Repeater, hub, bridge, switch, router comparison

A repeater or hub cannot isolate a conflict domain and cannot isolate a broadcast domain, a bridge or a switch can only isolate a conflict domain from the broadcast domain, and the router can isolate the conflict domain and isolate the broadcast domain.
Resolution

The first thing to know is the conflict domain and broadcast domain, when a piece of network card send information, it is possible to conflict with another NIC network adapter is called the conflict domain. A network card sends out a broadcast, the collection of all the network cards that can receive this broadcast is called a broadcast domain. In general, a network segment is a conflict domain, a local area network is a broadcast domain; First of all, let us first introduce a repeater, hub, bridge, switch, router is used to do, on this basis to discuss the conflict domain and broadcast domain will understand the deeper.

Repeater: In our contact with the network, the simplest is two computers through two network cards constitute a "dual-machine interconnection", the two NICs are generally made of unshielded twisted pair to act as a signal line. Because the signal power will gradually decay when the twisted-pair transmission signal, when the signal attenuation to a certain extent will cause signal distortion, so in order to ensure the quality of the signal, the maximum transmission distance of the twisted pair is 100 meters. When the distance between the two computers is more than 100 meters, in order to realize the dual-machine interconnection, people will install a "repeater" between the two computers, it is the function of the signal has been attenuated incomplete to collate, re-produce a complete signal and continue to transmit. When it comes to this, the amplifier, amplifiers and repeaters are all amplifying signals, except that the amplifier amplifies the analog signal, and the repeater amplifies the digital signal.

Hub: Repeater is the predecessor of the ordinary hub, the hub is actually a multi-port repeater. Hubs generally have 4, 8, 16, 24, 32 and so on the number of RJ45 interface, through these interfaces, the hub can be the corresponding number of computers to complete the "relay" function. Because it is in a "central" position on the network, the hub is also called "Hub." The hub works very simply, assuming that there is a 8-interface hub with a total of 8 computers connected to each other. The hub is in the "center" of the network, and the signal is forwarded through a hub, which can be interconnected between 8 computers. The specific communication process is this: if Computer 1 to send a message to computer 8, when the Computer 1 network card to send information through a twisted pair to the hub, the hub does not directly send information to computer 8, it will "broadcast"-the information is sent to 8 ports at the same time, When the computer on the 8 ports receives this broadcast message, the information is checked and if the information is found to be sent to itself, it is received or ignored. Because this information is computer 1 to the computer 8, so the final computer 8 will receive this information, and the other 7 computers after reading the information, the information is not their own without receiving this information, we use a real life example to Lenovo, if you are on a business trip, there is a strange call, then you found that the wrong call, It's going to cost a lot of roaming, aren't you angry? Of course very angry (conflict), so the hub all ports belong to a conflict domain, so the hub cannot split the conflict domain. Hubs can only transmit a set of information in a clock cycle, if a hub connected to a large number of machines, and many machines often need to communicate at the same time, will lead to poor efficiency of the hub, such as the occurrence of information jams, collisions and so on. Why is this so? For example, a hub connects 8 computers, and when computer 1 is sending information to computer 8 o'clock through a hub, if Computer 2 also wants to send information to computer 7 through a hub, when it tries to contact the hub, but discovers that the hub is busy with computer 1, then Computer 2 will "With" The data station waiting in front of the hub, and always ask the hub to stop the computer 1 of the work to help themselves. If Computer 2 succeeds in "grabbing" the hub (because the hub is "shared", so it is easy to grab the hand), at this time is in the transmission state of the computer 1 of the data will be stopped, so computer 1 will go to "Rob" The hub, it is visible, the real speed of each port on the hub in addition to the bandwidth of the hub, It is also related to the number of devices working at the same time. For example, a hub with a bandwidth of 10Mb is connected to 8 computers, and when these 8 computers are working at the same time, the true bandwidth per computer is 10/8=1.25MB.

