1. DCN286 Introduction to Data Communication Technology Session 7

2. Review 1) Which type of cabling is the most appropriate choice for Ethernet connectivity from a switch to a workstation? a) Coaxb) UTP c) Fibre-optic d) RJ-11 2) Comparing switches, hubs, repeaters and bridges, which of these devices typically have multiple ports that provide a convenient connection point for end-user computers (Select the two best answers)? a) Repeaterb) Switch c) Bridged) Hub 3) For which of the following do you need a cross-over cable? a) Connecting a switch to a switchb) Connecting a switch to a router c) Connecting a workstation to a hubd) Connecting a workstation to a switch 4) What data-transmission method does a WAN use? a) Parallelb) Serial c) Singled) None of the answers are correct 5) Which of the following best describes a DCE device? a) User device at the end of a networkb) Equipment that serves as the data c) Physical devices such as protocol source or destination translators and multiplexersd) Device that provides the clocking rate for a serial connection

3. Objectives Ethernet Naming Ethernet Standards Ethernet Frames MAC Addresses CSMA/CD Full Duplex, Half Duplex, Collision Domains Deterministic and Nondeterministic Media Access 10Mbps Ethernet 10BASE-T Ethernet 100Mbps Ethernet Gigabit Ethernet Note: Hubs are represented by the symbol: Switches are represented by the symbol:

4. Ethernet Names consist of three parts: Speed – Transmission Type – Cabling Speed – measured in Mbps 10 – 10Mbps 100 – 100Mbps 1000 – 1Gbps Transmission Type BASE – baseband transmission BROAD – broadband transmission Cabling – type of cable T – UTP F – Fibre # - coaxial, provides maximum length in 100m (2, 5, etc) 4 Ethernet Naming

5. Transmission Type BASE – baseband transmission Uses a single frequency for transmitting data BROAD – broadband transmission Uses a range of frequencies for transmitting data E.g. FM radio is BROADBAND, a range of 200kHz is used, with the station's defined frequency in the middle. Station: 97.5MHz (“97.5 on your FM dial” as the announcer would say) uses a range of frequencies from 97.4MHz to 97.6MHz 10BROAD36, 10BASE5, 100BASE-FX, 10BASE-T? 5 Ethernet Naming

6. IEEE Ethernet Standards Originated by Xerox in 1970s DIX Ethernet Xerox teamed up with Intel and Digital Equipment Corp (DEC) to release products and establish proprietary standards. DIXv2 Second release of DIX (version 2) publish in 1980. The basis for 10BASE5 IEEE took over Ethernet standards from the original companies in February 1980 (giving the committee its name: 802) 6 Ethernet Standards

7. IEEE802 created several sub-committees for different LAN standards: IEEE802.1 – LAN management and control functions IEEE802.2 – standards that apply to several types of LANs IEEE802.3 – Ethernet standards 10BASE5 – 1980 10BASE2 – 1985 10BASE-T – 1990 Fast Ethernet (100Mbps) – 1995 Gigabit Ethernet - 1Gbps 1998 10Gigabit Ethernet – 10Gbps - 2002 IEEE802.4 – Token Bus LANs IEEE802.5 – Token Ring LANs 7 Ethernet Standards

8. IEEE802.1 – LAN Management and control functions Management and control functions that could be used by any IEEE802 LAN – e.g. Spanning Tree Protocol IEEE802.2 – Standards that apply to several types of LANs Standardize features that encompassed three early LANs defined by 802.3, 802.4, 802.5. They determined that the LAN types needed to control the LAN using a set of logic and rules. The standard was named Logical Link Control - LLC 8 Ethernet Standards

9. Ethernet LAN Physical Layer 9 Ethernet Standards - OSI Model Data Link Layer Physical Layer ISO Layers Ethernet IEEE 802.2 (Logical Link Control - LLC) IEEE 802.3 (Media Access Control – MAC and physical details including cabling details) 10BASE2 802.3 - 10BASE5 10BASE-T 10BASE-F 802.3u - 100BASE-TX 100BASE-FX 100BASE-T4 802.3ab - 1000BASE-T 802.3z - 1000BASE-X Network Access Layer TCP/IP Layers LLC MAC

10. MAC Sublayer The MAC sublayer performs functions that the OSI Physical Layer cannot (by definition within standards): Physical Layer cannot communicate with upper layer protocols. MAC sublayer can Physical Layer cannot identify other computers. MAC sublayer defines physical addresses (MAC addresses) Physical layer defines how to send bits, but cannot interpret their meaning – MAC sublayer standard defines framing Physical Layer cannot manage the process of which device can send, and at what time. MAC Sublayer defines CSMA/CD 10 Ethernet Standards

