to underline a point made previously though: Tier-1 is a routing architecture term that doesn't have any useful direct bearing in how best to select a service provider. some of the best service providers in the world are not "tier-1" and some of the worst are ( i won't name members of either camp.).
The meaning of "tier 1" is not static. At one time it referred to providers with more-or-less national coverage who more-or-less owned their own facilities. Somewhere along the line, buyers decided that peering was an important factor in buying decisions and "tier 1" came to mean "companies who do not have blackholes because of lack of peering". Routing engineers interpreted this to mean "companies with settlement-free interconnect" since at the time, transit was seen as an inferior way to get connectivity. In today's world where latency and packet loss figures are more important to buying decisions, I suspect that "tier 1" refers to "companies who run good networks with no visible technical issues". In any case, "tier 1" is a marketing term that refers to the ranking of companies in terms of prefeability. Those companies whose services are highly preferred are in the TOP TIER of the ranking. After that there is a SECOND TIER which is good if you can't afford the top tier. There have always been people who made their buying decisions based on the NET EFFECT OF SEVERAL PROVIDERS rather than simply evaluating a provider standing alone. It is possible to buy service from two or three second tier providers and get BETTER THAN TIER 1 service. Mindless rankings and classification systems are not much help in making intelligent buying decisions. I really don't understand why people on this list care so much about marleting terminology. --Michael Dillon