The Medium Access Control Sublayer

1
The Medium Access ControlSublayer

• Chapter 4

2
The Channel Allocation Problem

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

3
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.

4
Multiple Access Protocols

• ALOHA
• Carrier Sense Multiple Access Protocols
• Collision-Free Protocols
• Limited-Contention Protocols
• Wireless LAN Protocols
• Wavelength Division Multiple Access Protocols
• Broadband Wireless
• VLANS/Bridge Spanning Tree

5
Wavelength Division Multiple Access Protocols

• Wavelength division multiple access.

6
Wireless LAN Protocols

• A wireless LAN. (a) A transmitting. (b) B
  transmitting.

7
Wireless LAN Protocols (2)

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

8
Gigabit Ethernet

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

9
Gigabit Ethernet (2)

• Gigabit Ethernet cabling.

10
IEEE 802.2 Logical Link Control

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

11
Wireless LANs

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

12
The 802.11 Protocol Stack

• Part of the 802.11 protocol stack.

13
The 802.11 MAC Sublayer Protocol

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

14
The 802.11 MAC Sublayer Protocol (2)

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

15
The 802.11 MAC Sublayer Protocol (3)

• A fragment burst.

16
Broadband Wireless

• Comparison of 802.11 and 802.16 (and radio
  telephony
• Design goals are very different!
• Fixed vs mobile, antenna, radio cost, distance,
  sectoring, traffic/QoS
• 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.

OFDM in 2GHz and 5 GHz
18
The 802.16 Physical Layer

• The 802.16 transmission environment.

19
The 802.16 Physical Layer (2)

• Frames and time slots for time division duplexing.

20
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

21
The 802.16 Frame Structure

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

22
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

23
Bluetooth Architecture

• Two piconets can be connected to form a
  scatternet.

24
Bluetooth Applications

• The Bluetooth profiles.

25
The Bluetooth Protocol Stack

• The 802.15 version of the Bluetooth protocol
  architecture.

26
The Bluetooth Frame Structure

• A typical Bluetooth data frame.

27
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

28
Data Link Layer Switching

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

29
Bridges from 802.x to 802.y

• Operation of a LAN bridge from 802.11 to 802.3.

30
Bridges from 802.x to 802.y (2)

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

31
Local Internetworking

• A configuration with four LANs and two bridges.

32
Spanning Tree Bridges
Problem of Packet forwarding loops with multiple
bridges

• Two parallel transparent bridges.

33
Spanning Tree Bridges (2)

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

34
IEEE 802.1D

• Algorithm due to Pearlman et al to construct
  spanning tree in a distributed manner.

35
IEEE 802.1D

• Basic ideas
• Node with least id becomes root
• For a given lan, bridge/port with least cost on
  path to root becomes the designated active
  bridge, all others are passive
• Bridges broadcast configuration BPDUs with id of
  self, id of presumed root, cost to root. Each
  bridges starts by believing it is root.
• If you get superior information on your presumed
  root path, forward downstream
• If you get inferior information, reply with yours

36
Remote Bridges

• Remote bridges can be used to interconnect
  distant LANs.

37
Repeaters, Hubs, Bridges, Switches, Routers and
Gateways

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

38
Repeaters, Hubs, Bridges, Switches, Routers and
Gateways (2)

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

39
Virtual LANs

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

40
Why VLANs if everything interconnects?

• LAN represents organizational hierarchy rather
  than geography
• Security
• Traffic Load/separation (research vs production)
• Limiting Broadcasts
• Legitimate (i.e ARP)
• Storms
• Do rewiring in software

41
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.

42
Grouping into VLANs

• Port level mapping
• All machines on a port must be on the same VLAN
  OK with completely switched networks.
• MAC level mapping
• What if docks are used with notebooks
• IP level mapping
• Violates layering

43
802.1q issues

• Can we identify the VLAN in the frame header
• Easy to do for new protocols, define a new header
  field
• What to do with (Old/Fast/Giga) Ethernet, which
  has no free header fields and max size frames ?
• Who generates this field
• What to do with legacy NICs
• Key point this field is only used by switches,
  not end machines

44
802.1Q

• Adds a new field to Ethernet header circa 98,
  raised frame size to 1522 from 1518
• 1st 2 bytes are protocol ID, fixed as 0x8100
  (gt1500 so type)
• 2nd byte has VLAN id (lower order 12 bits), 3 bit
  priority (used by 802.1P), 1 bit CFI to indicate
  802.5 traffic
• Required Bridges and switches to be VLAN aware,
  future NICs should be aware too (with Giga
  deployment?)
• Bridges/switches could add this field till then)

45
The IEEE 802.1Q Standard

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

46
The IEEE 802.1Q Standard (2)

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

47
UWB

• FCC definition bandwidth gt 25 of center
  frequency.
• 2(Fh-Fl)/(FhFl)
• 802.11b has 80MHz of usable spectrum in 2.4GHz
  band
• Uses Pulse position Modulation
• Low power on any particular frequency, fitting in
  under FCC Part 15 rules
• MAC issues QoS, TDMA and CDMA dont work well.
  P802.15.3, HiperLAN DM

48
Summary

• Channel allocation methods and systems for a
  common channel.