11. MAC Sublayer defines framing. Why? AAAAAAAAAAAAAAAB0004AC5824185004A0C82008004510028B77A40004006B08E0A000 0648ECC3987AF17001790B288C4C1A71588501016D026780000DE04 11 Ethernet Framing ETHERNET FRAME Network Transport Application

12. Fields of the Ethernet Frame Three styles of Ethernet Frames: DIX IEEE 802.3 (Original) IEEE 802.3 (1997) 12 Ethernet Framing Preamble 8 Destination 6 Source 6 Type 2 Data and Pad 46 - 1500 FCS 4 Preamble 7 SFD 1 Destination 6 Source 6 Length 2 Data and Pad 46 - 1500 FCS 4 Preamble 7 SFD 1 Destination 6 Source 6 Length / Type 2 Data and Pad 46 - 1500 FCS 4

13. Fields of the Ethernet Frame Preamble Synchronization (7 bytes of 10101010) Start Frame Delimiter (SFD) Signifies that the next byte begins the Destination MAC field (1 byte = 10101011) Destination Physical address of recipient of this frame Source Physical address of sender of this frame Length Defines the length of the frame's next data field (if present, Type is NOT present) 13 Ethernet Framing Preamble 7 SFD 1 Destination 6 Source 6 Length / Type 2 Data and Pad 46 - 1500 FCS 4

14. Fields of the Ethernet Frame Type Defines the type of protocol listed inside the frame (if present, Length is NOT present) Data and Pad Data from the higher layer protocols (Network, Transport, Application). Data field must be at least 46 bytes Frame Check Sequence (FCS) An error detection scheme. Uses CRC-32. Treats the message as if it is one large number. Performs division on 'number' using “generating polynomial”. The remainder (32 bits) is the FCS. The receiver performs the same calculation (including FCS) – if result is zero, no bits have been corrupted. 14 Ethernet Framing Preamble 7 SFD 1 Destination 6 Source 6 Length / Type 2 Data and Pad 46 - 1500 FCS 4

15. Fields of the Ethernet Frame Length / Type How do you know if it is a Type field or a Length field? Type Protocols are numbers > 0600 16, whereas Lengths are less than 0600 16 CRC-32 How reliable is it? Single bit errors = 100% Double bit errors = 100% Odd number of bits in error = 100% Error burst length < r + 1 = 100% Error burst length = r + 1 = 1 – (½) (r – 1) = 99.999999953% Error burst length > r + 1 = 1 – (½) r = 99.999999976% 15 Ethernet Framing Preamble 7 SFD 1 Destination 6 Source 6 Length / Type 2 Data and Pad 46 - 1500 FCS 4

16. Structure of MAC address Each MAC address is split into two parts: OUI – Organization Unique Identifier – 24 bits (3 bytes) that identify the manufacturer of the NIC card Vendor Assigned – 24 bits that uniquely identify a card within the OUI The MAC address is permanently assigned to a card and is burned into the hardware (also referred to as a BIA – Burned-In Address). All BIA assigned to a NIC must use the 24 bits assigned to the vendor All BIAs within the OUI must be unique 16 MAC Addresses

17. Interpreting OUI with Protocol Analyzer (Wireshark) 17 MAC Addresses

18. Carrier Sense Multiple Access with Collision Detection As the Ethernet network is a broadcast network, it is possible for two hosts to transmit at the same time. CSMA/CD resolves the problem: 1) Host listens for any other stations transmitting 2) If no Host is transmitting, send a message 3) Listen as you transmit for a corrupted message (collision) 4) Try to resend the message What are the ramifications of this type media access? 18 CSMA/CD

19. Carrier Sense Multiple Access with Collision Detection 1) Carrier Sense – listen for another station transmitting 2) Multiple Access – Two stations simultaneous transmit their messages (both did not hear a carrier) 3) Collision Detection – The signals collide, corrupting what each sending host hears compared to what they are sending 4) Transmitting hosts send a jamming signal (32 bits: 01010101010101010101010101010101) 5) Transmitting hosts each set a semi-random timer 6) When timer expires, repeat from step 1 19 CSMA/CD

