Ch 13. Wired LANs: Ethernet

13.1 IEEE Standards

• Project 802 launched in 1985– To set standards to enable intercommunication

among equipment from a variety of manufacturers

Data Link Layers

• Framing– Logical Link Control (LLC)

– Medium Access Control (MAC)

• CSMA/CD for Ethernet LAN• Token passing for Token Ring and Token Bus LAN

flow and error control

13.2 Standard Ethernet

• Ethernet– Originally developed at Xerox’s Palo Alto Research

Center (1976)• Generations– Standard Ethernet: up to 10 Mbps– Fast Ethernet: up to 100 Mbps– Gigabit Ethernet: up to 1 Gbps– Ten Gigabit Ethernet: up to 10 Gbps

Frame Format

• 802.3 MAC frame format

Frame Length

– Minimum length is required for collision detection– Maximum length is for small buffer size and preventing

monopoly of shared medium

Physical Address

• Addressing– 6-byte physical address, in hexadecimal notation

– Usually dedicated to network interface card (NIC)• Support unicast, multicast, and broadcast– Refer to the textbook

Multiple Access

• Access method– 1-persistent CSMA/CD– Slot-time = round-trip time + time to send the jamming

• Defined in bits: 512 bits (= 51.2 us over 10-Mbps Ethernet)• To detect collision on time, a station should be able to detect a

collision before it sends out the minimum-size frame (512 bits)

– Maximum network length• = propagation speed x slot time / 2• = (2x108m/s) x (51.2 us) / 2 = 5120m• Time for sending the jamming signal and others (e.g.,

repeater) reduces it to 2500m

Coding

• Now, we move from MAC to PHY • Manchester encoding and decoding

– Help synchronization owing to the transition in the middle

– Requires doubled signal rate of the original

Cables for Ethernet

• Implementations

13.3 Changes in the Standard

• Bridged Ethernet– Connect two or more Ethernet networks by

“bridge”

– Bridge acts as a station in each separate network, and prevents signals from propagating across networks

• Effects of bridge– Raising the bandwidth– Separating collision domains

domaindomain

• Switched Ethernet– Multi-port bridge allows the bandwidth is shared

only between the station and the switch

Layer 2 switch or switching hub

• Full-Duplex Ethernet– Increase the capacity of each domain from 10

Mbps up to 20 Mbps

13.4 Fast Ethernet

• IEEE 802.3u– Upgrade the data rate to 100 Mbps– Make it compatible with Standard Ethernet– Keep the same 48-bit address– Keep the same frame format – Keep the same min. and max. frame lengths

• MAC– CSMA/CD– Autonegotiation

• PHY– Point-to-point or start topologies only (no bus

topo.)• Implementation

13.5 Gigabit Ethernet

• IEEE 802.3z– Upgrade the data rate to 1 Gbps– Make it compatible with Standard or Fast Ethernet– Use the same 48-bit address– Use the same frame format– Keep the same min. and max. frame lengths– Support autoconfiguration as defined in Fast

Ethernet

Modes of Gigabit Ethernet

• Full-duplex mode with switch – mostly used• Half-duplex mode with hub– Traditional: 512-bit min. frame slot time = 0.512us max. network length = 25m

– Carrier extension: 512-byte min. frame slot time = 4.098us max. network length = 200m

– Frame bursting: combine multiple short frames as a single frame

• Topologies– Point-to-point, star,

two stars, and hierarchy of stars

• Implementation

Homework

• Exercise in Chapter 13– 16– 17– 18– 19