Lab/Tutorial :
SEHH2238 : Computer Networking
Session 4 : Data Link Control (Solution)
1) ARQ Control Scheme
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Fill in the name of frame being transmitted
(a) Error Free
(i) ___ACK(N+1)___
(ii) ___I(N+1)____
(iii) ___ACK(N+2)___ (ii)
Primary I(N)
Secondary (b) Loss ACK
(i) _ACK(N+1)_ Primary I(N)
2) Stop-and-Wait ARQ
(ii) ___I(N)____
(iii) __ACK(N+1)__ (ii)
(iv) ___I(N+1)___ (iv)
A system uses the Stop-and Wait ARQ Protocol. If each frame carries 1000 bits of data, how long does it take to send 1 million bits of data if the distance between the sender and receiver is 5000 km and the propagation speed is 2 x 108 ms-1? Assume the channel data rate is 1 Mbps and ignore processing delays and ACK transmission time. Further assume that no data or control frame is lost or damaged. Also ignore the overhead due to the header and trailer.
……… Repeat 1000 times
SEHH2238 Computer Networking
Tutorial 4
For a round trip:
Transmission delay (Tx) for I-frame = 1000 bit / 1Mbps = 0.001s Propagation delay (Tp) for I-frame = 5000 km / (2 x 108 ms-1)= 0.025s Transmission delay (Tx) for ACK = 0s 8
Propagation delay (Tp) for ACK = 5000 km / (2 x 10 ms
Round trip delay = 0.001 + 0.025 + 0 + 0.025 = 0.051s
No. of round trip = 1 Mb / 1000 bits = 1000 Total delay = 0.051 x 1000 = 51s
Continue from the previous question. Further assume that there is a data frame lost in every 10 data frames sent. Sender retransmits the lost frame after a timeout of 100 ms. How long does it take to send 1 million bits of data?
) = 0.025s
Time for transmitting 1 Mb without lost = 51s
Time for each timeout event = Tx + Tout = 0.001 + 0.1 = 0.101s
No. of frame lost = 1000 / 10 = 100
Lost also happens in retransmitted frames = 100 / 10 = 10, and 10 / 10 = 1
Total delay = 51 + 0.101 x (100 + 10 + 1) = 62.211s 3) Bit Stuffing
1. Bit stuff the following data 000111111100111110100011111111111000011111
What should be the content of the data frame to be sent? (Ignoring the header and trailer)
00011111011001111100100011111011111010000111110
SEHH2238 Computer Networking Tutorial 4 Page 2
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