The MPLS WG Archive

[Thomas Nadeau <tnadeau@cisco.com>]

> Pipe or uniform is the
> terminology adopted in the MPLS diffserv draft and carried forward into
> http://www.ietf.org/internet-drafts/draft-agarwal-mpls-ttl-01.txt

        Sorry, from the original context, I wasn't sure.

> The short story
> is: 
> - for uniform model TTL is independent of MPLS level.
> You copy TTL values up and down the stack as you push and
> pop. 
> - for pipe model, TTL is unique to each MPLS
> level. 
> So configuring this looks painful (get it from
> incoming label before x-connect entry, or get it from incoming IP
> payload, or set it to fixed value at ingress)
> :-(.

        

It looks
painful, but is flexible as to support different implementations.

> As to how to handle non-TTL
> capable links, an unsigned object added to InterfaceConfEntry
> (InterfaceTTLDec?) with a default value of 1 should be all that is
> required. The only wrinkle being that I don't fully grok pop and swap to
> be sure that a non-ttl link label under the top label would work
> correctly.

        

This is
certainly an option.

        

--Tom

        

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