Shulou(Shulou.com)06/03 Report--

I. introduction

1. The main Development process of computer Communication and Network

The first stage: terminal-oriented computer network.

The second stage: a computer network in which multiple computers are interconnected.

The third stage: facing the standardized computer network.

The fourth stage: the computer network for global interconnection.

two。 The present situation of Network Development in China

3. Definition and composition of computer Communication and Network

The definition of computer network: a system that connects multiple computers with independent functions distributed in different locations through communication equipment and lines, and aims to realize resource sharing in the network under the running environment of fully functional network software.

The composition of computer network: terminal system and communication subnet.

4. The types and characteristics of Network

Classified according to the network topology structure:

Zero star structure

The structure of the tree

ZOBUS structure

Zigzag ring structure

Tick network structure

Classified according to the scope of network coverage:

Personal area network PAN, local area network LAN (Ethernet, wireless local area network WLAN), man MAN, wide area network WAN, Internet

Wireless network:

Wireless personal area network WPAN (Bluetooth, ZigBee, UWB), wireless local area network WLAN, wireless metropolitan area network WMAN, wireless wide area network WWAN

5. Computer Communication Protocol and Network Architecture

Definition of network protocol: a collection of rules that must be followed by both sides of the communication to control the exchange of information.

Three elements:

Syntax: the structure or format of data and control information, determining the data format used in communication, coding and signal electrical equality.

Semantics: the interpretation of the meaning of the protocol elements that make up the agreement.

Synchronization: specifies the order of execution of time.

Network architecture: layering the network and defining the functions and protocols of each layer.

The protocol hierarchy model includes:

Entity: people and software and hardware facilities that can send and receive information when communicating.

Interface: the communication interface between the adjacent layers in the network hierarchical structure.

Layer N is the user of layer 1, which provides services for layer 1.

OSI-RM architecture (basic reference model for open systems interconnection)

Physical layer: using the transmission medium to establish, maintain and release physical connections between the communicating network nodes to realize the transparent transmission of the bit stream.

Data link layer: establishes a data link connection between communicating entities and transmits packets in frames.

Network layer: provides communication services for different hosts on the packet switching network, selects appropriate routes for packet used communication subnets in packet units, and realizes congestion control, network interconnection and other functions.

Transport layer: provide end-to-end data transmission services to users.

Session layer: responsible for maintaining the establishment, maintenance and disconnection of session connections between two nodes in communication, as well as data exchange.

Presentation layer: the main way to handle the exchange of information between two communication systems

Application layer: 2 serves the application through the network.

TCP/IP architecture:

Application layer

Transport layer

Interconnection network layer

Network access layer

Differences between the two architectures:

1. Starting points are different.

2.TCP/IP crossover layer

RFC documentation:

At present, the two most famous international standardization organizations are ISO and ITU-T. ITU-T is mainly responsible for recommendations and standards in the field of telephone and digital communications. IAB is responsible for the standardization of the Internet, and the task force is responsible for specific standards. For example, IETF is responsible for the engineering and standard issues of the recent development of the Internet, forming RFC documents.

II. Technical basis of data communication

1. Basic Concepts of data Communication

Information: content and interpretation of design data

Data: the carrier of information, a predetermined combination of numbers, symbols, and letters with a certain meaning.

Signal: electromagnetic coding of data.

Analog signal: the amplitude of the signal changes continuously over time.

Digital signal: discontinuous, discrete signal

Transmission media

Cable: twisted pair, coaxial cable, fiber optic cable

Wireless: radio wave, ground microwave, satellite microwave, infrared technology

Technical index of data communication system

Data transmission rate

Code rate NBd: the number of transmitted signal symbols per second, in baud Baud. If the duration of the letter number is T seconds, the transmission rate is 1 T baud.

Transmission rate Rb: the number of binary symbols transmitted per second, in bits per second. If M level: Rb=NBd*log2 M

Channel bandwidth: when a digital signal is developed, it becomes the data transmission rate.

