Chapter 4: The Medium Access Control Sublayer

1
Chapter 4 The Medium Access Control Sublayer

• By Dr. Kejie Lu
• Department of Electronic and Computer Engineering
• Spring 2009

2
Outline

• The channel allocation problem
• Multiple access protocols
• Ethernet
• Wireless LAN
• Wireless MAN
• Wireless PAN
• Data link layer switch

3
The Channel Allocation Problem

• Broadcast resource
• Static Channel Allocation in LANs and MANs
• Dynamic Channel Allocation in LANs and MANs

4
Static Channel Allocation

• TDM
• FDM
• Problem
• Might not be efficient if
• The number of users is large and continuously
  varying, or
• The traffic is bursty
• The peak traffic to mean traffic ratio can be
  10001

5
Dynamic Channel Allocation

• 1. Station Model
• 2. Single Channel Assumption
• 3. Collision Assumption
• 4.(a) Continuous Time4.(b) Slotted Time
• 5.(a) Carrier Sense
• 5.(b) No Carrier Sense

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Outline

• The channel allocation problem
• Multiple access protocols
• Ethernet
• Wireless LAN
• Wireless MAN
• Wireless PAN
• Data link layer switch

7
Multiple Access Protocols

• ALOHA
• Carrier Sense Multiple Access Protocols
• Collision-Free Protocols
• Limited-Contention Protocols
• Wavelength Division Multiple Access Protocols
• Wireless LAN Protocols

8
ALOHA

• History
• Designed at the University of Hawaii to solve the
  channel allocation problem
• For ground-based radio broadcasting
• Categories
• Pure Aloha
• Slotted Aloha
• Time is divided into fixed-size slots
• Global time synchronization

9
Pure Aloha

• Main idea
• Let users transmit whenever they have data to be
  sent
• Collision detection
• Directly
• Detection delay
• LAN negligible
• Satellite 270 msec
• Indirectly
• Via ACK frame
• Retransmission
• The sender wait a random amount of time to send
  again

10
Illustration

• In pure ALOHA, frames are transmitted at
  completely arbitrary times
• The throughput of ALOHA systems is maximized if
  the frame size is fixed (the same) for all frames

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Vulnerable Period of A Frame
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Performance

• Throughput
• t/T
• T the total amount of time
• t the total amount of time that are used to
  transmit frame without collision
• Assumption
• The number of stations is infinite
• The frame size is fixed
• The overall traffic (frame) incoming rate follows
  a Poisson distribution with rate G (frames per
  frame time)
• The probability that k frames are generated
  during a frame time is given by the Poisson
  distribution

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Performance

• The probability that no frame is generated during
  the vulnerable period (two frames) is
• The throughput of pure Aloha is
• The maximum throughput is S1/(2e) or about 0.184

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Slotted Aloha

• Time is divided into fixed-size slots
• Global time synchronization is required
• Throughput
• The maximum throughput is
• S 1/e or about 0.368

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Throughput of Aloha Systems
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Multiple Access Protocols

• ALOHA
• Carrier Sense Multiple Access Protocols
• Collision-Free Protocols
• Limited-Contention Protocols
• Wavelength Division Multiple Access Protocols
• Wireless LAN Protocols

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Carrier Sense Multiple Access Protocols

• Problem of Aloha system
• A station does not consider what the others are
  doing
• Key idea of CSMA
• A station can detect what other stations are
  doing and can then adapt its behavior accordingly

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Categories

• 1-Persistent
• Nonpersistent
• p-persistent

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1-Persistent

• A station that has a frame to send shall keep
  listening to (sensing) the channel
• If the channel is busy, the station will be
  waiting
• If the channel is idle, the station will transmit
  the frame

20
Nonpersistent

• A station shall listen to (sense) the channel at
  the moment that it has a frame to send
• If the channel is busy, then the station will
• Stop sensing
• Wait for a random amount of time to sense again
• If the channel is idle, then the station will
  send the frame

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p-Persistence

• Assumption slotted channel
• A station shall listen to (sense) the channel at
  the moment that it has a frame to send
• If the channel is busy, then the station will
• Stop sensing
• Wait for a random amount of time (slots) to sense
  again
• If the channel is idle, then the station will
  send the frame with a probability p, and defer a
  slot with a probability (1-p)

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Performance of CSMA

• Comparison of the channel utilization versus load
  for various random access protocols.

