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Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 1
Chapter 6
Multiple Radio Access
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 2
Outline
 Introduction
 Contention Protocols
 ALOHA
 Slotted ALOHA
 CSMA (Carrier Sense Multiple Access)
 CSMA/CD (CSMA with Collision Detection)
 CSMA/CA (CSMA with Collision Avoidance)
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 3
Introduction
 Multiple access control channels
 Each node is attached to a transmitter/receiver which
communicates via a channel shared by other nodes
 Transmission from any node is received by other nodes
Shared Multiple
Access Control
Channel to BS
Node 4
Node 3
Node 2
Node 1 …
Node N
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 4
Introduction (Cont’d)
 Multiple access issues
 If more than one node transmit at a time on the control
channel to BS, a collision occurs
 How to determine which node can transmit to BS?
 Multiple access protocols
 Solving multiple access issues
 Different types:
 Contention protocols resolve a collision after it occurs.
These protocols execute a collision resolution protocol
after each collision
 Collision-free protocols (e.g., a bit-map protocol and
binary countdown) ensure that a collision can never
occur.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 5
Channel Sharing Techniques
Channel Sharing
Techniques
Static
Channelization
Dynamic Medium
Access Control
Scheduling
Random Access
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 6
Classification of Multiple Access Protocols
Multiple access protocols
Contention-based Conflict-free
Random access Collision resolution
FDMA,
TDMA,
CDMA,
Token Bus,
DQDB, etc
ALOHA,
CSMA,
BTMA,
ISMA,
etc
TREE,
WINDOW,
etc
DQDB: Distributed Queue Dual Bus
BTMA: Busy Tone Multiple Access
ISMA: Internet Streaming Media Alliance
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 7
Contention Protocols
 ALOHA
 Developed in the 1970s for a packet radio network by Hawaii
University.
 Whenever a station has a data, it transmits. Sender finds out
whether transmission was successful or experienced a collision by
listening to the broadcast from the destination station. Sender
retransmits after some random time if there is a collision.
 Slotted ALOHA
 Improvement: Time is slotted and a packet can only be transmitted
at the beginning of one slot. Thus, it can reduce the collision
duration.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 8
Contention Protocols (Cont’d)
 CSMA (Carrier Sense Multiple Access)
 Improvement: Start transmission only if no transmission is ongoing
 CSMA/CD (CSMA with Collision Detection)
 Improvement: Stop ongoing transmission if a collision is detected
 CSMA/CA (CSMA with Collision Avoidance)
 Improvement: Wait a random time and try again when carrier is
quiet. If still quiet, then transmit
 CSMA/CA with ACK
 CSMA/CA with RTS/CTS
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 9
ALOHA
1 2 3 3 2
Time
Collision
Retransmission Retransmission
Node 1 Packet
Collision mechanism in ALOHA
Waiting a random time
Node 2 Packet
Node 3 Packet
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 10
Throughput of ALOHA
n
( )
!
n
(2G)
n
P
e 2G
-
=
• The probability that n packets arrive in two packets time is given by
where G is traffic load.
( ) G
e
P 2
0 -
=
• The probability P(0) that a packet is successfully received without
collision is calculated by letting n=0 in the above equation. We get
( ) G
e
G
P
G
S 2
0 -

=

=
• We can calculate throughput S with a traffic load G as follows:
184
.
0
2
1
max 
=
e
S
• The Maximum throughput of ALOHA is
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 11
Slotted ALOHA
1 2&3 2
Time
Collision
Retransmission Retransmission
3
Slot
Node 1 Packet
Nodes 2 & 3 Packets
Collision mechanism in slotted ALOHA
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 12
Throughput of Slotted ALOHA
( ) G
e
P -
=
0
• The probability of no collision is given by
( ) G
e
G
P
G
S -

=

= 0
• The throughput S is
368
.
0
1
max 
=
e
S
• The Maximum throughput of slotted ALOHA is
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 13
Throughput
G
8
6
4
2
0
0.5
0.4
0.3
0.2
0.1
0
Slotted Aloha
Aloha
0.368
0.184
G
S
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 14
CSMA (Carrier Sense Multiple Access)
 Max throughput achievable by slotted
ALOHA is 0.368.
 CSMA gives improved throughput compared
to Aloha protocols.
 Listens to the channel before transmitting a
packet (avoid avoidable collisions).
