S-72.1130 Telecommunication Systems Wireless Local Area Networks.

S-72.1130 TelecommunicationSystems

Wireless Local Area Networks

2

Outline LAN basics

Structure/properties of LANs WLANs

Link layer services Media access layer

frames and headers CSMA/CA

Physical layer frames modulation

Direct sequence Frequency hopping Infrared

Installation Security

LAN Basics

WLANBasics

802LANs

802.11Service Sets

802.11LLC

802.11MAC

802.11PHY

LANBasics

4

Typical Wired LAN

RAM

RAMROM

Ethernet Processor

Transmission Medium Network Interface

Card (NIC) Unique MAC “physical”

address

Reference: A. Leon-Garcia, I. Widjaja, Communication Networks , Instructor's Slide Set

NIC implements MAC protocol & physical port. Parallel interface to PC

Serial format in 10BASE5 ~ 10 Mb/s – baseband - 500 m

tko

how does the signal propagate in the cable?

5

Example: How Ring Networks Work

A node functions as a repeater Only destination station copies

the frame, all other nodes discard the frame

Unidirectional link Signal propagates

encoded by line codes Example: 802.5 Reliability:

link failure (FDDI appliesdouble ring)

A

C ignores the frame

A

BC A

A

BC

B transmits frame addressed to A

A copies the frameat the reception

A

A

BC

B absorbs the returning frame

A

A

BC

tko

- What is 802.5?- Have look on standard too!

6

Token Ring A ring consists of a single or dual (FDDI) cable in the shape

of a loop. Ring reservation supervised by the rotating token. Each station is physically connected to each of its two

nearest neighbors. Data in the form of packets passes around the ring from one station to another in uni-directional way.

Advantages : (1) Access method supports heavy load without

statistical multiplexing degradation of performance because the medium is shared for pair-wise stations

(2) In practice several packets can simultaneous circulate between different pairs of stations.

Disadvantages: (1) Complex management - especially for several rings (2) Re-initialization of the ring whenever a failure occurs

7

Example: Bus Network In a bus network, one node’s transmission traverses the entire

network and is received and examined by every node. The access method can be :

(1) Contention scheme : multiple nodes attempt to access bus; only one node succeeds at a time (e.g. CSMA/CD in Ethernet 802.3)

(2) Round robin scheme : a token is passed between nodes; node holding the token can use the bus (e.g.Token bus 802.4)

Advantages: (1) Simple access method (2) Easy to add or remove

stations Disadvantages:

(1) Poor efficiency with high network load in contention schemes

(2) Security taken care by upper network levels

term: terminator impedance

A B C D

Dterm term

- Line coded, serial data- Twisted pair or coaxial cable

tko

- Have a look on 802.3 and 802.4- Have a look on wikepedia

Wireless Local Area networks (WLANs) - basics

WLANBasics

802LANs

802.11Service Sets

802.11LLC

802.11MAC

802.11PHY

LANBasics

9

Wireless LANs (WLANs) - features High date rates

IEEE 802.11b supports rates up to 11 MBps (in practice 6 Mb/s), and 802.11g reaches up to 54 Mb/s, need to have the bandwidth

No new wiring and installation on difficult-to-wire areas Offices, public places, and homes Factories, vehicles, roads, and railroads

Mobility Increases working efficiency and productivity Roaming support: extended on-line times

-> universal access & seamless services Reduced installation time

No cabling time Easy setup

Standard enables interoperability between different vendors

Roaming with GSM and UMTS is a research issue

tko

- Check out from wikipedia wlans new features- What is the status of roaming with GSM and UMTS?

10

WLAN Technology Challenges Flexible error control: in physical, MAC and/or in upper levels Physical level takes care of physical transmission of packets

over a medium (modulation, line coding, channel coding) Interference & noise

Working in ISM band means sharing the frequency bands with microwave oven, cordless telephones, Bluetooth etc. -> Modulation and MAC design challenge:

Pros: Freedom from spectral regulatory constraints at ISM Band (Industrial, Science and Medical)

Multi-path propagation Remedies: channel coding / rake-reception

Dynamic network management Stations movable and may be operated while moved

addressing and association procedures interconnections (roaming)

11

Challenges … MAC protocol takes care of optimizing throughput

for the expected services Wireless channel is also the reason why access

method for 802.11 is CSMA/CA and not CSMA/CD Difficult to detect collisions in wireless

environment-> Hidden terminal problem (see PSTN lecture)

