Chandra Prakash
Assistant Professor
LPU
Ad Hoc Wireless Media Access Protocols
Lecture (7-8)
1 Chandra prakash, Lovely Pro...
Introduction
Introduction
Problems in Ad Hoc ChannelAccess: Issues and need
Classifications of Multicast Routing
Proto...
Introduction
 Ad hoc network does not rely on a pre-existing infrastructure,
such as routers in wired networks or access ...
4
Wireless LAN configuration
LAN
Server
Wireless
LAN
Laptops
Base station/
access point
Palmtop
radio obstruction
A B C
D
...
When do we need MAC?
 2 types of links:
 Point-to-point.
 Shared.
 If more than 1 node transmits at the same time:
 C...
Expanded Data Link Layer
 Sublayers of data link layer:
 Logical Link Control (LLC): flow and error control.
 MultipleA...
Media Access Protocols
7
MAC protocol is a set of rules or procedures to allow the
efficient use of a shared medium, such ...
Types of MAC
ChannelAccess Policy
 Random access (or contention-based)
 No scheduled time for transmissions.
 No order ...
Problems in Ad Hoc Channel
Access- Issues and need
 Distributed operation
 fully distributed involving minimum control o...
 A and C cannot hear each other.
 A sends to B, C cannot receiveA.
 C wants to send to B, C senses a “free” medium.
 C...
Exposed Terminal Problem
 A starts sending to B.
 C senses carrier, finds medium in
use and has to wait for A->B to
end....
MAC protocol categories
12
 Based on operation :
 Synchronous protocols:All nodes need to be synchronized.
Global time s...
Types of protocol
1. Synchronous MAC Protocols
 In synchronous MAC protocols, all nodes in the network are
synchronized t...
Contention-Based Protocols
 A nodes does not make any resource reservation a priori.
 Whenever it receive a packet to be...
Problems in Ad Hoc Channel Access
 HiddenTerminal Problem
 Shortcomings of the RTS-CTS Solution
 Exposed Node Problem
1...
Hidden Terminal Problem
16
• Found in contention-based protocols.
 A contention-based protocol (CBP) is a communications
...
Hidden Terminal Problem
17 Chandra prakash, Lovely Professional University, Punjab
Possible Solution
18 Chandra prakash, Lovely Professional University, Punjab
RTS-CTS handshake Protocol
19
 To avoid collision, all of the receiver's neighbouring nodes need to be
informed about the...
CSMA/CA: RTS-CTS Solution
 With collision avoidance, stations exchange small control
 packets to determine which sender ...
RTS-CTS handshake
21 Chandra prakash, Lovely Professional University, Punjab
Shortcomings of RTS-CTS Solution
22
The RTS-CTS method is not a perfect solution to the hidden
terminal problem.
Problemat...
a) Shortcomings of RTS-CTS Solution
23 Chandra prakash, Lovely Professional University, Punjab
a) Shortcomings of RTS-CTS Solution
24
 Cases when collisions occur and the RTS and CTS
control messages are sent by diff...
25
b) Shortcomings of RTS-CTS Solution
Multiple CTS messages are granted to different neighbouring nodes,
causing collisio...
b) Shortcomings of RTS-CTS Solution
26
Multiple CTS messages are granted to different neighboring
nodes, causing collision...
Exposed Node Problem
27
 Overhearing a data transmission from neighbouring nodes
can inhibit one node from transmitting t...
Solution to the exposed node problem
28
 Use of separate control and data channels
 Power-Aware Multi-Access Protocol wi...
Use of antennas.
29
 Mobile node using an
Omni-directional
antenna can result in
several surrounding nodes
being "exposed...
Use of antennas (cont…)
30
 If directional antennas are
employed, the problem of
network availability and system
throughp...
MAC protocol categories
31
 Based on operation :
 Synchronous protocols
 Asynchronous protocols
 Based on who initiate...
Media Access Protocols
32
 Receiver-Initiated MAC Protocols
The receiver (node B) first has to contact the sender (node A...