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CSMA with Collision Detection

• Main idea
• If two stations detect the collision after
  transmitting, they shall stop the transmission
• CSMA/CD is used in Ethernet

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Illustration of CSMA/CD

• CSMA/CD can be in one of three states
  contention, transmission, or idle.

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Design Issues

• The maximum propagation delay
• E.g. about 5us to transmit signal through 1 km
  cable
• The capability to distinguish two signals from
  different stations
• This is an analogue process
• CSMA/CD system is half-duplex

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Multiple Access Protocols

• ALOHA
• Carrier Sense Multiple Access Protocols
• Collision-Free Protocols
• Limited-Contention Protocols
• Wavelength Division Multiple Access Protocols
• Wireless LAN Protocols

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The Basic Bit-Map Protocol
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The Basic Bit-Map Protocol

• Suppose there are N stations in the network
• There are N slots in the contention period
• Bit map
• In each slot, a 0 means that the station has no
  frame to send a 1 means that the station has a
  frame to send
• All stations have the knowledge of which stations
  wish to transmit at the end of contention period
• Reservation protocols
• Protocols in which the desire to transmit is
  broadcast before the actual transmission

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Pros and Cons

• Pros
• No collision or contention
• Cons
• Access delay
• One station shall wait for the next contention
  period if it miss the current one
• Overhead
• Bit map shall be sent even if there is no frame
  to be sent
• Scalability issue
• Conditions
• Global synchronization

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The Binary Countdown Protocol

• The problem of the basic bit-map protocol
• Each station need one bit in the bit-map
• Not scalable
• Binary countdown
• Main idea
• A station wanting to use the channel can
  broadcast its address as a binary bit string,
  starting with the high-order bit
• Rule
• A station will stop transmitting if it sees that
  a high-order bit position that is 0 in its
  address has been overwritten with a 1

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The Binary Countdown Protocol
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Pros and Cons

• Pros
• No collision
• The overhead for the bit-map is limited
• High efficiency
• If the source address is the first field in the
  header, then the efficiency is 1
• Cons
• There is a fairness issue
• Higher-numbered stations have a higher priority
• Contention exists in the contention period
• Conditions
• Global synchronization

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Multiple Access Protocols

• ALOHA
• Carrier Sense Multiple Access Protocols
• Collision-Free Protocols
• Limited-Contention Protocols
• Wavelength Division Multiple Access Protocols
• Wireless LAN Protocols

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A Trade-off

• Two basic approaches
• Collision Aloha, CSMA
• Collision-free
• At low load, allowing collision can reduce the
  delay
• At high load, collision free protocols can lead
  to better efficiency
• Motivation
• To combine the good feature of these two
  protocols together

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Optimum Transmission Probability

• The symmetric assumption
• Each station attempts to acquire the channel with
  the same probability p
• If there are k stations in the network, then the
  probability that one of the stations successfully
  acquires the channel during a given slot is kp(1
  - p)k - 1
• The optimum p is 1/k

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Limited-Contention Protocols

• Acquisition probability for a symmetric
  contention channel

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A Possible Approach

• Divide the stations into groups, with index as 0,
  1,
• Only the members of group 0 are permitted to
  compete for slot 0
• Only the members of group 1 are permitted to
  compete for slot 1

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Adaptive Tree Walk Protocol

• The tree for eight stations.

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Adaptive Tree Walk Protocol

• Construct a tree and all stations are leafs
• Following a successful frame transmission, in the
  first contention slot, denoted as slot 0, all
  stations are permitted to try to acquire the
  channel
• If no collision, then continue
• If there is a collision, then during slot 1 only
  children of node 2 may compete
• If one of them acquires the channel, the slot
  following the frame is reserved for children of
  node 3
• If a collision occurs during slot 1, then only
  children of node 4 may compete in slot 2

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Multiple Access Protocols

• ALOHA
• Carrier Sense Multiple Access Protocols
• Collision-Free Protocols
• Limited-Contention Protocols
• Wavelength Division Multiple Access Protocols
• Wireless LAN Protocols

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WDMA Protocols

• Topology
• Passive star
• Two fibers are used to connect the station and
  the coupler
• The whole spectrum is divided into channels
  (WDM)
• Each channel in the frequency domain can be
  further divided into slots
• Global synchronization is required
• Each station can have two channels
• Control
• Data

