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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