the Internet Backbone

Vadim Antonov avg at
Fri Apr 5 07:34:03 UTC 1996

Paul A Vixie <paul at> wrote:

>Last time this term came up, I opined that there was no "backbone" any more
>and that 1996's Internet had a "hairball topology."  Vadim, among others,
>disagreed with me but we didn't pursue the topic.  Perhaps we should have.

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.

Note that this loose definition provides different idea of "backbone"
aka the first tier, quite unlike the "defaultless core".  To illustrate
it let's assume there are two regional dual-homed ISPs, A and B,
connected to, say ANS and MCI:

|   X   |
A--- ---B

Both A and B generally have to be defaultless.  But they are not
in the first tier, but rather in second tier, as they have to purchase
transit from first-tier providers to talk to each other.

May be we should classify ISPs by miles*bandwidth of their internode

>And in that sense, there is no backbone in 1996.

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

>Terminologically speaking, there's no discrete set of wires or routers or
>companies you can point to and say, "there, that right there, that is the
>Internet Backbone."

Well, you can do that in practice, and be pretty certain.

>We tend to reserve the term "NSP" for folks who peer at enough NAPs that they
>have no default route and aren't buying transit from anybody.

Ok, so here we agree :)

>We tend to use
>the term "ISP" when we mean someone in the packet or even the session business
>who _does_ have to buy transit from somebody.  Once in a while I hear the term
>"backbone provider" used synonomously with "NSP" (as defined above).

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.

>I am not even going to get started (here and now, at least) on the subject of
>peering politics/economics.  I just thought I'd chime in on the definitions of
>the words we're all using.


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