- Oct 30, 2017 -
The relay works in the physical layer of the OSI, is the center of all nodes on the LAN, its role is to amplify the signal, compensation signal attenuation, support long-distance communication. Relay. Work in the physical layer, but play a role in expanding the transmission distance, the high-level agreement is transparent. In fact, the network connected by the repeater is equivalent to the larger network of the same wire. The repeater also connects the networks of different transmission media (10Base 5 and 10Base 2) together and is used in the same LAN interconnection above the data link layer.
The repeater is a small invention that is designed to give you the network signal to push so that they are transmitted farther.
Due to the influence of transmission line noise, the digital signal or analog signal carrying information can only transmit a limited distance. The function of the repeater is to regenerate and transmit the received signal, thus increasing the distance of signal transmission. It connects two or more segments of the same network. For example, Ethernet often uses the repeater to expand the cable length of the bus. The length of the standard cable Ethernet is 185 meters long and can have up to 5 segments. Therefore, the maximum network cable length can be increased to 925 meters The In general, the network part of the repeater is the network segment, not the subnet.
The repeater can connect two LAN cables, re-timed and regenerate the digital signals on the cable, and then send them out, which is the first layer of the OSI model - the typical functionality of the physical layer. The role of the repeater is to increase the coverage area of the LAN. For example, the Ethernet standard specifies that the maximum length of the single-stage signal transmission cable is 500 meters. However, after connecting the 4-segment cable with the repeater, the maximum signal transmission cable in the Ethernet Up to 2000 meters. Some brands of repeaters can be connected to different physical media cable segments, such as fine coaxial cable and cable.
The repeater only sends data from any cable segment to another cable regardless of whether there is any data in the data or data that is not suitable for the segment.
(1) to expand the communication distance.
⑵ increase the maximum number of nodes.
⑶ each network segment can use different communication rates.
⑷ improve the reliability. When the network fails, the general only affect the individual network segment.
⑸ performance improved.
⑴ because the repeater to receive the attenuation of the signal regeneration (recovery) to send the state, and forwarded, increased the delay.
⑵ CAN bus MAC sub-layer and no flow control function. When the load on the network is very heavy, it may be due to the buffer in the repeater storage space is not enough to overflow, resulting in the phenomenon of frame loss.
⑶ If the relay fails, the work of two adjacent subnets will have an impact.