20. Half Duplex By nature of the CSMA/CD protocol, it is Half Duplex Full Duplex When using a switch, the frames that enter the switch are buffered when more than 1 frame is destined for a port 20 Full Duplex, Half Duplex, Collision Domains HostC HostB HostA HostD MessageB MessageC Turning on Full Duplex, disables CSMA/CD

21. Collision Domains The devices and ports that will experience collisions 21 Full Duplex, Half Duplex, Collision Domains

22. Nondeterministic Media Access CSMA/CD is nondeterministic – there is no way to determine the number of times a device will access the LAN or how much bandwidth will be used. If an unlucky host keeps colliding with other hosts, it may be a few seconds before it can send a message. As access is more of a probability, CSMA/CD is sometimes referred to as Probabilistic Deterministic Media Access Token Ring is deterministic – we can predict access to the media as the use of the token ensures equal or near equal access to the media. Works like First Nations “Circle Talk”. 22 Deterministic & Nondeterministic Media Access

23. 10BASE5 AUI (Attachment Unit Interface) and coaxial wiring 10BASE2 BNC (same as CATV) and coaxial wiring 10BASE-T RJ45 and UTP wiring 23 10Mbps Ethernet www.wikipedia.org

24. All three 10Mbps Ethernet standards support any of the three Ethernet Frame standards: DIX IEEE802.3 (original) IEEE802.3 (1997) Use logical bus topology Asynchronous Transmission (no electrical signals are present when no data is being sent – the media is idle) The preamble and SFD is how the NIC cards synchronize themselves with the incoming message Use CSMA/CD Half duplex 24 10Mbps Ethernet

25. 10BASE-T Physical star topology (10BASE5, 10BASE2 are physical bus topology) Support for Full Duplex after 1997 (IEEE802.3x), with the following restrictions Ethernet switches/bridges must be used (no hubs or repeaters) Only two Ethernet interfaces can be in the same collision domain Full Duplex Doubles the bandwidth (10Mbps each direction = 20Mbps) Wiring types: Cat3 UTP (installed for telephones, so piggyback on installed infrastructure) Cat5 UTP Cat5e UTP How do you wire a straight-through cable? How do you wire a crossover cable? 25 10Mbps Ethernet

26. Design – Hubs, CSMA/CD and Half Duplex What is the 5-4-3 Rule? Propagation delay is reason for limiting Hubs/Repeaters Does this satisfy the 5-4-3 Rule? What is the Collision Domain? 26 10BASE-T Ethernet

27. Does this satisfy the 5-4-3 Rule? 27 10BASE-T Ethernet

28. Does this satisfy the 5-4-3 Rule? 28 10BASE-T Ethernet

29. Design – Using Switches 5-4-3 Rule applies to each Collision Domain Does this satisfy the 5-4-3 Rule? What is the Collision Domain? 29 10BASE-T Ethernet

30. 100BASE-TX and 10BASE-T Ethernet Same Cat5/Cat5e cabling, with same 100m restriction Supports CSMA/CD, half duplex Support auto negotiation Ethernet frame is the same Uses same pinouts on RJ-45 connector Can disable CSMA/CD to use Full-duplex – same conditions as IEEE802.3x. 100BASE-TX Uses synchronous transmission – always transmitting bits Uses an 'idle frame' to indicate that no data is being sent Listens for idle frames when determining when to send data 30 100Mbps Ethernet

31. 100BASE-FX Was preceded by FDDI (Fibre Distributed Data Interface) Did not catch on as much as 100BASE-TX: Companies had already bought the infrastructure for FDDI Other Companies opted for ATM (Asynchronous Transfer Mode) running up to 622Mbps Introduction of 1000BASE-X doomed 100BASE-FX 31 100Mbps Ethernet

32. 1000BASE-X Covers three Gigabit Ethernet Standards: 1000BASE-X (fibre) 1000BASE-SX (short distance, fibre) 1000BASE-LX (long distance, fibre) 1000BASE-SX Multi-mode fibre (laser transmitter) 220m limit (can be extended to 500m) 1000BASE-LX Single-mode fibre 5000m limit 1000BASE-T Cat 5e UTP copper cable, all 4 pairs used 100m limit 32 Gigabit Ethernet

33. Advantages of 1000BASE-SX/1000BASE-LX over 1000BASE-T Noise immunity No grounding or potential electrical problems Various options for different types of cables, connectors, price points Greater cabling distances However, fibre is still more expensive than copper: CableLength (type)Cost ($2007) 1000BASE-SX33' (patch)$165 1000BASE-LX33' (patch)$354 1000BASE-T1000' (bulk) $260 33 Gigabit Ethernet