Security Traditional WEP (Wired Equivalent Privacy) now

replaced by WPA (Wi-Fi Protected Access) and 802.11i (WPA2)

AAA (Authentication, Authorization, Accounting) can be taken care by a dedicated server as RADIUS (Remote Authentication Dial In User Service )

CSMA/CA: Carrier Sense Multiple Access/Collision AvoidanceCSMA/CD: Carrier Sense Multiple Access/Collision Detection

IEEE 802 LAN Standards

WLANBasics

802LANs

802.11Service Sets

802.11LLC

802.11MAC

802.11PHY

LANBasics

13

IEEE 802-series of LAN Standards 802 standards free to

download from http://standards.ieee.org/getieee802

hubhub

hubhub

hubhub

hubhub

routerrouterserverserver

stationsstations

stationsstations

stationsstations

DQDB: Distributed queue dual buss, see PSTN lecture

Demand priority: A round-robin (token rings) method to provide LAN access based on message priority level

WiMAX

14

The IEEE 802 LAN Standards (http://www.ieee802.org/)

IEEE 802.3CarrierSense

IEEE 802.4TokenBus

IEEE 802.5TokenRing

IEEE 802.11Wireless

IEEE 802.2Logical Link Control (LLC)

MAC

OSI Layer 2(data link)

OSI Layer 1(physical)

Bus (802.3…) Star (802.3u…) Ring (802.5…)

a b gEthernet

LLC

Network

Physical Layers - options: twisted pair, coaxial, optical, radio paths;

(not for all MACs above!)

OSI Layer 3

b: Wi-Fi

IEEE 802.11 Wireless Local Area Networks (WLANs): Service Sets

WLANBasics

802LANs

802.11Service Sets

802.11LLC

802.11MAC

802.11PHY

LANBasics

16

PHY

IEEE 802.11 Architecture 802.11 networks can work in

Basic service set (BSS) Extended service set (ESS)

BSS can also be used in ad-hocnetworking

LLC: Logical Link Control LayerMAC: Medium Access Control LayerPHY: Physical LayerFHSS: Frequency hopping SSDSSS: Direct sequence SSSS: Spread spectrumIR: Infrared lightBSS: Basic Service SetESS: Extended Service Set

LLCMAC

FHSS DSSS IR

Network

802.

xx

Basic (independent) service set (BSS)

Extended service set (ESS)(infrastructure-mode)

Station A

Station B

Propagation boundary

Distributionsystem

BSS 1BSS 2

Access Point

Portal: gateway access to other networks/Internet

Internet

17

Basic and Extended Service Sets

Basic Service Set (BSS) – indoor radius of tens of meters with a single AP

Operates in Basic Service Area (BSA) that is much like the area of a cell in cellular mobile communications

BSSs may geographically overlap, be physically disjoint, or they may be collocated (one BSS may use several antennas)

Ad-hoc or Infrastructure (nomadic) mode: Access coordinated by the MAC protocols

Extended Service Set (ESS) Multiple BSSs interconnected by a Distribution System (DS) Each BSS is like a cell and stations in BSS communicate via

an Access Point (AP) with the DS Portals attached to DS provide gateways as access to

Internet or other ESS

18

Distribution system (DS) services DS provides distribution services:

Transfer MAC SDUs between APs in ESS (I) Transfer MSDUs between portals & BSSs in ESS (II) Transfer MSDUs between stations in same BSS (III)

Multicast, broadcast, or stations’s preference ESS looks like a single BSS to LLC layer

SDU: Service Data Unit (inter-layer data)LLC: Logical Link Control LayerMAC: Medium Access Control LayerMSDU: MAC Service Data UnitPHY: Physical LayerFHSS: Frequency hopping SSDSSS: Direct sequence SSSS: Spread spectrumIR: Infrared lightBSS: Basic Service SetESS: Extended Service SetAP: Access Point

Basic (independent) service set (BSS)

Extended service set (ESS)

Station A

Station B

Propagation boundary

Distributionsystem

BSS 1BSS 2

Access Point

Portal: gateway access to other networks/Internet

Internet

III

I

II

IIIb

III

19

IEEE 802.11 Mobility (b/g)

Standard defines the following mobility types: No-transition: no movement or moving within a local BSS BSS-transition: station movies from one BSS in one ESS to

another BSS within the same ESS ESS-transition: station moves from a BSS in one ESS to a

BSS in a different ESS (continuos roaming not supported) Especially: 802.11 don’t support roaming with

GSM! For fast, seamless

roaming802.11r

ESS 1ESS 2

- Address to destination mapping- seamless integration of multiple BSS

tko

How the mobility of 802.11 differs from PLMN mobility?

