[Irtf-rr] Re: Differentiated Routing, not only plain rambo-SPF

[shen jing]

Hi Hummel,

As DSCP is used for packet queueing in routers,  there may be many types of  queueing mechanism for scheduling of
different classes.

As mentioned in previous message that when overflow/congestion happens along some path, the flow of the same  DSCP
could be overflowed onto other path (?) or it could be dispersed onto multiple paths computed.
This means, if we want to adapt to time-varying network status  LSA must be triggered by overflow of any queue on its
outgoing interface. Because internet traffic's self-similarity characteristics and "heavy-tailed" flow sized distribution,
  we
could not expect the network status maintains a stable status. That is,  routing behavior have to be adjusted frequently.
Right ?  CBQ or the like may adjust the resource allocated dynamically according to load on routers, how could that be
reflected ?   I think, all these factors will do harm to routing stability and extensibility, esp. when we consider
inter-AS routing.

Well, I think some time to read those paper suggested.


>
>
> Hummel, was your original proposal same like Diffserv-aware-TE. I thought
> it was different.
>
> My answer:
> DiffRout is definitively different.
>
> My motivation and my key thoughts to open this discussions have been:
> - combine the best of Intserv/MPLS and Diffserv and as a result do stateless IP forwarding but get
>      what  Intserv/MPLS are providing: Qos/BW/Policy/Traffic balancing/rerouting.
>
> - therefore construct road systems and do IP forwarding/routing also based on DSCP.
>
> - the road systems may have assigned bandwidth. This is reasonable/feasable because some traffic can really
>   be locked into some slim road system (smallest size tree, smallest ring) just like MPLS traffic can be locked into
>   some LSP. Whereas with rambo-SPF bandwidth assignment makes no sense as the sum of all
>   shortest path trees computed by all the nodes would span the entire network, i.e. spread traffic all over it.
>   The price for staying within some road system should be acceptable: Eventually, make a few hops more.
>   Based on my computations, the smallest size tree may be smaller than the avarage shortest path tree by 15-20 %.
>   So I think the detour for the packets will not be very big either.
>
> - be guided by what you can observe on daily road traffic: Especially in the U.S. there are so many ramp-based
>   road junctions, which are more impressive than any traffic light controlled junction, so that motor-cyclists may
>   jump the queue of waiting cars (=DiffServ) if the traffic light is red.
>   There are so many observations that can be made watching how the traffic is managed for cars,
>   trains, airplanes, pedestrians, etc. We all are used to it and don't discern extra smartness in it. However there is.
>
> - and I realized what is the big obstacle: Yes it is this rambo-SPF routing paradigma. It does not represent the
>   surveillant view, only the egomanic view, combined with the hope that in total you get best results because
>   "the streets are emptiest when each car takes the shortest route":-).
>
> Heinrich
>
>
>
>
>
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--
Jing Shen

State Key Lab of CAD&CG
ZheJiang University(YuQuan)
HangZhou, Z.J. 310027
P.R.China

Tel: +86-571-87932423

Email: jshen@cad.zju.edu.cn

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