Bridge: See the switch below because the switch is a multi-interface bridge.

Switch: The switch is also called a switching hub, which is automatically addressable and exchanged by re-generating the information and forwarding it internally to the specified port, since the switch sends each packet from the source port to the destination port independently, depending on the destination address of the packet being delivered, avoiding collisions with other ports. Simply put, the host of a port connected to the switch wants to communicate with the host connecting to another port, the switch will send that port through forwarding, it is impossible to go to another port, there is no wrong port (that is, wrong number), so each port of the switch is a conflict domain, that is, the switch can isolate the conflict domain. How the switch works: In a computer network system, the switch is aimed at the weakness of the shared working mode. The hub is a representative of the shared work mode, if the hub is likened to a postman, then the postman is a "fool" who does not know the word, if he wants to send a letter, he does not know directly according to the address of the letter to the addressee, will only carry the letter to all the people, The receiver is then given the address information to determine whether it is their own, and the switch is a "smart" postman-the switch has a high-bandwidth back bus and internal switching matrix. All the ports on the switch are hooked up on the back bus, and when the control circuit receives the packet, the processing port looks up the in-memory address table to determine which port the destination MAC address should be emitted from, and quickly transmits the packet to the destination port via the internal switch fabric. If the destination MAC address does not exist, the switch broadcasts to all ports, and the receive port responds after the switch "learns" the new address (refer to the Textbook 95 page, which is easy to read, not explained), and adds it to the internal address table. As can be seen, the switch received a network card sent over the "letter", according to the above address information, as well as their own "resident residence booklet" Quickly send the letter to the recipient's hands. In case the addressee's address is not on the "hukou", the switch will distribute the letter to all people like a hub and then find the recipient. When the recipient is found, the switch will immediately register the person's information to the "hukou", so that in the future for the customer service, you can quickly sent the letter.

Because the switch intelligently sends data to the destination based on the address information, it does not "disturb" those non-senders as the hub transmits the data. This allows the switch to transfer data between multiple port groups at the same time. And each port can be considered as a separate network segment, the mutual communication between the two sides to enjoy the full bandwidth, no need to compete with other devices. For example, when a host sends data to a D host, the B host can send data to the C host at the same time, and the two transports all enjoy the full bandwidth of the network-assuming they are using a 10M switch at this time, the total flow of the switch at this time is equal to 2X10MB=20MB (at this point the switch has 4 interfaces, i.e. 2 pairs of interfaces, refer to the fifth line of the textbook, page 97).

Router: The simple is that the router sends data from one network to another network, as for the specific process see chapter Fourth Network layer.

We've already told you that a repeater or hub cannot isolate a conflict domain, the switch can isolate the conflict domain, and natural routing can certainly isolate the conflict domain (because there is also a forwarding post); First said that the broadcast can actually be seen as a separate network, if a host to send a broadcast data, so it should be heard throughout the network, but the hub and switch work in the physical layer and the data link layer, can not connect two different networks, So whether a hub or a switch encounters broadcast data is sent to each port one at a time (because each port connected to the network is still the same network), so there is a wrong phone call situation, so the hub and switch can not isolate the broadcast domain, but the router can connect to different networks, and routers are not forwarding broadcast messages by default (because each port is connected to a different network), so each port of the router is a broadcast domain, so the router can isolate the broadcast domain.

Supplemental Knowledge Points: Although switches are also called multiport bridges, there are differences between switches and bridges, listed below:
(1) The Port of the bridge is generally connected to the local area network, and the port of the switch is directly connected to the host.
(2) The switch allows multiple simultaneous communication to the computer, and the bridge allows the computers on each network segment to communicate at the same time.
(3) The bridge uses the storage and forwarding form for forwarding, and the Ethernet switch can also be forwarded through the way, and the Ethernet switch uses a dedicated switching mechanism chip, faster than the network bridge forwarding speed.

Repeater, Hub (hub), bridge, switch, router comparison