IEEE 802 LAN Standard: Logical Link Layer (LLC)

WLANBasics

802LANs

802.11Service Sets

802.11LLC

802.11MAC

802.11PHY

LANBasics

21

802.11 WLAN ArchitectureLogical Link Control (LLC)

LLC provides addressing and data link control – common to all 802 LANs

Utilizes services of HDLC(High-level Data Link Control)

Therefore, LLC SAPs separate upper layer data exchanges =>

NIC applies different buffer segments for each SAP (port)

LLC provides means to exchange frames between LANs using different MACs

CSMA/CA: Carrier Sense Multiple Accesswith Collision AvoidanceLLC: Logical Link Control LayerMAC: Medium Access Control LayerSS: Spread SpectrumFHSS: Frequency hopping SSDSSS: Direct sequence SSIR: Infrared lightNAV: Network Allocation VectorSAP: Service Access PointDCF: Distributed Coordination FunctionPCF: Point Coordination FunctionNIC: Network Interface Card


IEEE 802.4TokenBus

IEEE 802.5TokenRing

IEEE 802.11Wireless


a b g

MAC

Physical layer: DSSS, FHSS, IR PHY

LLC

Ethernet

b: Wi-Fi

22

Logical Link Control Layer (LLC) Specified by ISO/IEC 8802-2 (ANSI/IEEE 802.2) Objective: exchange data between users across LAN using

802-based MAC controlled link Provides addressing and data link control (routing) Independent of topology, medium, and chosen MAC access

method

LLC’s Protocol Data Unit (PDU)(SAP: Service Access Point)

Data to higher level protocols

Info: carries user dataSupervisory: carries flow/error controlUnnumbered: carries protocol control data

SourceSAP

23

SAP Addressing

IEE802.11 (CSMA/CA)...

ATM...

Reference: W. Stallings: Data and Computer Communications, 7th ed

IEE802.11 (CDMA)...

24

TCP makes logical connection to deliver the packet

LLC constructs PDU* by adding a control header

Controlheader

MAC lines up packets by using a MAC protocol

SAP (service access point)

MAC frame withnew control fields

PHY layer transmits packetusing a modulation method(DSSS, OFDM, IR, FHSS)

A TCP/IP PacketEncapsulation

Traffic to thetarget BSS / ESS

*Protocol data unit

25

Encapsulation …


26

LLC Services A Unacknowledged connectionless service

Point-to-point, multicast (assigned users), broadcast (group of users) addressing

no error or flow control - no ack-signal higher levels take care or reliability - thus fast Often referred as ‘Unnumbered frame mode of HDLC*’

B Connection oriented service connection phases: Connection setup, data exchange, and

release supports unicast only error/flow control (cyclic redundancy check (CRC)), sequencing ‘Asynchronous mode of HDLC’

C Acknowledged connectionless service Can handle several logical connections, distinguished by their

SAPs ack-signal used error and flow control by stop-and-wait ARQ faster setup than for B

*High-Level Data Link Control

IEEE 802.11 Wireless Local Area Networks (WLANs): Media Access Protocol

WLANBasics

802LANs

802.11Service Sets

802.11LLC

802.11MAC

802.11PHY

LANBasics

28

Selecting a Medium Access Control

Environment: Wired / Wireless? Applications:

What type of traffic? Voice streams? Steady traffic, low delay/jitter Data? Short messages? Web page downloads? Enterprise or consumer market? Reliability, cost

Scale: How much traffic can be carried? How many users can be supported?

Examples: Design MAC to provide wireless DSL-equivalent access

for rural communities Design MAC to provide Wireless-LAN-equivalent access

to mobile users (user in a car travelling at 130 km/h)

29

MAC techniques - examples Contention

Medium is free for all, packet collisions do happen A node senses the free medium and occupies it as long

as data packet requires it Example: Ethernet (IEEE 802.3 CSMA/CD)

Reservation (short term statistical access) Gives everybody a turn Reservation time depends on token holding time (set by

network operator) For heavy loaded networks Example: Token Ring/IEEE 802.5, Token Bus/IEEE 802.4,

FDDI Reservation (long term)

Link reservation for multiple packets (whole session) Example: scheduling a time slot: GSM using TDMA. FDMA

applied for uplink/dowlink separation. Hybrid… (example: contention+reservation)

