line efficiency

Question

solve in detail...........

Answer 1

Line efficiency = throughput / bandwidth ----- (1)

Throughput = window size / rtt ------(2)

So throughput = 65535/40 * 10^3 = 1638375

And bandwidth = 512 Mbps

 

Therofore Line efficiency(in %) = 2.56

Comments

Thanx

Answer 2

Maximum window size= $RTT*BW=512*10^6*40*10^{-3}$bits=$20480*10^3$ bits

As mentioned in question, We are sending $65,535$ Bytes whereas we could have sent above mentioned number of bytes

$\therefore$ Line efficiency=$\frac{65,535*8}{20480*10^3}*100\%=2.559\%$

Comments

Why did you not add TT in denominator? New window will be transmitted only after ACK which will be received only after 2* propagation Time + TT of packet + TT of ack(can be neglected if not given).

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Arjun Sir, I am finding the line efficiency in terms of bits sent in 1RTT vs Total number of bits that could have sent in the same time. In TCP, since after sending a packet, we wait for 1 RTT before sending the next packet so to use the link efficiently we should use that entire bandwidth to send as many bits as possible which is the bandwidth delay product, but a/q we are sending only 65,535 bits. So the answer. Sir, am I thinking in a wrong direction??

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Throughput:- as available BW is 512..but how much our channel is used...

BW used by the channel;-  it send 65535bytes of data wihin 1 RTT...means acheved  BW is

65535*8/40=13107bpms..this is called throughput...

Line efficiency = throughput / bandwidth

         13107bpms/512*10⁶bps  ....2.55%

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@Sukannya then why did you not include TT in RTT? Without a packet is transmitted ACK cannot arrive - so for ACK to reach back, TT time must also be passed.

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Sir, here first thing is total window size is given, so how can we find packet size in order to find transmission time from it? And as one way delay is given, I read somewhere that Tt is already included in it...!

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Yes, I missed that. But if a packet size is given you must add it.

Answer 3

line efficiency=  Tt/(Tt+2Tp)

                     =1.023/(1.023+2*20) =0.0255= 2.55%