The Medium Access Control (MAC) Sublayer

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TheMedium Access Control (MAC)Sublayer
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The Channel Allocation Problem

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

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Static Channel Allocation

• FDM Frequency Division Multiplexing
• T Mean time delay
• Arrival rate ? frames/sec
• Channel Capacity C bps
• Frame length Drawn from exponential function
• 1/µ bits/frame
• T 1 / (µC ?)
• FDM one central queue
• Single channel is divided into N independent
  sub-channels, each with capacity C/N bps.
• TN 1 / µ (C/N) (?/N) N / (µC ?) NT

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Dynamic Channel Allocation in LANs and MANs

1. Station Model N independent stations
2. Single Channel Assumption.
3. Collision Assumption the event of collision of
   2 frames can be detected by all stations
4. (a) Continuous Time.(b) Slotted Time.
5. (a) Carrier Sense.(b) No Carrier Sense.

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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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Pure ALOHA

• In pure ALOHA, frames are transmitted at
  completely arbitrary times.

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Pure ALOHA (2)

• Vulnerable period for the shaded frame.

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Static Channel Allocation

• Assumption Infinite Population
• N frames per mean frame time
• N gt 1 always collision
• K transmission attempts per frame. So G frames
  per second.
• G gt N
• Throughput S G.P0, where P0 is the prob. that
  a frame does not suffer collision.
• Prk (Gk . e-G)/ k!
• S G e-2G

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Pure ALOHA (3)

• Throughput versus offered traffic for ALOHA
  systems.

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Static Channel Allocation

• Variation of collision with G
• Probability that all other users are silent (1
  e-G)
• Probability that transmission requires exactly k
  attempts
• Pk e-G (1 e-G)k-1
• Expectation S k.Pk eG

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Persistent and Nonpersistent CSMA

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

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CSMA with Collision Detection

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

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CSMA/CD Performance

• A probability that exactly one station attempts
  a transmission in a slot and therefore acquires
  the medium binomial probability that any one
  station attempts to transmit and the others dont
• The function takes on a maximum over P when P
  1/N.

• Maximum throughput will be achieved if the
  probability of successful seizure of the medium
  is maximized.
• During periods of heavy usage, a station should
  restrain its offered load to 1/N.

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CSMA/CD Performance

• The summation converges to
• Max. utilization length of a transmission
  interval as a proportion of a cycle consisting of
  a transmission and a contention interval.

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Collision-Free Protocols

• The basic bit-map protocol.
• Performance
• Always 1 bit/station/frame transmitted is the
  overhead.
• Channel efficiency U d / d1, under high load
• U d/ dN, under low load
• N number of bits, d frame size

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Collision-Free Protocols (2)
Token
Station
Direction of transmission

• Token Passing.
• Performance
• Similar to bit-map protocol.
• Since all positions in the cycle are equivalent,
  there is no bias for low- or high-numbered
  stations.

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Collision-Free Protocols (3)

• The binary countdown protocol. A dash indicates
  silence.
• Performance
• Channel efficiency U d / d log2N

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Limited-Contention Protocols
Best value of p 1/k, where k is the no. of
stations. Substituting, Prsuccess with optimal
p (k 1)/kk 1

• Acquisition probability for a symmetric
  contention channel.

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Adaptive Tree Walk Protocol

• The tree for eight stations.

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Wavelength Division Multiple Access Protocols

• Wavelength division multiple access.

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(No Transcript)
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Wireless LAN Protocols

• A wireless LAN. (a) A transmitting. (b) B
  transmitting.
• Hidden Terminal and exposed terminal problem

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Wireless LAN Protocols (2)

• The Multiple Access with Collision Avoidance
  (MACA) protocol.
• (a) A sending an RTS to B.
• (b) B responding with a CTS to A.

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Ethernet (802.3)

• 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

• The most common kinds of Ethernet cabling.

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Ethernet MAC Sublayer Protocol

• Frame formats. (a) DIX Ethernet, (b) IEEE 802.3.