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WDMA Protocol

• Each station has two transmitters and two
  receivers, as follows
• A fixed-wavelength receiver for listening to its
  own control channel
• A tunable transmitter for sending on other
  stations' control channels
• A fixed-wavelength transmitter for outputting
  data frames
• A tunable receiver for selecting a data
  transmitter to listen to

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Illustration
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Illustration

• A wants to send data to B
• Procedure of A
• Listen to Bs data channel
• Know available slots in the controls channel
• Send request to B in an available slot of the
  control channel
• If B assign the channel to A in its data channel,
  A will then transmit data in the specified slot
  in its data channel

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Multiple Access Protocols

• ALOHA
• Carrier Sense Multiple Access Protocols
• Collision-Free Protocols
• Limited-Contention Protocols
• Wavelength Division Multiple Access Protocols
• Wireless LAN Protocols

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Wireless LAN Protocols

• Key problems
• Throughput
• Hidden terminal
• A station not being able to detect a potential
  competitor for the medium because the competitor
  is too far away
• Expose terminal
• A station not being able to transmit because of
  another transmission

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The MACA protocol

• MACA stands for multiple access with collision
  avoidance
• Key idea
• By overhearing control frames, other stations
  know when the other stations will transmit and
  when the frame transmission will be terminated

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Illustration

• Illustration
• (a) A sending an RTS to B.
• (b) B responding with a CTS to A

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The MACAW Protocol

• MACAW stands for MACA for wireless
• Key difference
• Use CSMA
• Use ACK frame to confirm a successful
  transmission
• Use a backoff counter for each source-destination
  pair
• Exchange congestion information

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Outline

• The channel allocation problem
• Multiple access protocols
• Ethernet
• Wireless LAN
• Wireless MAN
• Wireless PAN
• Data link layer switch

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Ethernet

• Ethernet Cabling
• Manchester Encoding
• The Ethernet MAC Sublayer Protocol
• The Binary Exponential Backoff Algorithm
• Ethernet Performance
• Switched Ethernet
• Fast Ethernet
• Gigabit Ethernet
• IEEE 802.2 Logical Link Control
• Retrospective on Ethernet

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Ethernet Cabling

• Notation
• 10Base5
• The maximum data rate is 10Mb/s
• The baseband signal will be transmitted
• The maximum distance is 500 meters

200m if CAT-5 twisted pair is used
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Ethernet Cabling Examples

• (a) 10Base5, (b) 10Base2, (c) 10Base-T

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Cable Topologies

• (a) Linear, (b) Spine, (c) Tree, (d) Segmented

• Each version of Ethernet has a maximum cable
  length per segment
• Maximum distance of the LAN
• Maximum of repeaters on a path

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Encoding

• (a) Binary encoding, (b) Manchester encoding,
  (c) Differential Manchester encoding.

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Encoding

• Why not use simple binary signal?
• To distinguish transmission of bit 0 and no
  transmission
• Why not transmit -1 for bit 0?
• The clock of sender and receiver are different
• Consider consecutive 1s
• Manchester encoding
• 0 edge from low to high
• 1 edge from high to low
• Cost requires twice bandwidth

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MAC Protocol

• Frame format

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Frame Formats

• (a) Original DIX Ethernet
• DIXDEC, Intel, Xerox
• (b) IEEE 802.3

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Frame Formats

• Preamble
• To allow the receiver to adjust its clock to
  synchronize with the sender's
• Pattern 10101010 repeat 8 times (7 for the IEEE
  standard)
• Date rate 10Mb/s
• Preamble time 6.4us
• Address
• 6-byte in most cases
• Unicast the first bit is 0
• Multicast a set of destination addresses
• Broadcast destination address is all 1s
• The second bit is used to indicate local or
  global
• The global address is assigned by IEEE such that
  each adapter has a unique MAC address

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Frame Formats

• Type (DIX) / Length (IEEE)
• DIX To indicate the upper layer (network)
• Payload
• Max 1500 bytes
• Limited by the RAM size
• In 1970s, RAM is very expensive
• Min 46 bytes
• Through padding
• The total size of the frame must be at least 64
  bytes
• The transmission time of the minimum frame must
  be larger than the maximum round-trip delay
  between two stations
• 648100ns51.2us
• 51.2us200m/us10 km
• Checksum
• 32-bit CRC

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MAC Protocol
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The Binary Exponential Backoff Algorithm

