Re: I-D ACTION:draft-takacs-asym-bw-lsp-00.txt

[Igor Bryskin <i_bryskin@yahoo.com>]

Hi,

Provided that we have 1.a - there is a clear requirement for  asymmetrical bidirectional services ? I tend to agree with Don on this.

 

If implementing a bidirectional service by an association of two reciprocal unidirectional LSPs is so great, then why do we need bi-directional LSPs in the first place? The answer is well recognized:

a)      the setup is faster;

b)      the CP state is smaller

c)      the management is simpler (fate-sharing, recovery, alarm distribution,,,,)

d)      solution for the opposite direction resource allocation contention problem

e)      ?

 

That?s why we decided to introduce Upstream Label and support bi-directional LSPs.

The introduction of Upstream T-SPEC/FLOWSPEC seems to me a natural and relatively inexpensive price for preserving the a),b),c)?..

 

 

Igor

  Adrian Farrel <adrian@olddog.co.uk> wrote:
>  Cutting to the chase (I hope):
>
> >>-> btw, where this requirement come from ?
> > [DF] Specifically GMPLS control of Ethernet.
> >
> >
> > [dp] i think i should be more precise WHY this specific req ?
> > is that specific to Ethernet ?
>
> 1.a. Do we have a clear requirement for an asymmetrical bidirectional 
> service?
>
> 1.b. Do we have a clear requirement for asymmetrical bidirectional LSPs?
> (Does 1.b follow from 1.a?)
>
> > [dp] the issue is threefold
> >
> > a) you will see from the above that asym bi-dir LSP do not
> > call for an upstream tspec
>
> 2. If 1.b, what should we use on
>  a Path message to indicate the bandwidth of 
> the forward flow.
> 2.a. an 'upstream' TSpec
> 2.b. a FlowSpec
>
> > b) the gain compared to the cost of having a real bi-dir.
> > setup is so low that setting unidir LSP is simpler
> >
> > c) but there is an operational issue in linking two LSPs
> > (asymmetric) together that one could think of associating
> > them, we have a very efficient technique for this, that
> > does not impact intermediate nodes (ASSOCIATION object)
> > and provides for full flexibility (common or diverse spatial
> > path for the upstream and downstream flow)
>
> 3. Even if 1.b. we can consider:
> 3.a. A single signaling exchange for both directions
> 3.b. Two 'associated' signaling exchanges
>
> Personally, I think that the discussion is confused by talking about 
> "bidirectional LSPs". The issue really seems to revolve around the signaling 
> exchanges. The data plane presence can be established
>  identically by 3.a. or 
> 3.b.
>
> Adrian

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