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 15
Collision Mechanism in CSMA
1 2 3
Time
Collision
4
Node 4 sense
Delay
5
Node 5 sense
Delay
Node 1 Packet
Node 2 Packet
Node 3 Packet
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 16
Kinds of CSMA
CSMA
Nonpersistent CSMA
Persistent CSMA
Unslotted Nonpersistent CSMA
Unslotted persistent CSMA
Slotted Nonpersistent CSMA
Slotted persistent CSMA
1-persistent CSMA
p-persistent CSMA
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 17
Nonpersistent/x-persistent CSMA Protocols
 Nonpersistent CSMA Protocol:
Step 1: If the medium is idle, transmit immediately
Step 2: If the medium is busy, wait a random amount of time and
repeat Step 1
 Random backoff reduces probability of collisions
 Waste idle time if the backoff time is too long
 1-persistent CSMA Protocol:
Step 1: If the medium is idle, transmit immediately
Step 2: If the medium is busy, continue to listen until medium
becomes idle, and then transmit immediately
 There will always be a collision if two nodes want to retransmit
(usually you stop transmission attempts after few tries)
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 18
Nonpersistent/x-persistent CSMA Protocols
 p-persistent CSMA Protocol:
Step 1: If the medium is idle, transmit with probability p, and delay
for worst case propagation delay for one packet with probability
(1-p)
Step 2: If the medium is busy, continue to listen until medium
becomes idle, then go to Step 1
Step 3: If transmission is delayed by one time slot, continue with Step 1
 A good tradeoff between nonpersistent and 1-persistent CSMA
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 19
How to Select Probability p ?
 Assume that N nodes have a packet to send and the
medium is busy
 Then, Np is the expected number of nodes that will
attempt to transmit once the medium becomes idle
 If Np > 1, then a collision is expected to occur
Therefore, network must make sure that Np < 1 to
avoid collision, where N is the maximum number of
nodes that can be active at a time
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 20
Throughput
0 1 2 3 4 5 6 7 8 9
G
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
S
Aloha
Slotted Aloha
1-persistent CSMA
0.5-persistent CSMA
0.1-persistent CSMA
0.01-persistent CSMA
Nonpersistent CSMA
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 21
CSMA/CD (CSMA with Collision Detection)
 In CSMA, if 2 terminals begin sending packet at the same
time, each will transmit its complete packet (although
collision is taking place).
 Wasting medium for an entire packet time.
 CSMA/CD
Step 1: If the medium is idle, transmit
Step 2: If the medium is busy, continue to listen until
the channel is idle then transmit
Step 3: If a collision is detected during transmission,
cease transmitting
Step 4: Wait a random amount of time and repeats
the same algorithm
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 22
CSMA/CD (Cont’d)
A B
( is the propagation time)
T0 A begins transmission
A B
B begins transmission
Time
T0+-
A B
B detects collision
T0+
A B
A detects collision just
before end of transmission
T0+2 -
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 23
CSMA/CA (CSMA with collision Avoidance)
 All terminals listen to the same medium as CSMA/CD.
 Terminal ready to transmit senses the medium.
 If medium is busy it waits until the end of current
transmission.
 It again waits for an additional predetermined time period
DIFS (Distributed inter frame Space).
 Then picks up a random number of slots (the initial value of
backoff counter) within a contention window to wait before
transmitting its frame.
 If there are transmissions by other terminals during this time
period (backoff time), the terminal freezes its counter.
 It resumes count down after other terminals finish
transmission + DIFS. The terminal can start its transmission
when the counter reaches to zero.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 24
CSMA/CA (Cont’d)
Time
Node A’s frame
Nodes B & C sense
the medium
Nodes B resenses the medium
and transmits its frame.
Node C freezes its counter.
Node B’s frame
Nodes C starts
transmitting.
Delay: B
Delay: C
Nodes C resenses the
medium and starts
decrementing its counter.
Node C’s frame
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 25
CSMA/CA Explained
DIFS
Next Frame
Medium Busy
DIFS Contention window
Defer access
Backoff after defer
Slot
Time
DIFS – Distributed Inter Frame Spacing
Contention
window
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 26
CSMA/CA with ACK
 Immediate Acknowledgements from receiver
upon reception of data frame without any need
for sensing the medium.
 ACK frame transmitted after time interval SIFS
(Short Inter-Frame Space) (SIFS < DIFS)
 Receiver transmits ACK without sensing the
medium.
 If ACK is lost, retransmission done.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 27
CSMA/CA/ACK
DIFS
Next Frame
ACK
Data
Other
Source
Destination
DIFS
SIFS
Contention window
Defer access Backoff after defer
SIFS – Short Inter Frame Spacing
Time
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 28
CSMA/CA with RTS/CTS
 Transmitter sends an RTS (request to send) after
medium has been idle for time interval more than
DIFS.
 Receiver responds with CTS (clear to send) after
medium has been idle for SIFS.
 Then Data is exchanged.