Receiver-Initiated MAC Protocols
33
 Passive form of initiation since the sender does not have to
initiate a request.
 T...
Media Access Protocols
34
 Sender-Initiated MAC Protocols
 This require the sender to initiate communications by informi...
Sender-initiated MAC protocols
35
 Node A sends an explicit RTS(ready to send) message to
node B (the receiver) to expres...
36
Classifications of MAC protocols
 Ad hoc network MAC protocols can be classified into three types:
 Contention-based ...
Existing Ad Hoc MAC Protocols
37
 Multiple Access with Collision Avoidance (MACA)
 MACA-BI (By Invitation)
 Power-Aware...
1. Multiple Access with Collision Avoidance (MACA)
 Aims to create usable, ad hoc, single-frequency networks.
 Sender in...
Multiple Access with Collision Avoidance (MACA)
39 Chandra prakash, Lovely Professional University, Punjab
Wireless LAN Protocols
• MACA protocol solved hidden, exposed terminal:
– Send Ready-to-Send (RTS) and Clear-to-Send (CTS)...
41
Multiple Access with Collision Avoidance (MACA)
 When a node wants to transmit a data packet, it first transmit a RTS
...
42
MACA Protocol
The MACA protocol. (a)A sending an RTS to B.
(b) B responding with a CTS toA.
Chandra prakash, Lovely Pro...
MACA
 Has Power control features :
 Key characteristic of MACA is that it inhibits a transmitter when
a CTS packet is ov...
44
 MACA avoids the problem of hidden terminals
 A and C want to
send to B
 A sends RTS first
 C waits after receiving...
MACA
 There is no carrier sensing in MACA so Collision occurs during the RTS-CTS
phase
 Each mobile host adds a random a...
MACAW (MACA wireless )
 The binary exponential back-off mechanism used in MACA
might starves flows sometimes.
 The probl...
MACAW
MACAW is proposed as a series of improvements to the
basic MACA algorithm.
1. Suggest a less aggressive backoff algo...
NPDU’s
 DATA Sending (DS) Packets :
 A DS packet should be sent after a successful RTS-CTS exchange, just before
the dat...
 MACA : RTS-CTS-DATA exchange mechanism
 MACAW : RTS-CTS-DS-DATA-ACK exchange mechanism49 Chandra prakash, Lovely Profes...
2. MACA-BI (By Invitation)
 MACA-BI uses only a two-way handshake.
 No RTS. , the CTS message is renamed as RTR (ReadyTo...
MACA-BI (By Invitation)
51 Chandra prakash, Lovely Professional University, Punjab
MACA-BI (By Invitation)
 Packet queue length and arrival rate information is
piggyback into each data packet so that the ...
MACA Vs MACA-BI
 As MACA-BI only uses a single control message, this turn around
limitation is reduced (i.e., up to 25 mi...
3. Power-Aware Multi-Access Protocol
with Signaling (PAMAS)
 PAMAS is based on the MACA protocol with the addition of a
s...
Power-Aware Multi-Access Protocol with
Signaling (PAMAS)
55 Chandra prakash, Lovely Professional University, Punjab
Power-Aware Multi-Access Protocol
with Signaling (PAMAS)
 Each node makes an independent decision about whether to
power ...
4. Dual Busy Tone Multiple Access
(DBTMA)
 The single shared channel is further split into 2 sub channels :
 Data Channe...
Dual Busy Tone Multiple Access
(DBTMA)
 Uses two busy tone on the control channel BTt (Transmit
busy tone) and BTr (Recei...
Dual Busy Tone Multiple Access
(DBTMA)
59
 BTMA was used to solve the hidden terminal problem
 BTMA relies on a wireless...
DBTMA (Cont…)
 An ad hoc node wishing to transmit first sends out an RTS message.
 When the receiver willing to accept t...
