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CHAPTE R 15 Wired LAN Topology: Ethernet

CECS 474 Computer Network Interoperability. CHAPTE R 15 Wired LAN Topology: Ethernet. Tracy Bradley Maples, Ph.D. Computer Engineering & Computer Science Cal ifornia State University, Long Beach. Notes for Douglas E. Comer, Computer Networks and Internets (5 th Edition) .

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CHAPTE R 15 Wired LAN Topology: Ethernet

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  1. CECS 474 Computer Network Interoperability CHAPTER15 Wired LAN Topology: Ethernet Tracy Bradley Maples, Ph.D. Computer Engineering & Computer Science Cal ifornia State University, Long Beach Notes for Douglas E. Comer, Computer Networks and Internets (5th Edition)

  2. Versions of Ethernet • Newer versions of Ethernet have managed to stay compatible with older versions (i.e., the are backwards compatible). • Newer Ethernet Versions: • • Increase the transmission speed • • Keep the same Ethernet frame format • a fixed length header • a variable-length payload • a fixed length CRC

  3. Speeds of LANs vs. Computers • Often LANs operate at a rate so fast that the computer's CPU cannot process bits at network speed. • Network Interface Hardware • Q:How can a computer attach to a network that sends and receives bits faster that the CPU can handle? • A:Special-purpose hardware connects the computer to the network and handles all the details of packet transmission and reception. • The special-purpose hardware is known as a network adaptor card or network interface card (NIC). • NICs appear to be I/O devices to the computer. • NICshandle: • MAC address recognition • CRC computation • frame recognition • sending/receiving frames

  4. NICs are built for a specific network technology.

  5. Ethernet Wiring • There are three schemes of Ethernet wiring corresponding to the three generations of Ethernet Standards. • Note: All three generations use the same frame format. • Original Ethernet Wiring (First Generation) • First Generation: • Used heavy coaxial cable • Formal name 10Base5 • Informally called thicknet

  6. First Generation Ethernet Wiring (Cont'd) In 10Base5 wiring, a connection multiplexor can be used to let multiple computers attach to a network through a single transceiver. The multiplexor delivers exactly the same electrical signals as a transceiver, so a computer does not know whether it is attached to a transceiver or a multiplexor.

  7. Second Generation Ethernet Wiring • Second Generation: • Used thinner coaxial cable • Formal name 10Base2 • Informally called thinnet

  8. Modern Ethernet Wiring • Second Generation: • Uses a hub • Formal name 10Base-T • Informally called twisted pair Ethernet

  9. Example: Ethernet Wiring in an Office

  10. The Ethernet Topology Paradox • Apparently… • Original Ethernet used bus topology • Modern Ethernet uses star topology • In fact, modern Ethernet is… • Physical star • Logical bus • Called star-shaped bus • Higher Speed Ethernets • Fast Ethernet • Operates at 100 Mbps • Formally 100Base-T • Two wiring standards • 10/ 100 Ethernet devices available • 1 Gbit & 10Gbit Ethernet • Operates at 1000/10000 Mbps (1 Gbps/10 Gbps) • And Also… 40 Gbit, 100 Gbit and 1Tbit under Standardization with IEEE 802

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