Question

this is not Home work!
I preparing my self to test in Networking :
i had this questen in the midterm test and i got half the points i cant figure it out

in this question i got reciver-sender connection.

link data rate is R(b/s)

Packet size is S(b)

Window Size is W(pkts)

Link distance is D(m)

medium propagation speed is p(m/s)

i need to write the utilisation Formula using those Letters

this is what i wrote:

Tp-Propagation time is D/p ===>this got me a big X on test page

i wrote that frame transmition (Tt) time is window size in bits (W*S)
divided by link Data Rate i.e (W*S)/R

thats why the formula is U=Tt/(Tt+2*tp)==>((W*S)/R)/(((W*S)/R)+2*(D/p))
(again X)

i guess somthing is wrong with the Propagation time calculation .
all the slides refaring to sliding window do not mention the utilisation
in referande to distance and propagation delay

i would love some help with this.
thank you .

Answer 1

It depends on how propagation time is supposed to be measured¹, but the general formula is:

Propagation time = (Frame Serialization Time) + (Link Media Delay)

• Link Media Delay = D/p
• Frame Serialization Time = S/R

I don’t see the relevance of TCP’s sliding window in this question yet; sometimes professors include extra data to discern how well you understand the principles.

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END-NOTES:

1. Does the professor measure propagation time at the bit-level or at the frame-level? My answer assumes it is a frame-level calculation (measured from first bit transmitted until the last bit in the frame is received), so I include frame serialization time.