Dual Busy Tone Multiple Access (DBTMA)
61 Chandra prakash, Lovely Professional University, Punjab
5. Media Access with Reduced
Handshake: MARCH
 MARCH exploits the overhearing characteristic
associated with an ad hoc mo...
MARCH: Media Access with Reduced Handshake
63 Chandra prakash, Lovely Professional University, Punjab
MARCH (cont…)
 Exploits the broadcast characteristic of omni-directional
antennas to reduce the number of required handsh...
 For an ad hoc route of n hops, the number of handshakes needed to
send a data packet from the source to the destination ...
MARCH: Media Access with Reduced
Handshake
66 Chandra prakash, Lovely Professional University, Punjab
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Lecture 7 8 ad hoc wireless media access protocols

  1. 1. Chandra Prakash Assistant Professor LPU Ad Hoc Wireless Media Access Protocols Lecture (7-8) 1 Chandra prakash, Lovely Professional University, Punjab
  2. 2. Introduction Introduction Problems in Ad Hoc ChannelAccess: Issues and need Classifications of Multicast Routing Protocols Synchronous Asynchronous MAC Protocols Receiver Sender initiated MAC Protocols VariousADHOC MAC protocols 2 Chandra prakash, Lovely Professional University, Punjab
  3. 3. Introduction  Ad hoc network does not rely on a pre-existing infrastructure, such as routers in wired networks or access points in managed (infrastructure) wireless networks.  In Ad-Hoc network Wireless media can be shared and any nodes can transmit at any point in time.This could result in possible contention over the common channel.  Each node participates in routing by forwarding data for other nodes, and so the determination of which nodes forward data is made dynamically based on the network connectivity.  Ad-hoc mobile device can be highly mobile, powerful and heterogeneous.  Routing protocol in ad hoc networks need to deal with the mobility of nodes and constraints in power and bandwidth. 3 Chandra prakash, Lovely Professional University, Punjab
  4. 4. 4 Wireless LAN configuration LAN Server Wireless LAN Laptops Base station/ access point Palmtop radio obstruction A B C D E Chandra prakash, Lovely Professional University, Punjab
  5. 5. When do we need MAC?  2 types of links:  Point-to-point.  Shared.  If more than 1 node transmits at the same time:  Collision at receiver!  MAC protocol:  Arbitrate access to medium.  Determine who can transmit when. Chandra prakash, Lovely Professional University, Punjab5
  6. 6. Expanded Data Link Layer  Sublayers of data link layer:  Logical Link Control (LLC): flow and error control.  MultipleAccess Control (MAC): multiple access resolution. Chandra prakash, Lovely Professional University, Punjab6
  7. 7. Media Access Protocols 7 MAC protocol is a set of rules or procedures to allow the efficient use of a shared medium, such as wireless.  Node: any host that is trying to access the medium.  Sender: is a node that is attempting to transmit over the medium.  Receiver: is a node that is the recipient of the current transmission. The MAC protocol is concerned with per-link communications, not end-to-end. While Routing Protocol deal with end-to-end communication. Chandra prakash, Lovely Professional University, Punjab
  8. 8. Types of MAC ChannelAccess Policy  Random access (or contention-based)  No scheduled time for transmissions.  No order for transmissions.  Controlled access  Stations coordinate access to channel.  Station only transmits when it has right to send.  Channelization  Bandwidth of channel is statically partitioned. Chandra prakash, Lovely Professional University, Punjab8
  9. 9. Problems in Ad Hoc Channel Access- Issues and need  Distributed operation  fully distributed involving minimum control overhead  Synchronization  Mandatory forTDMA-based systems  Hidden terminals  Can significantly reduce the throughput of a MAC protocol  Exposed terminals  To improve the efficiency of the MAC protocol, the exposed nodes should be allowed to transmit in a controlled fashion without causing collision to the on-going data transfer  Access delay 9 Chandra prakash, Lovely Professional University, Punjab
