
From Group | ccamp |
From Contact | Adrian Farrel |
To Group | ITU-T-SG-15-Q14 |
To Contacts | Greg Jones <greg.jones@itu.int> |
Cc | Kam Lam <hklam@alcatel-lucent.com> Stephen Trowbridge <sjtrowbridge@alcatel-lucent.com> Ross Callon <rcallon@juniper.net> David Ward <dward@cisco.com> Scott Bradner <sob@hardward.edu> CCAMP Mailing List <ccamp@ops.ietf.org> |
Response Contact | Adrian Farrel <adrian@olddog.co.uk> Deborah Brungard <dbrungard@att.com> |
Technical Contact | Adrian Farrel <adrian@olddog.co.uk> Deborah Brungard <dbrungard@att.com> |
Purpose | For action |
Deadline | 2007-11-15 Action Taken |
Attachments | (None) |
Body |
The CCAMP Working Group thanks you for your liaison of April this year (COM15-LS3-E) and for your interest in our work to develop GMPLS signaling extensions for the control of VCAT within TDM networks. The latest version of this work can be found at http://www.ietf.org/internet-drafts/draft-ietf-ccamp-gmpls-vcat-lcas-02.txt We expect a revision relatively soon, so if the referenced link fails, please also check at http://www.ietf.org/internet-drafts/draft-ietf-ccamp-gmpls-vcat-lcas-03.txt Here are our responses to the questions in your liaison. 1. Would CCAMP consider generalizing the draft so that it could be applied to any Inverse Multiplexing scheme? For example, if generalized, the method could be used to establish H.244, ML-PPP, ATM inverse mux, or BONDING connections. It is certainly our intention that any protocol extensions that we develop should be easily extensible to other technologies. But at the same time we have seen no immediate interest from the community in applying GMPLS as a control plane for any of the technologies that you list. It would, of course, be a prerequisite of using GMPLS for such an inverse multiplexing scheme, that GMPLS was also used to build network connections (i.e. LSPs) for the specific technology. If you have a requirement to use GMPLS to control these technologies, we would be interested to hear from you. In the mean time, we note that the inverse multiplexing schemes that you list are packet/cell forms rather than circuit forms of inverse multiplexing and hence may have different configuration parameters than VCAT. 2. Does the I-D describe VCAT call signalling? The I-D uses GMPLS Calls (RFC 4974) to achieve VCAT group signaling. The GMPLS Call is used to coordinate the setup of multiple server connections (LSPs) used to form a VCAT group (a connection in the VCAT layer). 3. Does the I-D allow LSPs in a server layer to be set up without any prior knowledge of a possible VCAT layer, and then at a later point in time allow those LSPs to become available to a VCAT layer? When a network connection is established at the request of an operator or a management system, we have assumed that there is some motivation, and that the motivation is expressed in the call that coordinates the connection. In RFC 4974, the nature of the call can be changed (as a matter of call parameter exchange that is within the scope of the call controller function, but the details of which, except for the message exchange rules, are outside the scope of the signaling protocol), but the connections cannot be moved from one call to another. Thus, LSPs that are set up in association with a specific call can only be used as directed by the call controller with responsibility for that call. If a call controller decides to use the connections (LSPs) for VCAT one day and for something else another day, that is entirely within its remit. However, this assumes that the call controller can suitably instruct and coordinate the necessary adaptation functions at each end of the network connections. An implementation might find it more convenient to release the call (and the associated connections), before setting up a new call and a new set of connections. Note that we are considering mechanisms to allow LSPs to be moved between VCAT Groups according to the requirements of the network. Such schemes necessarily mean that there is not always a 1:1 relationship between calls and VCAT groups since it remains the case that connections cannot be moved between calls. However, our understanding of G.707 and the ability to move component trails (VCAT group members) between VCAT groups while the trail is in service is unclear, and we would welcome clarification of the requirements before progressing this function further. 4. Does the I-D allow the association of a VCAT call to multiple server layer calls? This is not specifically addressed. There is no hierarchy of calls described in the draft. Instead, the draft provides for a single call that is used to coordinate all of the server layer connections that support the single VCAT service. In practice, this may not represent architectural purity, but we believe it is a protocol implementation simplification consistent with the way that VCAT is operated. We note that VCAT groups can only consist of a single server connection type and cannot be mixed, e.g., VC-3 and VC-4 components cannot both be in the same VCG. 5. Does release of a VCAT call automatically imply release of the server layer call(s)? This is not required by G.8080 as layers are assumed to be independent. As noted for point 4, the VCAT layer call is not specifically called out in the draft. You may consider that the draft provides a mechanism