From the flood of e-mail I've received, it seems my recent column defining a Tier 1 ISP struck a nerve with readers of this newsletter.My original column, prompted by a reader query, defined a Tier 1 ISP as a carrier that owns or controls sufficient portions of its underlying network infrastructure and can meet market-leading service-level agreements (SLA). The ISP must control enough of its underlying network infrastructure to connect 90% of its customers. This definition comes from Brownlee Thomas, principal analyst for Global Telecom Services at Forrester Research.My column pointed out this dilemma: What ISPs are considered Tier 1 for your company depends on the geographic layout of your company's network.\u00a0 So there is no definitive list of which companies are Tier 1 ISPs.If you run a regional network, you need to figure out which ISPs are considered Tier 1 for your region. Your list might include SBC or Verizon. If you run a national network, you might consider Sprint or Level 3 Communications to be Tier 1 for you. If you run a global network across many continents, you may need one of the major Tier 1 global ISPs, which include AT&T, MCI, British Telecom, Infonet and Equant.Here's where the marketing departments enter the fray. Every ISP wants to be considered Tier 1. It reminds me of the famous line from Garrison Keillor: "Welcome to Lake Wobegon, where the women are strong, the men are good looking, and all the children are above average."Among the ISPs that want to be considered Tier 1 are XO Communications and NTT\/Verio. I received an e-mail from a corporate communications manager at XO Communications who insists that XO is a Tier 1 ISP in the U.S. Similarly, NTT and its Verio subsidiary assert the company is a Tier 1 ISP in Asia and the U.S.My advice to corporate buyers of Internet services is to ignore the marketing hype from the ISPs. Start with a map of your network and figure out which ISPs own or control network infrastructure in the cities and towns where you need service. Then make sure the ISPs can meet the most demanding SLAs on the market for these cities. The companies still standing are the ones that are Tier 1 ISPs for you.