responsible for the actual unique identification of each device that resides on
a local network.
between routers, it is framed with control information at the Data Link
layer, but that information is stripped off at the receiving router and only the
original packet is left completely intact. This framing of the packet continues
for each hop until the packet is finally delivered to the correct receiving host.
It's really important to understand that the packet itself is never altered along
the route; it is only encapsulated with the type of control information
required for it to be properly passed on to the different media types.
placed on the media. Contention media access is "first come/first served"
access where everyone shares the same bandwidth--hence the name.
Physical addressing is defined here, as well as logical topologies. What's
a logical topology? It's the signal path through a physical topology. Line
discipline, error notification (not correction), ordered delivery of frames,
and optional flow control can also be used at this sublayer.
tifying Network layer protocols and then encapsulating them. An LLC
header tells the Data Link layer what to do with a packet once a frame is
received. It works like this: A host will receive a frame and look in the LLC
header to find out the packet is destined for, say, the IP protocol at the
Network layer. The LLC can also provide flow control and sequencing of
control bits.
both work at the Data Link layer and filter the network using hardware
(MAC) addresses. Layer-2 switching is considered hardware-based bridging
because it uses specialized hardware called an application-specific integrated
circuit (ASIC). ASICs can run up to gigabit speeds with very low latency rates.