



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
2

LAN
Basics
WLAN
Basics
802
LANs
802.11
Service Sets
802.11
LLC
802.11
MAC
802.11
PHY




Transmission Medium
Network Interface Card
(NIC)
Unique MAC “physical” address
Serial format in 10BASE5
~ 10 Mb/s
– baseband - 500 m
RAM
RAM
ROM
Ethernet
Processor
Reference: A. Leon-Garcia, I. Widjaja, Communication
Networks , Instructor's Slide Set
NIC implements MAC protocol & physical port. Parallel interface to PC
4







A node functions as a repeater
Only destination station copies the frame, all other nodes discard the frame
C
A
A
B transmits frame addressed to A
Unidirectional link
Signal propagates encoded by line codes
Example: 802.5
C
A
A
Reliability: link failure (FDDI applies double ring)
A copies the frame at the reception
B
B
C
A
C
A
C ignores the frame
A
A
B absorbs the returning frame
B
B
5





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
6




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: term


A
(1) Poor efficiency with high network load in contention schemes
(2) Security taken care by upper network levels
D
B C
- Line coded, serial data
D
- Twisted pair or coaxial cable term term: terminator impedance
7

LAN
Basics
WLAN
Basics
802
LANs
802.11
Service Sets
802.11
LLC
802.11
MAC
802.11
PHY






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
9




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)
10



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

Security
Difficult to detect collisions in wireless environment
-> Hidden terminal problem (see PSTN lecture)


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 Avoidance
CSMA/CD: Carrier Sense Multiple Access/Collision Detection
11

LAN
Basics
WLAN
Basics
802
LANs
802.11
Service Sets
802.11
LLC
802.11
MAC
802.11
PHY


802 standards free to download from http://standards.ieee.org
/getieee802 hub stations hub stations router hub stations hub
WiMAX server
Demand priority: A round-robin (token rings) method to provide LAN access based on message priority level
DQDB: Distributed queue dual buss, see PSTN lecture
13

( http://www.ieee802.org/ )
OSI Layer 3
Network
IEEE 802.2
Logical Link Control (LLC)
IEEE 802.3
Carrier
Sense
Ethernet
IEEE 802.4
Token
Bus
IEEE 802.5
Token
Ring b: Wi-Fi
IEEE 802.11
Wireless a b g
Physical Layers
- options: twisted pair, coaxial, optical, radio paths;
(not for all MACs above!)
LLC OSI Layer 2
(data link)
MAC
OSI Layer 1
(physical)
Bus (802.3…) Star (802.3u…) Ring (802.5…)
14

LAN
Basics
WLAN
Basics
802
LANs
802.11
Service Sets
802.11
LLC
802.11
MAC
802.11
PHY



802.11 networks can work in

Basic service set (BSS)

Extended service set (ESS)
BSS can also be used in ad-hoc networking
Propagation boundary
Network
LLC
MAC
FHSS DSSS IR
Internet
PHY
LLC: Logical Link Control Layer
MAC: Medium Access Control Layer
PHY: Physical Layer
FHSS: Frequency hopping SS
DSSS: Direct sequence SS
SS: Spread spectrum
IR: Infrared light
BSS: Basic Service Set
ESS: Extended Service Set
Station B
Distribution system
Station A
BSS 1
BSS 2
Basic (independent) service set ( BSS )
Access Point
Extended service set ( ESS )
( infrastructure-mode )
Portal: gateway access to other networks/Internet
16



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
17



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
Propagation boundary
III
III
SDU: Service Data Unit
(inter-layer data)
LLC: Logical Link Control Layer
MAC: Medium Access Control Layer
MSDU: MAC Service Data Unit
PHY: Physical Layer
FHSS: Frequency hopping SS
DSSS: Direct sequence SS
SS: Spread spectrum
IR: Infrared light
BSS: Basic Service Set
ESS: Extended Service Set
AP: Access Point
IIIb
Station A
Basic (independent) service set (BSS)
Access Point
Station B
Internet
BSS 1
II
Distribution system
I
BSS 2
Extended service set (ESS)
Portal: gateway access to other networks/Internet
18




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 roaming
802.11r
- Address to destination mapping
- seamless integration of multiple BSS
ESS 2
ESS 1
19

LAN
Basics
WLAN
Basics
802
LANs
802.11
Service Sets
802.11
LLC
802.11
MAC
802.11
PHY


