Ethernet Switch Technology Is Introduced - LevelOne GEU-2429 Manual

6 Ethernet switch technology is introduced

Today, is suitable for a variety of sophisticated applications (such as multimedia video conference
CAD/CAM) computer technology development is very rapid, in order to apply these techniques more
effectively to, to take on more traffic high-speed network put forward higher request.
Because realize on bandwidth and low latency communications more urgently need a lot of
technology, fast Ethernet technology to upgrade the existing 10 MBPS Ethernet is the most economic
and puts forward the feasible solution. However, fast Ethernet media side question method is still limited
to a large number of sites share access to a common transmission medium, the CSMA/CD, when a site
occupied transmission media, other sites can only wait for, its structure is still not meet a surge in traffic.
Switched Ethernet was born, on high greatly the performance of the local area network (LAN). And now
based on LAN topology structure of Bridges and routers Shared media, compared to a network switch
can significantly increase the bandwidth. Switching technology to join, can build the city location relatively
decentralized network, make the LAN switch each port can be parallel, safe, and transmit information to
each other, and make the LAN can be highly extended.
Now switching technology is a kind of improved local Bridges, compared with the traditional bridge, it
can provide more ports, better performance and stronger management functions and cheaper prices.
The principle of Ethernet switch is very simple, it detects the source and destination of data packets from
the Ethernet port to MAC (medium access layer) address, and then compared with the system internal
dynamic address table, if the MAC address of the packet is not in the address table, then add the
address to address table, and then sends the packet to the corresponding destination port: when the
destination address is not in the address table, switches will send data in the form of radio.
Ethernet switches and telephone exchange are similar, a store-and-forward (Store and Forward),
direct way (cut through). Direct way to understand for the port crisscrossed circuit matrix between the
telephone switchboard. It detected in I/o port a packet, check the package in baotou, input or output
junction connected, the packet directly to the corresponding port, realize the exchange function. Because
do not need to be stored, delay is very small, exchange, very fast, this is its advantage. Its defect is:
because the content of the packet has not been switches preserved, so can't check for error rate
transmission of packets, is unable to provide error detection ability, with no cache, not to direct I/o/output
connected with different rate, moreover, when the switch port increases, the switching matrix becomes
more and more complex, is very difficult to implement.
Store-and-forward mode is applied most widely in local area network mode, it's on the I/o port of
packet storage first, and then carries on the CRC check and the error packet processing after take out
the packet destination address, and through the address lookup table is converted into the corresponding
output port sends data packets. Because of this, store-and-forward mode in the data processing time
delay is big, but it can be to enter the exchange error code inspections of packets, especially important to
support the transformation between the different speed of input and output ports.
10/100/1000 m switched Ethernet still USES the star topology structure, it USES four pairs of
twisted-pair cable. A 5 UTP or STP can meet the requirements. As a result of the online data transmission
rate increased to 1000 MBPS, the signal frequency, attenuation, interference of more demanding, but
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