  10. 10.  A and C cannot hear each other.  A sends to B, C cannot receiveA.  C wants to send to B, C senses a “free” medium.  Collision occurs at B.  A cannot receive the collision.  A is “hidden” for C. Hidden Terminal Problem BA C 10 Chandra prakash, Lovely Professional University, Punjab
  11. 11. Exposed Terminal Problem  A starts sending to B.  C senses carrier, finds medium in use and has to wait for A->B to end.  D is outside the range of A, therefore waiting is not necessary.  A and C are “exposed” terminals A B C D 11 Chandra prakash, Lovely Professional University, Punjab
  12. 12. MAC protocol categories 12  Based on operation :  Synchronous protocols:All nodes need to be synchronized. Global time synchronization is difficult to achieve.  Asynchronous protocols:These protocols use relative time information for effecting reservations.  Based on who initiates a communication request.  Receiver-initiated protocols  Sender-initiated protocols Chandra prakash, Lovely Professional University, Punjab
  13. 13. Types of protocol 1. Synchronous MAC Protocols  In synchronous MAC protocols, all nodes in the network are synchronized to the same time.  Achieved by a timer master broadcasting a regular beacon.  All nodes listen for this beacon and synchronize their clocks to the master's time.  Central coordination is, needed to synchronize time events. 2.Asynchronous MAC Protocols  Nodes do not necessarily follow the same time.  A more distributed control mechanism is used to coordinate channel access  Access to the channel tends to be contention-based. 13 Chandra prakash, Lovely Professional University, Punjab
  14. 14. Contention-Based Protocols  A nodes does not make any resource reservation a priori.  Whenever it receive a packet to be transmitted, it contends with its neighbor nodes for access to the shared channel.  Nods are not guaranteed periodic access to the channel  Thus can’t provide QoS guarantees to sessions .  E.g. :  pure ALOHA, slotted ALOHA, CSMA, IEEE 802.11, etc  The "listen before talk" operating procedure in IEEE 802.11 is the most well known contention-based protocol. 14 Chandra prakash, Lovely Professional University, Punjab
  15. 15. Problems in Ad Hoc Channel Access  HiddenTerminal Problem  Shortcomings of the RTS-CTS Solution  Exposed Node Problem 15 Chandra prakash, Lovely Professional University, Punjab
  16. 16. Hidden Terminal Problem 16 • Found in contention-based protocols.  A contention-based protocol (CBP) is a communications protocol for operating wireless telecommunication equipment that allows many users to use the same radio channel without pre- coordination. • Two nodes are said to be hidden from one another (out of signal range) when both attempt to send information to the same receiving node, resulting in a collision of data at the receiver node Chandra prakash, Lovely Professional University, Punjab
  17. 17. Hidden Terminal Problem 17 Chandra prakash, Lovely Professional University, Punjab
  18. 18. Possible Solution 18 Chandra prakash, Lovely Professional University, Punjab
  19. 19. RTS-CTS handshake Protocol 19  To avoid collision, all of the receiver's neighbouring nodes need to be informed about the status of the channel.  This can be achieved by using a handshake protocol  reserving the channel using control messages  Resolves hidden node problems  An RTS (RequestTo Send) message can be used by a node to indicate its wish to transmit data.  The receiving node can allow this transmission by sending a grant using the CTS (ClearTo Send) message.  Because of the broadcast nature of these messages, all neighbors of the sender and receiver will be informed that the medium will be busy, thus preventing them from transmitting and avoiding collision. Chandra prakash, Lovely Professional University, Punjab
  20. 20. CSMA/CA: RTS-CTS Solution  With collision avoidance, stations exchange small control  packets to determine which sender can transmit to a receiver. Chandra prakash, Lovely Professional University, Punjab20
  21. 21. RTS-CTS handshake 21 Chandra prakash, Lovely Professional University, Punjab
