Posts Tagged ‘ethernet’
July 28th, 2008 | 
Author: Standards and Implementation:
The first LAN ever was Ethernet.
Robert Metcalfe and coworkers at Xerox in mid 70s.
The first Ethernet standard published 1980 by DigitalEquipCorp, Intel, Xerox (DIX).
Metcalfe wanted it to be a shared open standard.
1985 IEEE published standards for LANs.
For compatibility with OSI, small mods made to Ethernet standards with 802.3.
Ethernet –L1 and L2:
Ethernet implemented in MAC sublayer and L1 only.
LLC:
The use of these sublayers contributes significantly to compatibility between diverse end devices.
802.2 describes LLC sublayer functions.
802.3 describes the Media Access Control (MAC) sublayer and L1 functions.
LLC – software (drivers) – independent physical equipment.
Data Link Layer
2 primary functions:
1. Prepares L3 packets for transmission.
2. Controls access to the physical media.
Accessing the media:
A L3 exchange may involve many L2 and media transitions.
At each hop, routers decapsulate and re-encapsulate frames to match the right media.
The L3 protocol is not aware of which media is used.
L2 includes many types of media and access methods (eg. how it is getting to the wire).
L2 protocols specify the frame type and how to get a frame on and off each medium (media access control method, MAC method).
Devices use adapters to connect to a network (eg. NIC)
The adapter manages the framing and media access control (generates the signal transition).
Routers have different physical interfaces that frame the data as suitable for each link.