the Internet Backbone

Michael Dillon michael at
Sat Apr 6 01:37:14 UTC 1996

On Fri, 5 Apr 1996, Vadim Antonov wrote:

> Well, "backbone" is too vague.  I rather prefer to think of Internet
> topology as of "tiers".  The nodes in upper-levels cast "cones of
> influence" in lower tiers.  Nodes from lower tiers belonging to 
> different cones of influence do not generally speak to each other,
> and so have to purchase transit from higher tiers.

> Tier one is the "backbone".  Those are providers not purchasing
> transit from anybody else.

If we think like an onion (shades of TinyBASIC!) then the core of the
Internet are these providers who supply transit over their own national
and international backbones and who do not need to buy transit from other 
providers. The providers who form the Internet core are sometimes called
NSP's (Network Service Providers) and sometimes called Tier 1 providers

> That's pretty common usage.  Sounds much better than an-as-pee.
> The term for second-tier is "regional provider" and third tier is
> usually local providers.

The next layer of the onion is the Tier 2 providers sometimes referred to 
as regional providers although they may actually serve overlapping 
geographical regions. These providers do not provide transit but they do
supply other providers in a lower tier.

This brings us to the Tier 3 providers commonly known as ISP's (Internet 
Service Providers. These organizations may connect to Tier 2 providers
or Tier 1 providers but their distinguishing characteristic is that they
do no normally supply organizations who resell Internet access.

Tier 4 networks belong to those organizations who provide Internet access 
for their own members or employees. These could be corporations, schools,
or universities who operate both internal networks and provide dialup
services that are not available to the general public. Sometimes a Tier 4
network provides access to other organizations such as a company which 
supplies its subcontractors with their Internet connectivity.

Tier 5 is the end user. They may have a single PC that dials up to the 
Internet or they may be sitting in front of a workstation on a corporate LAN.

Unlike an onion skin, these layers are not precise and there is some overlap
especially in Tier 2. Until recently most ISP's connected directly to 
Tier 1 providers and although there are some providers who are starting 
to specialize in Tier 2 services it will remain common for both Tier 1 
and 3 organizations to be in that market.

This seems to explain the relationships in a way that I think the average
person or journalist could understand and still form concepts fairly 
close to the reality of today's global Internet. 

Michael Dillon                                    Voice: +1-604-546-8022
Memra Software Inc.                                 Fax: +1-604-546-3049                             E-mail: michael at

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