Flexible compromise: 802.11 WLANs

30

Medium sharing techniques

Static channelizatio

n

Dynamic medium access

control

Scheduling Random access (contention)

Media Access Control (MAC): Ways to Share a Medium

FDMA,TDMA, CDMA Uses partition

medium Dedicated

allocation to users Examples:

Satellite transmission

Cellular Telephone

Polling (take turns): Token ring 802.5

Reservation systems: Request for slot in transmission schedule 802.4

Loose coordination Send, wait, retry if

necessary Aloha CSMA/CD (Ethernet) CSMA/CA (802.11

WLAN)

Medium sharing required for multiple users to access the channel

Communications by unicasting multicasting broadcasting

31

Example 802.3: MAC of Ethernet (CSMA/CD*)

CSMA/CD:1. If the medium is idle, transmit; otherwise, go to step

22. If the medium is busy, continue listening (CS: carrier

sensing) until the channel is idle, then transmit immediately

3. If a collision is detected (CD) during transmission, transmit brief jamming signal to assure all stations know about collision and then cease transmission

4. After transmitting the jamming signal, wait a random time (back-off time), then attempt to transmit again

*Carrier sense multiple access/collision detection

32

Throughput Performance of CSMA/CD

(Load) ~ throughput

We can see that in Ethernet transfer delays grow very fast as the load increases for the given value of delay-bw product a. Note: Large value of parameter a scales results for propagation delay and/or signaling rate – if their product becomes larger, throughput (in terms of transfer delay) gets smaller.

tprop: one-way delay, R: signaling rate, L: frame length

Reference: A. Leon-Garcia, I. Widjaja, Communication Networks, 2nd ed

/

/

: normalized

delay-bandwidth product

: normalized load

: aggregated rate [frames/second]

propa t R L

L R

a

33

802.11 WLAN ArchitectureMedium Access Control (MAC) - Summary

802.11 MAC Services

Station service: Authentication, privacy, MSDU* delivery

Distributed system: Association**, participates to data distribution

Transmits frames based on MAC addresses (in NIC)

Connectionless/Connection oriented frame transfer service

Coordinates access to medium

Joining the network (NAV, addressing)

MAC scheme CSMA/CA: Contention-free

access (PCF) Contention access

(DCF)* MSDU: MAC service data unit** with an access point in extended or basic service set (ESS,BSS)


IEEE 802.4TokenBus

IEEE 802.5TokenRing

IEEE 802.11Wireless


a b g

MAC

Physical layer: DSSS, FHSS, IR PHY

LLC

Ethernet

b: Wi-Fi


34

IEEE 802.11 Coordination Functions


35

Media Access Control in 802.11 WLANs Distributed Wireless Foundation MAC (DWFMAC):

Distributed access control mechanism (CSMA/CA) Optional centralized control on top (PCF)

MAC flavours provided by coordination functions: Distributed coordination function (DCF) – CSMA/CA

Contention algorithm to provide access to all traffic Asynchronous, best effort-type traffic Application: bursty traffic, add-hoc networks

Point coordination function (PCF) – polling principle(rarely applied in practical devices)

Centralized MAC algorithm Connection oriented Contention free Built on top of DCF Application: timing sensitive, high-priority data

36

IEEE 802.11 MAC (DWFMAC): Timing in Basic Access


PCF: Point Coordination Function (asynchronous, connectionless access)DCF: Distributed Coordination Function (connection oriented access)DIFS: DCF Inter Frame Space (minimum delay for asynchronous frame access)PIFS: PCF Inter Frame Space (minimum poll timing interval)SIFS: Short IFS (minimum timing for high priority frame access as ACK, CTS, MSDU…)MSDU: MAC Service Data Unit

MAC frame: Control, management , data + headers(size depends on frame load and type)

duration depends on MAC load type

duration depends on network condition

37

IEEE 802.11 MAC Logic(DWFMAC)


IFS: Inter Frame Space (= DIFS, SIFS, or PIFS)DWFMAC: Distributed Wireless

Foundation MAC

duration depends on MAC load type

38

DWFMAC summarized Collision Avoidance

When station senses channel busy, it waits until channel becomes idle for DIFS period & then begins random backoff time (in units of idle slots)

Station transmits frame when backoff timer expires

If collision occurs, recompute backoff over interval

Receiving stations of error-free frames send ACK Sending station interprets non-arrival of ACK as

loss Executes backoff and then retransmits Receiving stations use sequence numbers to

identify duplicate frames

39

Carrier Sensing in 802.11 MAC - Summary

Physical Carrier Sensing Analyze all detected frames for errors Monitor relative signal strength from other sources

