the internet priciple

The Internet is a network of networks,It has a network hierarchy with weveral levels,starting from the end users up.

1 End user;

2 ISP:Internet service provider;

3 POP:Point of presence驻扎点;

4 NAP:Network access point互联网访问点.

when you connnect to your ISP,you become part of their network.The ISP may then connnect to a large network at point of presence(POP),and become part of their network.

The POP is a rack full of modems that the ISP's customers dial into.

Several highlevel networks connect to each other through Network Access Points(NAP) where the core of the Internet starts.

the core of othe internet is composed of:

1 NAPs;

2 Routers;

3 Backbones;

the Internet is one huge network made up millions of smaller networks,the use of routers is an absolute necessity.

Backbones are typically fiber optic trunk lines.fiber optic cables are designated OC for optical carrier,such as OC-12,OC-48,OC-192.They are capable of transmitting 622 MB/s,2488MB/s,and 9,952 MB/s,some trunk lines use multiple fiber optic cables combined to increase the capacity.Backbones across the continents are connected via undersea cables or satellite links.

In general,all of the machines on the Internet can be categorized as two types:servers and clients.The machines that provide services to other machines are servers.There are Web servers,e-mail servers,FTP servers and so on.

Clients send their requests to a server with a specific intnet.For example,if you try to read a web page,you want to access the web domain server on the server machine,not the e-mail server.The server finds the page you requested and sends it to you.

Ports and Protocols

A server machine may provide multiple services,for example,Web server,e-mail server and FTP server simultaneouslyl.Server machine makes its services available using numbered ports-one for each service on the server.For example,the Web server,the E-mail server,and the FTP server would be available on port80,25,and 21,respectively.Clients connect to a service at a specific IP address and on a specific port.

A protocol is the well defined agreement and convention that the hardware and software should follow to assure successful communications within that class of service.For example,every server or client follows internet protocol(IP) for net address and name.Every Web server on the internet conforms to the hypertext transfer protocol(HTTP).

The octets are split into two sections:Net and Host.