Learning notes: The first chapter--Computer network overview __ Computer network

Learning Notes: The first chapter--The Computer network overview

1.0 The definition of computer network: Some interconnected, autonomous computers set up called Computer Networks Road.

the role of 1.1 computer networks in the Information Age: connectivity and sharing.

1.2 Internet Overview:

Network Concept : A network (network) consists of a number of nodes (node) and a link (link) that connects those nodes.

Nodes in the network can be computers, hubs, switches and routers;

Network and network are connected by routers;

The internet is the largest network in the world.

1.3 The composition of the Internet:

From the way the Internet works, it is divided into the following two major fast:

(1) Edge part : composed of all the hosts linked on the Internet;

Role: Used directly by the user to communicate (transmit data, audio, video) and resource sharing.

The way of communication between the end system and the running program of the edge part can be divided into two main categories:

c/S (client/server):

This approach is the most common and traditional method. The customer is the service requester, the server is the service provider, and both parties use the services provided by the core portion of the network. Service procedures and client programs have their own characteristics and role.

Peer-to-peer Connection (p to P or peer-to-peer):

means that two hosts do not distinguish between a server requester or a service provider when communicating. Peer-to-peer communication can be done as long as they have peer-to-peer software installed.

(2) core : A large number of networks and understanding of these networks of routers;

Role: This section is for the edge part of the service.

The core of the network is the most complex part of the Internet, because the core of the network to provide connectivity to a large number of hosts at the edge of the network, so that any one of the edge parts of the host can communicate to other hosts.

In the core of the network are some special functions of the router;

A router is a dedicated computer (but not a host);

Router is the key component of packet switching, whose task is to forward the packets received, which is the most important function of the core part of the network.

The Exchange Mode of the core part route:

1 Circuit Switching : The entire message's bit flow continues from the source point directly to the endpoint, as if in a pipe transmission, with the actual line (such as fixed telephone), with the characteristics of line monopoly.

2 Message exchange : The entire message line to the adjacent nodes, all stored down to find the post, forwarding to the next node.

3 packet switching : A single packet (part of the entire message) is transmitted to adjacent nodes, stored down to find the post, and forwarded to the next node. Disassemble and send and divide into blocks of data.

Our main use is the way of packet switching, which has the following advantages:

Efficient: Dynamic allocation of transmission bandwidth, improve bandwidth utilization;

Flexible: Packet transmission Unit and lookup, small delay, flexible line strong;

Quick: No connection is established

Reliability: The guarantee of many network protocols

Of course, the disadvantages are not no:

There is a certain delay in queueing first, and then the information for each header can cause a certain amount of overhead.

link TYPE of 1.4 computer network:

(1) Star type (most common);

(2) bus type;

(3) Ring type (common in the core equipment);

(4) also has the compound type. is to synthesize the several types of collections above.

1.5 several different types of networks:

Wan Wan (Wide area network) such as a transnational network;

Man of man (metropolitan area Network) is 5~10km by the action distance;

LAN LAN (local area network) such as Campus network, enterprise network;

Personal Area Network Pan (Personal area network) such as wireless personal Zone network.

the performance index of 1.6 computer network:

(1) rate;

(2) bandwidth;

(3) throughput; (the first three say it's the same thing, but the unit name is different)
(4) Delay: including the transmission, transmission, processing and queuing of delay; we usually say that the increase in the rate of data transmission actually only reduces the time delay of sending data;

(5) Delay bandwidth Product: = propagation delay * bandwidth;

(6) Roundtrip time RTT;

(7) Utilization rate: The utilization rate reaches certain degree, the delay will increase drastically, so the utilization ratio of the channel reaches above%50 should consider the expansion, increase the line bandwidth.

1.7 has a five-layer protocol architecture:

(1) Application layer: The highest level of the whole system. The application layer provides services directly to the user's process; dns,rtp,smtp,http

(2) Transport layer: responsible for providing services to communication between processes in two mainframe; TCP,UDP,SCTP

(3) Network layer: The network layer is responsible for providing communication services for the different hosts of the packet switching networks;

(4) Data link layer: Short link layer. The link layer assembles the IP data of the network layer into frames, and transmits the data in the frame "transparently" on the link between the two neighboring nodes.

(5) Physical layer: unit (bit bit). The task of the physical layer is to transparently transfer the bit stream.

1.8 Entity/Protocol/service and service access points:

When studying the exchange of information in open systems, it is often used to express any hardware or software process of sending or receiving information by using the more abstract noun of entity.

A protocol is a collection of rules that govern the communication of two peer entities (or multiple entities);

Under the control of the Protocol, communication between two peer entities enables the layer to provide services up to the next level, and the services provided below are required for the implementation of this layer protocol;

A place where two layers of entities in the same system interact (that is, information exchange) is often referred to as a service access point.

Above is my summary, the picture comes from the network, slightly inferior, here recommends a great God's summary: http://www.cnblogs.com/kzang/articles/2581199.html#a4