Computer networks

Question

Selective repeat protocol requires more sequence numbers than Go-back-N protocol.

True or false?

Comments

ohkk i got ur point....
see m nt talking about window size...if GBN has N window size for sender....and 1 for reciever...in SR we have same for both

dont calculate seq no through any formula....just see ho many could be required if we wan no duplication and efficiency

in GBN..we can send full N but reciever will take only 1 at a time...and if it gets lost u need to resend again whole window back

thats why we need N+1 seq no for GBN.....like u can give 0,1,2,3 to sender but give one differenct say 4 to reciever...so that it could be known what has lost

i think u got it now

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thing is suppose u use formula say for stop and wait..u found window size using (1+2a)...now taken log to find seq no..fine it will work
but say they already restricted the seq no field as 2...so u wont be able to generate all the sequence nos in that window...

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yup thanks...

Answer 1

for all sliding window protocols sequence no should be greater than or equal to the sum of sender and reciever window size...because

in GBN......we have (N+1) sequence no..because here sender can send with a buffer of N but reciever's buffer is 1 only..means to detect duplicate packets we need to give sender N seq no and 1 more (different) to reciever
and

in SR we have (Ws +Wr) or u can say (N+N)...means here we require more buffer...more buffer means more sequence nos simply...or u can say we need to give N sequence no to sender and N to reciever...

conclusion:-

in GBN...we need (N+1) seq no

in SR...we need 2N seq no....so yes in SR we need more seq no...simply because here reciever window size is not 1 like that of GBN....

Comments

Cool! Thanks. Got it.

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ok :)

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@sudsho.In you answer you gave an example where you are maintaining windows size N.But question does not say that we need to maintain same window size.I think this is false.The statement should be true if it says the condition is that window size in both protocols should be same.