Cogent service

Fri Sep 20 17:11:51 UTC 2002

Bill,

Thanks for assuming I know a bit about networking ;-)

Actually I just received an off-list email, but the sender has a 
incorrect reply to.  So I will partly address his question here.

At Netrail we used ATM layer 2 to map express routes.  We did this 
for many reasons.  Yes helping with hope count doesnt always help 
with latency, it does keep customers happy.  Where it does help is 
with routers like GRFs where you do NOT want to piggy back load from 
one hope to another, and then have those routers make decisions.  It 
also didnt make sense to hand off all traffic from an ATM box, to a 
router box and then back.  Do we need to mention the ATM boxes were 
more reliable then those routers?

With Junipers or today's ciscos we would not have done it that way 
probably.  They other issue to consider Bill is that depending on 
your IP network design, you can add a great deal of complexity with a 
67 city network where you have more then 1 router in many cities.

The off-list question was whether we had peering in LA as Netrail and 
yes we did.  1 Wilshire is a good location, although much of the 
peering is international.  Ren likes LA a lot as a peering center.  A 
lot of people will tell u voice traffic to Pacific rim is big there. 
We did map most of this back to our regional center in that area 
which is San Fran and exited the peering there.  We had 3 peering 
exchanges there and private peering, so people in LA did in fact 
enjoy good performance.  Mario if you are seeing packet loss or 
latency issues, you should address it with Cogent's noc or with Chris 
who is working on peering there.  Im sure they would appreciate the 
feedback.  You may see issues as a result of integrating several 
backbones.

The hop count question is interesting.  Is the consensus that it's 
mostly a customer service issue, where latency isnt affected but 
customer perception is?  Or is it a real latency issue as more 
routers take a few CPU cycles to make a routing decision.

Dave

At 9:54 -0700 9/20/02, William B. Norton wrote:
>At 10:31 AM 9/20/2002 -0400, David Diaz wrote:
>>    The only negative routing comments Ive heard are complaints 
>>about extra hop counts.
>
>Dave - I know you know this and you are referring to an issue that 
>both of us have heard....
>
>The hidden assumption here is that the extra hops implies worse 
>performance. This is perception rather than real. One could quite 
>easily put in place a VPN or MPLS substrate and make all 
>destinations appear "one hop away" without changing the underlying 
>technology or performance of the network.
>
>A network application with clear latency/jitter/packet loss 
>characteristics would be a more effective way to evaluate network 
>fitness. I suspect what really happens is
>a) the is a performance problem somewhere in the path
>b) a traceroute is done
>c) the traceroute is misinterpreted - "the problem is packets go all 
>over the place!"
>d) the misinterpretation is generalized to "more hops is bad"
>
>from what I've seen anyway.
>
>Bill

-- 

David Diaz
dave at smoton.net [Email]
pagedave at smoton.net [Pager]
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