The MPLS WG Archive

["Busschbach, Peter B (Peter)" <busschbach@lucent.com>]

> -----Original Message-----
> From: Naidu, Venkata [mailto:Venkata.Naidu@Marconi.com]
> Sent: Tuesday, November 18, 2003 6:28 PM
> To: 'Busschbach, Peter B (Peter)'; Naidu, Venkata;
> 'curtis@fictitious.org'
> Cc: 'David Allan'; 'tnadeau@cisco.com'; mpls@UU.NET
> Subject: RE: on documenting ECMP (was on the mpls oam framework) 
> 
> 
> Peter,
> 
> -> It may be helpful if I reword my original point, which was:
> -> 
> -> 1) ECMP leads to non-deterministic behavior. We should 
> -> develop OAM mechanisms that accept that as a given
> 
>   Agreed. ECMP is non-deterministic. Note also that non-determinism 
>   leads to freedom and innovation. If there is no requirement
>   to follow a standard and there is no requirement to interoperate
>   with other vendor's implementation, vendor's can develop
>   innovative mechanisms to support ECMP. Why are we restricting
>   our community and trying to enumerate *current* practices ?
> 
> -> 2) Nevertheless, for certain types of traffic it might be 
> -> possible to use tools from the connection-oriented world. 
> -> E.g. if a Service Provider uses RSVP-TE to reserve bandwidth 
> -> between two points, it will result in a path without 
> -> intermediate splits. 
> 
>   No. Not always.
> 
> -> That last statement was my assumption. Curtis argued that 
> -> there are exceptions, such as the case of hierarchical hops 
> -> where a logical link consists of multiple physical links. 
> -> You argue that path calculations can theoretically deal with 
> -> ECMP splits. 
> 
>   Yes.
> 
> -> I stand corrected. I do wonder how routers will distribute 
> -> traffic over the multiple paths with bandwidth guarantees. 
> -> As far as I know, current hashing algorithms leave the 
> -> packet sequence of micro flows intact, but there is nothing 
> -> that prevents them from sending 90% of the traffic over one 
> -> path and 10% over another. Or is there?
> 
>   No. Nothing preventing from doing so. But, finally, note that 
>   any problem may be non-determinisic in nature, but proposed 
>   solutions, algorithms and/or implementations are infact 
>   deterministic for known-agreed-upon approximations/limitations.
>   And a solution is not required to conver all degeneracies or corner
>   cases. 

Forgive me for being simple-minded:

My question is: if I use RSVP-TE to be guaranteed that 10 Mb/s of bandwidth is reserved for my aggregate traffic, would I ever want to use ECMP splits in the end-to-end path?

I understand that that is theoretically possible within agreed-upon limitations. But are these limitations narrow enough to make this a realistic scenario. Or do I just have to reserve 10 Mb/s along each of the multiple paths?

> 
> Venkata.
>