Selective repeat

Question

A computer uses the following sequence numbers:0,1,2,3,4,5,6,7,0,1,2,3,...

What will be sender's and receiver's window size that are not possible in SR protocol?

a )4,4 b)5,3 c)7,1 d)5,4

Answer 1

D. 5,4

Since in SR, Ws+Wr = Sequence number
Here sequence number is 0 to 7 = 8 and 5+4=9 thus 5,4 is wrong.

C. option is also wrong,
Wr, Ws both should not be 1 in SR, as Ws=7 here, it will become Go Back N.

Comments

why can't it go to Go-Back-N? There is no such restriction. 

https://gateoverflow.in/3725/gate2004-it_81

---

Sir, in Selective Repeat , is it necessary to have Ws = Wr ?

---

If Wr=1 SR will not accept out of order. And SR should accept out of order packets.