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34 Cards in this Set

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Wireless Hosts
- laptop, PDA, IP phone
- run applications
- may be stationary
- (non-mobile) or mobile
- wireless does not always mean mobility
Wireless Links/Wireless Communication Link
- 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
Infrastructure Mode
- base station connects mobiles into wired network
- handoff: mobile changes base station providing connection into wired network
ad hoc networks
- no base stations
- nodes can only transmit to other nodes within link coverage
- nodes organize themselves into a network: route among themselves
handoff
mobile changes base station providing connection into wired network
Network Infrastructure
larger network with which a wireless host may wish to communicate.
Elements of a wireless network
-Wireless hosts
-Wireless Links
-Base Station(key part)
-Network Infrastructure
Base Station
- 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
Types of Wireless Networks
-Single-Hop, Infrastructure-based
-Single-Hop, Infrastructure-less
-Multi-Hop, infrastructure-based
-Multi-Hop, , Infrastructure-less
Single-hop, infrastructure-based
host connects to base station (WiFi, WiMAX, cellular) which connects to larger Internet
Issues of Wireless Link
- 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
wireless types and characteristics
Indoor (range of 10-30m)
802.11n - 200Mbps, 802.11a,g - 54 Mbps, 802.11b - 5 to 11Mpbs, 802.15 - 1Mbps

Outdoor
single hop- no infrastructure
no base station, no connection to larger Internet (Bluetooth, ad hoc nets)
multiple hops-Infrastructure
host may have to relay through several wireless nodes to connect to larger Internet: mesh net
multiple hops-no infrastructure
no base station, no connection to larger
Internet. May have to relay to reach other a given wireless node MANET, VANET
Wireless Link Characteristics
- 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)
Wireless network characteristics
Multiple wireless senders and receivers create additional problems (beyond multiple access): Hidden terminal problem, Signal Attenuation
Code Division Multiple Access (CDMA)
- 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”)
What are 4 types of IEEE 802.11 Wireless LAN?
- 802.11a, 802.11b, 802.11g, 802.11n
- all use CSMA/CA for multiple access
- all have base-station and ad-hoc network versions
802.11b
- 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
802.11a
- 5-6 GHz range
- up to 54 Mbps
802.11g
- 2.4-5 GHz range
- up to 54 Mbps
802.11n: multiple antennae
- 2.4-5 GHz range
- up to 200 Mbps
802.11 LAN architecture
- 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
passive scanning
(1)beacon frames sent from APs
(2)association Request frame sent:
H1 to selected AP
(3)association Response frame sent:
H1 to selected AP
active scanning
(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
IEEE 802.11: multiple access
- avoid collisions
- 802.11: CSMA -sense before transmitting
- 802.11: nocollision detection!
ATM - Asynchronous Transfer Mode
High-speed networking standard designed to support both voice and data communications.
ARP - Address Resolution Protocol
converts an Internet Protocol (IP) address to its corresponding physical network address.
ASP - Application Service Provider
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.
API - Application Programming Interface
An API defines data structures and subroutine calls.
Signal Attenuation
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
Backbone
Central conduit designed to transfer network traffic at high speeds.
bandwidth
data transmission rate supported by a network connection or interface.