Hubs and switches

Hubs and switches

If, due to the popularity of microcomputers, several microcomputers are connected to each other, resulting in a local area network, then due to the universal application of the network, in order to meet the need to achieve mutual communication and resource sharing on a larger scale, it has led to Interconnection. This section will introduce the general network interconnection hardware equipment.
When interconnecting networks, the following problem must be solved: how to physically connect the two networks. How a network can communicate and communicate with another network, how to solve the difference in protocol between them, how to deal with the difference in rate and bandwidth, solve these problems, coordination, conversion mechanism components are repeaters, bridges , Routers and gateways.
Use hardware to solve the differences between the networks:

l. Repeater:

After the transmission medium exceeds the length of the network segment, repeaters can be used to extend the distance of the network to regenerate and attenuate weak signals. The IEEE802 standard specifies that up to four repeaters can be connected to five network segments. The repeater works at the physical layer and does not provide network segment isolation.
2. Special repeater:

Hubs and switches (multi-port repeaters):
(1) Hub:
It is a device that uses a star topology to consolidate communication lines. It is equivalent to a bus. It works at the physical layer. It is the most widely used connection device in a local area network. Three stacked hubs.
The intelligent hub improves the shortcomings of the general hub, increases the bridging capability, can filter out frames that do not belong to its own network segment, increase the bandwidth of the network segment, and has network management capabilities and the ability to automatically detect the speed of the PC network card connected to the port .
There are common hubs with 10M, 100M and other rates on the market.
(2) Switch:
The destination address of the switched Ethernet data packet will send the Ethernet packet from the original port to the destination. When sending Ethernet packets to different destination ports, these Ethernet packets can be transmitted at the same time to achieve the effect of improving the actual throughput of the network. The switch can establish multiple transmission paths at the same time, so it can receive obvious effects on the network segment where the application connects multiple servers. Mainly used for connecting hub, server or decentralized backbone network.
Classify the switch according to the technology used:
Through exchange. (cut-through): Once the destination address in the packet is received, it will be forwarded before the full frame is received. It is suitable for environments with the same rate port and low collision error rate.
Store-and-forward: (store-and-forward): Confirm received frames, filter and process bad frames. It is suitable for environments with different rate ports and collisions, and high bit error string.

Application note:
(1) Choose 10 / 100M to adapt to the exchange.
(2) Choose two or more technology switches.

3. Network bridge:
(1) Filter and forward.
(2) Learning function.
(3) Connect different transmission media without path selection capability.

4. Router: A device that realizes network interconnection between multiple networks and media. It is a more complicated network interconnection device than a bridge.

The main function:
(1) Packet forwarding provides the best path and interconnects networks of different hardware technologies. Convert the packet format and packet length when necessary.
(2) Provide isolation and divide subnets. Each port of the router is a separate subnet.
(3) Provide economical and reasonable WAN access.
(4) Support backup network path, support mesh network topology, switch, bridge requirements, loop-free topology. Interconnect various local area networks and wide area networks. Suitable for large switching networks. It can be considered that after using Route, all kinds of communication subnets are integrated to form a larger network. From a macro perspective, it can be considered that the communication subnet is actually a network composed of routers, and the communication between routers is It is realized through the communication capabilities of various communication subnets.

4. Gateway: Used to interconnect completely different networks.

Main functions: change one protocol into another protocol, one data format into another data format, and one rate into another rate, in order to achieve the unity of the two. Provide a transit intermediate interface. In the Internet, the gateway is a computer device, which can define whether to send the information sent by the user out of the local network based on the IP address of the computer used for user communication. At the same time, it also receives the information sent from the outside world to the local network computer.