  22. 22. Shortcomings of RTS-CTS Solution 22 The RTS-CTS method is not a perfect solution to the hidden terminal problem. Problematic scenario occurs when 1. RTS and CTS control messages are sent by different nodes. 2. Multiple CTS messages are granted to different neighboring nodes, causing collisions. Chandra prakash, Lovely Professional University, Punjab
  23. 23. a) Shortcomings of RTS-CTS Solution 23 Chandra prakash, Lovely Professional University, Punjab
  24. 24. a) Shortcomings of RTS-CTS Solution 24  Cases when collisions occur and the RTS and CTS control messages are sent by different nodes. 1. Node B is granting a CTS to the RTS sent by nodeA. 2. This collides with the RTS sent by node D at node C. Node D is the hidden terminal from node B. 3. As node D does not receive the expected CTS from node C, it retransmits the RTS. 4. When nodeA receives the CTS, it is not aware of any collision at node C and hence it proceeds with a data transmission to node B. 5. Unfortunately,It collides with the CTS sent by node C in response to node D's RTS. Chandra prakash, Lovely Professional University, Punjab
  25. 25. 25 b) Shortcomings of RTS-CTS Solution Multiple CTS messages are granted to different neighbouring nodes, causing collisions. Chandra prakash, Lovely Professional University, Punjab
  26. 26. b) Shortcomings of RTS-CTS Solution 26 Multiple CTS messages are granted to different neighboring nodes, causing collisions. 1. Two nodes are sending RTS messages to different nodes at different points in time. 2. Node A sends an RTS to node B.When node B is returning a CTS message back to node A, node C sends an RTS message to node B. 3. Because node C cannot hear the CTS sent by node B while it is transmitting an RTS to node D, node C is unaware of the communication between nodes A and B. 4. Node D proceeds to grant the CTS message to node C. 5. Since both nodes A and C are granted transmission, a collision will occur when both start sending data. Chandra prakash, Lovely Professional University, Punjab
  27. 27. Exposed Node Problem 27  Overhearing a data transmission from neighbouring nodes can inhibit one node from transmitting to other nodes.This is known as the exposed node problem.  An exposed node is a node in range of the transmitter, but out of range of the receiver. Chandra prakash, Lovely Professional University, Punjab
  28. 28. Solution to the exposed node problem 28  Use of separate control and data channels  Power-Aware Multi-Access Protocol with Signaling (PAMAS)  Dual BusyTone Multiple Access (DBTMA) .  Use of Antennas  Directional antennas Chandra prakash, Lovely Professional University, Punjab
  29. 29. Use of antennas. 29  Mobile node using an Omni-directional antenna can result in several surrounding nodes being "exposed“  Thus prohibiting them from communicating with other nodes.  Lowers network availability and system throughput. Omni-directional antenna radiates radio wave power uniformly in all directions in one plane,with the radiated power decreasing with elevation angle above or below the plane,dropping to zero on the antenna's axisChandra prakash, Lovely Professional University, Punjab
  30. 30. Use of antennas (cont…) 30  If directional antennas are employed, the problem of network availability and system throughput can be mitigated.  Node C can continue communicating with the receiving palm pilot device without impacting the communication between nodesA and B.  The directivity provides spatial and connectivity isolation not found in omni-directional antenna systems. Chandra prakash, Lovely Professional University, Punjab
  31. 31. MAC protocol categories 31  Based on operation :  Synchronous protocols  Asynchronous protocols  Based on who initiates a communication request.  Receiver-initiated protocols  Sender-initiated protocols  Single-channel sender-initiated protocols:A node that wins the contention to the channel can make use of the entire bandwidth.  Multichannel sender-initiated protocols:The available bandwidth is divided into multiple channels. Chandra prakash, Lovely Professional University, Punjab
