The document discusses multiple access protocols for network communication, focusing on Aloha, CSMA, CSMA/CD, and CSMA/CA. It explains the mechanics of these protocols, including their vulnerabilities and throughput rates, particularly emphasizing the differences between CSMA/CD and CSMA/CA regarding collision detection and prevention. The document highlights the conditions under which these protocols operate in wired and wireless networks.

1. Protocols :
ALOHA, CSMA , CSMA/CD, &
CSMA/CA

2. Multiple-access protocols

3. RANDOM ACCESS
In random access,
•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.

4. RANDOM ACCESS
1. ALOHA (Additive Links On-line Hawaii Area)
• Pure ALOHA
• Slotted ALOHA
2. Carrier Sense Multiple Access
3. Carrier Sense Multiple Access with Collision Detection
4. Carrier Sense Multiple Access with Collision Avoidance

5. Frames in a pure ALOHA network

6. Vulnerable time for pure ALOHA protocol
• The vulnerable time is in
which there is a possibility of
collision.
• We assume that the stations
send fixed-length frames with
each frame taking Tfr
Seconds to send.

7. The total period of time when collision might occur
for a packet is called vulnerable period.

8. The throughput for pure ALOHA is
S = G × e −2G
.
The maximum throughput
Smax = 0.184 when G= (1/2).
Note

9. Frames in a slotted ALOHA network

10. The throughput for slotted ALOHA is
S = G × e−G
.
The maximum throughput
Smax = 0.368 when G = 1.
Note

11. Vulnerable time for slotted ALOHA protocol

12. Carrier Sense multiple access (CSMA)
• Carrier Sensed Multiple Access (CSMA) : CSMA is a network access method used on shared network
topologies such as Ethernet to control access to the network. Devices attached to the network cable listen
(carrier sense) before transmitting. If the channel is in use, devices wait before transmitting.

13. There Are Three Different Type of CSMA Protocols

14. CSMA/CD
• Carrier-sense multiple access with collision detection
(CSMA/CD) is a media access control (MAC) method used most
notably in early Ethernet technology for local area networking.
• When this collision condition is detected, the station stops
transmitting that frame, transmits a jam signal, and then waits for
a random time interval before trying to resend the frame.

16. CSMA/CA
• CSMA/CD stands for Carrier Sense Multiple Access / Collision
Avoidance is a network protocol for carrier transmission.
• Like CSMA/CD it is also operated in the medium access control
layer.
• Unlike CSMA/CD(that is effective after a collision) CSMA / CA
is effective before a collision.

17. RTS (Request to Send)
CTS (Clear to Send)

18. DIFS = distributed inter frame spacing
SIFS = spacing between transmission and ACK

19. Difference between CSMA/CA and CSMA/CD
S.NO CSMA/CD CSMA/CA
1. CSMA / CD is effective after a
collision.
Whereas CSMA / CA is effective
before a collision.
2. CSMA / CD is used in wired
networks.
Whereas CSMA / CA is commonly
used in wireless networks.
3. It only reduces the recovery
time.
Whereas CSMA/ CA minimizes
the possibility of collision.
4. CSMA / CD resend the data
frame whenever a conflict
occurs.
Whereas CSMA / CA will first
transmit the intent to send for
data transmission.
5. CSMA / CD is used in 802.3
standard.
While CSMA / CA is used in
802.11 standard.
6. It is more efficient than
simple CSMA (Carrier Sense
Multiple Access).
While it is similar to simple CSMA
(Carrier Sense Multiple Access).