Communication Network (I) -------- communication network Overview

 

 

Communication network technology is a technology for planning, designing, constructing and maintaining networks. To build and maintain a communication network well, you must understand the structures, interfaces, protocols, and technical indicators of various types of communication networks, and understand the relationships and connections between various communication networks, network technology has become a specialized discipline with rich content and has become an important basic knowledge in the field of communication engineering.

1. Concepts of Communication Networks

1.1 Basic components of the Communication System

The basic components include: Source Converter channel noise source anti-converter sink

Point-to-Point unidirectional communication system composition model

For bidirectional communication, another communication system is required to transfer information in the opposite direction. To achieve multi-user communication, multiple communication systems must be organically integrated so that they can work together to form a communication network.

1.2 concepts and elements of Communication Networks

Definition: a communication network is organically organized by a certain number of nodes (including terminal nodes and exchange nodes) and the transmission system connecting these nodes, the communication system for information exchange between any users is completed according to the agreed signaling or protocol. Function: information of any two or more users in the transmission network that meets the user's call needs. On the communication network, information can be exchanged between two users, between two computer processes, and between a user and a device. Information exchanged includes user information (such as voice, data, images, etc.), control information (such as signaling information, routing information, etc.), and network management information. Because information is transmitted on the Internet in the form of electricity or optical signals, modern communication networks are also called telecommunication networks.

The actual communication network is a communication system composed of software and hardware in a specific way. Each communication must be completed through coordination of hardware and software facilities.

From the perspective of hardware composition: the communication network consists of terminal devices, exchange devices and transmission systems. They complete the basic functions of the communication network: Access, exchange and transmission. From the perspective of software facilities: software facilities include signaling, protocol, control, management, and billing. They mainly implement control, management, operation, and maintenance of the communication network, and achieve intelligent communication network.

1.3 layered structure of Communication Networks

Vertical description of the Network Structure

The network is divided into multiple functional layers based on different features, and the relationship between the upper and lower layers is the customer/service provider relationship.

In the vertical structure, the communication network is divided into application layer, service network and transmission network. application Layer: network layer of various information application and service types: it indicates the means and equipment for supporting various information service services. It is the main body of modern communication networks, it is a network that provides users with various communication services, such as telephone, telegraph, fax, data, and images. Transport Network Layer: This layer supports the transmission methods and infrastructure of the service network, including backbone transmission network and access network. Support Network Layer: This layer is used to support all three levels of work and provides various control and management capabilities to ensure the effective and normal operation of the communication network. The traditional communication support network includes the signaling network, synchronization network, and telecom management network. Horizontal description of the network structure horizontal description is the user's resident Network (CPN: Customer Premises Network) Access Network (an: Access Network) core network (CN: core network) UNI: User Network Interface SNI: Business node interface LAN (LAN: Local Area Network) MAN: Metropolitan Area Network (WAN: Wide Area Network)

 

1.4 communication network business and network Classification

The purpose of the construction and operation of modern communication networks is to provide users with all kinds of communication services they need to meet their needs for different service quality. Therefore, communication services are most directly oriented to users.

There is no unified method for business classification, which helps operators to plan their networks and manage their operations.

Based on different types of information, services can be divided:

Speech Service

Fixed telephone, mobile phone, VoIP, conference telephone, and telephone voice information services. This type of business does not require complex terminal devices. The required bandwidth is 64kb/s and is carried by circuit or group.

Data Service

The bandwidth required for email, data retrieval, Web browsing, file transmission, lan interconnection, and transaction-oriented data processing services varies greatly. Generally, the bandwidth must be larger than 64kb/s, it is carried by circuit and grouping.

Image Service

Fax, CAD/CAM image transmission, etc. This type of business requires a large bandwidth difference, G4 Fax requires 2.4-64 KB/s with width, while CAD/CAM requires 64 KB/s-34Mb/s bandwidth.

Video and multimedia services

Videophone, video conferencing, on-demand video, normal TV, High Definition TV, etc. The bandwidth required for such services varies greatly. For example, for conference TVs, the bandwidth required is 64 KB-2 Mb/s, and for HDTV, the bandwidth required is about 140 Mb/s.

