5. Importance Relevance Significance
• To maximize the
bandwidth
utilization
• ALOHA
• Carrier Sense
Multiple Access
• Carrier Sense
Multiple Access with
Collision Detection
• Carrier Sense
Multiple Access with
Collision Avoidance
• In random access or
contention methods, no
station is superior to
another station and none
is assigned the control
over another. No station
permits, or does not
permit, another station
to send. At each instance,
a station that has data to
send uses a procedure
defined by the protocol
to make a decision on
whether or not to send.
6. • No idle state
How to achieve the maximum utilization?
• Multiple send/receive
• Avoid Collision
• Avoid Trafficking
2
1
3
4
20. Note In CSMA/CA, if the station
finds the channel busy, it
does not restart the timer
of the contention window;
it stops the timer and
restarts it when the
channel becomes idle.In CSMA/CA, the
IFS can also be
used to define the
priority of a
station or a frame.
23. Controlled Access
In controlled access, the stations
consult one another to find which
station has the right to send. A station
cannot send unless it has been
authorized by other stations. We
discuss three popular controlled-
access methods.
1. Reservation
2. Polling
3. Token Passing
28. Channelization
Channelization is a multiple-
access method in which the
available bandwidth of a link
is shared in time, frequency,
or through code, between
different stations. In this
section, we discuss three
channelization protocols.
1. Frequency-Division Multiple Access (FDMA)
2. Time-Division Multiple Access (TDMA)
3. Code-Division Multiple Access (CDMA)
40. 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.
1. Data Link Layer
2. Physical Layer
41. STANDARD ETHERNET
The original Ethernet was created in 1976 at Xerox’s Palo
Alto Research Centre (PARC). Since then, it has gone
through four generations. We briefly discuss the
Standard (or traditional) Ethernet in this section.
1. MAC Sublayer
2. Physical Layer
47. Note
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.
56. CHANGES IN THE STANDARD
The 10-Mbps Standard Ethernet has
gone through several changes before
moving to the higher data rates. These
changes actually opened the road to the
evolution of the Ethernet to become
compatible with other high-data-rate
LANs.
1. Bridged Ethernet
2. Switched Ethernet
3. Full-Duplex Ethernet