1. The Medium Access Control Sublayer
Chapter 4
The Medium Access Control Sublayer

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

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 cabling.

10. IEEE 802.2: Logical Link Control
(a) Position of LLC. (b) Protocol formats.

11. Wireless LANs
The Protocol Stack
The Physical Layer
The MAC Sublayer Protocol
The Frame Structure
Services

12. 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 and (and radio telephony
Design goals are very different!
Fixed vs mobile, antenna, radio cost, distance, sectoring, traffic/QoS
The Protocol Stack
The Physical Layer
The MAC Sublayer Protocol
The Frame Structure

17. The 802.16 Protocol Stack The 802.16 Protocol Stack.
OFDM in 2GHz and 5 GHz

18. The 802.16 transmission environment.
The Physical Layer
The transmission environment.

19. Frames and time slots for time division duplexing.
The 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. (a) A generic frame. (b) A bandwidth request frame.
The 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 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. Operation of a LAN bridge from 802.11 to 802.3.
Bridges from 802.x to 802.y
Operation of a LAN bridge from to

30. The IEEE 802 frame formats. The drawing is not to scale.
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. Two parallel transparent bridges.
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 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. A building with centralized wiring using hubs and a switch.
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 MAC 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 (>1500 so type)
2nd byte has VLAN id (lower order 12 bits), 3 bit priority (used by 802.1P), 1 bit CFI to indicate 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 802.3 (legacy) and 802.1Q Ethernet frame formats.
The IEEE 802.1Q Standard (2)
The (legacy) and 802.1Q Ethernet frame formats.

47. UWB FCC definition – bandwidth > 25% of center frequency.
2(Fh-Fl)/(Fh+Fl)
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 don’t work well. P , HiperLAN DM

48. Channel allocation methods and systems for a common channel.
Summary
Channel allocation methods and systems for a common channel.