T1 vs. T2 [WAS: Apology: [Tier-2 reachability and multihoming]]

Tue Mar 29 11:20:13 UTC 2005

> And how, pray tell, does one actually "measure" T1 vs. T2 networks? 

That's easy. You define a set of criteria by which you can measure
the networks on some scale, and then set two thresholds. Networks
which exceed the higher threshold are Tier 1, those which only
exceed the lower threshold are Tier 2.

I have seen people do this by counting the number of ASes that
a network connects to. And I have seen this done with nodes by
summing up the bandwidth of all circuits connected to a node.

Even though the network is a dynamic partial mesh, researchers
can learn a lot about the behavior by imposing various types
measurement hierachy on the network.

Thus, Tier 1 and Tier 2 are not inherent characteristics of
the Internet; rather they are characteristics of a particular
view of the network at a particular point in time. There are
probably people who are trying to measure a hierarchy of latency
or a hierarchy of jitter. The more views, the merrier.

--Michael Dillon