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RE: [PWE3] PWE3 question
There are many ways to build a network.
The virtual "network" you describe is one way, in which case
the tunnel is not created explicitly for PW transport. But
others may choose to create a tunnel explicitly for PW transport.
In the later case, the tunnel is closely tied to the PW. No, the
tunnel is not created in direct response to any PW stream. But it
is still created directly for the PW service.
Same goes with the choice of whether to use an E-LSP. Network
design decision.
Clearly, using a common LSP for all traffic between two nodes
and using E-LSPs has certain scaling and restoration advantages
(fewer restore faster for the entire network).
But, some carriers may want to seperate the fate of the different
traffic. For example, the carrier may want to restore PW services
before voice services because the PW users pay more for the bandwidth.
John
> -----Original Message-----
> From: Sasha Vainshtein [mailto:Sasha@AXERRA.com]
> Sent: Wednesday, May 15, 2002 10:11 AM
> To: 'Rutemiller, John'
> Cc: 'pwe3@ietf.org'
> Subject: RE: [PWE3] PWE3 question
>
>
> John,
> Please see some comments/responses inline.
> Hopefully they will clarify my position.
> With best regards,
> Sasha Vainshtein
> email: sasha@axerra.com <mailto:sasha@axerra.com>
> tel: +972-3-7659993 (office)
> +972-8-9254948 (res.)
> +972-58-674833 (cell.)
>
>
>
> > -----Original Message-----
> > From: Rutemiller, John [mailto:John.Rutemiller@marconi.com]
> > Sent: Wednesday, May 15, 2002 12:12 PM
> > To: 'pwe3@ietf.org'
> > Subject: RE: [PWE3] PWE3 question
> >
> >
> >
> >
> > > -----Original Message-----
> > > From: Sasha Vainshtein [mailto:Sasha@AXERRA.com]
> > > Sent: Friday, May 10, 2002 2:57 AM
> > > To: 'Shahram Davari'
> > > Cc: 'pwe3@ietf.org'; Danny McPherson (E-mail); 'Andrew G.
> > > Malis'; Neil.
> > > 2. Harrison (E-mail)
> > > Subject: RE: [PWE3] PWE3 question
> > >
> > >
> > > Shahram and all.
> > > Please see a brief comment inline.
> > >
> > [SNIP]
> > >
> > > I would suggest a very simple criterion regarding exertion or
> > > non-exertion of control over PSN: if setup/teradown of a PW
> > > requires modification of the FIB in at least one PSN node that
> > > does not act as the PE for this PW, it means that control over
> > > this router has been exerted.
> > >
> > > This criterion does not depend on the protocol being used
> > > (static,LDP, RSVP or else).
> > >
> > > The single-label model requires allocation of a new label per PW
> > > in each interior node on the path fromingress to egress, and hence
> > > means exertion of control over the PSN unless the the pair of
> > > PEs are adjacent (the "single hop" case mentioned by Neil).
> > >
> > > Can we agree on that?
> > >
> >
> >
> > Creation of a Pseudo wire requires a tunnel label.
> >
> Correct. You must associate every direction of a PW
> over an MPLS network with an LSP leading from the
> ingress PE (for this direction) to egress PE.
> >
> >The creation of this tunnel must be configured.
> >
> It can be created regardless of any specific PW that would use it.
> And it could be created in many ways, including hop-by-hop forwarding
> provided by the vanilla LDP.
> Once created, such a tunnel can be used by - and, for scalability
> reasons, SHOULD be used - by more than one PW between the
> same pair of PEs.
>
> And it could be created in many ways, including "vanilla" LDP
> in DU mode.
> >
> >The establishment of the tunnel will affect the FIB if the P
> routers.
> >
> Correct. However, as I said above, creation of the tunnel (to be used
> by multiple PWs) is not caused by creation of the PWs. Creation
> of PWs using an already existing tunnel would not affect FIB in the
> P routers, only in PEs.
> >
> >Furthermore, the tunnel must be created with a forwarding class
> >that is sufficient to carry the desired pseudo wire traffic.
> >
> There are many ways to associate a certain forwarding behavior
> with the EXP bits across an LSP. E.g., one can use
> Preconfigured EXP<-->PHB Mapping in LSPs that have been
> created by LDP in DU mode.
>
> Such an method cannot be used if reservation of resources
> must be associated with an LSP. But even then nothing
> prevents creation of a "planned" network of DiffServ-enabled
> LSPs with BW reservation beforehand regardless of any
> specific PW, and then creation of PWs that use available
> capaity on this "network".
> >
> > If traffic classes are to be separated (e.g, ATM CBR gets EF and
> > ATM UBR gets best effort), then multiple tunnels must be created
> > across the network.
> >
> Not necessarily. A single E-LSP will may support up to 8 different
> traffic classes. And this can be done by using preconfigured
> EXP<-->PHB mappings, too.
> >
> >
> > Therefore, the PW has in some way exerted control over the P routers
> > even with the tunnel creation.
> >
> This would only happen if you apply the "One PW = One Tunnel" model
> that originated this thread. And that is exactly why I said
> that, IMHO,
> this model is beyound the chartered PWE3 scope. The model that
> separates creation of transport tunnels from creation of PWs is
> within this scope.
> >
> > John
> >
> > _______________________________________________
> > pwe3 mailing list
> > pwe3@ietf.org
> > https://www1.ietf.org/mailman/listinfo/pwe3
> >
>
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