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The Medium Access Control Sublayer

The Medium Access Control Sublayer. Chapter 4. The Channel Allocation Problem. Static Channel Allocation in LANs and MANs Dynamic Channel Allocation in LANs and MANs. Dynamic Channel Allocation in LANs and MANs. Station Model. Single Channel Assumption. Collision Assumption.

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The Medium Access Control Sublayer

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  1. The Medium Access ControlSublayer Chapter 4 Infrastructure de Communications – CR 4107 Chapter 4 1

  2. The Channel Allocation Problem Infrastructure de Communications – CR 4107 Chapter 4 2 • Static Channel Allocation in LANs and MANs • Dynamic Channel Allocation in LANs and MANs

  3. Dynamic Channel Allocation in LANs and MANs Infrastructure de Communications – CR 4107 Chapter 4 3 • Station Model. • Single Channel Assumption. • Collision Assumption. • (a) Continuous Time.(b) Slotted Time. • (a) Carrier Sense.(b) No Carrier Sense.

  4. Multiple Access Protocols Infrastructure de Communications – CR 4107 Chapter 4 4 • ALOHA • Carrier Sense Multiple Access Protocols • Collision-Free Protocols • Limited-Contention Protocols • Wavelength Division Multiple Access Protocols • Wireless LAN Protocols

  5. Pure ALOHA Infrastructure de Communications – CR 4107 Chapter 4 5 • In pure ALOHA, frames are transmitted at completely arbitrary times.

  6. Pure ALOHA (2) Infrastructure de Communications – CR 4107 Chapter 4 6 • Vulnerable period for the shaded frame.

  7. Pure ALOHA (3) Infrastructure de Communications – CR 4107 Chapter 4 7 • Throughput versus offered traffic for ALOHA systems.

  8. Persistent and Nonpersistent CSMA Infrastructure de Communications – CR 4107 Chapter 4 8 • Comparison of the channel utilization versus load for various random access protocols.

  9. CSMA with Collision Detection Infrastructure de Communications – CR 4107 Chapter 4 9 • CSMA/CD can be in one of three states: contention, transmission, or idle.

  10. Collision-Free Protocols Infrastructure de Communications – CR 4107 Chapter 4 10 • The basic bit-map protocol.

  11. Wireless LAN Protocols Infrastructure de Communications – CR 4107 Chapter 4 11 • A wireless LAN. (a) A transmitting. (b) B transmitting.

  12. Ethernet Infrastructure de Communications – CR 4107 Chapter 4 12 • Invented at XEROX by Dr. R. Metcalfe in 1975 • Formal specifications published in 1980 by DEC-Intel-Xerox • Became IEEE 802.3 standard in 1985 - adopted by ISO • 10 Mbps • Coaxial cable • Updated to include new technologies • Twisted pair • 100 Mbps Fast Ethernet - IEEE 802.3U • Gigabit Ethernet - IEEE 802.3Z • Wireless versions

  13. Elements of the Ethernet System Infrastructure de Communications – CR 4107 Chapter 4 13 • Physical Medium • Medium Access Control (MAC) • Ethernet Frame • Operation of Ethernet • No central control • Stations are connected to a shared medium • Ethernet signals are transmitted serially, one bit at a time, to every connected station • To send data a station listens to the channel and if it is idle it transmits its data in the form of an Ethernet frame. • Access to the medium is determined by the MAC • CSMA/CD protocol

  14. CSMA/CD Protocol Infrastructure de Communications – CR 4107 Chapter 4 14 The Ethernet MAC is based on the Carrier Sense Multiple Access / Collision Detection protocol A station that wants to transmit • Listens to the channel • If the channel is idle, it transmits its data • If the channel is busy it waits until it is free and then transmits its data. • If two stations transmit at the same time we have a collision ---- Jam signal • Truncated binary exponential backoff algorithm • nth re-transmission will be attempted with a delay between 0 and 2n-1 time units (ex. 53s) • maximum of 16 attempts to re-transmit

  15. Collision detection Infrastructure de Communications – CR 4107 Chapter 4 15 Collision detections can take as long as 2t

  16. Ethernet MAC Sublayer Protocol Infrastructure de Communications – CR 4107 Chapter 4 16 • Frame formats. (a) DIX Ethernet, (b) IEEE 802.3.

  17. Ethernet Addresses Infrastructure de Communications – CR 4107 Chapter 4 17 Ethernet addresses (48 bits) are unique and controlled by IEEE • 24 bit Organizationally Unique Identifier (OUI) by the IEEE • 24 bit by the organization Multicast and Broadcast addresses • High order address bit is 1 for multicast and broadcast • A destination address of only 1s is accepted by all stations

  18. Higher level addresses Infrastructure de Communications – CR 4107 Chapter 4 18 • Ethernet is a trucking system and can operate with different higher level protocols, like TCP/IP, AppleTalk, Novel etc. • Higher level protocols have their own addressing schemes. • They must find the right Ethernet address in order to communicate with each other. • Example in TCP/IP : Address Resolution Protocol (ARP) • Station A sends a broadcast requesting the Ethernet address the station B that has the specific IP address • All stations receive the message • Only the station with the requested IP address reply

