Hub is a machine that gathers network cables together, that is, the connector of multiple hosts and devices. The main function of the hub is to synchronously shape and amplify the received signal to expand the transmission distance of the network, so it belongs to a kind of repeater. The only difference is that the hub can provide more connection ports, while the repeater is just a connector from 1 to 1 to extend the transmission distance. Features of the center:
A. The hub belongs to the first physical layer device in the OSI model. As can be seen from the OSI model, it only plays the role of synchronization, amplification and shaping in data transmission, and cannot effectively deal with short frames and fragments in data transmission, and cannot guarantee the integrity and correctness of data transmission.
B. All ports share a bandwidth, only two ports can transmit data at the same time, and other ports can only wait, so they can only work in half-duplex mode, and the transmission efficiency is low. If it is an 8-port hub, the bandwidth obtained by each port is only 1/8 of the total bandwidth. At present, most hubs on the market are 10/ 100Mbps bandwidth adaptive.
C moreover, the hub is a broadcast working mode, which means that when one port of the hub works, all other ports can hear information, which is easy to cause a broadcast storm. In addition, the security is poor, all network cards can receive the sent data, but the non-destination network card will automatically discard the packet that was not sent to it.
Broadcast storm: When the network card or network equipment is damaged, broadcast packets will be sent continuously, which will lead to broadcast storm and paralyze network communication. 〕
Hubs are mostly used in small LAN networking, but with the overall price reduction of switches, the cost performance of hubs is obviously low, and they are on the verge of elimination. At present, the main hubs are 8 ports, 16 ports and 24 ports, but a few brands provide non-standard ports, such as 4 ports and 12 ports. The 4-port 10/ 100 Mbps adaptive hub can be used in families with 2-3 computers. Some hubs will have an uplink port dedicated to connecting other network devices (such as switches, routers, etc.). Other concepts, such as modularity and stackability, belong to high-end professional fields and are not involved in this paper.
2. Bridge
They work at Layer 2 (data link layer) of the OSI model; They are smarter than hubs; They build and maintain address tables.
Step 3: Transform
When used in the star structure, as the central node to amplify the signal, the port does not enjoy the bandwidth. If it is a 10M switch, then the bandwidth of each port is 10M, and each port has its own MAC address.
The main functions of the switch include physical addressing, network topology, error checking, frame sequence and flow control. At present, some high-end switches have some new functions, such as supporting VLAN (Virtual Local Area Network), supporting link aggregation, and some even have the functions of routing and firewall.
Switches can not only connect the same type of networks, but also interconnect different types of networks (such as Ethernet and Fast Ethernet). Nowadays, many switches can provide high-speed connection ports supporting fast Ethernet or FDDI, which can be used to connect other switches in the network or provide extra bandwidth for key servers with large bandwidth occupation.
It is a network device with some functions of a router. It can decide where to send the received data, which is faster than the router.