Layer 1 (physical media) only describes bit streams and cannot communicate with upper layers in OSI model

Layer 2 can and its sub-layers can

Data Link layer has 2 sub-layers LLC closer to Network layer and MAC (media access control) closer to physical layer

IEEE (institute of electrical and electronic engineers) 802.3 & 802.5 are dominant and best known LAN standards 

MAC Add 48 bits (12 Hex digits) first six Manufacturer OUI (organizational unique identifier) and last six vendor assigned number

BIA’s (burned in MAC addresses/this is what all MAC addresses are) MAC address in ROM and copied to RAM when in use

MAC addresses are flat – they have no structure

Layer 1 puts out a meaningless bit stream in layer two it is interpreted and given a meaning

OSI Model

Layer 7-4 hosts
Layer 3 layer that routers operate at
Layer 2 is the layer switches operate at
Layer 1 Repeater, hubs, cables, etc.

PDU (protocol Data Unit)
Layer 1 Bits
Layer 2 Frames 
Layer 3 Packets
Layer 4 Segments
Layer 5-7 Data











Ethernet (802.3 Frame)




Preamble	

Destination Address	

Source Address	

Length/
Type	


Data	

FCS
(Frame Check Sequence)

6.1.5 know three primary ways and process of FCS