- Propagation delay = distance traveled / propagation speed
- Transmission delay = # of bytes to transfer / transmission speed (or bandwidth)
- Signal-to-noise ratio (dB) = 10 log10 (S/N)
- Attenuation in decibels = 10 log10 (Transmitted power/received power)
- Nyquist Theorem : Maximum data rate = 2 H log2V bits/sec where H is in Hz and V is # of levels
- Shannon’s Result : Maximum number of bits/sec = H log2 (1+S/N) where H is in Hz
- Pure ALOHA throughput T = Ge-2G Max throughput occurs at G = 0.5
T = throughput per frame time e = 2.718
G = attempts per packet time
Throughput in bits per sec = T x transmission speed
Vulnerable period = 2 x frame transmission time
- Slotted ALOHA throughput T=Ge-G Max throughput occurs at G = 1
- TCP round-trip time
RTT = α RTTOLD + M(1 – α) RTTOLD = previously observed round-trip time
α = smoothing factor
M = observed round-trip time (actual time to receive an ACK)
D = βDOLD + (1 – β) · |RTT – M| DOLD = previously observed standard deviation
β = smoothing factor (may be α)
TCP Timeout = RTT + 4D
- Ethernet / IEEE 802.3 (p. 280)
Channel efficiency = t / (t + 2G/A)
t = ave time to transmit a frame
G = end-to-end propagation time (time for frame to traverse entire Ethernet network)
2G = duration of each time slot
A = probability that some station acquires channel in a particular contention slot
= kP(1 – P)k-1
k = # of stations ready to transmit
P = probability that each station transmits during a contention slot
Channel efficiency = 1/(1 + 2BLe/cF)
B = network bandwidth c = signal propagation speed
L = cable length F = frame length
e = contention slots per frame (2.718)
Maximum throughput = channel efficiency x transmission speed
Minimum frame length = 2 x propagation delay x transmission speed (data rate)
* 802.3 minimum frame length = 64 bytes