delays and throughput
control signals assumed to take no transmission delay penalty, since it's comparable to a single bit
3rd type of delay
	processing (Tproc) - delay introduced by intermediary network devices, usually given or assumed to be 0
4th type of delay
	queueing (Tq) - delay within router other than processing while data is waiting to go out on a link
if a message has to be retransmitted, total delay is (#retrans+1)*(2Tprop + Ttrans)
effective throughput = bits/Ttotal

talking about layered architecture
tcp/ip protocol suite/stack
application/transport/netowrk/link/physical