Question

packet switch receives a packet and determines the outbound link to which the packet should be forwarded. When the packet arrives, one other packet is halfway done being transmitted on this outbound link and four other packets are waiting to be transmitted. Packets are transmitted in order of arrival. Suppose all packets are 1,500 bytes and the link rate is 2 Mbps. What is the queuing delay for the packet

Answer 1

Answer: 0.027 sec

Explanation:

Within the switch, waiting to be transmitted, we have 4 + ½ = 4.5 packets

1 packet = 1500 bytes  

4.5 packets = 6750 bytes.

So, before any arriving packet can be delivered, it will wait for these 6750 bytes to be transmitted.

Data rate = 2 Mbps  

1 byte = 8 bits

Data rate = 2.106 bits/sec = 250 KB/s

Time for a byte to be transmitted:

TB = 1/250 KB/s

Time to transmit 6750 Bytes:

T= 1/250 KB/s . 6750 Bytes = 0.027 sec = 27 msec.

In order to be transmitted, an arriving packet must wait at least 27 msec.

Queing delay = 0.027 sec. = 27 msec.