Re: [Bier] Comment on BIER-TE

[IJsbrand Wijnands <[e-mail]>]

Hi,

> I mentioned how this could btw. equally be a question for BIER: If you had such
> a large multi-are network and you would randomnly assign BFR-IDs to BFERs and end
> up having in one region BFER with different SI's, then you would also need to 
> send per-SI copies into that region, which would not be traffic-optimal. Aka:
> You would also like to assign BFR-ID in SI groups in topological vicnity to maximize
> the replication efficiency in BIER if you have such large networks.

The big difference with BIER is that when using multiple SI’s, the forwarding tables for each SI are build throughout the whole network. So there is never a problem that BIER packets get stuck because there is no BIFT for a particular SI. I agree it might be more efficient if BFER’s within an SI are co-located to have a more efficient forwarding, but its not a requirement to avoid packet loss.

IMO, the concept of SI does not apply to BIER-TE in order to scale up. One can create multiple “domains” of BFR’s that use bits out of the same BitString (like sub-domains), but these domains act completely independently (like Segmented Inter-AS scenario). 

The power of BIER-TE is that one can traffic engineer on a per packet basis without creating state in the network. Unfortunately, the scope is small. 

If traffic engineering on a bigger scale is needed, it may not be required to do it on a per flow basis but rather on a topology. This can be done with normal BIER and different topologies (sub-domains) created BIFT’s. Maybe this is similar to what Greg Mirsky was saying on the other thread, but I don’t think we would run BIER over RSVP-TE. We run it over different topologies.

Thx,

Ice.