North American Network Operators Group

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Re: Operational issue: Packet loss at Pacbell NAP

  • From: Kent W. England
  • Date: Tue Mar 31 18:22:52 1998

>Several of my peers at PB NAP are reporting significant loss (>10%) over
>PB NAP.  All are OC3 connected, and it seems that PB doesn't have the
>ability to look too closely at OC3 connections.
>Death of the 'net predicted: film at 11.
>So, does this mean that ATM NAPs also have problems with high traffic load?
>Dave Rand
>[email protected]

I wouldn't jump to conclusions. Not likely that the ATM switches are
backplane loaded like the MAEs. These are Stratacom BPXs that replaced the
Newbridge 36150s over three years ago.

High bandwidth-delay product paths on a heavily loaded OC-3 to OC-3 virtual
circuit will strain the ATM switch buffers. If you can detect regularly
recurring losses on a high BDP path across an all-OC3 virtual circuit, then
look for buffer exhaustion on the OC3 interfaces. If no one at Pac Bell
knows what to do, tell them to look in the files in Fred Chang's Network
Engineering Group for Kent England's ATM NAP switch test plan and go out and
get some test gear that will stress an OC3 link in the lab. Mike Rudik in
the lab knows what to do to test for this. But my recollection was that the
BPX had enough buffers to run UBR over a full OC3.

If the loss is on DS3-OC3 virtual circuits then perhaps you are pushing more
than 45 Mbps toward the DS3. There might be a Kentrox ADSU or two left on
the NAP that could have trouble with the cisco OC3 interface at much less
than 45 Mbps.

If the cisco OC3 interfaces haven't been thoroughly shaken down, you might
look there for things like buffer exhaustion. If the ciscos are losing, my
test plan should show that effect if the ciscos are included in the test

If no one at PacBell seems interested in the problem, you can talk to the
Texans who run the place now. I can give you some names to call in
Richardson, Texas but I wouldn't hold my breath. If you happen to be a
Texan, then you can probably get something to happen, but if you are an
avocado-sucking Hawaiian-shirt-wearing ears-pierced laid-back California
dude, then you won't get far with the prime-rib-for-lunch crowd.  ;-)