Attempt to summarize Links on the Blink

Dave O'Leary doleary at
Mon Nov 13 21:39:58 UTC 1995

Various responses included below.

>From: Avi Freedman <freedman at>
>Subject: Re: Attempt to summarize Links on the Blink
>To: cook at
>Date: Mon, 13 Nov 1995 11:16:14 -0500 (EST)
>Cc: nanog at
>> I would like to try to understand better where this discussion seems to 
>> have come to rest.  Yesterday the suggestion was made that the major 
>> providers add more bandwidth to their backbones.  There seemed to be no 
>> assertion as to how this could be done.
>> 1.  OC-3 is not yet routable on backbones.  Is that correct?
>Well, I was told that the Cisco AIP card can talk point-to-point to another
>AIP card at OC-3 speed using either HDLC or PPP.

It is true that AIPs can talk back to back through an OC3 link, however
it doesn't use PPP or HDLC, just sending and receiving cells (i.e. std
ATM, just no switch).  So you get 155 Mb/s minus the ATM overhead,
or about 130 Mb/s (depending on what you count as data, type of traffic, 

>> 2.  What is the routing impact of parrallel T-3s?  Or the creation of
>> mesh of T-3s? I have the impression that this is not feasible because it 
>> would expand the routing tables unacceptably or because of the questions 
>> of how you would load balance among them??
>If data can be routed on parallel T3s on a per-connection basis so that
>there isn't a scrambling of ordering of packets per connection, then some
>benefit is achived, though no single application or site can use more
>than a T3 of bandwidth.

This is the way that our boxes work (i.e. destination locked onto a 
single interface).  Packet reordering isn't too much of a problem
from a functionality perspective for TCP, it just ( ;-) ) affects the
performance.  It is also atypical for a single site to need more than
T3 bandwidth (well, they may want it but they can't really but it yet).

>> 3.  There seems to be some consensus that we will see an increase in the 
>> numbers of NAP or MAE like interchange points which could cut down on the 
>> traffic that must traverse long haul backbones.  *BUT* doesn't each 
>> additional interchange point used by all the top level providers mean 
>> another new set of global routes crowding router memories?
>It depends.  If routing decisions are made locally and the routes heard
>at smaller or private exchange points by NSP x are not distributed to
>NSP x's larger peering/route-decision routers, then possibly no.  That
>would mean only hearing routes at private exchange points that were also
>heard elsewhere (at a major peering point).

Private interconnects (point to point) between the larger backbone
providers and new "public" interconnects can be used as appropriate
depending on what problem you are trying to solve, and what tradeoffs
you are ready to make.

>> 4.  How much help will regional NAPs like Tucson be?  Their goal is to 
>> keep local traffic local and off long haul backbones.  What liklihood is 
>> there that these will grow in numbers quickly enough to make a 
>> difference?  If the majors start showing up at these points does their 
>> arrival mean that the problem of crowding memory in their backbone 
>> routers will be increased?
>See above.

This depends on a number of factors like how well the local providers
are able to aggregate routes, and how the local interconnects link
into the rest of the world - for example of the group of local providers
gets a large CIDR block to use as a group then they can appear as a 
single prefix to the rest of the net, while providing portability of 
numbers for customers that might move between them.  


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