DataLink Layer

1. DataLinkLayer Department of Computer and System Instituto Tecnológico de Morelia jcolivar@itmorelia.edu.mx 19.72388 lat, -101.1848 long M.C. Juan Carlos Olivares Rojas

2. Disclaimer Some material in this presentation has been obtained from various sources, each of which has intellectual property, so in this presentation will only have some rights reserved. These slides are free, so you can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on my part. In return for use, I only ask the following: if you use these slides (e.g., in a class) in substantially unaltered form, that you mention their source.

3. Outline Concepts. MAC Addressing. Framming Medium Access Control IEEE 802.x Technologies Basic Principles. Token Ring. Ethernet and its variants. FDDI

4. Objectives of theSession • The students will know the basis of intenrnational computer networks standards. • The students will know and apply the LAN concepts.

5. Concepts DataLink Services • Provide services to the Network Layer • Send and receive data in a frame format • Processing and error correction • DataFlow Control • Medium Access Control ***

6. Where is the link layer implemented? in each and every host link layer implemented in “adaptor” (aka network interface card NIC) Ethernet card, PCMCI card, 802.11 card implements link, physical layer attaches into host’s system buses combination of hardware, software, firmware application transport network link link physical host schematic cpu memory host bus (e.g., PCI) controller physical transmission network adapter card

7. MAC Addressing • MAC (or LAN or physical or Ethernet) address: • function:get frame from one interface to another physically-connected interface (same network) • 48 bit MAC address (for most LANs) • burned in NIC ROM, also sometimes software settable

8. LAN Addresses 5: DataLink Layer Each adapter on LAN has unique LAN address Broadcast address = FF-FF-FF-FF-FF-FF 1A-2F-BB-76-09-AD LAN (wired or wireless) = adapter 71-65-F7-2B-08-53 58-23-D7-FA-20-B0 0C-C4-11-6F-E3-98

9. Framming sending side: encapsulates datagram in frame adds error checking bits, rdt, flow control, etc. receiving side looks for errors, rdt, flow control, etc extracts datagram, passes to upper layer at receiving side datagram datagram controller controller receiving host sending host datagram frame

10. Medium Access Control • There are a lot of technices for sharing the transmision medium. The more used in computer networks are: • ALOHA • CSMA • Protocols without colision • Wireless Protocol • Other Multiplexation

11. ALOHA The frames are transmitting in arbitrary moment

12. CSMA (Carrier Sense Multiple Access) 5: DataLink Layer CSMA: listen before transmit: If channel sensed idle: transmit entire frame • If channel sensed busy, defer transmission • human analogy: don’t interrupt others! • collisions can still occur: • propagation delay means • two nodes may not hear • each other’s transmission • role of distance & propagation delay in determining collision probability

13. Persistent and Not PersistenteCSMA

14. CSMA/CD (Collision Detection) 5: DataLink Layer CSMA/CD: carrier sensing, deferral as in CSMA • collisions detected within short time • colliding transmissions aborted, reducing channel wastage • collision detection: • easy in wired LANs: measure signal strengths, compare transmitted, received signals • difficult in wireless LANs: received signal strength overwhelmed by local transmission strength • human analogy: the polite conversationalist

15. CSMA Collision Detection CSMA/CD can be in 3 states: contention, transmission, or idle

16. Token Passing • control token passed from one node to next sequentially. • token message • concerns: • token overhead • Latency • single point of failure (token) T (nothing to send) T data

17. IEEE 802.x Technologies • The group of standards 802.x is concern about the implementation and use of Local Area Network (e.g. TokenRing, Ethernet) and Wide Area Network (e.g. FDDI, WiMax). • These standars are focused in DataLink Layer. The transmission medium can be wired o wireless. • Some standards are focused in define services in DataLink Layer such quality of service, security, among others.

18. Basic Principles • The standards only indicate how computer networks must be works guarantee interoperability between another Equipments. • The main functions in the 802.x standards are the framming and Medium Access Control.

19. Token Ring • Token ring is a local area network protocol which resides at the data link layer (DLL) of the OSI model. It uses a special three-byte frame called a token that travels around the ring. Token ring frames travel completely around the loop. • Cabling is generally IBM "Type-1" shielded twisted pair, with unique hermaphroditic connectors.

20. Token Ring • Initially (in 1985) token ring ran at 4 Mbit/s, but in 1989 IBM introduced the first 16 Mbit/s token ring products and the 802.5 standard was extended to support this. • Token ring LANs normally use differential Manchester encoding of bits on the LAN media.

21. Token Ring

22. Token Ring

23. Ethernet and itsvariants “dominant” wired LAN technology: • cheap $20 for NIC • first widely used LAN technology • simpler, cheaper than token LANs and ATM • kept up with speed race: 10 Mbps – 10 Gbps Metcalfe’s Ethernet sketch

24. Ethernet: Unreliable, connectionless • connectionless: No handshaking between sending and receiving NICs • unreliable: receiving NIC doesn’t send acks or nacks to sending NIC • stream of datagrams passed to network layer can have gaps (missing datagrams) • gaps will be filled if app is using TCP • otherwise, app will see gaps • Ethernet’s MAC protocol: unslotted CSMA/CD

25. Manchester encoding 5: DataLink Layer • used in 10BaseT • each bit has a transition • allows clocks in sending and receiving nodes to synchronize to each other • no need for a centralized, global clock among nodes! • Hey, this is physical-layer stuff!

26. Ethernet Evolution

27. 802.3 MAC Frame

28. Categories of Standard Ethernet

29. Encoding in a Standard Ethernet

30. 10Base5 implementation

31. 10Base2 implementation

32. 10Base-T implementation

33. 10Base-F implementation

34. Summary of Standard Ethernet implementations

35. A network with and without a bridge

36. Switched Ethernet

37. Fast Ethernet implementations

38. Encoding for Fast Ethernet

39. Summary of Fast Ethernet

40. Gigabit Ethernet

41. Encoding in Gigabit Ethernet

42. Summary of Gigabit Ethernet

43. Summary of Ten-Gigabit Ethernet

44. Exam for Unit 6 • Deadline: Friday, December 5, 2008 at Professor Cubicle. • Equipments: 3 persons maximum • Research Structured Cabling (All the contents of Unit 6). • Documentation 70% • Oral Exam 30%

45. Unidad VI Fundamentos de Construcción de una LAN 6.1 Fundamentos 6.2 Cableado estructurado. 6.2.1 Estándares vigentes. 6.2.2 Diseño y documentación básicos de redes. 6.2.3 Seguridad física. 6.2.4 Planificación del cableado estructurado. 6.2.4.1 Backbone 6.2.4.2 Cableado horizontal.

46. Unidad VI Fundamentos de Construcción de una LAN 6.2.5 Especificación del centro de cableado (SITE). 6.3 Análisis de necesidades. 6.4 Diseño de una LAN. 6.5 Instalación y configuración.

47. Wireless Ethernet Basic Service Sets

48. IEEE 802.11 Extended Service Sets

49. MAC Layers in WiFi

50. CSMA/CA with NAV