 RTS/CTS is used for reserving channel for data
transmission so that the collision can only occur
in control message.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 29
CSMA/CA with RTS/CTS (Cont’d)
DIFS
Next Frame
CTS
RTS
Other
Source
Destination
DIFS
SIFS
Contention window
Defer access Backoff after defer
SIFS
Data
SIFS
ACK
Time
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 30
RTS/CTS
Node A Node B
Propagation delay

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Chapt-06.ppt

  • 1. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 1 Chapter 6 Multiple Radio Access
  • 2. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 2 Outline  Introduction  Contention Protocols  ALOHA  Slotted ALOHA  CSMA (Carrier Sense Multiple Access)  CSMA/CD (CSMA with Collision Detection)  CSMA/CA (CSMA with Collision Avoidance)
  • 3. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 3 Introduction  Multiple access control channels  Each node is attached to a transmitter/receiver which communicates via a channel shared by other nodes  Transmission from any node is received by other nodes Shared Multiple Access Control Channel to BS Node 4 Node 3 Node 2 Node 1 … Node N
  • 4. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 4 Introduction (Cont’d)  Multiple access issues  If more than one node transmit at a time on the control channel to BS, a collision occurs  How to determine which node can transmit to BS?  Multiple access protocols  Solving multiple access issues  Different types:  Contention protocols resolve a collision after it occurs. These protocols execute a collision resolution protocol after each collision  Collision-free protocols (e.g., a bit-map protocol and binary countdown) ensure that a collision can never occur.
  • 5. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 5 Channel Sharing Techniques Channel Sharing Techniques Static Channelization Dynamic Medium Access Control Scheduling Random Access
  • 6. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 6 Classification of Multiple Access Protocols Multiple access protocols Contention-based Conflict-free Random access Collision resolution FDMA, TDMA, CDMA, Token Bus, DQDB, etc ALOHA, CSMA, BTMA, ISMA, etc TREE, WINDOW, etc DQDB: Distributed Queue Dual Bus BTMA: Busy Tone Multiple Access ISMA: Internet Streaming Media Alliance
  • 7. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 7 Contention Protocols  ALOHA  Developed in the 1970s for a packet radio network by Hawaii University.  Whenever a station has a data, it transmits. Sender finds out whether transmission was successful or experienced a collision by listening to the broadcast from the destination station. Sender retransmits after some random time if there is a collision.  Slotted ALOHA  Improvement: Time is slotted and a packet can only be transmitted at the beginning of one slot. Thus, it can reduce the collision duration.
  • 8. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 8 Contention Protocols (Cont’d)  CSMA (Carrier Sense Multiple Access)  Improvement: Start transmission only if no transmission is ongoing  CSMA/CD (CSMA with Collision Detection)  Improvement: Stop ongoing transmission if a collision is detected  CSMA/CA (CSMA with Collision Avoidance)  Improvement: Wait a random time and try again when carrier is quiet. If still quiet, then transmit  CSMA/CA with ACK  CSMA/CA with RTS/CTS
  • 9. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 9 ALOHA 1 2 3 3 2 Time Collision Retransmission Retransmission Node 1 Packet Collision mechanism in ALOHA Waiting a random time Node 2 Packet Node 3 Packet
  • 10. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 10 Throughput of ALOHA n ( ) ! n (2G) n P e 2G - = • The probability that n packets arrive in two packets time is given by where G is traffic load. ( ) G e P 2 0 - = • The probability P(0) that a packet is successfully received without collision is calculated by letting n=0 in the above equation. We get ( ) G e G P G S 2 0 -  =  = • We can calculate throughput S with a traffic load G as follows: 184 . 0 2 1 max  = e S • The Maximum throughput of ALOHA is
  • 11. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 11 Slotted ALOHA 1 2&3 2 Time Collision Retransmission Retransmission 3 Slot Node 1 Packet Nodes 2 & 3 Packets Collision mechanism in slotted ALOHA
  • 12. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 12 Throughput of Slotted ALOHA ( ) G e P - = 0 • The probability of no collision is given by ( ) G e G P G S -  =  = 0 • The throughput S is 368 . 0 1 max  = e S • The Maximum throughput of slotted ALOHA is
  • 13. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 13 Throughput G 8 6 4 2 0 0.5 0.4 0.3 0.2 0.1 0 Slotted Aloha Aloha 0.368 0.184 G S
  • 14. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 14 CSMA (Carrier Sense Multiple Access)  Max throughput achievable by slotted ALOHA is 0.368.  CSMA gives improved throughput compared to Aloha protocols.  Listens to the channel before transmitting a packet (avoid avoidable collisions).
