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 = Wlog 2
(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/(d f
* d r
) ... where d f
= fwd delivery rate, d r
= 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 - 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
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