1 Network Edge
The device such as computers and mobiles connect to the Internet. So they are referred as end systems(who run the application programs) sitting at the edge of the Internet. And we use host and end system interchangeably, that is host=end system which is
divided into two categories: clients and servers.
2 Network Core
Network Core is the set of router-like and the Internet that implement the network and communication. And there are two type of Network Cores: circuit-switching and packet-switching.
2.1 Circuit Switching
Circuit-switching reserves dedicated circuit for each call or communication. When there are several circuits the network will divide the link bandwidth or switch capacity into several pieces - FDM and TDM.
In fact, the resource are divided according to the amount of users or links. For details in the example below: the 24 denotes that there are 24 circuits.
2.2 Packet Switching
Users share network resources in packet-switching. And the properties of packet-switching as follows:
- each packet uses full link bandwidth;
- Share network resources;
The free way of switching must take some disadvantages, as follows:
- the demanded resources in network may exceed the available - because of the second character
- the free link may cause congestions, build a waiting queue - because the packets are put into network sharing the resources and links.
The freedom is not absolute but relative. The resources in network are used on demand. So we also use the idea of multiplexing like circuit-switching. But the difference is that each slot or bandwidth is used on demand not fixed for a particular link or
something else.
Be care of the delay affairs in the Packet-Switching Network. Briefly, transmission delay -> propagation delay.
2.3 Packet Switching versus Circuit Switching
Packet Switching allows more users to use network.
The disadvantages of packet switching.
3 Delay, Loss, and Throughput
4 Protocol Layers and Service Models
Introduction and Basic concepts,布布扣,bubuko.com
Introduction and Basic concepts
原文：http://blog.csdn.net/siyumato/article/details/27961187
