Interesting Tier 1. You'd only have 2 Tier 1s in this case, MCI with their OC12 backbone and Sprint with their OC3 backbone. UUNET, ANS, BBN (the other big three) operate a DS3 backbone--UUNET is not yet at OC12 to the best of my knowledge. Put things into persepective.
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....:)