1. Ethernet Kenneth Castelino

2. Network Architecture - Protocols Physical: Actual signal transmission Data-Link: Framing / Error Detection Network: Routing / Addressing Transport: Congestion / Flow Control Application: Specific to user needs

3. Layered Protocols – (HTTP)

4. Data Link Layer - Ethernet Invented in 1973 @ Xerox. (IEEE 802.3) Originally a LAN technology – extended to MAN / WAN. Same frame format, different wiring schemes, data rates across generations. Most common version (10BaseT) – 1990.

5. Ethernet Generations Original Ethernet: Coaxial cable (10Base5) Thicknet. Next Generation: Thin coax cable (10Base2) Thinnet. Modern Ethernet: Twisted pair ethernet (10BaseT) Uses hub: physical star but logical bus.

6. Ethernet Components NIC – Network Interface Card Integrated Tx/Rx – direct interface to medium. MAU – Media Attachment Unit Attaches network interface to the medium (integrated into NIC). AUI – Attachment Unit Interface Decouple physical layer -reuse MAC design with different media. MII – Media Independent Interface Like AUI for gigabit / faster ethernets.

7. Ethernet Addressing 48-bit address Address assigned when NIC card is manufactured. Packets can be sent to Single address – Unicast All stations on network – Broadcast (address = all 1s.) Subset of stations – Multicast Broadcast (address = all 1s.) All receivers accepts unicast / broadcats. Half addresses reserved for multicast (2 47 ) NIC can accepts zero or more multicasts.

8. Ethernet Frame Sender adds: Senders address is source Recepients addreess in destination Type of data in frame type Error check data (CRC) Receiver NIC: Gets transmitted frame. Examines address and either accepts or rejects. Passes frame to system software.

9. Shared medium – stations take turns at sharing the medium. Media access control ensures fairness. CSMA / CD Carrier Sense: wait till medium is idle before sending frame. Multiple Access: multiple computers use the same shared media. Each uses same access algorithm. Collision Detection: Listen to medium – detect if another station’s signal interferes – back off and try again later. Media Access Control - MAC

10. CSMA / CD If collision occurs: wait a random time t 1 - 0< t 1 <d. D depends on transmission speed – time for frame width or 512 bits. If second collision occurs, wait a random time t 2 - 0< t 2 <2d. Double range for each succesive collision. Exponential backoff No acknowledgement like TCP. CSMA/CA used in wireless networks where not all stations receive message. Both sides send small message followed by data: X is about to send to Y Y is about to receive from X Data frame sent from X to Y.

11. Recent Developments 100Base-FX LED light source / MMF / 2 km max distance. Modal dispersion – limited bandwidth 100Base-SX (IEEE 802.3z) Short wavelength laser (850 nm) Max distance = 5 km. 100Base-LX Long wavelength laser (1310 nm) Max distance = 5 km.

12. Beyond Gigabit Ethernet 10 Gb/s Ethernet No CSMS/CD, same frame format. Applications Upgrade LANs / Backbone. MAN applications.

13. References [1] I.P. Kaminow, Tingye Li, Ed., “Optical Fiber Telecommunications IV”, Chapter 11, Academic Press, 2002. [2] John Chuang, SIMS 250, UC Berkeley, Fall 2001.