for handling the (single hop) VCAT call and the server layer call as a single item. We would be interested to hear from you the operational circumstances under which a single VCAT layer call might give rise to multiple server layer calls. The signaling of the release of a GMPLS Call is rejected if connections are still in place (per RFC 4974 section 6.6.4) which is consistent with the connections having been set up under the instructions of the call controller and in support of the call. Thus, operationally, the release of a call will require the release of the associated connections. At this point it may be worth clarifying that a VCAT layer connection is created under the control of a VCAT layer call. The VCAT connection may require server layer connections (indeed, this is always the case with VCAT) and those connections need to be associated and controlled by a call. it is this second type of call that we are we are describing in this draft. Thus, the release of a VCAT call would lead to the release of the VCAT connection. The network policy may determine whether to release the server layer call or not. If the server layer call is released, the server layer connections will also be released. 6. Is VCAT layer addressing assumed to be the same as that of the server layer? GMPLS only supports IP addressing. The link connections in the VCAT layer created by/from network connections in the server layer may be given different addresses from the addresses used to represent the endpoints in the server layer, or may use the same addresses. 7. Are the two VCAT layer Call Controllers assumed to have direct signalling connectivity? Yes, adjacent call controllers in any layer are assumed to be able to exchange call control messages without the intervention of any proxy, agent, or extra-layer entity. 8. If multiple client layers are using the same VCAT layer as their server layer, how can the VCAT layer call be identified for use in the client layer signalling? How is this problem any different from any other n:1 client/server relationship? Please supply details of why the fact that the server layer is a VCAT layer should make this scenario any different. Please also note that, as for point 5 above, the VCAT layer call is not what is being addressed in this draft. We are addressing the server layer call that coordinates the server layer network connections that are used as VCAT group members to construct a VCAT group that can be presented as a link connection in the VCAT layer. 9. Have you considered using the ASON call id [RFC3474] at all layers to achieve separate call control of the VCAT and server layers? The format of the call ID is deliberately out of scope for this work as we would not wish to control or enforce the applicability of this work in any one environment. However, RFC 4974 (as noted in a recent separate liaison from us on GMPLS Calls) allows any format call ID to be encoded in GMPLS calls. Thus, the ASON call id format described informationally in RFC 3474 can be supported and used in an ASON environment at the choice of the operator and/or the implementer of the call controller. Can you please confirm that the normative definition of the ASON call ID is in G.7713.2? Other Recommendations (such as G.7713.3) also appear to have call IDs defined, and we want to make sure that we can reference a single, protocol- independent definition of a call ID 10. In the ASON architecture [G.8080], it is not assumed that a single signalling protocol is used in all domains. Even in the case the same protocol is used in all domains, the RSVP session changes between domains. Could you explain how the Notify mechanism used for call control would work across multiple domains where the RSVP session changes? This question clearly has wider relevance than this VCAT draft and should be seen in the context of RFC 4974, and not in reference to this draft. We note that G.8080 makes no assumptions about connection signaling protocols in adjacent domains, but we believe that the architecture does assume an E-NNI reference point in association with one or more call controllers at such domain interfaces. The E-NNI call controllers are responsible for requesting the necessary network connections in each domain and, where the E-NNI is externalised, for requesting any inter-domain connections. Call messages are exchanged between adjacent call controllers and relate to the network connections established at the request of those call controllers. When two adjacent GMPLS domains support the same end-to-end network connection, we do not recommend that the session object be changed. Please clarify where in G.8080 there is any reference to RSVP sessions. There should be no such discussion of protocol implementations in an architecture document. We would welcome your opinions on these responses and the direction of our work. In your liaison you stated that you had the intention to review the draft further at your June meeting. But in the liaison from your June meeting (COM15-LS170-E) you say that you deferred this review pending further revisions of the I-D. This is quite reasonable, but we would nevertheless welcome any further high-level comments that you may have. We will notify you as this draft is updated. Best regards, Adrian Farrel and Deborah Brungard IETF CCAMP Working Group Co-Chairs |