Virtual Carrier Sensing at MAC sublayer (avoids hidden-terminal problem)

Source stations inform other stations of transmission time (in sec) for an MPDU (MAC Protocol Data Unit)

Carried in Duration field of RTS (Request to send) & CTS (Clear to send)

Stations adjust their Network Allocation Vector (NAV) to indicate when the channel will become idle

Channel busy if either sensing is busy


40

DataDIFS

SIFS

Defer (postpone) accessfor other stations Wait for

Reattempt Time

ACK

DIFS

NAV

Source

Destination

Other

Transmission of MPDU without RTS/CTS


NAV: Network allocation vectorDIFS: DCF Inter Frame Space (async)SIFS: SIFS: Short IFS (ack, CTS…)RTS: Request to sendCTS: Clear to sendMPDU: MAC Protocol Data UnitDCF: Distributed Coordination FunctionPCF: Point Coordination Function

41

Data

SIFS

Defer access

Ack

DIFSNAV (RTS)

Source

Destination

Other

RTSDIFS

SIFSCTS

SIFS

NAV (CTS)

NAV (Data)

Transmission of MPDU with RTS/CTS (DCF)


RTS: Request to SendCTS: Clear to Send

NAV: Network allocation vectorDIFS: DCF Inter Frame Space (async)SIFS: SIFS: Short IFS (ack, CTS…)RTS: Request to sendCTS: Clear to sendMPDU: MAC Protocol Data UnitDCF: Distributed Coordination FunctionPCF: Point Coordination Function

Hidden terminal solution

42

CF End

NAV

PIFS

B D1 + Poll

SIFS

U 1 + ACK

D2+Ack+Poll

SIFS SIFS

U 2 + ACK

SIFS SIFS

Contention-free repetition interval (PCF)

Contention period (DCF)

CF_Max_duration

Reset NAV

D1, D2 = frame sent by point coordinatorU1, U2 = frame sent by polled stationTBTT = target beacon transmission timeB = beacon frame (initiation)

TBTT

PCF Frame Transfer

Fixed super-frame interval

NAV: Network allocation vectorPIFS: PCF Inter Frame Space DIFS: DCF Inter Frame Space (async)SIFS: SIFS: Short IFS (ack, CTS…)RTS: Request to sendCTS: Clear to sendMPDU: MAC Protocol Data UnitDCF: Distributed Coordination FunctionPCF: Point Coordination Function

43

Point Coordination Function PCF provides connection-oriented, contention-free

service through polling Point coordinator (PC) in AP performs PCF Polling table up to implementer Contention free period (CFP) repetition interval

Determines frequency with which contention free period occurs

Initiated by beacon frame transmitted by Point Coordinator (PC) in AP

During CFP stations may only transmit to respond to a poll from PC or to send ACK

All stations adjust Network Allocation Vector (NAV) to indicate when channel will becomes idle


44

MAC Frame Types Management frames

Station association & disassociation with AP (this establishes formally BSS)

Timing & synchronization Authentication & de-authentication (option for

identifying other stations) Control frames

Handshaking ACKs during data transfer

Data frames Data transfer


45

MAC Frame

frame check sequence (CRC)

control info (WEP, data type as management, control, data ...)

next frame duration

-Basic service identification BSSID*-source/destination address-transmitting station-receiving station

frame specific,variable length

frame orderinginfo for RX

*BSSID: a six-byte address typical for a particular access point (network administrator sets)CRC: Cyclic Redundancy CheckWEP: Wired Equivalent Privacy

NOTE: This frame structure is common for all data send by a 802.11 station

IEEE 802.11 Wireless Local Area Networks (WLANs): Physical Level

WLANBasics

802LANs

802.11Service Sets

802.11LLC

802.11MAC

802.11PHY

LANBasics

47

802.11 WLAN bands and technologies - summary IEEE 802.11 standards and rates

IEEE 802.11 (1997) 1 Mbps and 2 Mbps (2.4 GHz band ) [FH, DS]

IEEE 802.11b (1999) 11 Mbps (2.4 GHz band) = Wi-Fi [QPSK]

IEEE 802.11a (1999) 6, 9, 12, 18, 24, 36, 48, 54 Mbps (5 GHz band) [OFDM]