• Purpose
• Randomization process when a collision occurs
• Slot 51.2us
• Worst-case round-trip propagation delay
• Procedure
• After the first collision, each station waits
  either 0 or 1 slot times before trying again
• After the second collision, each one picks either
  0, 1, 2, or 3 at random and waits that number of
  slot times
• After the k-th collision, each station choose
  02k-1 slots, if k lt 10
• If kgt10, each station randomly choose 01023
  slots to defer its transmission

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Ethernet Performance

• Assumption
• A constant retransmission probability (p) in each
  slot
• The probability of successful transmission is
• Akp(1-p)k-1
• k is the number of nodes in the network
• Optimum p1/k
• Optimum A1/e as k-gtinfinity
• Mean contention period is 2t/A
• 2t is the slot time, or the max round trip time
• Channel efficiency
• P/(P 2t/A)
• P is the mean frame transmission time

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Impact of Number of Nodes and Frame Size
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Switched Ethernet

• A simple example of switched Ethernet.

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Fast Ethernet

• The original fast Ethernet cabling.

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Gigabit Ethernet

• (a) A two-station Ethernet
• (b) A multistation Ethernet.

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Gigabit Ethernet (2)

• Gigabit Ethernet cabling.

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Acknowledgement

• There is no ACK in the Ethernet standard
• By contrast, ACK is used in IEEE 802.11
• CSMA/CA protocol

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IEEE 802.2 Logical Link Control

• (a) Position of LLC. (b) Protocol formats.

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Retrospective on Ethernet

• History of Ethernet gt 20 years
• Simple
• Inexpensive
• Flexible
• Evolving

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The IEEE 802.11 Wireless LANs

• Protocol Stack
• Physical Layer
• MAC Sublayer Protocol
• Frame Structure
• Services

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Protocol Stack
74
Physical Layer

• Infrared
• FHSS Frequency hopping spread spectrum
• 2.4-GHz band (ISM band)
• Possible interference Cordless phone, microwave
  oven,
• Max. data rate 2Mb/s
• DSSS Direct sequence spread spectrum
• 2.4-GHz band
• Max. data rate 2Mb/s

75
Physical Layer

• 802.11a
• 5.1-GHz band
• Max. data rate 54Mb/s
• OFDM is used
• 802.11b
• 2.4-GHz band
• Max. data rate 11Mb/s
• 802.11g
• 2.4-GHz band
• Max. data rate 54Mb/s
• OFDM is used

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Channels and Bandwidth

• 2.4-GHz Band
• 14 Channels
• Bandwidth 20MHz
• Non-overlapped channels 3

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Channels and Bandwidth

• 5-GHz Band
• Bandwidth 20MHz
• Non-overlapped channels 12
• Channel numbering
• Central frequency 50005n (MHz)

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Channels and Bandwidth
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Transceiver

• Half-duplex
• Cannot transmit and receive at the same time
• Cannot use CSMA/CD

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MAC Sublayer

• Main problem
• Coordination function
• CSMA/CA protocol
• PCF protocol
• Central control
• Interframe spacing
• Acknowledgement

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Main Problems

• (a) The hidden station problem.
• (b) The exposed station problem.

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Coordination Function

• DCF
• Distributed coordination function
• CSMA/CA
• PCF
• Point coordination function
• TDMA
• Rarely used

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CSMA/CA Protocol

• Two options
• Basic
• RTS/CTS
• Virtual carrier sensing in CSMA/CA

NAV Network Allocation Vector
84
Fragmentation
NAV Network Allocation Vector
85
Fragmentation

• Fragmentation is used to improve the throughput
  in error-prone wireless conditions

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PCF

• A central controller is used to allocate channel
  in the PCF mode
• The controller is called point coordinator (PC)
• PCF mode is overlay above DCF
• The controller broadcast beacon frame
  periodically, and polling the requests from all
  stations in the network

87
PCF Timing
88
PCF Timing
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Interframe Spacing
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SIFS

• To allow the parties in a single dialog the
  chance to go first
• For example, SIFS is used between RTS and CTS,
  CTS and DATA, DATA and ACK
• The duration of SIFS depends on the physical
  layer specifications
• The duration of SIFS shall be enough for the
  signal to propagate and for the transceiver to
  switch from one mode to another (e.g. from
  transmitting to receiving)

