Wireless And Mobile Networks Concepts And Defintion

Front 1

Wireless Hosts

Back 1

- laptop, PDA, IP phone
- run applications
- may be stationary
- (non-mobile) or mobile
- wireless does not always mean mobility

Front 2

Wireless Links/Wireless Communication Link

Back 2

- typically used to connect mobile(s) to base station
- also used as backbone link
- multiple access protocol coordinates link access
- various data rates, transmission distance

Front 3

Infrastructure Mode

Back 3

- base station connects mobiles into wired network
- handoff: mobile changes base station providing connection into wired network

Front 4

ad hoc networks

Back 4

- no base stations
- nodes can only transmit to other nodes within link coverage
- nodes organize themselves into a network: route among themselves

Front 5

handoff

Back 5

mobile changes base station providing connection into wired network

Front 6

Network Infrastructure

Back 6

larger network with which a wireless host may wish to communicate.

Front 7

Elements of a wireless network

Back 7

-Wireless hosts
-Wireless Links
-Base Station(key part)
-Network Infrastructure

Front 8

Base Station

Back 8

- typically connected to wired network
- relay - responsible for sending packets between wired network and wireless host(s) in its “area”
- e.g., cell towers, 802.11 access points

Front 9

Types of Wireless Networks

Back 9

-Single-Hop, Infrastructure-based
-Single-Hop, Infrastructure-less
-Multi-Hop, infrastructure-based
-Multi-Hop, , Infrastructure-less

Front 10

Single-hop, infrastructure-based

Back 10

host connects to base station (WiFi, WiMAX, cellular) which connects to larger Internet

Front 11

Issues of Wireless Link

Back 11

- decreased signal strength: radio signal attenuates as it propagates through matter (path loss)
- interference from other sources: standardized wireless network frequencies (e.g., 2.4 GHz) shared by other devices (e.g., phone); devices
(motors) interfere as well
- multipath propagation: radio signal reflects off objects ground, arriving ad destination at slightly different times

Front 12

wireless types and characteristics

Back 12

Indoor (range of 10-30m)
802.11n - 200Mbps, 802.11a,g - 54 Mbps, 802.11b - 5 to 11Mpbs, 802.15 - 1Mbps

Outdoor

Front 13

single hop- no infrastructure

Back 13

no base station, no connection to larger Internet (Bluetooth, ad hoc nets)

Front 14

multiple hops-Infrastructure

Back 14

host may have to relay through several wireless nodes to connect to larger Internet: mesh net

Front 15

multiple hops-no infrastructure

Back 15

no base station, no connection to larger
Internet. May have to relay to reach other a given wireless node MANET, VANET

Front 16

Wireless Link Characteristics

Back 16

- SNR: signal-to-noise ratio - larger SNR – easier to extract signal from noise (a “good thing”)
- SNR versus BER tradeoffs - given physical layer: - increase power -> increase - SNR->decrease BER
- given SNR: choose physical layer that meets BER requirement, giving
highest thruput - SNR may change with mobility: - dynamically adapt physical layer (modulation technique, rate)

Front 17

Wireless network characteristics

Back 17

Multiple wireless senders and receivers create additional problems (beyond multiple access): Hidden terminal problem, Signal Attenuation

Front 18

Code Division Multiple Access (CDMA)

Back 18

- used in several wireless broadcast channels (cellular, satellite, etc) standards
- unique “code” assigned to each user; i.e., code set partitioning
- all users share same frequency, but each user has own “chipping” sequence (i.e., code) to encode data
- encoded signal = (original data) X (chipping sequence)
- decoding: inner-product of encoded signal and chipping sequence
- allows multiple users to “coexist” and transmit simultaneously with minimal interference (if codes are “orthogonal”)

Front 19

What are 4 types of IEEE 802.11 Wireless LAN?

Back 19

- 802.11a, 802.11b, 802.11g, 802.11n
- all use CSMA/CA for multiple access
- all have base-station and ad-hoc network versions

Front 20

802.11b

Back 20

- 802.11b: 2.4GHz-2.485GHz spectrum divided into 11 channels at different frequencies
Host must associate with an AP
- up to 54 Mbps
- up to 11 Mbps

Front 21

802.11a

Back 21

- 5-6 GHz range
- up to 54 Mbps

Front 22

802.11g

Back 22

- 2.4-5 GHz range
- up to 54 Mbps

Front 23

802.11n: multiple antennae

Back 23

- 2.4-5 GHz range
- up to 200 Mbps

Front 24

802.11 LAN architecture

Back 24

- wireless host communicates with base station - base station = access point (AP)
- Basic Service Set (BSS)(aka “cell”) in infrastructure mode contains: wireless hosts; access point (AP): base station; ad hoc mode: hosts only

Front 25

passive scanning

Back 25

(1)beacon frames sent from APs
(2)association Request frame sent:
H1 to selected AP
(3)association Response frame sent:
H1 to selected AP

Front 26

active scanning

Back 26

(1)Probe Request frame broadcast from H1
(2)Probes response frame sent from APs
(3)Association Request frame sent: H1 to selected AP
(4)Association Response frame sent: H1 to selected AP

Front 27

IEEE 802.11: multiple access

Back 27

- avoid collisions
- 802.11: CSMA -sense before transmitting
- 802.11: nocollision detection!

Front 28

ATM - Asynchronous Transfer Mode

Back 28

High-speed networking standard designed to support both voice and data communications.

Front 29

ARP - Address Resolution Protocol

Back 29

converts an Internet Protocol (IP) address to its corresponding physical network address.

Front 30

ASP - Application Service Provider

Back 30

Application Service Provider (ASP) is a business that offers software services to customers, using computer networks and the Internet as the mechanism to deliver and manage the service.

Front 31

API - Application Programming Interface

Back 31

An API defines data structures and subroutine calls.

Front 32

Signal Attenuation

Back 32

loss of signal strength measured in decibels (dB).

- range - both wireless and wired transmissions gradually dissipate in strength over longer reaches
- interference - on wireless networks, radio interference or physical obstructions like walls also dampen communication signals
- wire size - on wired networks, thinner wires suffer from higher (more) attenuation than thicker wires

Front 33

Backbone

Back 33

Central conduit designed to transfer network traffic at high speeds.

Front 34

bandwidth

Back 34

data transmission rate supported by a network connection or interface.