  19. Ethernet Topology Infrastructure de Communications – CR 4107 Chapter 4 19 • The total size of an Ethernet LAN is defined by the round trip propagation delay. • All stations should by able to respond to signals within a specified amount of time. • Ethernet segments can be connected at any physical topology (star, tree, bus ...) as long as the timing restrictions are fulfilled. • Repeaters • A repeater is simply re-transmits the signal extending the overall size of the LAN • Switching hubs • Divides a set of Ethernet segments to multiple LANs • Packet switching

  20. Ethernet Cabling Infrastructure de Communications – CR 4107 Chapter 4 20 • The most common kinds of Ethernet cabling.

  21. Ethernet Cabling (2) Infrastructure de Communications – CR 4107 Chapter 4 21 • Three kinds of Ethernet cabling. • (a) 10Base5, (b) 10Base2, (c) 10Base-T.

  22. Ethernet Cabling (3) Infrastructure de Communications – CR 4107 Chapter 4 22 • Cable topologies. (a) Linear, (b) Spine, (c) Tree, (d) Segmented.

  23. Ethernet Cabling (4) Infrastructure de Communications – CR 4107 Chapter 4 23 • (a) Binary encoding, (b) Manchester encoding, (c) Differential Manchester encoding.

  24. Ethernet Performance Infrastructure de Communications – CR 4107 Chapter 4 24 • Efficiency of Ethernet at 10 Mbps with 512-bit slot times.

  25. Switched Ethernet Infrastructure de Communications – CR 4107 Chapter 4 25 • A simple example of switched Ethernet.

  26. Fast Ethernet Infrastructure de Communications – CR 4107 Chapter 4 26 • The original fast Ethernet cabling.

  27. Gigabit Ethernet Infrastructure de Communications – CR 4107 Chapter 4 27 • (a) A two-station Ethernet. (b) A multistation Ethernet.

  28. Gigabit Ethernet (2) Infrastructure de Communications – CR 4107 Chapter 4 28 • Gigabit Ethernet cabling.

  29. Ethernet problems Infrastructure de Communications – CR 4107 Chapter 4 29 Capture effectA station with high traffic load can capture the network for a considerable amount of time Security Packets are received by all stations

  30. IEEE 802.2: Logical Link Control Infrastructure de Communications – CR 4107 Chapter 4 30 • (a) Position of LLC. (b) Protocol formats.

  31. The 802.11 (WLAN) Protocol Stack Infrastructure de Communications – CR 4107 Chapter 4 32 • Part of the 802.11 protocol stack.

  32. The 802.11 MAC Sublayer Protocol Infrastructure de Communications – CR 4107 Chapter 4 33 • (a) The hidden station problem. • (b) The exposed station problem.

  33. Bluetooth Architecture Infrastructure de Communications – CR 4107 Chapter 4 47 • Two piconets can be connected to form a scatternet.

  34. Bluetooth Applications Infrastructure de Communications – CR 4107 Chapter 4 48 • The Bluetooth profiles.

  35. Data Link Layer Switching Infrastructure de Communications – CR 4107 Chapter 4 51 • Bridges from 802.x to 802.y • Local Internetworking • Spanning Tree Bridges • Remote Bridges • Repeaters, Hubs, Bridges, Switches, Routers, Gateways • Virtual LANs

  36. Data Link Layer Switching Infrastructure de Communications – CR 4107 Chapter 4 52 • Multiple LANs connected by a backbone to handle a total load higher than the capacity of a single LAN.

  37. Bridges from 802.x to 802.y Infrastructure de Communications – CR 4107 Chapter 4 53 • Operation of a LAN bridge from 802.11 to 802.3.

  38. Bridges from 802.x to 802.y (2) Infrastructure de Communications – CR 4107 Chapter 4 54 • The IEEE 802 frame formats. The drawing is not to scale.

  39. Repeaters, Hubs, Bridges, Switches, Routers and Gateways Infrastructure de Communications – CR 4107 Chapter 4 59 • (a) Which device is in which layer. • (b) Frames, packets, and headers.

  40. Repeaters, Hubs, Bridges, Switches, Routers and Gateways (2) Infrastructure de Communications – CR 4107 Chapter 4 60 • (a) A hub. (b) A bridge. (c) a switch.

  41. Virtual LANs Infrastructure de Communications – CR 4107 Chapter 4 61 • A building with centralized wiring using hubs and a switch.

  42. Virtual LANs (2) Infrastructure de Communications – CR 4107 Chapter 4 62 • (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.

  43. The IEEE 802.1Q Standard Infrastructure de Communications – CR 4107 Chapter 4 63 • Transition from legacy Ethernet to VLAN-aware Ethernet. The shaded symbols are VLAN aware. The empty ones are not.

  44. The IEEE 802.1Q Standard (2) Infrastructure de Communications – CR 4107 Chapter 4 64 • The 802.3 (legacy) and 802.1Q Ethernet frame formats.

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