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PIFS

• PIFSPCF IFS
• PIFS is used so that the PCF has more chance to
  acquire the channel

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DIFS

• DIFSDCF IFS
• After the end of a dialog, all stations shall
  wait at least for DIFS before another attempt
• Notice that some stations may need to backoff

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EIFS

• Used by a station that has just received a bad or
  unknown frame to report the bad frame
• Example
• A is sending a DATA frame to B
• After the end of the frame, C realize that the
  received frame is not correct
• By check the FCS
• In this case, C must defer for EIFS
• EIFSDIFSSIFSduration of transmission the ACK
  or CTS frame

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Acknowledgement

• Positive acknowledgement
• A receiving station shall send back an ACK frame
  if the FCS for the received data frame is correct

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Backoff

• Binary exponential backoff
• Contention window
• The duration of collision may not be fixed
• Basic access
• RTS/CTS

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Frame Structure

• Data frame format
• Control frame format

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Frame Control

• Version
• Type
• Data
• Control
• Management
• Subtype
• RTS, CTS, etc.
• To DS and From DS
• Indicate the frame is going to or coming from the
  intercell distribution system (e.g., Ethernet)

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Frame Control

• MF
• More fragments
• Retry
• Retransmission of a previous frame
• Power management
• From base station to put the receiver into sleep
  state or take it out of sleep state
• More
• Indicate that the sender has additional frames
  for the receiver
• WEP
• Specify that the frame body has been encrypted
  using the WEP (Wired Equivalent Privacy)
  algorithm
• Order
• Tell the receiver that a sequence of frames with
  this bit on must be processed strictly in order

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Frame Format

• Duration/ID
• The duration of this dialog (until ACK)
• 15-bit (first bit is 0)
• The duration for NAV
• Address
• 6-byte each
• 2 address fields are used for frame forwarding
• Inside or outside WLAN
• Sequence control
• 4-bit for fragment number
• 12-bit for sequence number

100
Services

• Infrastructure mode
• AP access point
• Ad hoc mode
• No AP
• Distributed services
• Intracell services

101
Distributed Services

• Association
• Disassociation
• Reassociation
• Distribution
• Integration

102
Distributed Services

• Association
• This service is used by mobile stations to
  connect themselves to base stations.
• Disassociation
• Either the station or the base station may
  disassociate, thus breaking the relationship
• A station should use this service before shutting
  down or leaving, but the base station may also
  use it before going down for maintenance
• Reassociation
• A station may change its preferred base station
  using this service
• This facility is useful for mobile stations
  moving from one cell to another

103
Distributed Services

• Distribution
• This service determines how to route frames sent
  to the base station
• If the destination is local to the base station,
  the frames can be sent out directly over the air.
  Otherwise, they will have to be forwarded over
  the wired network.
• Integration
• If a frame needs to be sent through a non-802.11
  network with a different addressing scheme or
  frame format, this service handles the
  translation from the 802.11 format to the format
  required by the destination network

104
Intracell Services

• Authentication
• Deauthentication
• Privacy
• Data Delivery

105
Intracell Services

• Authentication
• A station must authenticate itself before it is
  permitted to send data
• After a mobile station has been associated by the
  base station, the base station sends a special
  challenge frame to it to see if the mobile
  station knows the secret key (password) that has
  been assigned to it
• A station is fully enrolled in the cell if the
  result is correct.
• Deauthentication
• When a previously authenticated station wants to
  leave the network, it is deauthenticated

106
Intracell Services

• Privacy
• This service manages the encryption and
  decryption
• Data delivery
• Transmission over 802.11 is not guaranteed to be
  100 reliable
• Higher layers must deal with detecting and
  correcting errors

107
802.16 Broadband Wireless

• Comparison
• The Protocol Stack
• The Physical Layer
• The MAC Sublayer Protocol
• The Frame Structure

108
Comparison of 802.11 and 802.16

• Main difference
• Mobility
• System complexity
• 802.16 can support full duplex communication
• Distance
• Security
• Bandwidth
• Number of users

109
Comparison of 802.16 with Mobile Phone System

• Mobile phone system
• Mainly voice service
• Low data rate
• Mobile
• Low power

110
The Protocol Stack
111
The Protocol Stack

• More sublayers
• Service convergence
• Security
• Transmission convergence

112
The Physical Layer

• High frequency band
• Line-of-sight transmission
• Sector
• Modulation
• OFDM

113
Multiplexing

• FDM and TDM
• OFDMA
• Asymmetric
• Downstream
• Upstream

114
Other Features

• Packet aggregation
• Error correction
• Hamming code is used

115
The MAC Sublayer Protocol

• Mode
• PMP
• Mesh
• Service Classes
• Constant bit rate service
• Real-time variable bit rate service
• Non-real-time variable bit rate service
• Best efforts service

116
The Frame Structure

• (a) A generic frame
• (b) A bandwidth request frame.

