Re: Switching technologies requiring bidirectional asymmetric LSPs?

[Igor Bryskin <i_bryskin@yahoo.com>]

Adrian, Lou

Please,see in line.

Adrian Farrel <adrian@olddog.co.uk> wrote:
>  Hi,
>
> I'm a bit surprised that there was no follow-up to Lou's email.
>
> Does silence indicate that this was put to bed in Prague and no-one is 
> interested in these LSPs?
>
> > So a few of us have been having been discussing the asymmetric work 
> > presented in Prague and it seems to me we have an open question on 
> > requirements.
> >
> > It's clear that at least one switching technology (i.e., ethernet/PBB-TE) 
> > requires support for bidirectional asymmetric LSPs.
>
> Is this clear? I continue to hear talk of service requirements, but not so 
> much of how those services are required to be supported.
>
> The benefits I have heard are:
> 1. Fewer control plane messages
> 2. Ease of enforecement of
>  fate-sharing
>
> IB>> Adrian, you enumerated here the benefits of bidirectional LSPs, and BTW you forgot to mention the most important one. Ethernet OAM is designed, as I understand, on assumption that the trafic  takes the same  paths in both directions. So, if we want to preserve the Ethernet native OAM (which we certainly do , because this is half of Ethernet functionality) we must map a bidiretcional service on either a single bidirectional LSP or two unidirectional LSPs using the same path. This is different form MPLS where there are no such OAM requirements.
> Lou is talking about asymetrical bi-directional LSPs, and what is not clear (at least for me) whether we need asymetrical p2p Ethernet services.
>
> These are significant, but not dramatic, requirements.
>
> > The question is:
> >
> > Is the *requirement* for bidirectional asymmetric LSPs:
> > (a) a technology specific requirement, or
> > (b) one that is common (this
>  is CCAMP after all!) to multiple switching 
> > technologies?
>
> CCAMP deals in transport networks. As far as I can see the service 
> requirements would be pretty much the same all transport networks and would 
> certainly be applicable to packet, L2, and TDM (the latter because TDM will 
> be called on to support L2).
>
> IB>> See my comment above: there is a differnce between MPLS and Ethernet services. Also there are certainly differences between MPLS and lambda services (use of the same lambda in both directions, for example). So each transport technology may have distinct requirements WRT bidirectional services and connections on which the services are mapped.
>
> > Please keep in mind that service requirements are not the same thing as 
> > switching technology requirements.  For example, we have long built 
> > bidirectional asymmetric services on unidirectional MPLS LSPs.
>
> Well, exactly!
> Perhaps someone can explain why
>  the Ethernet hardware is forced to require 
> bidirectional asymmetric LSPs when MPLS is happy without?
>
> IB>> Again, IMO the answer is to be able to use native Ethernet OAM.
>
> Igor
>
> > The answer to this question will help determine if we should have a 
> > technology specific solution or a generic CCAMP solution (as well as the 
> > complexity of the solution.)
>
> We should not take any action that deliberately precludes or makes more 
> complex the genericisation (is that an American word?) of the solution 
> unless there is a significant difference in simplicity of solutions.
>
> But we should take no action at all unless there is some more evidence of 
> support for this work!
>
> Adrian

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