Computer Network Chapter One Review Notes

1. Computer network

1. Concept: a plurality of nodes and connecting these nodes links consisting of:

2. feature:

• Computers must be geographically dispersed
• The computer must have independent computer capabilities
• All computers are connected by a communication system
• Provide sharing of multiple resources
• Remind users of information exchange methods

3. The main function

Hardware resource sharing
Software resource sharing
User messaging
Distributed management

4. Host communication method

C/S: client-server
P2P: peer-to-peer connection

5. development of
   1969 ARPANET
   1983 TCP/IP (co-drafters are Robert Kahn and Winton Cerf)
   China connected to the Internet in 1994, becoming the 77th country to access the Internet

2. The core part of the Internet (router)

1. Circuit switching:

Before data transmission, the two nodes must establish a dedicated physical communication path, which passes through multiple intermediate nodes and is occupied during data transmission until the end of the communication.

advantage:

1. Small communication delay
2. Orderly transmission
3. No conflict
4. Wide application range
5. Real-time performance (only signal propagation delay)
6. No channel access delay
7. Stable data transmission rate

Disadvantages:

1. Long time to establish a connection
2. Exclusive line
3. High flexibility
4. Difficult to standardize
5. Cannot give full play to the potential of the transmission medium
6. Long-distance circuit establishment time
7. Poor scalability (hardware cost)

2. Message exchange:

The unit of data exchange is a message. The message carries information such as a destination address, source address, etc. The message exchange uses a store-and-forward method when switching nodes.
Advantages:

No need to establish a connection, dynamically allocate routing, improve the reliability of the line, improve the utilization of the line, and improve the efficiency of information transmission (a message sends multiple addresses at the same time)

Disadvantages:

Large delay (store and forward, send delay ) There is no limit to the size of the message exchanged

3. Packet switching

The store and forward method is also used to limit the size of message transmission (packet switching requires data to be divided into small data pieces of the same size, and control information (such as destination address) must be added to each piece).
Advantages:

High line utilization, no need to consume time delay when establishing a connection, speed up transmission data transmission error rate, reliable transmission

Disadvantages:

There is a transmission delay, and the packet switching channel utilization rate is high. The propagation delay depends on the propagation medium and the distance between the sending and receiving parties. Packet switching does not require connection-oriented communication

4. Examples:

• When the amount of transmitted data is too large and the transmission time is longer than the call time, circuit switching is more appropriate
• When the end-to-end path consists of many links, use packet switching to transmit data
• Improve the channel utilization to look at the problem. Message switching and packet switching are better than circuit switching. Packet switching has a smaller delay than message switching, and is especially suitable for burst data communication between computers.

Repeater: network interconnection equipment, single function, physical layer work, strengthen the signal.
Hub: a kind of repeater, work in the local area network, provide more port repeater, multi-port repeater

5. Network classification

(1) Wide Area Network (WAN)
(2) Metropolitan Area Network (MAN)
(3) Local Area Network (LAN)
(4) Personal Network (PAN)

3. Computer network performance indicators

• Rate: data transfer rate
• Broadband: the ability of a computer network to transmit data
• Delay: queuing delay, processing delay, transmission delay , sending delay

• Throughput: the actual number of passing through a network in unit time
• Round trip time RTT, utilization
• Three elements of network protocol:
  Syntax, semantics, synchronization

Triple play refers to the integration of three types of networks: telecommunications network, cable television network, and computer network. The
computer network can provide users withConnectedwithsharedservice

4. Services provided by computer networks

Connection-oriented service and connectionless service
Reliable service and unreliable service

Five, OSI model and TCP/IP model

OSI seven-layer architecture

Application layer: provide data transmission services for applications.
Presentation layer: perform data encryption and decryption.
Session layer: create and manage sessions.
Transport layer: provide data transmission services for processes.
Network layer: provide data transmission services for hosts.
Data link layer: for the same The host on the link provides data transmission services.
Physical layer: shield the differences in transmission media and communication means as much as possible, so that the data link layer does not feel the differences

Five-layer protocol architecture

Application layer: through the interaction between application processes to complete specific network applications (data transmission unit calledMessage)
Transport layer: Responsible for providing general data transmission services for the communication between two hosts

Includes two agreements:

• Transmission Control Protocol TCP: connection-oriented, reliable data transmission protocol (unit:Segment）
• User Datagram Protocol UDP: Provide connectionless, best-effort data transmission service (unit: userDatagram）

Network layer: encapsulate the message segment or user datagram generated by the transport layer intoGroupingorpackageTo transfer.

Data link layer: encapsulate the IP datagram handed over from the network layer intoframe
Physical layer: The unit of data transmitted isBit