IEEE 802.11g (2001 ... 2003) up to 54 Mbps (2.4 GHz) backward compatible to 802.11b [OFDM]

IEEE 802.11 networks work on license free Industrial, Science, Medicine (ISM) bands:

902 928 2400 2484 5150 5350 5470 5725 f/MHz

26 MHz 83.5 MHz 200 MHz

100 mW

Equipment technical requirements for radio frequency usage defined in ETS 300 328

255 MHz

200 mWindoors only

1 WEIRP power in Finland

EIRP: Effective Isotropically Radiated Power - radiated power measured immediately after antenna

48

802.11-wireless LANs, Dec. ’07

Ref: http://en.wikipedia.org/wiki/802.11n

49

802.11 WLAN ArchitecturePhysical Level (PHY)

802 Physical level specifies Star, bus or ring

topology Cabling and electrical

interfaces: Twisted pair, coaxial, fiber…

Line coding (wired LANs) or modulation (WLANs)

Three physical layers for 802.11

FHSS: Frequency Hopping Spread Spectrum (SS)

DSSS: Direct Sequence SS IR: Infrared transmission


IEEE 802.4TokenBus

IEEE 802.5TokenRing

IEEE 802.11Wireless


a b g

MAC

Physical layers PHY

LLC

Ethernet

b: Wi-Fi


50

Physical Levelof 802.11: DSSS

802.11 supports 1 and 2 Mbps data transmission, uses BPSK and QPSK modulation (802.11b,a,g apply higher rates)

802.11 applies 11 chips Barker code for spreading - 10.4 dB processing gain

Defines 14 overlapping channels, each having 22 MHz channel bandwidth, from 2.401 to 2.483 GHz

Power limits 1000mW in US, 100mW in EU, 200mW in Japan Immune to narrow-band interference, cheaper hardware

DSSS-transmitter

PPDU:Baseband Data Frame Unit, BPSK: Binary Phase Shift Keying, QPSK: Quadrature PSKDSSS: Direct Sequence Spread Spectrum, PN:Pseudo Noise

51

Physical Level of 802.11: FHSS Supports 1 and 2 Mbps data transport and applies two level -

GFSK modulation* (Gaussian Frequency Shift Keying) 79 channels from 2.402 to 2.480 GHz ( in U.S. and most of EU

countries) with 1 MHz channel space 78 hopping sequences with minimum 6 MHz hopping space,

each sequence uses every 79 frequency elements once Minimum hopping rate

2.5 hops/second Tolerance to multi-path,

narrow band interference, security

Low speed, small range due to FCC TX power regulation (10mW)

* , 160kHzc nomf f f f

52

Exam

ple

: PH

Y o

f 8

02

.11

a

Operates at 5 GHz band Supports multi-rate 6 Mbps, 9 Mbps,… up to 54 Mbps Uses Orthogonal Frequency Division Multiplexing (OFDM) with

52 subcarriers, 4 us symbols (0.8 us guard interval) Applies inverse discrete Fourier transform (IFFT) to combine

multi-carrier signals to single time domain symbol

902 928 2400 2484 5150 5350 5470 5725 f/MHz

26 MHz 83.5 MHz 200 MHz 255 MHz

Review questions

WLANBasics

802LANs

802.11Service Sets

802.11LLC

802.11MAC

802.11PHY

LANBasics

54

Review questions

Logical link control (LLC) services in 802.11 What is the role of Distributed Coordination

Function (DCF) and Point Coordination Function (PFC) in 802.11 MAC?

Describe 802.3 MAC Scheme What is the basic difference between CSMA/CD and

CSMA/CA? Which one is applied in 802.11 and why? Discuss factors than should be considered while

choosing a medium access technique Carrier sensing in 802.11 MAC Mobility support in 802.11b/g MAC frame types

55

References and Supplementary Material- A. Leon-Garcia, I. Widjaja: Communication

Networks (2th ed.)- W. Stallings: Data and Computer Communications,

7th ed- Kurose, Ross: Computer Networking (2th ed.)- Jim Geier: Wireless LANs, SAMS publishing- 802 Standards, IEEE

Supplementary Material (distributed by Edita): HDLC: A. Leon-Garcia, I. Widjaja: Communication

Networks, 2th ed.: pp. 333-340 WLANs: W. Stallings: Data and Computer

Communications, 7th ed, pp. 544-568

S-72.1130 Telecommunication Systems Wireless Local Area Networks.

Documents

Transcript of S-72.1130 Telecommunication Systems Wireless Local Area Networks.