Suppose a client is connecting with the server through TCP$.$ In the last packet of the three$-$way handshake, the client adds a message to ask server send a file with L bytes. There are some

assumptions:

$$ The transmission speed between client and server is R bytes per second. The round trip time

between them is a fixed value, RTT$.$

$$ The payload of a TCP packet is M bytes, and the TCP window size is M $($e$.$g$.$ n packets per TCP window$).$

$$ There is no packet loss on the link and all ACKs arrive at the client before the timeout.

$$ You can ignore the header construction, header length and other header related time overhead. Let's denote T is the time duration from the client sends the TCP connection request to the client successfully receives the file. Then, we have,

T$=2$RTT$+$L$/$R$,$ when nM $>$ R$*$RTT$+$M

T $=\{2$RTT $+$ L$/$R$+($K $-1)($M$/$R$+$ RTT $$ nM$/$R$\},$when nM $<$ Rx RTT $+$ M

Where K $=[$L$/$nM$],$ round down of L$/$nM

$1.$ What does $2$RTT mean in the equation?

$2.$ What does the condition, nM $>$ Rx RTT $+$ M$,$ mean?

$3.$ Please proof the equation when nM $>$ Rx RTT $+$ M$.$ Hint: you can draw a figure.