Subject: Re: Traffic Shaping for Multicast flows

From: [email-masked]
Date: Tue, 18 Feb 97 09:27:44 PST

*> 
  *> All the above issues affect scalability, primarily from the host's
  *> perspective, and some form of flow aggregation or aggregated 
  *> traffic shaping would greatly help.

Ashish,

Your comments seem reasonable up to this point, but I am confused about
this "scaleability" issue.  How many different realtime streams do you
expect a host to need?  Ten?  Maybe a large server might have 100?
This is not the kind of scaling problem we have talked about before: a
backbone router that has 100,000 flows, say.

Bob Braden

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From: Ashish Mehra <[email-masked]>
Date: Tue, 18 Feb 1997 13:14:58 -0500 (EST)

> backbone router that has 100,000 flows, say.

Bob,

You are absolutely right that the scalability requirement at backbone
routers is perhaps two orders of magnitude more than at servers. I 
can envision a server supporting say thousands of realtime streams.
But then it also depends on how the "service provider"
lays out the server infrastructure. It could be that there is 
a cluster of individual server machines feeding into a single
box feeding into the outside world, with only this box performing
shaping etc. (but not all the functions of a router) with
perhaps some additional transformations/manipulations on the data.
In this case the aggregate number of flows crossing this box could
be significantly higher, especially if the service is really popular.

Even without the above scenario, the main point of my comments 
was to highlight OS-related overheads that may limited scalability
even at routers, especially if traffic is shaped via OS timers.
It is important to note again that routers may need to perform
reshaping even when the traffic specification at the host is not
violated, i.e., could occur with sufficient frequency to make 
it an important issue. Perhaps it is not an issue at backbone 
routers - I would appreciate if you (or someone) can clarify what 
mechanisms routers rely on to realize shaping. 

Ashish