Inside Look at the Internet
1.5 ISPs and Internet Backbones
Chapter 1
1.1 What Is the Internet?
1.1.1 Nuts-and-Bolts Description
1.1.2 A Service Description
1.1.3 What Is a Protocol?
1.2 The Network Edge
1.2.1 End Systems, Clients, and Servers
1.2.2 Connectionless and Connection-Oriented Service
1.3 Network Core
1.3.1 Circuit Switching and Packet Switching
1.3.2 Packed-Switched Networks: Datagram Networks and Virtual-Circuit Networks
1.4 Access Networks and Physical Media
1.4.1 Access Networks
1.4.2 Physical Media
1.5 ISPs and Internet Backbones
1.6 Delay and Loss in Packets-Switched Networks
1.6.1 Types of Delay
1.6.2 Queuing Delay and Packet Loss
1.6.3 Delay and Routes in the Internet
1.7 Protocol Layers and Their Service Models
1.7.1 Layered Architecture
1.7.2 Layers, Messages, Segments, Datagrams, and Frames

When two ISPs are directly connected to each other, they are said to peer with each other. Within an ISP's network, the points at which the ISP connect to other ISP's are known as Points of Presence (POP). A POP is simply a group of one or more routers in the ISP's network at which routers in other ISPs or in the metworks belonging to the ISP's customers can connect.

In addition to connectiong to each other at pricate peering points, ISPs often interconnect at Network Access Points (NAPs), each of which can be owned and operated by either sone third party telecommunications company or by and Internet backbone provider. NAPs exchange huge quantities of traffic among many ISPs.

  • Directly connected to each of the other tier-1 ISPs. Tier-1 ISPs also known as Internet backbone networks.
  • Connected to a large number of tier-2 ISPs and other customer networks. A tier-2 ISP typically has regional or national coverage and connects to only a few of the tier-1 ISPs.
  • International in coverage.

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