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Preamble of 8 bytes, each containing the bit
pattern 10101010 (with the exception of the last
byte, in which the last 2 bits are set to 11).
This last byte is called the Start of Frame
delimiter for 802.3. Destination address 1
means multicast 1111 broadcast Source Address
Mac Address To do this, the first 3 bytes of
the address field are used for an OUI
(Organizationally Unique Identifier). indicate a
manufacturer. manufacturer assigns the last 3
bytes of the address
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Length and Protocol lt 1536 is length and higher
is Type
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IEEE 802.2 Logical Link Control

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

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Length of the packet cannot be too small -- 64
bytes long
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Ethernet MAC Sublayer Protocol (2)
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Switched Ethernet

• A simple example of switched Ethernet.

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• A switch improves performance over a hub in two
  ways.
• Since there are no collisions, the capacity is
  used more efficiently.
• With a switch multiple frames can be sent
  simultaneously (by different stations).
• These frames will reach the switch ports and
  travel over the switchs backplane to be output
  on the proper ports.
• Two frames might be sent to the same output port
  at the same time,
• the switch must have buffering so that it
• can temporarily queue an input frame until it can
  be transmitted to the output port.

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Wireless LANs

• The 802.11 Protocol Stack
• The 802.11 Physical Layer
• The 802.11 MAC Sublayer Protocol
• The 802.11 Frame Structure
• Services

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The 802.11 Protocol Stack

• Part of the 802.11 protocol stack.

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The 802.11 MAC Sublayer Protocol

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

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CSMA

• Exponential Back-off

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END
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The 802.11 MAC Sublayer Protocol (2)

• The use of virtual channel sensing using CSMA/CA.

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The 802.11 MAC Sublayer Protocol (3)

• A fragment burst.

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The 802.11 MAC Sublayer Protocol (4)

• Interframe spacing in 802.11.

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The 802.11 Frame Structure

• The 802.11 data frame.

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802.11 Services
Distribution Services

• Association
• Disassociation
• Reassociation
• Distribution
• Integration

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802.11 Services
Intracell Services

• Authentication
• Deauthentication
• Privacy
• Data Delivery

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Broadband Wireless

• Comparison of 802.11 and 802.16
• The 802.16 Protocol Stack
• The 802.16 Physical Layer
• The 802.16 MAC Sublayer Protocol
• The 802.16 Frame Structure

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The 802.16 Protocol Stack

• The 802.16 Protocol Stack.

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The 802.16 Physical Layer

• The 802.16 transmission environment.

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The 802.16 Physical Layer (2)

• Frames and time slots for time division duplexing.

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The 802.16 MAC Sublayer Protocol

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

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The 802.16 Frame Structure

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

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Bluetooth

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

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Bluetooth Architecture

• Two piconets can be connected to form a
  scatternet.

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Bluetooth Applications

• The Bluetooth profiles.

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The Bluetooth Protocol Stack

• The 802.15 version of the Bluetooth protocol
  architecture.

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The Bluetooth Frame Structure

• A typical Bluetooth data frame.

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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

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Data Link Layer Switching

• Multiple LANs connected by a backbone to handle a
  total load higher than the capacity of a single
  LAN.

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Bridges from 802.x to 802.y

• Operation of a LAN bridge from 802.11 to 802.3.

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Bridges from 802.x to 802.y (2)

• The IEEE 802 frame formats. The drawing is not
  to scale.

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Local Internetworking

• A configuration with four LANs and two bridges.

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Spanning Tree Bridges

• Two parallel transparent bridges.

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Spanning Tree Bridges (2)

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

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Remote Bridges

• Remote bridges can be used to interconnect
  distant LANs.

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Repeaters, Hubs, Bridges, Switches, Routers and
Gateways

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

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Repeaters, Hubs, Bridges, Switches, Routers and
Gateways (2)

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

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Virtual LANs

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

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Virtual LANs (2)

• (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.

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The IEEE 802.1Q Standard

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

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The IEEE 802.1Q Standard (2)

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

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Summary

• Channel allocation methods and systems for a
  common channel.

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Ethernet Cabling (2)

• Three kinds of Ethernet cabling.
• (a) 10Base5, (b) 10Base2, (c) 10Base-T.

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Ethernet Cabling (3)

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

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Ethernet Cabling (4)

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