 

Services are divided

Bearer Service: A simple information transmission service provided by the network at uni. The Network transparently transmits information from one uni to another in a circuit or group exchange mode, without any processing or interpretation of the information. It has nothing to do with the terminal type. A bearer service is usually defined by the bearer mode (grouping or circuit switching), the bearer rate, and the bearer capability (voice, data, and multimedia. User Terminal Business: all user-oriented businesses are provided on interfaces with terminals. It not only reflects the information transmission capability of the network, but also the capability of terminal devices. Terminal Services include telephone, fax, data, and multimedia. Generally, user terminal services are formed by adding high-level functions on the basis of carrying services. Supplementary business: Also known as additional business, it is provided by the network and carries additional business performance on the basis of the business and user terminal business. Supplementary Services cannot exist independently and must be provided together with basic services. Common supplementary services include caller ID Display, call transfer, third-party call, and virtual private network.

Currently, communication network services have the following main problems:

Most businesses are implemented based on old technologies and existing network structures.

In addition to basic voice and low-speed data services, the service performance of most services is significantly different from the actual requirements of users.

Classification of Communication Networks

Business types are classified by communication, that is, the business network includes: fixed telephone communication networks, mobile phone communication networks, fax communication networks, data communication networks, computer communication networks, broadcast and television networks, multimedia communication networks, and integrated business digital networks. It is classified by communication media: Cable Communication Network, optical fiber communication network, microwave communication network, and satellite communication network. Classification by communication transmission processing signal: analog communication network and digital communication network. Services are classified as follows: local communication networks, long-distance communication networks, international communication networks, lan, man, and wan. Service objects are classified as public communication networks and private communication networks. Divided by communication activity: fixed communication network and mobile communication network.

 

2. Communication Network Structure

During the planning, design, construction and optimization of the communication network, each node (or network element) in the network needs to be reasonably configured and connected, to achieve a reliable, rapid, high-quality and economical modern communication network, that is, to establish a reasonable network. The network structure is generally described by the network topology. The so-called topology refers to the connection mode between nodes that constitute a communication network. 2.1 Basic Network Structure mesh (Dot-link) Number of transmission links H = N (N-1)/2 mesh advantages: dot-link, each node has a direct line, fast Information Transmission; high flexibility and high reliability. When any of the lines is blocked, there are many loose lines and the communications can be guaranteed to be smooth. The communication nodes do not need the exchange function and the exchange cost is low. Disadvantages: because each node is interconnected, there are many lines, the total length is long, and the construction investment and maintenance costs are high. When the communication service volume is small, the line utilization is low.

The mesh network structure is suitable for scenarios where the number of nodes is small, there is sufficient communication traffic between nodes, or there is a high reliability requirement.

 

Star Network (radiation)

It is also called the radiation network. It sets a central node in the center of the network, and other nodes have lines connected to the central node. Communication between nodes is transferred by the central node.

Number of transmission links H = N-1

Advantages of the star network:

The architecture is simple, the number of lines is small, the total length is short, and the construction investment and maintenance costs are relatively low. Because the central node has the exchange function, the communication business volume is concentrated and the line utilization is improved; A single communication can only be transferred once. Disadvantages: low reliability and no detour. If a link fails, the node cannot be connected. In particular, if the center node fails, the whole network is paralyzed; the communication traffic is concentrated on one central node. When the load is too heavy, the exchange capability of the central node will affect the transmission speed. It is suitable for communication nodes with scattered distribution, long distances, and a small amount of traffic between them, and most of the communication flows between central nodes.

Ring Shaped Network

All nodes are connected in a closed loop.

Number of transmission links H = N

In the case of the same number of nodes, the ring network requires less lines than the mesh network, and the reliability is higher than that of the star network. When the line between any two points is blocked, the communication can still be achieved through a detour, however, the communication speed will be affected due to the large number of transfers. The ring network can be a unidirectional or Bidirectional Ring, And the bidirectional self-healing Ring Structure can automatically protect the network. Currently, the ring structure is mainly used in computer LAN, optical fiber access network, Metropolitan Area Network, optical transmission network, and other networks.

Cable Network

The network structure of a line-shaped network is different from that of a ring-shaped network.

 

Total Line Network

Information sent by one node can be received by multiple nodes on the network.

Advantages: Easy node access and low cost. Disadvantages: when the network communication load is heavy, the latency increases, the network efficiency decreases, and the transmission delay is not fixed. If the transmission media is damaged, the entire network may be paralyzed.

Currently, it is mainly used in computer LAN and access networks.

2.2 Non-basic network structure Compound Network (radiation convergence)

Based on the Star Network, a network is formed between the exchange centers with large communication traffic.

