[Macha]

At the T1 level it's more completely a mesh type setup, but even lower tier ISPs might set up peering agreements to bypass their main higher tier ISP where it makes sense for cost or service quality reasons. Or refuse to to extract more money as in the comcast vs level1 disputes over netflix traffic a while back

[lillecarl]

Who is T1, T2 and T3? I really don't see it. Seems like that tiering has aged about as well as the OSI model.