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Basic principles of LAN design

Basic principles of network design

The goal of network design is to choose the right technology and equipment and configure it correctly, but how to make it "appropriate"? It depends on everyone's understanding of customers and their needs. Network builders can realize network design in different ways, but successful network design must follow some basic principles.

Practicality.

The purpose of building local area network is to meet the needs of users, and the needs of users are the basis of planning. Network design that does not fully understand the needs of users will inevitably fail to meet the construction requirements. The network often needs to meet the different needs of each user, so as to meet all the business needs of the whole organization. Practicality refers to people-oriented network design.

Scalability.

When designing networking, we should pay attention to the future development direction of technology and not adopt technical standards that restrict the development of new technologies. For example, multicast is the future development trend, and network designers should ensure that when new technologies are popularized, the designed local area network does not need to replace all existing equipment, but only needs hardware and software with network expansion and upgrade options to realize new functions.

Openness

Networking design should adopt the latest international standard software and hardware, as well as open technology, open structure, open system components and user interface, so that the network system has the characteristics of interconnection with computer communication networks of various protocols, and provides necessary conditions for future horizontal expansion.

Cost-effectiveness.

Fully consider the capital investment ability and build the best cost-effective network system. Network design does not blindly pursue high performance, because high performance often means high investment. If the investment of the network system exceeds the profit brought by the system, it is obviously inappropriate, and the high-performance network system may not be fully utilized. Therefore, the networking design should be based on the application requirements of users, meet the system performance and give consideration to the advanced nature in the foreseeable period, and make the whole system investment reasonable and practical as far as possible.

Manageability.

Computer network has a certain complexity, and with the development of the network, its management will inevitably become more and more heavy. Therefore, network designers should establish a set of perfect network management solutions. Through advanced management strategies and tools, the manageability and reliability of network operation are improved and network maintenance is simplified.

Safe and reliable.

In order to ensure the realization of various applications, the designed network must have high reliability. We should try our best to avoid a single point of failure of the system, provide redundant measures, adopt advanced network management technology to monitor the network information flow in real time, and process the data to find and eliminate the failure in time. At the same time, take appropriate security measures, such as setting up a firewall.

Characteristics of (1) LAN

Functionally, LAN has the following characteristics:

* * * Enjoy the transmission channel.

In a local area network, each system device is connected to a communication device shared by * * *.

Limited in scope.

The small one is one room or several rooms, such as the local area network built in student dormitory, and the big one is only within a few kilometers or more, such as the local area network of school or company.

High transmission rate.

The maximum transmission rate of telephone digital line is only 56Kbps, and local area network adopts baseband transmission. The transmission rate has changed from the initial 1000Mbps to the current 1000 Mbps, and the LAN technology of10 Mbps has also come out.

Reliable work,

Low bit error rate. Local area network mostly adopts distributed control and broadcast communication, and the communication error rate can be lower or even lower.

From the perspective of network architecture and transmission control regulations, the characteristics of computer local area network are:

The underlying protocol is simple. Due to the short distance, small delay, high transmission rate and low bit error rate of local area network, channel utilization is no longer the main problem to be considered, so the underlying protocol is relatively simple, allowing messages to have a larger header size.

Small computer LAN does not need intermediate switching, and there is no separate network layer. However, if the LAN is connected through switches and routers and needs to provide various services, the network layer is needed. Generally speaking, the architecture of LAN is equivalent to the lowest two layers in OSI model.

Adopt a variety of access control methods. Due to the diversity of transmission media, there are many media access control methods in LAN, including carrier sense multiple access/collision detection technology, token ring control technology, token bus control technology, optical fiber distributed data interface technology and so on.

(2) LAN reference model

1982 In February, the American Institute of Electrical and Electronics Engineers (IEEE) established the IEEE 802 Committee, and then the Committee formulated a series of LAN standards, called IEEE 802 standards. 1983, which was accepted as the American national standard by the American National Bureau of Standards (ANSI). 1984 in March, ISO designated this standard as an international standard.

According to IEEE 802 standard, LAN architecture consists of physical layer, media access control sublayer (MAC) and logical link control sublayer (LLC).

(3) LAN topology

Network topology refers to the geometry of interconnection between computer nodes in the network. The access control mode of any LAN specifies its own network topology. The network topology of LAN is usually divided into three types, namely, bus topology, star topology and ring topology.

Bus-like topology.

All nodes are connected to a passive public bus through corresponding hardware interfaces, and the information sent by any node can be transmitted along the bus and received by any other node on the bus. Its transmission direction is from the sending point to both ends, and it is a broadcasting structure. In LAN, carrier sense multiple access with collision detection is adopted, that is, CSMA/CD mode. There is a transceiver on the network card of each node. When the destination address sent by the sending node matches the interface address of a node, the node receives the information. The advantages of bus structure are simple installation, easy expansion and high reliability. If one node is damaged, it will not affect the whole network. The disadvantage is that only one end user can send data at a time, and other end users have to wait until they get the right to send, so the media access acquisition mechanism is more complicated.

Star topology.

Also known as radial network, it takes a point as the central node and connects with other nodes through lines. A star network with n nodes needs at least n–1transmission links. The central node of the star network is the switching center, and other N- 1 nodes communicate with each other through the central node. In a data network, the device is a host or a hub. Therefore, the switching ability and reliability of equipment will affect all users in the network. The advantages of star topology are: it is convenient to provide services and reconfigure the network by using the central node; The fault of a single connection point only affects one device, but not the whole network, so it is easy to detect and isolate the fault and facilitate maintenance; Any connection only involves a central node and a site, so the method of controlling media access is very simple, so the access protocol is also very simple. The disadvantages of star topology are: each site is directly connected to the central node, which requires a lot of cables, so the cost is high; If the central node fails, the whole network cannot work, so the reliability and redundancy of the central node are very high. The central system usually adopts dual-machine hot backup to improve the reliability of the system.

Ring network topology.

Each node in the ring structure is connected into a closed ring communication line through an active interface, which is a point-to-point structure. The information flow sent by each node in the ring network flows according to the flow direction of the loop design. In order to improve the reliability, double-ring or multi-ring redundancy measures can be adopted to solve this problem. At present, multiple access components MAU are adopted in the ring structure. When a node fails, it can automatically bypass and isolate the failure point, which also improves the reliability. The advantages of ring structure are good real-time performance and large information throughput. The perimeter of the network can reach 200km and the number of nodes can reach hundreds. But because it is a closed loop, it is not convenient to expand. After IBM introduced token ring network in 1985, this structure has been accepted by people. At present, FDDI network is using this double-ring structure.