Click to see additional instructions A host is regulated by a token bucket. The

Question

Click to see additional instructions A host is regulated by a token bucket. The token bucket is continuously filled at a rate of 0.2M tokens/sec. It is initially filled to capacity with 0.5M tokens. It takes 1 token for a data packet to be released into the network. Now suppose that data comes in three 1M-packet bursts (i.e., each burst contains 1M packets). Bursts occur at the beginning of the first, second, and third second, and eaclh lasts for 500 msecs. Assume all packets are of the same size, and packets can depart at the same rate they arrive if tokens are available. A. Just before the second burst arrives, there would be packets left in the buffer B.Just before time 3 seconds, there would be packets left in the buffer C.The computer would release all the packets into the network after seconds.

Explanation / Answer

Before 1st wave:

remaining: 0.5M tokens

During 1st Second:

Data: 1M packets

tokens: 0.5M (remaining) + 0.2M (newly filled)

so remaining packets: 0.3M (Answer A)

remaining tokens: 0

During 2nd Second:

Data: 0.3(remaining) + 1M (new) packets

tokens: 0.2M (newly filled)

so remaining packets: 1.1M (Answer B)

remaining tokens: 0

During 3rd Second:

Data: 1.1(remaining) + 1M (new) packets

tokens: 0.2M (newly filled)

so remaining packets: 1.9M

remaining tokens: 0

During 4th Second:

Data: 1.9(remaining)

tokens: 0.2M (newly filled)

so remaining packets: 1.7M

remaining tokens: 0

During 5th Second:

Data: 1.7(remaining)

tokens: 0.2M (newly filled)

so remaining packets: 1.5M

remaining tokens: 0

During 6th Second:

Data: 1.5(remaining)

tokens: 0.2M (newly filled)

so remaining packets: 1.3M

remaining tokens: 0

During 7th Second:

Data: 1.3(remaining)

tokens: 0.2M (newly filled)

so remaining packets: 1.1M

remaining tokens: 0

During 8th Second:

Data: 1.1(remaining)

tokens: 0.2M (newly filled)

so remaining packets: 0.9M

remaining tokens: 0

During 9th Second:

Data: 0.9(remaining)

tokens: 0.2M (newly filled)

so remaining packets: 0.7M

remaining tokens: 0

During 11th Second:

Data: 0.7(remaining)

tokens: 0.2M (newly filled)

so remaining packets: 0.5M

remaining tokens: 0

During 12th Second:

Data: 0.5(remaining)

tokens: 0.2M (newly filled)

so remaining packets: 0.3M

remaining tokens: 0

During 13th Second:

Data: 0.3(remaining)

tokens: 0.2M (newly filled)

so remaining packets: 0.1M

remaining tokens: 0

During 14th Second:

Data: 0.1(remaining)

tokens: 0.2M (newly filled)

so remaining packets: 0

remaining tokens: 0.1M

So it would take 14 seconds to empty the bucket (Answer C)

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