Project ForgeFrames of 1000 bits are sent over a 10⁶ bps duplex link between two hosts. The propagation time is 25ms. Frames are to be transmitted into this link to maximally pack them in transit (within the link). What is the minimum number of bits (l) required to represent the sequence numbers distinctly? Assume that no time gap needs to be given between transmission of two frames.
- Al=2
- Bl=3
- Cl=4
- l=5
Explanation
Transmission time per frame = 1000 bits / 10⁶ bps = 1ms. With back-to-back transmission, the number of frames simultaneously 'in flight' within the link equals propagation time / transmission time = 25ms/1ms = 25 frames. To give 25 simultaneously-outstanding frames distinct sequence numbers requires 2^l ≥ 25, so l=5 (2⁵=32≥25, while 2⁴=16<25).
Source: GATE CS 2009 (2009)
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