Networking Quick Reference
1 second = 1,000 milliseconds (msec)
1 second = 1,000,000 microseconds (µsec)
1 second = 1,000,000,000 nanoseconds (nsec)
1 bps = 1 bit per second
1 Kbps = 1,000 bits per second
1 Mbps = 1,000,000 bits per second
1 Hz = 1 cycle per second
1 KHz = 1,000 Hz
1 MHz = 1,000,000 HZ
Speed of light (c)
in vacuum: 3 x 108meters/sec
in copper wire: 2.3 x 108meters/sec
in optical fiber: 2 x 108meters/sec
Well-known Ports
7 – echo
20 – FTP data connection
21 – FTP connection-control
23 – telnet
25 – SMTP
53 – DNS
79 – finger
80 – HTTP daemon
110 – POP3
143 – IMAP
Well Known Ports range: 0 - 1023
Registered Ports range: 1024 - 49151
Dynamic and/or Private Ports range: 49152 - 65535
IEEE Network Standards
802.3 – Uses Length field instead of Type
Ethernet – (DIX Ethernet or Ethernet II) uses Type field instead of Length
802.5 – Token Ring
802.11 – Wireless
802.11a – Uses OFDM
802.11b – Uses HR-DSS
802.11g – Enhanced 802.11b using OFDM
802.15 – Bluetooth (physical and data link layers)
802.16 – Wireless MAN
OSI Reference Model
Application
Presentation
Session
Transport (segments,datagrams)
Network (packets)
Data link (frames)
Physical
Networking Equations
·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)
·NyquistTheorem : Maximum data rate = 2 H log2V bits/secwhere 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 ALOHAthroughputT = Ge-2GMax throughput occurs at G = 0.5
T = throughput per frame timee = 2.718
G = attempts per packet time
Throughput in bits per sec = T x transmission speed
Vulnerable period = 2 x frame transmission time
·Slotted ALOHAthroughputT=Ge-GMax 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 =avetime 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 bandwidthc = signal propagation speed
L = cable lengthF = 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
ARQ ProtocolChannel UtilizationWindow Size
Ws(Sender)WR(Receiver)
Stop-and-Wait11
Maximum channel utilization with no errors:
Go-Back-Nif Ws>2m–
11
if Ws<
Selective-Repeatif Ws>2m-12m-1
if Ws<
Maximum throughput (data rate) = channel utilization x transmission speed
f= frame size
BW= channel transmission rate (bandwidth)
RTT= round trip propagation delay
ct= bandwidth-delay product
a= round trip propagation delay / transmission delay=BWxRTT/ 2f= number of frames to fill the channel one way
P= probability of transmission error
m= # of bits in sequence #
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