Bit error rate and group error rate

Bit error rate P=e1 (number of bits in error) / E2 (total number of transmitted bits)

Group error rate P=b1 (number of groups in error) / b2 (total number of transmission groups)

Time delay

Delay = transmission delay + propagation delay + processing delay

Transmission delay = block length (b) / channel bandwidth (b)

Propagation delay = channel length (m) / propagation speed of electromagnetic wave on the channel (m)

two。 Data transmission mode

Parallel and serial transmission

Parallel transmission: data is transmitted in groups on multiple parallel channels simultaneously.

Serial transmission: several bits of binary codes that make up characters are arranged into a data stream and transmitted bit by bit on a channel. It is a kind of transmission mode which is mainly used in remote communication.

Asynchronous and synchronous transmission

Asynchronous transmission: start bit one symbol length, polarity is 0, stop bit length can choose 1, 1.5, 2 symbol length, polarity is 1.

Synchronous transmission: the data signal is transmitted at a fixed clock beat, and the transmitted data is in frames, with synchronous characters and ending characters before and after a frame of data. User communication is mainly used in high-speed environment.

Simplex, half-duplex and full-duplex transmission

Analog transmission and digital transmission

3. Data transmission technology

Electrical signal representation of data sequence

Unipolar code and bipolar code

Non-return to zero code and return to zero code

Differential coding

Pseudo ternary code

Manchester code

Differential Manchester code

The concept of channel capacity

Nyquist theorem C=2Wlog2M

Shannon Theorem C=Wlog2 (1+S/N), where (Shammer N) dB=10lg (signal frequency / noise frequency)

Baseband transmission

The inherent frequency band of the rectangular pulse signal is called the basic frequency band. on the digital communication channel, the data in the computer is directly transmitted by the rectangular pulse signal, this kind of transmission method is called baseband transmission.

Band transmission

Amplitude shift keying (digital amplitude modulation)

Frequency shift keying (digital FM)

Phase shift keying (digital phase modulation)

Digital data transmission

Sampling

Quantification

Coding

4. Multiplexing technology

Frequency division multiplexing

Time division multiplexing

Static time division multiplexing: the data signals of multiple users are placed in predetermined time slots respectively.

Dynamic time division multiplexing: allocating resources on demand

Code division multiplexing

The sequences of chips are different and orthogonal to each other.

Wavelength division multiplexing

5. Data exchange technology

Switching is centralization and forwarding.

Circuit switching

Three stages

Call establishment phase: static time division multiplexing technology is adopted.

Communication phase

Connection release phase

The physical connection established means that the connection established between the principal and the called is exclusive between the called and the called.

Message exchange

Each message is processed in a "store-and-forward" way, but the time is prolonged.

Packet switching

There are two ways to serve:

Virtual circuit: early packet switching network use, connection-oriented, routing, dynamic time division multiplexing.

Datagram: adopted by Internet. Multiple packets from the same message may take different routes without establishing a connection.

Compared with circuit switching, the biggest disadvantage is that it can not meet real-time applications, and other disadvantages such as high control overhead.

6. Error control technology

Basic principles

Errors can be divided into random errors and sudden errors.

Control mode

Automatic request for retransmission

Forward error correction

Mixed mode

information feedback

Coding

Parity check code

Hamming code

Cyclic redundancy check code CRC

Characteristics

After any two allowable code groups in a code are added according to module 2, the new sequence is still an allowable code group; if two identical allowable code groups are added, a full zero sequence is obtained, so the cyclic redundancy check code must contain all zero codewords.

The result of each cyclic shift of a permitted code group must also be another allowable code group in the codeword set.

Coding

(1) find the codeword corresponding to M (think) and multiply it by x ^ (nmelk)

(2) divide the codeword by G (x) and find the remainder.

(3) get x ^ (r) M (x) XOR R (x), which is the codeword required.

Characteristics of data communication interface

The digital data sent by DTE (data terminal equipment) reaches the DCE (data circuit termination equipment) of the receiver through the communication interface, and then is transmitted to the server through the communication interface, and vice versa.

Mechanical, electrical, functional and regulatory characteristics

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