One, the Internet overview
1, the computer network overview:
(1) we often say that the Internet refers to the Internet, the Internet originated in the United States, it is now the world's largest, covering the global computer network,
(2) we referred to as "the network is to point to by a number of nodes (node) and connect the computer network of links (link),
(3) to the Internet through a router (i.e., composed) network, interconnecting constitute a greater computer network coverage, known as the Internet (internetwork or the Internet),
Note: the network is more computer to connect together, and the Internet is a lot of the Internet through a router connected together, which are connected to the network computer, smart phone, such as intelligent machines is often referred to as the host,
2, the three stages of the development of the Internet infrastructure:
(a) the first stage: from a single network ARPANET development process, from the Internet in 1983, TCP/IP protocol become a standard protocol of the ARPANET, all computer using TCP/IP protocol to use the Internet to communicate with each other, as a result, people in 1983 as the birth of the Internet time, and the ARPANET officially closed in 1990,
(2) the second stage: build the tertiary structure of the Internet, which is a divided into backbone, regional networks and campus network (or corporate network) level 3 computer network,
(3) the third stage: gradually formed a multi-level Internet Service Provider your ISP (Internet Service Provider) structure of the Internet,
(1) at this stage, the commercial, or any organizations and individuals as long as an ISP to pay the prescribed fee, from the ISP can obtain the needed to use the IP address, and can through the ISP access to the Internet,
(2) to provide the service and according to the area covered by size and have the IP address of the number of different, isps are divided into different levels of the ISP: backbone ISP, ISP and a local ISP,
(3) in the present, the Internet has become the World's largest and fastest growth rate of the computer network, no one can tell just how the Internet, and the rapid development of Internet in the 1990 s, the development of the World Wide Web by CERN CERN WWW (World Wide Web) is widely used on the Internet, greatly facilitate the use of the non network professionals to network, make the World Wide Web the primary drivers of this exponential growth of the Internet,
Second, the composition of the Internet
The composition of the Internet from the point of view of the way it works, can be divided into two areas:
(a) edges: consists of all the connections of host on the Internet, this part is the user to use directly, used to communicate (send data, audio or video) and resource sharing,
1, a part that is on the brink of the Internet is to connect all the hosts on the Internet, and the host system (end system) is also known as end,
2, the end system may have very big difference on the function,
3 and the meaning of the communication between end systems: "to communicate with the host A and host B" actually refers to "A program running on the host A and run on the host B another program to communicate", namely "A process of host A and host B to communicate with another process", referred to as "communication between computers,"
4, communication between end systems usually can be divided into two categories:
Way (1) the Client - Server describes the relationship between service and be service process, namely the Client/Server mode, referred to as C/S mode, the Client and the Server is refers to the two application involved in the communication process, among them, the customer is the requester to the service, the Server is a service provider, they all have to use the services provided by the network core part,
(2) Peer way, is the point at which the two hosts in communication do not distinguish between what is a service requester or the provider, the Peer - to - Peer way, referred to as P2P mode, as long as the two hosts are running the peer-to-peer connection software (P2P) software, they can be equal, peer-to-peer connection communication, at this time, both sides can download the other side has stored in hard disk of Shared documents,
5, the characteristics of the client software:
(1) do not require special hardware and operating system is complex,
(2) be run after the user calls, when going to communication to remote server communication service (request), as a result, the client must know the address of the server program,
6, the server software features:
(1) general need powerful hardware and advanced operating system support,
(2) after system boot automatically calls and has been constantly running, passively waiting for and accept the request of customers from all over the world communication, therefore, the server program do not need to know the address of the client,
(3) after the construction of the relationship between client and server communication, communication can be a two-way, client and server can send and receive data,
(4) a specially used to provide a service program, can handle multiple remote or local customer requests at the same time,
7, peer-to-peer connection features:
(1) peer connection mode in essence is still using client/server mode, only peer connection for each of the host is both client and server, for example: the host service request D C, C is the customer, D is the server, but if C and at the same time to provide service to F, then C again to play the role of a server at the same time,
