Introduction to Networking I. ISPs and Internet Backbones: Tier-1 ISP

Introduction to Networking I ISPs and Internet Backbones: Tier-1 ISP   ISPs are roughly hierarchical, categorized into tiers (no group officially ...
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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 Tier 1 ISP interconnect (peer) privately NAP 

Tier 1 ISP

Adapted from Computer Networking, Kurose, Ross

Tier 1 ISP

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 ISP pays Tier-1 ISP for connectivity to the rest of Internet

Tier-2 ISP

Tier-2 ISP

Tier-2 ISPs also peer privately with each other, and interconnect at NAP

Tier 1 ISP Tier-2 ISP is customer of Tier-1 provider

IXP POP Tier 1 ISP

Tier 1 ISP

Tier-2 ISP Adapted from Computer Networking, Kurose, Ross

Tier-2 ISP

Tier-2 ISP 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 ISP pays Tier-1 ISP for connectivity to rest of Internet

Tier-2 ISP

Tier-2 ISP

Tier-2 ISPs also peer privately with each other, and interconnect at NAP

Tier 1 ISP Tier-2 ISP is customer of Tier-1 provider

NAP/ IXP POP

High speed links leased from 3rd party providers

Tier 1 ISP

Tier 1 ISP

Tier-2 ISP Adapted from Computer Networking, Kurose, Ross

Tier-2 ISP

Tier-2 ISP 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

Local and Tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet

Tier 3 ISP

local ISP

local ISP

Tier-2 ISP

local ISP

Tier-2 ISP Tier 1 ISP NAP

Tier 1 ISP

Tier 1 ISP

Tier-2 ISP local ISP Adapted from Computer Networking, Kurose, Ross

Tier-2 ISP local ISP

Tier-2 ISP local ISP

local ISP Dr. Nazli Hardy

Introduction to Networking I

The Travels of a Packet 

A packet passes through many networks!

local ISP

Tier 3 ISP

local ISP

local ISP

Tier-2 ISP

local ISP

Tier-2 ISP Tier 1 ISP

NAP

Tier 1 ISP

Tier 1 ISP

Tier-2 ISP local ISP Adapted from Computer Networking, Kurose, Ross

Tier-2 ISP local ISP

Tier-2 ISP local ISP

local ISP Dr. Nazli Hardy

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