Discussion point: Telco quality?

Paul Ferguson ferguson at cisco.com
Fri Oct 9 13:10:11 UTC 1998


At 08:28 AM 10/9/98 -0400, Bill St. Arnaud wrote:

>Although the telcos talk a great deal about SONET rings and how reliable the
>telco circuits are and so forth its is surprising how few major Internet
>trunks are carried on SONET rings.  And yet the Internet manages to carry
>on. Despite some local inconviences mot Internet users never notice these
>outages which goes to show how resilient the Internet really is.

Funny you should mention this. Actually, aren't most data circuits (excluding
copper pairs into the home) fed into the telco DACS network(s), which subsequently
may be muxed into a fiber infrastructure along with traditional TDM voice traffic?
The DACS network can certainly be an overlay on a fiber infrastructure, and usually
is just that.

This kind of reminds me of a discussion I have had with several folks on a couple
of occasions on the issue of VPN's. To make a long story short, one of the important
roles of a VPN is to provide some sort of segmentation of traffic, and this can be
achieved at virtually any layer of the protocol stack -- even the physical layer.
An example of this sort of segmentation could be either a timing slot in a SONET
pipe or even a separate wavelength in a WDM system. And in most cases, at the lowest
levels, you have voice and data traffic riding the same light rails anyway, like
ships in the night. You get the idea.

Discussions on true optical networking aside, for the moment anyway.

It is no surprise that both voice & data services are affected by fiber cuts.

>It begs the question then, if the Internet can work quite well today without
>all the supposed telco 99.99999+, do we really need telco "reliability" -
>SONET rings etc?

This kind of reminds me of Bullwinkle trying to pull a rabbit out of his hat.
"Nothing up my sleeve..... Presto!"

I don't think it is quite that straightforward. You first need to ask yourself,
"What problem am I trying to solve?"

>As you know it is our contention that you don't need it.  We believe that a
>99.9999+ reliable Internet can be built without the underlying (supposedly
>"relaible") telco infrastructure.

Define "reliable".

Well, my observation is that the principle difference in reliability between
the "traditional" voice network (PSTN) and "traditional" data services is
in how the underlying delivery services are fundamentally designed. This is
just a byproduct -- a fundamental difference in the underlying technologies --
circuit-switching vs. packet-switching. Each were designed with different
constraints in mind.

Let's not forget that IP is a connectionless, store-and-forward, datagram
delivery mechanism.

The remainder of this exercise is left to the reader.

- paul




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