Switched LAN connection technology


(1) From the point of view of the unit of information e […]

(1) From the point of view of the unit of information exchange, LAN switching technology can be divided into: Frame Switching and Cell Switching. The former is the basis for 10 Mbps switched Ethernet and switched Fast Ethernet; the latter is the basis for ATM switching technology.
(2) From the perspective of the internal working mechanism of the switch, common switches can be divided into cut-Through and Store-Forward switches.
1 The straight-through converter works in the same way as the circuit-switched mode of operation. When the information frame is transmitted to the switch port, the port site address mapping table is consulted upon reading the destination address of the frame header. If it matches the address of a certain site, the frame is transmitted to the corresponding port. If there is no corresponding site, it is ignored and no error detection is performed.
The advantage of the straight-through switch is that the information frame has a small transmission delay between ports and is fast.
The shortcomings of the straight-through switch are: it is possible to send bad frames to the destination; it is not possible to connect links with different transmission rates, so it is not suitable for hybrid networks; when the output ports are busy with other transmission tasks, it causes conflicts, therefore, cannot It is suitable for connecting small-scale workgroup workstations on a network with a bidirectional load.
2 Store a forwarding switch to the information frame transmitted to the port, first read the frame header address, and store the frame, and compare the port-site address mapping table after receiving the complete frame. If it matches the address of a site. The frame is all read into the switch's cache, error checked, and passed to the appropriate port. This technique reduces errors in line transmission, but adds some delay, due to the storage-forwarding of the cache, which is suitable for connecting media with different transmission rates. Support for heterogeneous network interconnection. For example, FDDI-Ethernet, in the cut-Through mode, after the cut, the network type and address are completely different, and it cannot be sent out at all. The store-and-forward mode is adopted, and translation is performed during storage, and multiple Ethernet frames are formed into FDDZ frames or FDDI is converted into Ethernet frames.