- How a
receiver
decide on
reception/loss:
-
If a received frame
passes the
CRC-checksum test, the
frame will be
received:
- If a received frame
fails the
CRC-checksum test, the
frame will be
rejected:
A rejected frame is lost !!!
-
If a received frame
passes the
CRC-checksum test, the
frame will be
received:
- Recall:
There are 2 kinds of
networks:
- Switched Networks
- Broadcast Networks
- Switched Networks
- Properties of
switched networks:
- Switched networks
spans long distances
- Transmissions over
long distance are
more
susceptable
to transmission error
- Reason: noise !!!
- The main cause of
frame losses is:
- bit errors (due to noise ) in the received frame
- Switched networks
spans long distances
- Properties of
broadcast networks:
- Broadcast network
is always
a Local Area Network
that spans
short distances
- Transmissions over
short distance
will
rarely contain
transmission errors
- The main cause
of frame losses in
broadcast networks is:
- collisions caused by simultaneous frame transmissions by different sources
- Broadcast network
is always
a Local Area Network
that spans
short distances
- Consequently:
- The Datalink layer in
switched networks
will focus on:
- How to
recover
a
(lost) frame
(to make sure the receiver will get a frame correctly).
- How to
recover
a
(lost) frame
- The Datalink layer in a
broadcast network will
focus on:
- How to
access
the transmission medium
(to make sure there is only one transmission at a time !!!)
- How to
access
the transmission medium
- The Datalink layer in
switched networks
will focus on:
- We will discuss the
Datalink layer of
switched networks first...
Then the Datalink layer of broadcast networks