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Switching Type

 

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Q5. Choose the switching type that has the lowest latency?

A. Fragment-Free

B. Store-and-Forward

C. Cut-through

D. Connect-On

  Correct Answer: C

 

Explanation:

Store-and-Forward switching: Here the LAN switch copies the entire frame into its buffers and computes the CRC. The frame is discarded if there are any CRC errors. Giant ( more than 1518 bytes0 and Runt (less than 64 bytes) frames are also dropped, if found

In cut-through switching, the switch copies into its memory only the destination MAC address (first 6 bytes of the frame) of the frame before making a switching decision. A switch operating in cut-through switching mode reduces delay because the switch starts to forward the Ethernet frame as soon as it reads the destination MAC address and determines the outgoing switch port. Problem related with cut-through switching is that the switch may forward bad frames. 

Fragment-free (runtless switching) switching is an advanced form of cut-through switching. The switches operating in cut-through switching read only up to the destination MAC address field in the Ethernet frame before making a switching decision. The switches operating in fragment-free switching read at least 64 bytes of the Ethernet frame before switching it to avoid forwarding Ethernet runt frames (Ethernet frames smaller than 64 bytes). 

Connect-On is not a Cisco recognized switching method.

Ref.:
http://www.omnisecu.com/cisco-certified-network-associate-ccna/methods-of-switching.php

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