(2) peer connection works can support a lot of peer users (such as a few million) to work at the same time,
(2) core: consisting of a large number of network and connect the network router, this section is to provide service for the edges (provide connectivity and exchange),
The core part 1, the network is the most complicated part of the Internet,
2, the core part of the network to provide connectivity to network edge of a large number of hosts, the edges of any host to other hosts communications (that is, the various forms of data sent or received),
3, in the network core part of the special role is the router (router),
4, the router is to realize the packet exchange (packet switching) is the key component, its task is to forward received packet, it is the most important function of network core part,
5, in order to understand the packet switching, first understand circuit switching (circuit switching) the basic concepts of:
(1) when increased the number of telephone switches are used to complete the entire network exchange task, every phone is directly connected to the switch, the switch exchange method is circuit switching, it can make telephone users can be very convenient communication between each other,
(2) here, the meaning of "exchange" is the transfer, which put a line through to another telephone line and connect them together, and from the Angle of communication resource allocation, "exchange" is in a certain way to dynamically allocate the resources of the transmission lines,
(3) the characteristics of the circuit switching:
(A) circuit switching is A connection-oriented,
(B) circuit switching is divided into three stages:
Connection is established (a) : set up a dedicated physical pathway, to ensure the communication of both sides communication required resources are occupied by other users when communication;
(b) communication: the calling and called on both sides can call each other;
(c) released connection (hang up) : just use a dedicated physical pathways (release just take up all the communication resources),
(4) circuit switching faults:
(C) computer data with a sudden,
(D) of computer data for transmission, communication lines of utilization rate is very low (used to transmit data is often less than 10% or even 1% of the time),
6, the main characteristic of packet switching:
(1) packet switching using store-and-forward technology,
(2) in the sending end, make a longer message is divided into short, fixed-length data segment,
(3) in front of each data segment again add first packet (packet),
(4) packet switched network to "group" as the data transmission unit (i.e., was based on the grouping of the basic unit in the network transmission), and in turn to each packet is sent to the receiver,
(5) the receiver strip first back into a message after receipt of the grouping,
7, the importance of the group's first:
(1) each group first contains the address (such as the destination address and source address), and other control information,
(2) switches in packet-switched networks nodes according to the received packet address information in the first, the packet is forwarded to the next node switches,
(3) each packet in the Internet in the choice of independent transmission path,
(4) in this way to store and forward, the group will be able to reach the final destination,
8, there is no direct connection between input and output port of the router,
9, routers process grouping process is:
(1) received are grouped into the first cache (temporary storage);
(2) find the published, find out what port to a destination address should forward;
(3) the packet to the appropriate port forwarding out,
10, the host and the function of the router is different:
(1) the host is information processing for users, and sends a group to the network receives the packet from the network,
(2) the router is to store and forward of grouping, finally put the packet delivery destination host,
11, the advantage of packet switching:
Efficient: (1) in the process of packet transmission, dynamic allocation of transmission bandwidth of communication link is piecewise,
(2) flexible: for each group of independent select the most appropriate forward routing,
(3) : quickly by group as transmission unit, can not establish a connection first can send other host grouping,
(4) : reliable guarantee the reliability of the network protocol; Distributed routing packet-switched networks, the network has good survivability,
12, the disadvantages of packet switching:
(1) packet queue, the need when the nodes in the store-and-forward will cause a certain delay,
(2) packet must carry the first () there are essential to the control information caused certain overhead,
13, store-and-forward principle is not totally new concept, in the 1940 s of the telegraph communication also USES the principle based on store-and-forward message exchange (message switching),
14, the comparison of three kinds of exchange:
(1) if you want to send large amounts of data in a row, and the delivery time is greater than the connection setup time, the choice of circuit switching transmission rate faster,
(2) the message switching and packet switching does not require pre-allocated transmission bandwidth, can improve the network of emergency data for transmission channel utilization,
(3) because of a packet length is often far less than the length of the entire message, so packet-switched than message switching time delay is small, but also has better flexibility,