117
The Frame Structure

• The Checksum is optional
• Header CRC x8x2x1

118
Bluetooth

• Architecture
• Applications
• The Protocol Stack
• The Radio Layer
• The Baseband Layer
• The L2CAP Layer
• The Frame Structure

119
Architecture

• Two piconets can be connected to form a
  scatternet.

120
Applications
121
The Protocol Stack

• The 802.15 version of the Bluetooth protocol
  architecture.

122
The Radio Layer

• Frequency band 2.4 GHz
• Channel bandwidth 1MHz
• Frequency hopping 1600 hops/second
• Total number of channels 79
• Modulation FSK (1 bit / symbol)
• Data rate 1Mb/s
• TDM total slots per second 1600
• Uplink 800 slots/s
• Downlink 800 slots /s
• Problem interference with 802.11b
• Co-existence issue

123
The Baseband Layer

• Odd slots are used for uplink
• Slave -gt master
• Even slots are used for downlink
• Master -gt slave
• A frame can utilize 1, 3, or 5 slots
• Frame overhead
• 250260 per slot for frequency hopping settling
  time
• 72 bits for access code
• 54 bits for header
• Service
• ACL Asynchronous Connection-Less
• SCO Synchronous Connection Oriented (maximum
  64Kbps)

124
The L2CAP Layer

• Accept packets with up to 64 Kbytes size
• Multiplexing and demultiplexing
• Quality of service

125
The Frame Structure

• A typical Bluetooth data frame
• Only 8 active devices
• 18354
• Stop-and-wait protocol

126
Data Link Layer Switching

• Bridges from 802.x to 802.y
• Local Internetworking
• Spanning Tree Bridges
• Remote Bridges
• Repeaters, Hubs, Bridges, Switches, Routers,
  Gateways
• Virtual LANs

127
Data Link Layer Switching

• Multiple LANs connected by a backbone to handle a
  total load higher than the capacity of a single
  LAN
• Bridge is used to connect two or more LANs

Routing?
128
Reasons for Bridging

• Multiple LANs may have been set up with different
  standards
• The distance of two or more LANs can be very
  large
• It is not appropriate to use a single LAN in such
  a case
• It may be necessary to split what is logically a
  single LAN into separate LANs to accommodate the
  load
• Reliability
• Security
• Most LAN interfaces have a promiscuous mode

129
Bridges from 802.x to 802.y

• Operation of a LAN bridge from 802.11 to 802.3

130
Difficulties of Bridging

• Different frame formats
• Different data rates
• Different frame length
• Different security policies
• For example, encryption
• Different quality of service policies

131
Local Internetworking

• A configuration with four LANs and two bridges.

132
Spanning Tree Bridges

• Two parallel transparent bridges
• Loop

133
Spanning Tree Bridges

• (a) Interconnected LANs. (b) A spanning tree
  covering the LANs. The dotted lines are not part
  of the spanning tree.

134
Remote Bridges

• Remote bridges can be used to interconnect
  distant LANs.

135
Repeaters, Hubs, Bridges, Switches, Routers and
Gateways

• (a) Which device is in which layer.
• (b) Frames, packets, and headers.

136
Repeaters, Hubs, Bridges, Switches, Routers and
Gateways

• (a) A hub. (b) A bridge. (c) a switch.

137
Virtual LANs

• A building with centralized wiring using hubs and
  a switch.

138
Virtual LANs

• (a) Four physical LANs organized into two VLANs,
  gray and white, by two bridges
• (b) The same 15 machines organized into two VLANs
  by switches.

139
The IEEE 802.1Q Standard

• Transition from legacy Ethernet to VLAN-aware
  Ethernet. The shaded symbols are VLAN aware.
  The empty ones are not.

140
The IEEE 802.1Q Standard

• The 802.3 (legacy) and 802.1Q Ethernet frame
  formats.

141
Summary