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 108 meters/sec

in copper wire: 2.3 x 108 meters/sec

in optical fiber: 2 x 108 meters/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)

 

·         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)
                                2
G = 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

 


ARQ Protocol                      Channel Utilization                                                                             Window Size

Ws (Sender)          WR (Receiver)

 

Stop-and-Wait                                                                                                              1                               1

 

                                                Maximum channel utilization with no errors:

                                                     

              

Go-Back-N                                                                  if Ws >                      2m – 1                       1

                                                                                                                                                                 

                                                         if Ws <

 

Selective-Repeat                                                            if Ws >                      2m-1                                        2m-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  =  BW x RTT / 2f = number of frames to fill the channel one way

P = probability of transmission error

m = # of bits in sequence #