Leveraging the advantages of the mesh network and the star network, it is more economical and reasonable, and has a certain degree of reliability. Hierarchical compound network structures are widely used in large-scale LAN and communication backbone networks. In actual use, the composite network series should be considered based on the actual situation and development trend. Lattice Network

Grid networks are also called grid networks.

Most nodes in the network are connected by lines. A small number of nodes are directly connected to other nodes without lines. Which nodes do not need direct lines, depending on the specific situation (generally, the traffic between these nodes is relatively small ). Compared with the mesh network, GRID network can save some lines, that is, the line utilization is improved, and the economy is improved. The network reliability is reduced. It can be evolved from a composite network structure or degraded by a mesh network, which is the intermediate state of the development of a composite network to a mesh network.

 

Tree Network

 

The tree network is an extension of the star network topology.

Nodes are connected by hierarchy, and information exchange mainly occurs between upstream and downstream nodes.

Compared with the star structure, this structure reduces the cost of communication lines, but increases the network complexity. Except for the lowest-Layer Nodes and their connections, faults of any node or connection lines affect the normal operation of the branch network. The tree structure is mainly used in the user access network. In addition, the clock distribution network in the master-slave network synchronization mode also adopts the tree structure. Cellular Network

It is a common structure in wireless access networks.

The objective is to solve the problems of low spectrum, small capacity, poor service quality, and low spectrum utilization in conventional mobile communication systems. It features point-to-point and multi-point transmission of wireless transmission media (microwave, satellite, infrared, etc. Applicable to Mobile Communication wireless networks, man networks, and local networks. 3. Communication Network Quality Requirements 3.1 General Communication Network Quality Requirements

Arbitrary and fast connection

A user in a network can quickly connect to any other user in the network. If some users cannot communicate with other users, problems may occur if these users are not in the same network or in the same network. If they cannot be quickly connected, the information to be transmitted may lose value, this connection will be invalid.

The main factors that affect the randomness and speed of connection include the topology structure of the communication network, which increases the number of connections if the network topology is unreasonable, increases the blocking rate and delay, and network resources of the communication network: the consequence of insufficient network resources is to increase the blocking probability. The reliability of the Communication Network: a lower reliability may cause transmission link or switch equipment failure or even the loss of its functions. Transparency of information transmission and consistency of transmission quality

All information within the specified business scope can be transmitted over the network without any restrictions on users.

Consistency of transmission quality

Communication between any two users in the network, regardless of the distance between the two users, should have the same or similar transmission quality, regardless of the distance between the two users. The communication network transmission quality directly affects the communication effect. Therefore, it is necessary to set transmission quality standards and make reasonable allocation so that all parts in the network can meet the requirements of transmission quality indicators.

Network Reliability and economic rationality Reliability

An unreliable or frequently interrupted network cannot be used. However, the absolutely reliable network does not exist. Reliability means that MTBF (mean time between failure) meets the requirements in the sense of probability.

Economic rationality

It is related to user requirements. A network investment is often carried out in stages to achieve maximum economic benefits. The construction of network capacity in each phase is closely related to the prediction of demand. The loss of idle equipment causes economic losses, and the loss of opportunities to generate benefits because the construction fails to meet the requirements, this is economically unreasonable.

Reliability must be combined with economic rationality. Increasing investment is often required to improve reliability, but the cost is too high and difficult to achieve. Therefore, a compromise and balance between reliability and economics should be achieved based on actual needs.

3.2 quality requirements for telephone communication networks

Connection Quality

It reflects the speed and difficulty of the phone network connection user's call, usually measured by the connection loss (call loss rate, referred to as call loss) connection delay.

The connection Standard of the telephone network is defined:

Call loss

City calls: less than 3%

Long Talk: 10%

Connection latency: less than 1 min.

 

Transmission Quality

Sound level: the volume of the voice that you listen to. Definition: Voice comprehensibility, that is, the clarity and comprehensibility of the voice you listen to. fidelity: Voice Tone, it refers to the degree to which the voice tone and features are not distorted. In reality, the above three indicators are generally assessed by the user's subjective. Stability Quality refers to the reliability failure rate of the communication network: the probability that the system fails within the unit time. mean Time To repair (MTTR): Average MTBF = 1/λ mean time to repair adjacent faults ): average troubleshooting time for fixing a fault

MTTR = 1/µ

System Effectiveness (a): the probability that the system completes the specified function within the specified time and conditions

A = MTBF/(MTBF + MTTR)

System unavailability (u): the probability that the system will lose the required function within the specified time and conditions

U = 1-A = MTTR/(MTBF + MTTR)

Communication Network (I) -------- communication network Overview