Gateforum Correspondence Course ( Page# 85 Q# 15 )

Question

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

What will be the 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 given is D, but I don't understand why B and C is possible. Please explain.

Answer 1

In SR protocol ,

Ws + Wr <= ASN  

5+4  <= 8  is false hence D is not possible

Comments

Point to be noted!!

Answer 2

That is not necessarily that receiver window always same as sender window...

We just need to make receiver window must be less than sender window...

This is needed because buffer at receiver side,that means duplicate sequence num should not appear in the receiver space..

D is given because total sequence num is 8 but here we get 5+4 = 9

Comments

@payal,gabbar ,tauhin,manoj  do u have any reference for sr protocol saying reciver window<=sender wndow

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@Gabbar,

"That is not necessarily that receiver window always same as sender window..."

Can you provide any reference to support this..?