The Medium Access Control Sublayer

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The Medium Access ControlSublayer
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The Channel Allocation Problem in Multi-access or
random-access

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

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Dynamic Channel Allocation in LANs and MANs

• Station Model.
• Single Channel Assumption.
• Collision Assumption.
• (a) Continuous Time.(b) Slotted Time.
• (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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Slotted ALOHA

• Frames are transmitted only within the slotted
• Collision can only occur within the slotted

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Vulnerable period (Slotted ALOHA)
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Pure ALOHA (3)

• Throughput versus offered traffic for ALOHA
  systems.

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Persistent and Non-persistent 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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Limited-Contention Protocols

• Acquisition probability for a symmetric
  contention channel.

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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

• The most common kinds of Ethernet cabling.

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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.

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Ethernet MAC Sublayer Protocol

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

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How collision happen

• More than 2 stations transmit frames at the same
  time
• More than 2 stations have enter to contention
  period (trying to gain access to the media). Once
  the media available, those stations transmit
  frame at the same time.

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Ethernet MAC Sublayer Protocol (2)
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Why PAD is needed

• Enlarge frame to minimal length, when data is
  very small

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How fast do electrons move?

• As fast as you can get them going! Well not
  quite. One of the facts of life discovered in the
  20th century is that the speed of light (300,000
  kilometers per second) is the ultimate speed
  limit. As you add energy to the electron, it will
  go faster, but as you get it to go close to the
  speed of light, you find that you have to add
  even more energy just to bump it a bit faster.
  For example, with just over 220,000 eV (which
  stands for a convenient unit of energy called the
  "electron-volt"), you can get the electron up to
  90 of the speed of light. But to get it to 99.9
  (just another 9.9), you need a total of over 11
  million eV! One way of looking at this is that
  the electron gets "heavier" (more massive) as it
  goes ever faster. So it's harder to push it
  faster. At Jefferson Lab, a typical energy for
  the electrons in the beam is 4 GeV which is 4
  billion eV. That means the electron is traveling
  at 99.9999992 of the speed of light. Close but
  still not 100.
• You may wonder how fast the electrons are
  whizzing around in the atoms around you. A good
  example (and the most simple to calculate) is the
  hydrogen atom which is in all our water. A
  calculation shows that the electron is traveling
  at about 2,200 kilometers per second. That's less
  than 1 of the speed of light, but it's fast
  enough to get it around the Earth in just over 18
  seconds. Read up on what happens when nothing can
  go faster than the speed of light.

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Example

• What is the max length of the Ethernet LAN
• 10 Mbps and 100 Mbps
• Assume that electron move at 2200km/s

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Binary Exponential Backoff

• When collision occur ?
• An algorithm for dealing with contention in the
  use of a network. To transmit a packet the host
  sets a local parameter, L to 1 and transmits in
  one of the next L slots. If a collision occurs,
  it doubles L and repeats.

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• The retransmission is delayed by an amount of
  time derived from the slot time and the number of
  attempts to retransmit.
• After i collisions, a random number of slot times
  between 0 and 2i - 1 is chosen. For the first
  collision, each sender might wait 0 or 1 slot
  times. After the second collision, the senders
  might wait 0, 1, 2, or 3 slot times, and so
  forth. As the number of retransmission attempts
  increases, the number of possibilities for delay
  increases.

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Ethernet Performance

• Efficiency of Ethernet at 10 Mbps with 512-bit
  slot times.

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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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IEEE 802.2 Logical Link Control

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

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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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Repeaters, Hubs, Bridges, Switches, Routers and
Gateways

• Which device is in which layer.
• 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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Summary

• Channel allocation methods and systems for a
  common channel.