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)
 flow and error control
– Medium Access Control (MAC)
• CSMA/CD for Ethernet LAN
• Token passing for Token Ring and Token Bus LAN
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
domain
– Connect
domain
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
• Switched Ethernet
Layer 2 switch or
switching hub
– Multi-port bridge allows the bandwidth is shared
only between the station and the switch
• 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