+1 vote
586 views
If the Sender Window size is 128 using selective repeat ARQ. Then the sequence number of frame to be send after sending 400 th frame is ?
0

In case of GBN

in GBN there is n bits sequence number

then senders window size = 2 n - 1

and receiver windows size  = 1

total sequence number = 2n - 1 + 1   = 2(0 to 2 n- 1 sequences we use)

0
Here in this case available sequence number = 128 + 128 = 256 that's why (0 to 255)

for goback n Available sequence number = 128 + 1 = 129 so (0 to 128)

because sender WS = 2^k - 1 and receiver is 1.

Am i correct ?
0

Na462  yes you are right

+1
in slective repeat : #sequence number = sender ws + receiver ws

= 128 +128 (since sws=rws)

total size of sequence number = 256(0-255)

therefore for 4oo frame , we have 400mod 256 =144 answer
+1

arvin  why not  be 143 ?? as seq no start from "0"

0

sequence number of the frame to be send after sending 400thframes

check the question once.. @magma

0
got it :p
0
@magma please can you solve it for GBN and tell the answer. using same data!
+1
yeah sure ,

In GBN

No of sequence number = Sender's window size + 1 (receiver window size)

= 128 +1

= 129  [sequences  0 to 128]

No of sequence number consumed after sending the 400 frames  = 400 % 129 = 13

it means  0 to 12 sequences  we used already

after this we send a frame with sequence no : 13

understood ??
0
Yes magma! Perfect, thank you! :)

For selective repeat ARQ, we know that sender window size=receiver window size

and total no number of sequence numbers=2N (where N is the sender window size)

Hence 0-255 would be consumed for sending 256 frames.Next 0-143 would be consumed for sending 144 frames hence total number of frames sent=256+144=400.Hence the sequence number for next frame should be 144.

the sequence no of 400th frame will be 143

sequence number of frame to be send after sending 400 th frame is ?