Frage zu "Store-and-Forward"!!!

Zitat von DaClockerPhreak

@ das cAws,

ne echt! toll das ichs jetzt weiss!!!

es ist der unterschied zu nem hub.

HUB: DUMM / kein SF
SWITCH: SCHLAU / wegen SF

Phreak

Zitat

Hubs

The term ‘hub’ is sometimes used to refer to any piece of network equipment that connects PCs together, but it actually refers to a multi-port repeater. This type of device simply passes on (repeats) all the information it receives, so that all devices connected to its ports receive that information.

Hubs repeat everything they receive and can be used to extend the network. However, this can result in a lot of unnecessary traffic being sent to all devices on the network. Hubs pass on traffic to the network regardless of the intended destination; the PCs to which the packets are sent use the address information in each packet to work out which packets are meant for them. In a small network repeating is not a problem but for a larger, more heavily used network, another piece of networking equipment (such as a switch) may be required to help reduce the amount of unnecessary traffic being generated.


Switches

Switches control the flow of network traffic based on the address information in each packet. A switch learns which devices are connected to its ports (by monitoring the packets it receives), and then forwards on packets to the appropriate port only. This allows simultaneous communication across the switch, improving bandwidth.

This switching operation reduces the amount of unnecessary traffic that would have occurred if the same information had been sent from every port (as with a hub).

Switches and hubs are often used in the same network; the hubs extend the network by providing more ports, and the switches divide the network into smaller, less congested sections.

Zitat

There are three sorts of layer 2 switches:

* Cut-through switches. These switches only examine the address in the MAC header. The switch consults its MAC address look-up table to decide which port to forward the frame to. It then creates a virtual link (point-to-point connection) and forwards the frame. Cut-through switches do not examine the frame's check sequence (cyclic redundancy check) to ascertain if it is corrupt, therefore they can forward corrupted data. The destination will then request a retransmission. This, and the resultant retransmission will increase network traffic.

* Store and forward switches. A store and forward switch reads the whole incoming frame into a buffer and calculates its own frame check sequence. The switch then compares its CRC figure to the frame's CRC. If the two CRCs are the same, the switch will consult its address look-up table, create the virtual link and then forward the frame. Store and forward is slower than cut-through, but it won't forward corrupted frames.

* Error-free cut-through switches. These switches read the MAC address and the CRC for each frame. If the CRC is correct, the switch configures its port for cut-through (fast) switching. If the CRC is incorrect, the switch configures its port for store and forward (error-checked) switching. As the amount of corrupted frames diminishes to a pre-set threshold, the switch will reconfigure the store and forward port back to cut-through.

Zitat von DaClockerPhreak

sorry auch @cAws.