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
IEEE 802.2
Logical Link Control (LLC) b: Wi-Fi
IEEE 802.3
Carrier
Sense
Ethernet
IEEE 802.4
Token
Bus
IEEE 802.5
Token
Ring
IEEE 802.11
Wireless a b g
Physical layer: DSSS, FHSS, IR
CSMA/CA: Carrier Sense Multiple Access with Collision Avoidance
LLC: Logical Link Control Layer
MAC: Medium Access Control Layer
SS: Spread Spectrum
FHSS: Frequency hopping SS
DSSS: Direct sequence SS
IR: Infrared light
NAV: Network Allocation Vector
SAP: Service Access Point
DCF: Distributed Coordination Function
PCF: Point Coordination Function
NIC: Network Interface Card
LLC
MAC
PHY
21





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
Data to higher level protocols
Info: carries user data
Supervisory: carries flow/error control
Unnumbered: carries protocol control data
Source
SAP
LLC’s Protocol Data Unit (PDU)
(SAP: Service Access Point)
22

IEE802.11 (CDMA)...
IEE802.11 (CSMA/CA)...
ATM...
Reference: W.
Stallings: Data and Computer
Communications,
7th ed
23

Control header
MAC frame with new control fields
Traffic to the target BSS / ESS
*Protocol data unit
TCP makes logical connection to deliver the packet
SAP (service access point)
24

Reference: W.
Stallings: Data and Computer
Communications,
7th ed
25




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 26

LAN
Basics
WLAN
Basics
802
LANs
802.11
Service Sets
802.11
LLC
802.11
MAC
802.11
PHY





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)
28





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
29

Medium sharing techniques
Static channelization
Dynamic medium access control


Medium sharing required for multiple users to access the channel
Communications by
 unicasting

 multicasting broadcasting




FDMA,TDMA, CDMA
Uses partition medium
Dedicated allocation to users
Examples:

Satellite transmission

Cellular
Telephone


Scheduling Random access
(contention)
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)
30


CSMA/CD:
1. If the medium is idle, transmit; otherwise, go to step 2
2. 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 know about collision and then cease transmission
, transmit brief jamming signal to assure all stations
4. After transmitting the jamming signal, wait a random time (back-off time), then attempt to transmit again
*Carrier sense multiple access/collision detection
31



 a
 t prop
/ a : normalized
delay-bandwidth product r

: normalized load
: aggregated rate [frames/second] r
(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.
t prop
: one-way delay, R: signaling rate,
L: frame length
Reference: A. Leon-Garcia, I. Widjaja,
Communication Networks, 2nd ed 32


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 802.2
Logical Link Control (LLC) b: Wi-Fi
IEEE 802.3
Carrier
Sense
Ethernet
IEEE 802.4
Token
Bus
IEEE 802.5
Token
Ring
IEEE 802.11
Wireless a b g
Physical layer: DSSS, FHSS, IR
LLC
MAC
PHY
CSMA/CA: Carrier Sense Multiple Access with Collision Avoidance
LLC: Logical Link Control Layer
MAC: Medium Access Control Layer
SS: Spread Spectrum
FHSS: Frequency hopping SS
DSSS: Direct sequence SS
IR: Infrared light
NAV: Network Allocation Vector
SAP: Service Access Point
DCF: Distributed Coordination Function
PCF: Point Coordination Function
NIC: Network Interface Card 33

Reference: W.
Stallings: Data and Computer
Communications,
7th ed
34



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
35

duration depends on MAC load type duration depends on network condition
MAC frame: Control, management , data + headers
(size depends on frame load and type)
Reference: W.
Stallings: Data and Computer
Communications,
7th ed
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
36

IFS: Inter Frame Space (= DIFS, SIFS, or
PIFS)
DWFMAC: Distributed Wireless Foundation
MAC
Reference: W. Stallings: Data and Computer Communications,
7th ed duration depends on MAC load type
37



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
38




Physical Carrier Sensing

Analyze all detected frames for errors

Monitor relative signal strength from other sources
Virtual Carrier Sensing at MAC sublayer (avoids hiddenterminal problem)



Source stations inform other stations of transmission time (in m sec) for an MPDU (MAC Protocol Data Unit)
Carried in Duration
CTS (Clear to send) field of RTS (Request to send) &
Stations adjust their Network Allocation Vector to indicate when the channel will become idle
(NAV)
Channel busy if either sensing is busy
Reference: A. Leon-Garcia, I. Widjaja, Communication
Networks , Instructor's Slide Set
39

DIFS
Source
Data
SIFS
ACK
NAV: Network allocation vector
DIFS: DCF Inter Frame Space (async)
SIFS:
SIFS: Short IFS (ack, CTS…)
RTS: Request to send
CTS: Clear to send
MPDU: MAC Protocol Data Unit
DCF: Distributed Coordination Function
PCF: Point Coordination Function
Destination
DIFS
Other
NAV
Defer (postpone) access for other stations
Reference: A. Leon-Garcia, I. Widjaja, Communication
Networks , Instructor's Slide Set
Wait for
Reattempt Time
40

