Chapter 14 Local Area Networks

1. Chapter 14 Local Area Networks Prof. Choong Seon HONG

2. Introduction • Three Generations of Ethernet

3. 14.1 Traditional Ethernet • Mac Sublayer • Physical Layer • Physical Layer Implementation • Bridged Ethernet • Switched Ethernet • Full-Duplex Ethernet

4. Traditional Ethernet • Designed to operate at 10 Mbps • Access through CSMA/CD • Media shared between all stations

5. 802.3 MAC frame • Preamble – 7 bytes of alternating 0s and 1s to alert the receiver and allow it to synchronize • Start Frame Delimiter (SFD) – 1 byte – 10101011 signals the beginning of a frame, last chance for synchronization – last 2 bits are 11 • Destination address (DA) – 6 bytes – contains the physical address of the destination station or stations • Source address (SA) – 6 bytes – contains the physical address of the sender • Length/type – if less than 1518 then it defines the length of the data field – if more than 1536 then it defines the type of the PDU packet that is encapsulated • Data – data encapsulated from upper-layer protocols : 46 ~ 1500 bytes • CRC – CRC-32

6. Minimum and maximum length of a Frame

7. Addressing • Ethernet addresses in hexadecimal notation • Each station on an Ethernet network has its own network interface card (NIC) • NIC provides the station with a 6-byte physical address

8. Unicast and Multicast and Broadcast Address • Source address is always unicast • Destination can be unicast, multicast, or broadcast • Unicast specifies one recipient • Multicast specifies multiple recipients • Broadcast sends to all stations on the network – destination address is forty-eight 1s

9. Physical Layer • Physical layer for 10-Mbps Ethernet

10. Physical Layer Signalling(PLS) • PLS sublayer encodes and decodes data • Using Manchester Encoding • Data rate of 10 Mbps

11. Attachment Unit Interface (AUI) • A Specification that defines the interface between the PLS and MAU. • Developed to create a kind of medium-independent interface interface.

12. Medium Attachment Unit (MAU) • MAU (transceiver) : transmitter and receiver • Transmitting signals over the medium; receiving signals over the medium; detecting collisions • Medium dependent • Transceiver is a transmitter and receiver, can be external or internal • Position and Functions of a Transceiver

13. Medium Dependent Interface (MDI) • To connect the transceiver (internal, external) to medium, we need a MDI. • For an external transceiver, it can be a tap or a tee connector. • For an internal transceiver, it can be a jack.

14. Physical Layer Implementation • Categories of traditional Ethernet

15. 10Base5 : Thick Ethernet • thick Ethernet or Thicknet • bus topology, external transceiver • Connection of a station to the medium using 10Base5

16. 10Base2 : Thin Ethernet • Connection if stations to the medium using 10Base2 • Thin Ethernet or Cheapernet • bus topology, internal transceiver or a point-to-point connection via an external transceiver

17. 10Base-T : Twisted Pair Ethernet • physical star topology • stations connected to a hub with internal or external transceiver

18. 10Base-FL : Fiber Link Ethernet • fiber link Ethernet • uses star topology to connect stations to a hub • normally implemented with external transceiver having two pairs of fiber-optic cables connecting it to the hub

19. Bridged Ethernet • Raising the bandwidth • Separating collision domains

20. Sharing Bandwidth

21. Raising the Bandwidth • A Network with and without a Bridge • 10/6 Mbps vs 10/12 Mbps in case that traffic is not going through the bridge

22. Separating Collision Domains

23. Switched Ethernet • Bandwidth is shared only between the station and the switch (5 Mbps each) • N-port switch; Switched Ethernet

24. Full-Duplex Ethernet • A Limitation of 10Base5 and 10Base2 half-duplex. • Evolution : switched Ethernet  full duplex Switched Ethenet • 10Base-T is always Full-duplex. • Full duplex mode increases the capacity of each domain from 10 to 20 Mpbs.

25. Full-Duplex Ethernet • No need for CSMA/CD, this functionality can be turned off. • Each link is a point-to-point dedicated path between the station and the switch. • For flow and error control • Adding a sublayer called MAC Control between MAC sublayer and LLC sublayer

26. 14.2 Fast Ethernet • Evolution from 10 to 100 Mpbs doesn’t change the MAC sublayer. • Access method is CSMA/CD, which is kept for backward compatibility. • Frame format, minimum and maximum frame lengths, and addressing are the same.

27. Autonegotiation • Allowing two devices to negotiate the mode or data rate of operation. • To allow incompatible devices to connect to one another. For example, between 10 Mbps-device and 100 Mbps-device • To allow one device to have multiple capabilities • To allow a station to check a hub’s capabilities

28. Physical Layer

29. Reconciliation • Replacing PLS sublayer in 10 Mbps Ethernet • But, encoding and decoding, which were performed by the PLS, are moved to the PHY sublayer (transceiver), because encoding in Fast Ethernet is medium-dependent. • Is responsible for passing of data in 4-bit format (nibble) to the MII.

30. MII • The AUI is replaced with the medium-independent interface (MII) • Can be used with both a 10-and 100Mbps data rate • Features a parallel data (4 bit at a time) path between the PHY sublayer and the reconciliation sublayer

31. PHY (Transceiver) and MDI • Transceiver is responsible for encoding and decoding. • MDI is need to connect the transceiver to the medium.

32. Physical Layer Implementation

33. 100Base-TX Implementation • Uses two pairs of twisted-pair cable • Physical star topology • Internal or external transceiver • Transceiver – responsible for transmitting, receiving, detecting collisions, and encoding/decoding data

34. Encoding and decoding in 100Base-TX • Encoding/decoding – first performs block encoding using 4B/5B, then encoded using MLT-3 (multiline transmission, three level)

35. 100Base-T4 • uses category 3 (voice-grade twisted pair) or higher UTP • uses 4 pairs • Encoding/Decoding – 8B/6T

36. Transmission Using Four Wires

37. Giga-bit Ethernet • No longer possible to keep the MAC sublayer untouched • Two distinctive approaches: half-duplex using CSMA/CD or full-duplex with no need for CSMA/CD

38. Physical Layer in Gigabit Ethenet

39. Physical Layer in Gigabit Ethenet • RS – reconciliation sublayer – sends 8-bit parallel data to the PHY sublayer via GMII interface • GMII – gigabit medium-independent interface) defines how reconciliation sublayer is to be connected to the PHY sublayer (transceiver) • does not exist outside the NIC • operates only at 1 Gbps • no connecter or cable • PHY (transceiver) – medium-dependent – encodes and decodes – can only be internal • MDI medium-dependent interface – connects transceiver to the medium – RJ-45 AND fiber-optic connectors

40. Gigabit Ethernet Implementation

41. 1000Base-X implementation • uses two fiber-optic cables • internal transceiver • encoding – 8B/10B then NRZ

42. Encoding in 1000Base-X

43. 1000Base-T implementation • designed to use category 5 UTP • four twisted pairs • encoding – 4D-PAM5 (4-dimensional, 5-level pulse amplitude modulation)

44. Encoding in 1000Base-T

45. Questions !