Working principle of physical layer and data link layer network device, physical layer Link

Working principle of physical layer and data link layer network device, physical layer Link

Physical layer network devices include relay devices and hubs.

The repeater function is to zoom in the received signal and transmit it out. The function is to expand the physical range of the network device signal transmission. The disadvantage is to expand the data signal while also expanding the noise, broadcast isolation is not allowed, and the network utilization is very low. Now it has basically been eliminated.

In fact, a hub can be understood as a repeater with multiple ports. All ports of the hub share a backplane bus. Therefore, all ports are in the same conflict domain and the network utilization is low, which is basically eliminated.

Data link layer network devices include bridges and switches.

The bridge works on the data link layer. It can create its own "mac-port" table through the mac address of the source host. Once this "mac-port" table is created, when data communication is performed between hosts next time, the data will be routed to the target host through the "mac-port" table, so that multiple hosts can communicate at the same time. In the mac-port table of the bridge, a port can correspond to multiple mac addresses. The mac address is obtained through ARP broadcast, the "mac-port" table is blank after the bridge starts up. The source host sends an ARP broadcast packet without data content to broadcast to all ports, when the target host receives this packet, it returns a unicast ARP packet to the source host. Similarly, it is not until all the "mac-port" tables are created. The bridge is isolated from the physical network segment and belongs to the unified network segment of different physical areas, which is easily misunderstood. The destination bridge has two ports, which are generally used to connect to the hub and then connect to the host for communication. The bridge isolates conflicting domains and divides large conflicting domains into two small conflicting domains, which improves network utilization. However, its applications are managed by software, which has bottlenecks and has been replaced by switches with more powerful functions.

A switch can be considered as a bridge with multiple ports, and each port is a conflict domain. The backplane of A vswitch is integrated with a hardware chip and has a large bandwidth. It can forward data quickly through a certain data array algorithm. Generally, a vswitch directly connects to the host. The "port number and mac address" in the mac address table correspond one to one, and is also obtained through self-learning, automatically checks the mac address status of the port host. If the mac address of a host is not detected after the aging time, this option is deleted from the mac address table. Vswitches are currently the mainstream network products. Currently, there are L2 network switches, L3 network switches, and even higher-level network switches. They also feature more and more powerful and faster.