  • 15. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 15 Collision Mechanism in CSMA 1 2 3 Time Collision 4 Node 4 sense Delay 5 Node 5 sense Delay Node 1 Packet Node 2 Packet Node 3 Packet
  • 16. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 16 Kinds of CSMA CSMA Nonpersistent CSMA Persistent CSMA Unslotted Nonpersistent CSMA Unslotted persistent CSMA Slotted Nonpersistent CSMA Slotted persistent CSMA 1-persistent CSMA p-persistent CSMA
  • 17. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 17 Nonpersistent/x-persistent CSMA Protocols  Nonpersistent CSMA Protocol: Step 1: If the medium is idle, transmit immediately Step 2: If the medium is busy, wait a random amount of time and repeat Step 1  Random backoff reduces probability of collisions  Waste idle time if the backoff time is too long  1-persistent CSMA Protocol: Step 1: If the medium is idle, transmit immediately Step 2: If the medium is busy, continue to listen until medium becomes idle, and then transmit immediately  There will always be a collision if two nodes want to retransmit (usually you stop transmission attempts after few tries)
  • 18. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 18 Nonpersistent/x-persistent CSMA Protocols  p-persistent CSMA Protocol: Step 1: If the medium is idle, transmit with probability p, and delay for worst case propagation delay for one packet with probability (1-p) Step 2: If the medium is busy, continue to listen until medium becomes idle, then go to Step 1 Step 3: If transmission is delayed by one time slot, continue with Step 1  A good tradeoff between nonpersistent and 1-persistent CSMA
  • 19. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 19 How to Select Probability p ?  Assume that N nodes have a packet to send and the medium is busy  Then, Np is the expected number of nodes that will attempt to transmit once the medium becomes idle  If Np > 1, then a collision is expected to occur Therefore, network must make sure that Np < 1 to avoid collision, where N is the maximum number of nodes that can be active at a time
  • 20. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 20 Throughput 0 1 2 3 4 5 6 7 8 9 G 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 S Aloha Slotted Aloha 1-persistent CSMA 0.5-persistent CSMA 0.1-persistent CSMA 0.01-persistent CSMA Nonpersistent CSMA
  • 21. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 21 CSMA/CD (CSMA with Collision Detection)  In CSMA, if 2 terminals begin sending packet at the same time, each will transmit its complete packet (although collision is taking place).  Wasting medium for an entire packet time.  CSMA/CD Step 1: If the medium is idle, transmit Step 2: If the medium is busy, continue to listen until the channel is idle then transmit Step 3: If a collision is detected during transmission, cease transmitting Step 4: Wait a random amount of time and repeats the same algorithm
  • 22. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 22 CSMA/CD (Cont’d) A B ( is the propagation time) T0 A begins transmission A B B begins transmission Time T0+- A B B detects collision T0+ A B A detects collision just before end of transmission T0+2 -
  • 23. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 23 CSMA/CA (CSMA with collision Avoidance)  All terminals listen to the same medium as CSMA/CD.  Terminal ready to transmit senses the medium.  If medium is busy it waits until the end of current transmission.  It again waits for an additional predetermined time period DIFS (Distributed inter frame Space).  Then picks up a random number of slots (the initial value of backoff counter) within a contention window to wait before transmitting its frame.  If there are transmissions by other terminals during this time period (backoff time), the terminal freezes its counter.  It resumes count down after other terminals finish transmission + DIFS. The terminal can start its transmission when the counter reaches to zero.
  • 24. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 24 CSMA/CA (Cont’d) Time Node A’s frame Nodes B & C sense the medium Nodes B resenses the medium and transmits its frame. Node C freezes its counter. Node B’s frame Nodes C starts transmitting. Delay: B Delay: C Nodes C resenses the medium and starts decrementing its counter. Node C’s frame
  • 25. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 25 CSMA/CA Explained DIFS Next Frame Medium Busy DIFS Contention window Defer access Backoff after defer Slot Time DIFS – Distributed Inter Frame Spacing Contention window
  • 26. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 26 CSMA/CA with ACK  Immediate Acknowledgements from receiver upon reception of data frame without any need for sensing the medium.  ACK frame transmitted after time interval SIFS (Short Inter-Frame Space) (SIFS < DIFS)  Receiver transmits ACK without sensing the medium.  If ACK is lost, retransmission done.
  • 27. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 27 CSMA/CA/ACK DIFS Next Frame ACK Data Other Source Destination DIFS SIFS Contention window Defer access Backoff after defer SIFS – Short Inter Frame Spacing Time
  • 28. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 28 CSMA/CA with RTS/CTS  Transmitter sends an RTS (request to send) after medium has been idle for time interval more than DIFS.  Receiver responds with CTS (clear to send) after medium has been idle for SIFS.  Then Data is exchanged.  RTS/CTS is used for reserving channel for data transmission so that the collision can only occur in control message.
  • 29. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 29 CSMA/CA with RTS/CTS (Cont’d) DIFS Next Frame CTS RTS Other Source Destination DIFS SIFS Contention window Defer access Backoff after defer SIFS Data SIFS ACK Time
  • 30. Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 30 RTS/CTS Node A Node B Propagation delay