Chapter Objectives After completing this chapter you will be able to: Describe in detail the following Local Area Network (LAN) technologies: Ethernet Token Ring - Fibre Distributed Data Interface (FDDI) - Wireless LAN

LAN Protocols

Ethernet Ethernet is one of a family of network architectures governed by a protocol called Carrier Sense Multiple Access/Collision Detect (CSMA/CD). This type of network follows the Institute of Electrical and Electronic Engineers (IEEE) standard 802.3

CSMA/CD Collision Detect Carrier Sense Multiple Access Listen Wait Send & Listen Access All Terminals Detect Calculate Send

Ethernet Access Media

Ethernet Hubs There are two kinds of hub:  Repeater hubs - Each port of a repeater hub links individual Ethernet media segments together to create a larger network that operates as a single Ethernet LAN.  Switching hubs - This kind of hub provides packet switching, typically based on bridging ports. Each port of a packet switching hub provides a connection to an Ethernet media system that operates as a separate Ethernet LAN. Unlike a repeater hub whose individual ports combine segments together to create a single large LAN, a switching hub makes it possible to divide a set of Ethernet media systems into multiple LANs that are linked together by way of the packet switching electronics in the hub.

Components in an Ethernet System

Twisted-Pair Media System

Destination Address Source Address FCS Number of bytes: SOF = Start of frame FCS = Frame check sequence Minimum frame size = 64 bytes Maximum frame size = 1518 bytes Ethernet Frame Format

MAC Addressing There are two, MAC Layer addresses in an Ethernet frame. The first is the address of the source device and the second is the intended destination device. Each address consists of 48 bits, or 12 hexadecimal digits, which are typically denoted by six, two- digit hexadecimal numbers: C The first six digits (high order) identify the manufacture and the last six digits (low order) are used for a serial number

Multicast Serial NumberManufacturer's Address Octet OrderBit Order Multicast Bit

Fast Ethernet Transmission Medium

Gigabit Ethernet  Latest extension to Ethernet  1000 Mbit/s - 10 times faster than Fast Ethernet  Compatible with existing Ethernet

Token Ring Network

Advantages of Token Ring  High reliability, the ring can continue normal operation despite any single fault  Bypassing inactive stations  Effective use, 95% in Token Ring only whilst 30-40% in Ethernet  Excellent traffic handling  Large maximum frame length  High bandwidth efficiency. 70% in Token Ring, 30% in Ethernet  Many media choices: UTP, STP, coaxial or optical fibre  Supports transmission priority

Frame Formats

Token Ring Management  Sending out a new token if one is lost  Re-sending messages  Ensuring that the token is passed in its proper sequence  Managing congestion  Automatically correcting network errors

Token Ring MSAU Token PC

FDDI Rings Outer ring used for data Inner ring unused except during failure Workstation Failed Station Inner ring unused except during failure Workstation AB

Station Types  Dual attached station (DAS), which is connected to both rings  Single attached station (SAS), which is attached only to the primary ring  Dual attached concentrator (DAC), which is connected to both rings and provides connection for additional stations and concentrators. It is actually the root of a tree  Single attached concentrator (SAC), which is connected only to the primary ring (through a tree)

Main Steps in a Normal Frame Transmission 1. Sending station waits for token. 2. Sending station captures and strips token, and then transmits frames. 3. Sending station issues token at the end of transmission. 4. Destination station copies the transmitted frame and sets the A and C bits (address recognised and frame copied indicators). 5. Sending station removes the data from the ring by stripping the sent (and acknowledged) frame. 6. The first bytes of the frame are not stripped, and continue to circulate on the ring (as a fragment). Each repeating station strips one byte from the fragment, and a transmitting station completely strips it

Frame Formats

Wireless LAN

Peer-to-Peer