Subject: LSP hierarchy comments

From: Olle Pers <[email-masked]>
Date: Wed, 12 Jul 2000 18:05:03 +0200

Hallo, 

I had a look at draft-ietf-mpls-lsp-hierarchy-00.txt. 
Here are some questions, and a few comments: 

The Link Mux Capability TLV: 

- is it flexible enough to allow more integrated nodes? How should one
describe a network element that can switch both wavelengths, TDM channels,
and packets, on the same interface?  As having multiple capability values
(using sub-TLVs?), or as being a cluster of nodes and links with different
capabilites? 

- you should be aware that TDM capabilities may be more complex than a
single value can convey. See draft-mannie-mpls-sdh-control-00.txt. 

- would it be useful to identify ATM or Frame Relay nodes from packet-LSRs?
(these are covered by MPLS as specified today. Circuit-switched nodes are
not, yet). 

- which value should we use for IP routers that do not understand MPLS?
PCS-0? 

- more important, could there be any problems with having the LSRs advertise
the capabilities of other nodes, instead of having each router advertise its
own capabilities? The words "coordinated configuration" can easily make an
operator think about "manual" and "errors".  

- a small comment on terminology: In section 4.3.1-2 "link type" means
having certain "Link Mux Capabilities". But in 4.1.1 "link type" is a
parameter that is set to "point-to-point".  

FA-LSP endpoint: 

- To correctly advertise an FA-LSP, one must identify the "tail end", and
know which is the "last link". Could there be any problems to agree where
the LSP ends, if PHP is used at the far end? 

Signalling aspects: 

- The routing aspects cover both ISIS and OSPF, but all the signalling
examples are for RSVP-TE only. Would there be any principal differences if
LDP was used instead?  

- It is stated that an FA-LSP can be torn down by the LSR at the head-end.
But more generally, any LSP can be closed by any LSR along its path, for
reasons that we may not always know, can't it?  The expectations on the
head-end LSR seems to be that it withdraws the FA-LSP from being advertised,
and that it tries to save the tunneled LSPs.  

Olle Pers
Telia, Sweden

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From: Yakov Rekhter <[email-masked]>
Date: Wed, 12 Jul 2000 10:14:10 -0700

Olle,

> Here are some questions, and a few comments: 

I'll try to answer *some* of your questions...

> (using sub-TLVs?), or as being a cluster of nodes and links with different

There is no requirements for all the links of a given node to have 
the same Link Mux Capability.

> single value can convey. See draft-mannie-mpls-sdh-control-00.txt. 

I am aware of this :-)

> (these are covered by MPLS as specified today. Circuit-switched nodes are

I don't have an opinion on this. 

> operator think about "manual" and "errors".  

I think your last sentence answers your question.

> and that it tries to save the tunneled LSPs.  

Correct.

Yakov.