Introduction to Networking I ISPs and Internet Backbones: Tier-1 ISP . ISPs are roughly hierarchical, categorized into tiers (no group officially sanctions Tier status) . Tier-1 Networks (ISPs): top of the hierarchy e.g., Global Crossing (Bermuda), AT&T, Sprint Nextel, Verizon, Qwest & Qwest International, Cable & Wireless, Level 3, Verizon, NTT/ Verio (Japan)…. also known as the Internet Backbone relatively small in number same as any other network in that it has links, routers and is connected to other networks but different in that the link speeds are often 622 Mbps or higher up to 10 Gbps and thus their routers must consequently be able to forward packets at extremely high rates . Tier-1 ISPs are categorized by being: directly connected to each of the other Tier-1 ISPs (peering agreements/ transit free) connected to a large number of Tier-2 ISPs and other customer networks (non-peering/ transit fee) International in coverage Highly politicized/ economic impact/ terms of hierarchy misused Tier-1 providers also interconnect at public network access points (NAPs) Tier-1 providers interconnect (peer) Tier 1 ISP privately NAP Tier 1 ISP Tier 1 ISP Adapted from Computer Networking, Kurose, Ross Dr. Nazli Hardy Introduction to Networking I Tier Rules (tacit if not explicit) . All Tier 1 ISPs peer with each tier 1 . Cannot become Tier 1 without peering agreement with every tier 1 ISP . Tacit collusion not to allow other members . Will drop ISP if they charge less to tier 2 or 3 . Tier 1 do not have alternate transit paths – therefore their peering relationships are crucial – or it has the chance of partitioning the Internet (Cogent, Level 3) . Tier 1 – connected to other Tier 1s and some big Tier 2s . Tier 2s are motivated to connect with as many ISPs as possible – better service Adapted from Computer Networking, Kurose, Ross Dr. Nazli Hardy Introduction to Networking I Tier-1 ISP: Example of Backbone Network AT&T Adapted from Computer Networking, Kurose, Ross Dr. Nazli Hardy Introduction to Networking I Physical Media: Fiber Optic Networks Adapted from Computer Networking, Kurose, Ross Dr. Nazli Hardy Introduction to Networking I Physical Media: Fiber Optic Networks Adapted from Computer Networking, Kurose, Ross Dr. Nazli Hardy Introduction to Networking I NTT Adapted from Computer Networking, Kurose, Ross Dr. Nazli Hardy Introduction to Networking I Tier-2 ISP . Tier-2 ISPs are smaller than Tier-1 ISPs Regional and national coverage Connect to only a few of the Tier-1 ISPs (fee-based relationship) Peer privately with other Tier-2 ISPs Large companies often connect their enterprise’s network directly into Tier-1 or Tier-2 ISP, thus becoming a customer of that ISP Services are often better than Tier-1, despite hierarchical inferences Bandwidth, length of cable, routers, number of customer are comparable Competitive Customer service Tier-2 ISPs also peer privately with each other, and interconnect Tier-2 ISP pays Tier-1 ISP Tier-2 ISP for connectivity to the rest Tier-2 ISP at NAP of Internet Tier 1 ISP Tier-2 ISP is customer of Tier-1 provider IXP POP Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Adapted from Computer Networking, Kurose, Ross Dr. Nazli Hardy Introduction to Networking I POPs & NAPs . Points of Presence (POPs): within an ISP’s network, the points at which the ISP connect to other ISPs (hierarchically below or above) A POP is a group of one or more routers in the ISP’s network at which routers of other ISPs can connect . Network Access Points (NAPs): in addition to connecting to each other at private peering points, ISPs often interconnect at NAPs, each of which can be owned and operated by a 3rd party telecom company or an Internet backbone provider NAPs are complex, high speed switching networks, often concentrated in a single building and relay and switch tremendous volumes of traffic Tier-2 ISPs also peer privately with each other, and interconnect Tier-2 ISP pays Tier-1 ISP Tier-2 ISP for connectivity to rest of Tier-2 ISP at NAP Internet Tier 1 ISP Tier-2 ISP is customer of Tier-1 provider NAP/ IXP POP High speed links leased Tier 1 ISP Tier 1 ISP from 3rd party providers Tier-2 ISP Tier-2 ISP Tier-2 ISP Adapted from Computer Networking, Kurose, Ross Dr. Nazli Hardy Introduction to Networking I Tier-3 and Local ISPs . “Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems) local ISP Tier 3 local local ISP local ISP ISP ISP Local and Tier- 3 ISPs are customers of Tier-2 ISP Tier-2 ISP higher tier ISPs connecting them to rest Tier 1 ISP of Internet NAP Tier 1 ISP Tier 1 ISP Tier-2 ISP local Tier-2 ISP Tier-2 ISP ISP local local local ISP ISP ISP Adapted from Computer Networking, Kurose, Ross Dr. Nazli Hardy Introduction to Networking I The Travels of a Packet . A packet passes through many networks! local ISP Tier 3 local local ISP local ISP ISP ISP Tier-2 ISP Tier-2 ISP Tier 1 ISP NAP Tier 1 ISP Tier 1 ISP Tier-2 ISP local Tier-2 ISP Tier-2 ISP ISP local local local ISP ISP ISP Adapted from Computer Networking, Kurose, Ross Dr. Nazli Hardy .