by @Mohamed Safwat

• $File\ send\ time = \frac{file\ size}{Bandwidth}$

(Don’t forget to convert file size to bits)

• $Propagation\ delay = \frac {Distance} {speed\ of\ light}$

(speed of light $C$ can equal $2 \times 10^8 m/s$ OR $3\times10^8 m/s$)

• $Bandwidth = \frac {packet\ size}{propagation\ delay}$

(for propagation delay = transmission delay)

• $\frac{KH}{KH+M}$

($K$ = no. of protocol layers, $H$ = header size, $M$ = Message size, $KH$ = total no. of headers)

Stop-And-Wait ARQ —> $SWS = RWS = 1$

Go-Back-N ARQ —> $SWS = N$ , $RWS = 1$

Selective-Repeat ARQ —> $SWS = N_1$ , $RWS = N_2$ (usually $N_1 = N_2$)

• $SWS = \frac {RTT \times Bandwidth}{frame\ size}$
  • if $RWS = 1$ (Go-Back-N) $N \ge SWS + 1$ $N \approx \log_2(SWS+1)$ (to the nearest Unit)
  • if $RWS = SWS$ (Selective-Repeat) $N \ge 2\times SWS$ $N \approx \log_2(2\times SWS)$ (to the nearest Unit)

(SWS = Sender Window Size, RWS = Receiver Window Size, N = no. of sequence bits)

• $RTT = 2 \times Propagation \ Delay$
• $BDP = Bandwidth \times Delay$
• $\text{Bandwidth delay product} = Bandwidth \times Delay$
• $U = \frac{frame \ size}{BDP}$