Hidden terminal solution
DIFS
RTS Data
Source
SIFS
CTS
SIFS
Destination
NAV: Network allocation vector
DIFS: DCF Inter Frame Space (async)
SIFS:
SIFS: Short IFS (ack, CTS…)
RTS: Request to send
CTS: Clear to send
MPDU: MAC Protocol Data Unit
DCF: Distributed Coordination Function
PCF: Point Coordination Function
SIFS
Ack
DIFS
Other
NAV (RTS)
NAV (CTS)
NAV (Data)
Reference: A. Leon-Garcia, I. Widjaja,
Communication Networks , Instructor's Slide Set
Defer access
RTS: Request to Send
CTS: Clear to Send
41

TBTT Fixed super-frame interval
Contention-free repetition interval (PCF)
B
SIFS
D1 +
Poll
SIFS SIFS
D2+Ac k+Poll
U 1 +
ACK
PIFS
SIFS SIFS
CF
End
U 2 +
ACK
Contention period (DCF)
Reset NAV
NAV
CF_Max_duration
D1, D2 = frame sent by point coordinator
U1, U2 = frame sent by polled station
TBTT = target beacon transmission time
B = beacon frame (initiation)
NAV: Network allocation vector
PIFS: PCF Inter Frame Space
DIFS: DCF Inter Frame Space (async)
SIFS: SIFS: Short IFS (ack, CTS…)
RTS: Request to send
CTS: Clear to send
MPDU: MAC Protocol Data Unit
DCF: Distributed Coordination Function
PCF: Point Coordination Function
42







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
Coordinator (PC) in AP transmitted by Point
During CFP stations may only transmit to respond to a poll from PC or to send ACK
All stations adjust Network Allocation Vector indicate when channel will becomes idle
(NAV) to
Reference: A. Leon-Garcia, I. Widjaja, Communication
Networks , Instructor's Slide Set
43




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
Reference: A. Leon-Garcia, I. Widjaja, Communication
Networks , Instructor's Slide Set
44


NOTE: This frame structure is common for all data send by a 802.11 station control info (WEP, data type as management, control, data ...) next frame duration frame ordering info for RX
-Basic service identification BSSID*
-source/destination address
-transmitting station
-receiving station frame specific, variable length
*BSSID: a six-byte address typical for a particular access point
(network administrator sets)
CRC: Cyclic Redundancy Check
WEP: Wired Equivalent Privacy frame check sequence
(CRC)
45

LAN
Basics
WLAN
Basics
802
LANs
802.11
Service Sets
802.11
LLC
802.11
MAC
802.11
PHY



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:
26 MHz 83.5 MHz 200 MHz 255 MHz
EIRP power in Finland
902 928 2400 2484 5150 5350 5470 5725 f/MHz
100 mW
200 mW indoors only
1 W
EIRP: Effective Isotropically Radiated Power - radiated power measured immediately after antenna
Equipment technical requirements for radio frequency usage defined in ETS 300 328
47

Ref: http://en.wikipedia.org/wiki/802.11n
48









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 802.2
Logical Link Control (LLC) b: Wi-Fi
IEEE 802.3
Carrier
Sense
Ethernet
IEEE 802.4
Token
Bus
IEEE 802.5
Token
Ring
IEEE 802.11
Wireless a b g
Physical layers
LLC
MAC
PHY
CSMA/CA: Carrier Sense Multiple Access with Collision Avoidance
LLC: Logical Link Control Layer
MAC: Medium Access Control Layer
SS: Spread Spectrum
FHSS: Frequency hopping SS
DSSS: Direct sequence SS
IR: Infrared light
NAV: Network Allocation Vector
SAP: Service Access Point
DCF: Distributed Coordination Function
PCF: Point Coordination Function
NIC: Network Interface Card 49

DSSS-transmitter





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
PPDU:Baseband Data Frame Unit, BPSK: Binary Phase Shift Keying, QPSK: Quadrature PSK
DSSS: Direct Sequence Spread Spectrum, PN:Pseudo Noise
50



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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)
* f
 f c f , f nom

160 kHz
51

26 MHz 83.5 MHz 200 MHz 255 MHz
902 928 2400 2484 5150 5350 5470 5725 f/MHz
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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 multicarrier signals to single time domain symbol
52

LAN
Basics
WLAN
Basics
802
LANs
802.11
Service Sets
802.11
LLC
802.11
MAC
802.11
PHY

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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
54

- 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
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WLANs: W. Stallings: Data and Computer
Communications, 7th ed, pp. 544-568
55