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RP repeater is a device to connect network lines. It is commonly used for bidirectional forwarding between two network nodes. The repeater is the simplest network interconnected device, which mainly completes the function of the physical layer, and is responsible for transmitting information on the physical layer of the two nodes, and completing the function of copying, adjusting and amplifying the signal in order to extend the length of the network. Its location in the OSI reference model is shown in Figure 1.
Because of the loss, the signal power transmitted on the online road will gradually decay. When it reaches a certain level, it will cause signal distortion, which will lead to the reception error. Repeater is designed to solve this problem. It completes the connection of physical lines, amplifies the attenuated signals, and keeps the same data as the original ones.
In general, the two ends of repeaters are connected by the same media, but some repeaters can also complete the transfer work of different media. Theoretically speaking, repeaters are infinite and network can be extended indefinitely. In fact, this is not possible, because the network standards are specific to the delay range of the signal, the repeater can only work within the scope of this regulation, otherwise it will cause the network failure. In Ethernet network standard, only one Ethernet network is allowed to appear only 5 network segments, with up to 4 repeater, and only 3 of them can be connected to the computer terminal.
Hub (Hub) is a form of repeater. The difference is that hub can provide multi port services, also known as multi port repeater. The hub's position in OSI / RM is shown in Figure 2.
Hub products develop faster. LAN concentrator is usually divided into five different types. It will have a direct impact on the development of LAN switch technology.
1. single relay network segment hub
In the hardware platform, the first class hub is a simple relay LAN segment, and the best example is the superimposed Ethernet hub or token ring network multi station access component (MAU). Some vendors try to draw a line between the managed hub and the non manageable hub, so as to classify the hardware. It ignores the core characteristics of network hardware itself, that is, what functions it implements, rather than how to configure it simply.
More than 2. network segment hub
The multi segment hub is derived from the first class hub directly. The hub has multiple relay nodes. Multi network hub is usually a chassis system with multiple interface cards. However, some non modular superimposed hubs now also support multiple relay networks. The main technical advantage of the multi segment hub is that users can be distributed over multiple relay networks to reduce the traffic load of each network segment, and the traffic between segments generally requires an independent bridge or router.
3. port switched hub
The port switched hub automate the connection process between the user port and the multiple backboard network segments on the basis of the multiple network segment hub, and by adding the port exchange matrix (PSM). PSM provides an automatic tool to connect any foreign user port to any relay network segment on the hub backplane. The key of this technology is "matrix". A matrix switch is a cable switch. It can't operate automatically, and requires users to intervene. It can't replace bridges or routers, and does not provide connectivity among different LAN segments. Its main advantage is the automation of mobile, adding and modifying.
4. network interconnected hub
Port switched hub focuses on port switching, and network interconnections actually provide some types of integrated connections between multiple segments of the backplane. This can be done through a comprehensive bridge, router or LAN switch. At present, most of them are in the form of chassis.
5. switch hub
At present, the boundaries between hub and switch have become blurred. The switch hub has a core switch backplane, which uses a pure switching system instead of the traditional shared medium relay network segment. Such products are listed, and hybrid (relay / switch) hub is likely to control this market in the next few years. It should be pointed out that the characteristics between hub and switch are almost the same.
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