[Nsi-wg] UvA/TUD topology exchange proposal

[Henrik Thostrup Jensen]

Hi again (sorry for the slow response time)

On Mon, 8 Sep 2014, Ralph Koning wrote:

> Hi Henrik,
>
> Thanks for your comments; it seems that some things are left unclear and
> let me elaborate on this. Naturally, we will improve the text in the
> next document version. As both Miroslav and me will be present at the
> Nordunet conference we can further elaborate and clarify the model.
>
> #0  The document is a proposal for a topology exchange
>    - It is not a requirements document (upcoming/promised by Chin/John)
>    - It is not a comparison of routing techniques
>
> #1  Topology exchange != routing
>    We distinguish between 'topology exchange' and 'path calculation'.

You cannot separate these. The requirements inherently affect what 
information is published/exhanges between networks/NSA. Similarly the 
routing algorithm affects how the information gets passed around.

The basic shortcoming of the system is that it is based around a single 
representation of each network (the NML way of thinking). However this is 
practially never the case.

You can try and encode switching capabilities into each network 
description and do pathfinding (the current approach for some in the NSI 
group), but this falls to the ground when there are restrictive policies 
about re-transit (i.e., I am allowed to transit a service into another 
network, but the entity I am selling to is not allowed to re-transit).

I wish more people would look at BGP. There is a notion in the group, that 
BGP is somehow bad or restrictive. However, the reason BGP is successfull 
it because it allows representing the underlying policy of the network AND 
being able to change up/downstream.  This is completely impossible with 
the single description-per-network idea of NML (which mainly seems to come 
out of multi-layer pathfinding research, and if you are just interesting 
in hardware capabilities that approach is fine). It is not BGP that 
creates the policy, it just exposes it.


     Best regards, Henrik

  Henrik Thostrup Jensen <htj at nordu.net>
  Software Developer, NORDUnet