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Authors:
James F. Kurose, Keith W. Ross
Chapter:
The Network Layer
Exercise:
Problems
Question:2 | ISBN:9780132856201 | Edition: 6

Question

Consider a virtual-circuit network. Suppose the VC number is an 8-bit field.

a. What is the maximum number of virtual circuits that can be carried over a link?

b. Suppose a central node determines paths and VC numbers at connection setup. Suppose the same VC number is used on each link along the VC’s

path. Describe how the central node might determine the VC number at con- nection setup. Is it possible that there are fewer VCs in progress than the maximum as determined in part (a) yet there is no common free VC number? c. Suppose that different VC numbers are permitted in each link along a VC’s path. During connection setup, after an end-to-end path is determined, describe how the links can choose their VC numbers and configure their for- warding tables in a decentralized manner, without reliance on a central node.

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Answer

a)

Suppose the VC number bit field(n)=8.

 The maximum number of virtual circuits that can be carried over a link is  2n=28=256

b)

  • Suppose a central node determines paths and VC numbers at connection setup.
  • Suppose the same VC number is used on each link along the VC’s path. So, as there are 256 VCs, it is not possible that there are fewer VCs in progress than the maximum length.

c)

During connection setup, each link contains the VC number from 0 to 255. It does not contains same number link for path. Replace VC path instead of packet link.

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