COMPUTER NETWORK SUM || Andrew Tanenbaum || Data link layer sum



An upper-layer packet is split into 10 frames, each of which has an 80 percent chance of arriving undamaged. If no error control is done by the data link protocol, how many times must the message be sent on average to get the entire thing through?

Sol:-

Since each frame has a chance of 0.8 of getting through, the chance of the whole message getting through is 0.8^10, which is about 0.107. Call this value p. The expected number of transmissions for an entire message is then

E= 1 / p

E= 1 / 0.107

E= 9.3


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