Wired LANs: Ethernet

Wired LANs: Ethernet

IEEE Standards
Standard Ethernet
Changes in the Standard
Fast Ethernet
Gigabit Ethernet


IEEE Standards

In 1985, the Computer Society of the IEEE started a project, called Project 802, to set standards to enable intercommunication among equipment from a variety of manufacturers. Project 802 is a way of specifying functions of the physical layer and the data link layer of major LAN protocols.

IEEE 802 Working Group

Active working groups Inactive or disbanded working groups
802.1 Higher Layer LAN Protocols Working
Group
802.3 Ethernet Working Group
802.11 Wireless LAN Working Group
802.15 Wireless Personal Area Network
(WPAN) Working Group
802.16 Broadband Wireless Access Working
Group
802.17 Resilient Packet Ring Working Group
802.18 Radio Regulatory TAG
802.19 Coexistence TAG
802.20 Mobile Broadband Wireless Access
(MBWA) Working Group
802.21 Media Independent Handoff Working
Group
802.22 Wireless Regional Area Networks 802.2 Logical Link Control Working Group
802.4 Token Bus Working Group
802.5 Token Ring Working Group
802.7 Broadband Area Network Working
Group
802.8 Fiber Optic TAG
802.9 Integrated Service LAN Working
Group
802.10 Security Working Group
802.12 Demand Priority Working Group
802.14 Cable Modem Working Group

Logical Link Control (LLC)

Framing: LLC defines a protocol data unit (PDU)
To provide flow and error control for the upper-layer protocols that actually demand these services

Standard Ethernet

The original Ethernet was created in 1976 at Xerox’s Palo Alto Research Center (PARC). Since then, it has gone through four generations

MAC Sublayer

Preamble: alerting the receiving system to the coming frame and enabling it to synchronize its input timing
CRC: CRC-32

Addressing

The least significant bit of the first byte defines the type of address.If the bit is 0, the address is unicast; otherwise, it is multicast
The broadcast destination address is a special case of the multicast address in which all bits are 1s
Ethernet address in hexadecimal notation


Ethernet

Access method: 1-persistent CSMA/CD
Slot time = rount-trip time + time required to send the jam sequence
512 bits for Ethernet, 51.2 μs for 10 Mbps Ethernet

Slot time and collision

Slot time and maximum network length
MaxLength = PropagationSpeed x SlotTime/2
MaxLength = (2 x 108) x (51.2 x 10-6/2) = 5120 m
MaxLength = 2500 m 48 % of the theoretical calculation by considering delay times in repeaters and interfaces, and the time required to send the jam sequence

Fast Ethernet

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


MAC Sublayer
CSMA/CD for the half-duplex approach
No need for CSMA/CD for full-duplex Fast Ethernet

Autonegotiation: allow two devices to negotiate the mode or data rate of operation



Gigabit Ethernet

Under the name of IEEE 802.3z
Upgrade the data rate to 1 Gbps
Make it compatible with Standard or Fast Ethernet
Keep the same 48-bit address and the same frame format
Keep the same min. and max. frame length
Support autonegotiation as defined in Fast Ethernet

MAC Sublayer
Most of all implmentations follows full-duplex approach
In the full-duplex mode of Gigabit Ethernet, there is no collision; the maximum length of the cable is determined by the signal attenuation in the cable.
Half-duplex mode (very rare)
Traditional: 0.512 μs (25m)
Carrier Extension: 512 bytes (4096 bits) min. length
Frame bursting to improve the inefficiency of carrier extension



Ten-Gigabit Ethernet

Under the name of IEEE 802.3ae
Upgrade the data rate to 10 G bps
Make it compatible with Standard, Fast, and Giga Ethernet
Keep the same 48-bit address and the same frame format
Keep the same min. and max. frame length
Allow the interconnection of existing LANs into a MAN or WAN
Make Ethernet compatible with Frame Relay and ATM