Wireless Networks Flashcards
How does single hop with infrastructure work?
host connects to base station which connects to internet
How does single hop with no infrastructure work?
no base station, no connection to internet
How does multiple hops with infrastructure work?
hosts may have to relay through several wireless nodes to connect to internet
How does multiple hops with no infrastructure work?
no base station, no connection to internet, may have to relay to reach other wireless node
What are the SNR characteristics of a wireless link?
Larger SNR = easier to extract signal from noise
What are the SNR vs BER tradeoffs for a wireless link?
given physical layer: increase power = increase SNR = decrease BER
given SNR: choose physical layer that meets BER giving highest throughput
What is the worldwide interoperability for microwave access (WiMAX)?
- radio access technology providing broadband and long distance wireless data delivery
- supports QoS and multicasting
- for mobile environments provides high-bandwidth services
- low cost of deploying
What is WiFi? (wireless fidelity)
- radio access technology designed to provide in-building broadband coverage
- doesn’t guarantee QoS
- not originally designed for high-speed mobility
WiFi vs WiMAX, range
Range:
wifi = local network, few hundred metres
wimax = single antenna up to 60km
WiFi vs WiMAX, scalability
Scalability:
wifi = LAN application so users scale from one to tens with one subscriber for each consumer premises equipment device (CPE)
wimax = efficiently supports from one to hundreds of CPEs, unlimited subscribers behind CPE
WiFi vs WiMAX, bit rate
Bit rate:
wifi = 2.7bps/Hz (peak 54Mpbs in 20 Mhz channel)
wimax = 5bps/Hz (peak100Mbps in 20MHz channel)
WiFi vs WiMAX, QoS
QoS:
wifi = doesn’t guarantee, no ubiquitous broadband
wimax = several levels, ubiquitous broadband
What is bluetooth?
- family of radio access standards
- short range connectivity solution for hand held devices
- creates personal areas networks (PANs) with high security
- benefit of omni-directionality
- elimination of line of sight requirement of RF connectivity
What is ZigBee?
- family of radio access standards
- provide networking solution for low data rate/low power consumption apps
What are the 3 roles of a ZigBee network?
End device:
- FFD or RFD executing apps, doesn’t have child node
Router:
- FFD relaying messages, usually has child and parents
Coordinator:
- FFD controlling network, also gateway to external world, trust centre, access authenticator
What is an FFD?
full function device
What is an RFD?
reduced function device
What is a wireless LAN architecture (WiFi)?
basic service set in infrastructure mode contains wireless hosts, access point base station
wireless host communicated with base station
How do wireless networks avoid collisions?
CSMA/CA
How does the sender in CSMA/CA work?
- if snese channel idle for DIFS transmit entire frame
- if sense channel busy, start random backoff time, counts down, while channel idle transmit when timer expires
- if no ack, increase random backoff interval and go back to sense channel
How does the receiver work in CSMA/CA?
if frame received ok, return ack after SIFS
What is SIFS?
short inter frame space
What is DIFS?
distributed inter frame space
What are some advanced capabilities of wireless networks?
Rate adaption: dynamically change transmission rate as mobile moves
Power management: agreement between mobile node and AP
