Ch 6

802.11 Advanced Feature

1.) Rate Adaptation 2.) Power Management

4G LTE

4th Generation Long Term Evolution, supports less than 1 Gbps

EVDO

Enhanced Voice-Data Optimized

GSM

Global System for Mobile Communications

Encoding Signal

(original data) X (chipping sequence)

802.15.1

-Low power, short range, low rate -Sometimes called wireless personal area network (WPAN) -Replacement for cables(mouse, keyboard, headphones) -ad hoc: no infrastructure -Are organized into a piconet of up to eight active devices. One is master AKA "Bluetooth" evolved.

Power Management

-Node-to-AP: "I'm sleeping until next beacon frame" ---AP knows not to transmit frames to this node ---node wakes before next beacon frame -Beacon Frame: contains list of mobile with AP-to-mobile frames waiting to be sent ---node will stay awake if AP-to-mobile frames to be sent: otherwise sleep until next beacon.

Wireless Link Characteristics

-decreased signal str. : radio sig atteunates(weakens) as it propagetes(travels) through mattter (path loss) -interference from other sources: standard wireless network freq. (e.g 2.4 Ghz) shared by other devices (e.g. phone); devices (motors) interferes as well -multipath propagation: radio sig reflects off objects groud, arriving at dest. at slightly different times.

ad hoc mode

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

MANET (mobile ad hoc network)

-sometimes called mobile mesh network/wireless ad hoc network -is a self-configuring network of mobile devices connected by wireless links -each device in this network type is free to move independently in any direction, and thus change its links to other devices frequently. Each must forward.

802.11 Sender

1.) If sense channel idle for DIFS (Distributed Coordination Function Interframe Space) Then... -transmit entire frame (no CD) 2.)If sense channel busy then... -start random backoff time -timer counts down while channel idle -transmit when timer expires -if no ACK, increase random backoff interval, and repeat 2.)

802.11 Active Scanning

1.) Probe request frame broadcast from Host 1 (Laptop) 2.) Probe Response frames sent from APs 3.) Association Request frame sent: H1 to selected AP 4.)Assocaition Response frame sent: AP to H1 (Think opposite of other method)

802.11 Passive Scanning

1.) beacon frames sent from APs (routers) 2.) Association Request frame sent: Host 1 (laptop) to selected AP 3.) Association Response frame sent from AP to H1 (Think of scanning for wifi on laptop)

802.11b

2.4 - 2.485 GHz 11Mbps divided into 11 channels at different freq. -AP admin chooses freq for AP -Intereference possible: channel can be same as the one chose by neighboring AP

VANET (vehicular ad-hoc networks)

A form of MANET, to provides communication among nearby vehicles between vehicles and nearby fixed equipment, usually described as roadside equipment -Main goal is providing safety and comfort for passengers. For this, a special electronic device is placed inside each vehicle which will provide ad-hoc network connectivity for passengers.

SSID (Service Set Identifier)

A unique character string used to identify an access point on an 802.11/WLAN network. Sometimes called "network name. Allows stations to connect to desired network when multiple independent networks operate in same physical area (I.E. apartment complexs)

802.11 Frame addressing

Addr 1: MAC Addr of wireless host or AP to receive* this frame Addr 2: MAC addr of wireless host or AP transmitting* this frame Addr 3: MAC addr of router interface to which AP is attached. Addr 4: Used only in ad hoc mode NOTE: Addr 3 plays a crucial role for internetworking between wired LAN with BSS

Infrastructure Mode

Base station connects mobiles into wired network. Handoff: mobile changes base station providing connection into wired network

Rate Adaptation

Base station, mobile dynamically change transmission rate (physical layer modulation technique) as mobile moves, SNR varies. (i.e. when phones work really fast in certain city areas, then internet dies when in countryside.)

Wireless Hosts

Ex. Laptop, Smartphone They are able to run applications. May be stationary(non-mobile) or mobile. "Wireless" does not always mean mobility.

HSPDA

High-Speed Downlink Packet Access - A WAN wireless protocol used by At&t and T-Mobile

802.11 Receiver

If frame received OK -return ACK after SIFS(ACK needed due to hidden terminal problem)

Basic Service Set (BSS)

In wireless networking, a single access point servicing a given area. AKA "cell". Contains: wireless hosts (laptops,phones, etc) access point: base station(router) ad-hoc mode: hosts only

IEEE 802.11 MAC Protocol: CSMA/CA

Protocol divided into Sender and Receiver

IEEE 802.11 Types

Several versions: -.11b : 2.4-5 Ghz unlicensed spectrum, up to 11 Mbps -.11a : 6-6 Ghz range, up to 54 mbps -.11g 2.4-5 GHz range, up to 54 Mbps -.11n 2.4-5 GHz range, up to 200 Mbps All use CSMA/CA for multiple access All have base-station and ad-hoc network versions

SNR

Signal to Noise Ratio - We want to be high. -Higher means easier to extract signal from noise.

Two Wireless and Mobile Networks Challenges

Wireless: Communication over a wireless link. Mobility: Handling a mobile user who changes point of attachment to network.

WiFi Jungle

any physical location where a wireless station receives a sufficiently strong signal from two or more APs.

BER

bit error rate

SNR vs BER tradeoff

given physical layer: increased power means increased SNR means decreased BER given SNR: choose physical layer that meets BER requirement, given highest throughput. -SNR may change with mobility: dynamically adapt physical layer (modulation technique, rate)

host association

host: must associate with an AP -scans channels, listening for beacon frames containing AP's name(SSID) and MAC addr. -select AP to associate with -may authenticate -will typically run DHCP to get IP addr in AP's subnet

Avoiding Collisions

idea is to allow sender to "reserve" channel rather than random access of data frames" avoids collisions of long data frames -send 1st transmits small request-to-send (RTS) packets to BS using CSMA (RTS may still collide, but its short) -BS broadcasts clear-to-send CTS in response to RTS -CTS heard by all nodes (sender transmits data frame, while other stations defer transmissions)

Decoding

inner-product of encoded signal and chipping sequence.

802.15.4-2006

standard of specification for physical layer and media access control for low-rate wireless personal area networks. maintained by IEEE 802.15 working group. -basis for ZigBee -inital version 802.15.1 was made from bluetooth specs., and thus is fully compatible with bluetooth 1.1

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

MAC address for AP and Hosts

wireless stations have 6-byte MAC and also AP has MAC for its wireless interface (like ethernet devices)

Base Station

These typically connect to a wired network. Relay- Responsible for sending packets between wired networks and wireless host(s) in its area. Ex. Cell Towers, 802.1 Access Points.

Wireless Link

This is typically used to connect mobile(s) to base station. Also used as backbone link. Multiple access protocol coordinates link access. Various data rates, various transmission distance.

CDMA (Code Division Multiple Access)

Unique "code" assigned to each user, i.e. code set partitioning. -all user share same freq, but each user has own "chipping" seq.(code) to encode data -allow multiple users to "coexist" and transmit simultaneously with minimal intereference (if codes are "orthogonal")

UMTS

Universal Mobile Telecommunications System