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+2 votes
in Computer Networks by (user.guest)

Suppose two packets arrive to two different input ports of a router at exactly the same time. Also suppose there are no other packets anywhere in the router.

a. Suppose the two packets are to be forwarded to two different output ports. Is it possible to forward the two packets through the switch fabric at the same time when the fabric uses a shared bus?

b. Suppose the two packets are to be forwarded to two different output ports. Is it possible to forward the two packets through the switch fabric at the same time when the fabric uses switching via memory?

c. Suppose the two packets are to be forwarded to the same output port. Is it possible to forward the two packets through the switch fabric at the same time when the fabric uses a crossbar?

1 Answer

+1 vote
by (user.guest)
 
Best answer

a.

Fabric uses a shared bus:

In shared bus topology to avoid the data collision and to maintain the traffic, only one user can become the master of the bus at a time, simultaneous transfer of data is not possible in shared bus topology.

b.

Fabric uses switching via memory:

Two packets cannot be forwarded at the same time even though there are two different output ports. Because, the memory can perform read or write operation at a time through the shared bus.

Therefore, the two packets forwarded to the two different output ports at a time is not possible in switching via memory.

Therefore, it is not possible for the switch fabric to forward two packets to two different output ports at a time using shared bus topology.

c.

Fabric uses crossbar:

Crossbar can forward two packets to two different output ports at the same time but it cannot forward to the same output port. Any one of the packet should wait to reach the same output port.

Therefore, the two packets forwarded to the same output port is not possible when a fabric uses crossbar.


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