RE: [nsp] Imux'ing T3s?

From: Martin, Christian (cmartin@gnilink.net)
Date: Mon Sep 18 2000 - 21:04:26 EDT


Based on my experience with real-world traffic over a 6xDS3 CEF per-packet
load sharing connection, you will have no problem doing this on a VXR -
certainly no issue on an RSP4/8 platform. But 6 DS3s != 270 Mbps used
bandwidth, unless you are way oversubscribed, and with limited
source-destination pair distribution (assuming a private link), you may not
see even bit rates on the DS3s. I usually see DS3's peak at about 42 Mbps
before latency and TCP flow control begin throttling things back. WRED
helps smooth this behavior. If you have 6 DS3s doing 42 Mbps, you will see
latency and some loss. If you can get 7 or 8, you may be in business, but
how to load-share across them is the question. Of course, Juniper supports
16 parallel paths, but that is for another list. In the Cisco world, you
may be able to be slick and use recursive routes to add more capacity. I
believe I have seen it done before. Just create three loopbacks on each
router, route 1 loopback across 4 DS3s, the other across the other 4 DS3s,
then the third loopback across the 2 loopbacks. CEF sees this as a 2x4
recursive adjacency per loopback. The load share shows only the 2
loopbacks, and then their recursive routes, so ip routing doesn't "know"
there are 8 paths. YMMV.

./chris

> -----Original Message-----
> From: Deepak Jain [mailto:deepak@ai.net]
> Sent: Monday, September 18, 2000 7:41 PM
> To: cisco-nsp@puck.nether.net
> Subject: [nsp] Imux'ing T3s?
>
>
>
> I need to provision about 250mb/s of clearchannel IP capacity
> between two
> POPs. I'd prefer to do this over OC12POS, but WCOM is 6 months behind
> capacity for us right now, and can't provide us any additional optical
> services into that building.
>
> So I am stuck using DS3s with the ILEC. I'd rather not stick
> 2 6port DS3
> cards (1 in each router) to get the job done while we are
> waiting for WCOM
> capacity. Are there any good DS3-IMUX solutions to either 100Mbit/s or
> 1000Mbit/s ethernet? Or can anyone recommend a good (emphasis on small
> rack space requirements) Cisco box that can handle that?
>
> If I have to terminate the DS3s in a router, I was thinking
> (from a rack
> space point-of-view) either an M20 or a 7206VXR. The Juniper
> seems like
> overkill because there are no complex routing needs and even a 4-5xDS3
> bridge would be more than sufficient.
>
> Any ideas would be most appreciated.
>
> Deepak Jain
> AiNET
>



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