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

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. NICs handle: 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 H igher 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