Inside Look at the Internet
1.7.1 Layered Architecture
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

A layered architecture allows us to discuss a well-defined, specific part of a large and complex sy;stem. This simplification itself is of considerable value by providing modularity, making it much easier to change the implementation of the service provided by the layer. As long as the layer provides the same service to the layer above it, and uses the same service from the layer below it, the remainder of the system remains unchanged when a layer's implementation is changed.

  • Protocol Layering--the design of network protocols, network designers organize protocols--and the network hardware and sfotware that implement the protocols--in layers. Each protocol belongs to one of the layers.
  • Application Layer--where network applications and their applications-layer protocols reside.
  • Transport Layer--transports application-layer messages between the client and server sides of an application.
  • Network Layer--responsible for moving network-layer packets known as datagrams from one host to another.
  • Link Layer--passes the datagram up to the network layer.
  • Physical Layer--is to move teh individual bits within the frame from one node to the next.