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Cheatography

Wireless Networks Cheat Sheet (DRAFT) by

Intro to wireless networks midterm review

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Physical Layer

radios, coaxial cable, optical fibers
bits "on the wire"
spread spectrum
reduces narrowband interf­erence by spreading a signal's frequency to create a wider bandwidth
DSSS
direct sequence spread spectrum
FHSS
frequency hopping spread spectrum
DSSS and FHSS require time synchr­oni­zation between sender and receiver.

Maximum (Data) Bandwidth

Shannon Channel Capacity
data rate = Wlog2(1 + S/N)
(theor­etical) maximum number of bits that can be transm­itted per second by a physical channel
data rate = bps
W = frequency range = bandwidth = Hz
S/N = signal noise ratio = no unit

Variables

Signal
sending signal
Noise
thermal noise, background radiation (aka AWGN - additive white gaussian noise)
Interf­erence
signals from other transm­itting sources
SINR or SNR
S/(N + I)

Path Loss Formulas

free space model
--
two-ray ground reflection model
--

Effects on Signal Propag­ation

path loss, shadowing, reflec­tion, refrac­tion, scatte­ring, diffra­ction, fading

Multip­lexing

space, time, frequency, code

TODO: pros/cons of each

Modulation

AM, FM, PM
amplitude modula­tion, frequency modula­tion, phase modulation

TODO:
pros/cons of each
 

Link Layer

WiFi, Ethernet
data transfer btwn neighb­oring network elements
IEEE 802.11 DCF CSMA/CA
CSMA/CA
carrier sensing medium access / collision avoidance
DCF
distri­buted coordi­nation function - approp­riate for multi-hop ad hoc networks
RTS/CTS
request to send, clear to send
hidden terminal problem
A and C want to send to B but A and C cannot see each other. both send to B and msg collides. solved by RTS/CTS

Security

 
TODO WEP insecure as heck
 

Network Layer

IP, routing protocols
routing of datagrams from src to dest
knows addresses, routes from src to dest, elems = hosts and routers
LS
link state
DV
distance vector
types of networks
MANET (mobile ad hoc network), mesh network, sensor network, DTN (delay tolerant network)

Mobile IP

TO mobile system
CN -> HA -> FA -> MN
FROM mobile node
MN -> FA -> CN
CN = corres­pondent node (aka FN = fixed node??)
HA = home agent
FA = foreign agent
MN = mobile node

DTN

ALGORITHM
WHO
WHEN
TO WHOM
flood
all nodes
new contact
all new
direct
src only
dest
dest
simple replic­ation (r)
src only
new contact
r first contacts
history (r)
all nodes
new contact
r highest ranked
erasure coding (ec-r)
src only
new contact
kr (k >= 1) first contacts (k is related to coding algorithm)
TODO: review history and erasure coding

Sensor Network

GPSR
greedy perimeter stateless routing
BVR
beacon vector routing
TODO: study implem­ent­ation and write in chart in word or something

Mesh Networks

ETX
expected transm­ission count
 
= 1/(df * dr) ... where df = fwd delivery rate, dr = rev delivery rate
ETT
estimated transm­ission time TODO: this is some combo of SETT and something right???

MANET

DSR
destin­ation source routing
AODV
ad hoc on-demand distance vector
DSDV
destin­ati­on-­seq­uenced distance vector
DSR can be used for wireless mesh networks
 

Transport Layer

TCP, UDP
host-host data transfer
UDP
user datagram protocol
TCP (wired)
transm­ission control protocol
Mobile TCP

TCP - not pipelined

Stop and wait

TCP - pipelined

GBN
go-back-N
selective repeat

Questions

Why can't we just use NACK?

Formulas

Transm­ission
T = L/R
Utiliz­ation - fraction of time sender is busy sending
U = (L/R) / (RTT + L/R)
Speed of light (to convert distance to propag­ation delay)
3E8 m/s
Don't forget to use proper units (convert)
T = transm­ission time in seconds
L = pack length in bits
R = transm­ission rate in bps
U = utiliz­ation no unit
RTT = round trip time seconds = propag­ation delay * 2