tiers?

Fri Jul 18 16:31:02 UTC 1997

A number of ISP's and backbone providers (national and international) all
colocate on our facilities.  One of the most asked questions I recieve from
everyone is the question asked regarding Tiers.  I have come up with IMHO a
response to them that seems to be well accepted.  Now I'm not saying this
is true in all instances, but it seems acceptable.

I define a Tier 1 network as a company who has a robust OC3 backbone and
peers at a majority of the major NAPs (and private peering) in the U.S. and
around the world.  Now, this OC3 backbone should not only go East to West
but North to South,be somewhat fault tolerant, and provide reasonable
connectivity to ISP's throughout the country and serve as gateway
connections to international backbone ISPs.  If you use this loose
definition of Tier 1 network, you see immediately you have the big 10 or 15
who are very selective in choosing their peering partners.

A Tier 2 network could be defined as a DS3 backbone (maybe with some OC3
but a majority DS3) who would have a large amount of bandwidth East to West
or North to South but does not have as large a communications
infrasturcture or network mesh as a Tier 1 provider.  These companies would
peer at some of the major NAPs (plus private peering) but would also appear
as many of the other exchange points where the Tier 1 providers wouldnt
bother appearing.  These Tier 2 players may peering with some ot the Tier 1
but not all of them.  Or even if they should because their network is not
as robust as the Teir 1 they would fall into the Tier 2 catagory.

A Tier 3 network provider I consider to be a Regional backbone company.
This is a company to has a minimum of a 10 meg backbone within a region.
This is a company who is providing transit services to other smaller ISPs
within his region.  He may connect at some of the regional exchange points
or conduct private peering with other Tier 3 providers in his area.
Typically this level network would not peering with a Tier 1 at all and
most Tier 2 providers will not peer either.

Below Tier 3 are the ISP ranks, or smaller ISPs.

Using this type of philosphy for defining Tiers could work with the U.S.
Domestic network providers but falls apart when you begin looking at a
global view.  There are companies who would be considered a Tier 1 provider
within their own country but when they run their own bandwidth to the U.S.
they are often times considered a Tier 2 or lower Tier network when looking
for peering partners.  As such they are often forced to purchase transit
from the U.S. Tier 1 or 2 providers.  With this there is still an
inequality when trying to apply a Tier structure on an international basis.
There is no throught to the cost of the communications lines and and
sometimes the benefit that can be derived through a peering process with
international backbone networks (those with DS3 international lines).  I'm
not saying this is true in all instances, but it appears to the the norm
rather than the exception.

I think, IMHO, that by using this approach, combining both the size of the
physical network, technology and peering provides a starting point for
looking at or trying to define a Tier Structure.  Will this work in all
cases??? I doubt it because there are always exceptions.  But it is a
starting point for looking at networks from a global view.

Rick
Telehouse America
(718)355-2559

P.S.  The opinions present above are personal and in no way reflect the
views of Telehouse....:)