  32. 32. Media Access Protocols 32  Receiver-Initiated MAC Protocols The receiver (node B) first has to contact the sender (node A), informing the sender that it is ready to receive (RTR) data. This is a form of polling, as the receiver has no way of knowing for sure if the sender indeed has data to send. Chandra prakash, Lovely Professional University, Punjab
  33. 33. Receiver-Initiated MAC Protocols 33  Passive form of initiation since the sender does not have to initiate a request.  There is only one control message used, compared to the RTS-CTS approach. Example: MACA-BI (By Invitation) Chandra prakash, Lovely Professional University, Punjab
  34. 34. Media Access Protocols 34  Sender-Initiated MAC Protocols  This require the sender to initiate communications by informing the receiver that it has data to send. Chandra prakash, Lovely Professional University, Punjab
  35. 35. Sender-initiated MAC protocols 35  Node A sends an explicit RTS(ready to send) message to node B (the receiver) to express its desire to communicate.  Node B can then reply if it is willing to receive data from nodeA. If positive, it returns a CTS (Clear to send ) message to nodeA. NodeA then subsequently proceeds to send data.  Examples:  MACA (MultipleAccess with CollisionAvoidance),  MACAW (MACA with Acknowledgment), and  FAMA (FloorAcquisition MultipleAccess). Chandra prakash, Lovely Professional University, Punjab
  36. 36. 36 Classifications of MAC protocols  Ad hoc network MAC protocols can be classified into three types:  Contention-based protocols  Contention-based protocols with reservation mechanisms  Contention-based protocols with scheduling mechanisms  Other MAC protocols MAC Protocols for Ad Hoc Wireless Networks Contention-Based Protocols Contention-based protocols with reservation mechanisms Other MAC Protocols Contention-based protocols with scheduling mechanisms Sender-Initiated Protocols Receiver-Initiated Protocols Synchronous Protocols Asynchronous Protocols Single-Channel Protocols Multichannel Protocols MACAW FAMA BTMA DBTMA ICSMA RI-BTMA MACA-BI MARCH D-PRMA CATA HRMA RI-BTMA MACA-BI MARCH SRMA/PA FPRP MACA/PR RTMAC Directional Antennas MMAC MCSMA PCM RBAR Chandra prakash, Lovely Professional University, Punjab
  37. 37. Existing Ad Hoc MAC Protocols 37  Multiple Access with Collision Avoidance (MACA)  MACA-BI (By Invitation)  Power-Aware Multi-Access Protocol with Signalling (PAMAS)  Dual BusyTone Multiple Access (DBTMA) Chandra prakash, Lovely Professional University, Punjab
  38. 38. 1. Multiple Access with Collision Avoidance (MACA)  Aims to create usable, ad hoc, single-frequency networks.  Sender initiated MAC Protocol  Proposed to resolve the hidden terminal and exposed node problems.  Ability to perform per-packet transmitter power control, thus increase the carrying capacity of a packet radio.  Uses a three-way handshake, RTS-CTS-Data.  Sender first sends an RTS to the receiver to reserve the channel.This blocks the sender's neighboring nodes from transmitting.  The receiver then sends a CTS to the sender to grant transmission.This results in blocking the receiver's neighboring nodes from transmitting, thus avoiding collision.  Sender can now proceed with data transmission.38 Chandra prakash, Lovely Professional University, Punjab
  39. 39. Multiple Access with Collision Avoidance (MACA) 39 Chandra prakash, Lovely Professional University, Punjab
  40. 40. Wireless LAN Protocols • MACA protocol solved hidden, exposed terminal: – Send Ready-to-Send (RTS) and Clear-to-Send (CTS) first – RTS, CTS helps determine who else is in range or busy (Collision avoidance). sender receiver other node in sender’s range RTS CTS ACK data other node in receiver’s range 40 Chandra prakash, Lovely Professional University, Punjab
  41. 41. 41 Multiple Access with Collision Avoidance (MACA)  When a node wants to transmit a data packet, it first transmit a RTS (RequestTo Send) frame.  The receiver node, on receiving the RTS packet, if it is ready to receive the data packet, transmits a CTS (Clear to Send) packet.  Once the sender receives the CTS packet without any error, it starts transmitting the data packet.  If a packet transmitted by a node is lost, the node uses the binary exponential back-off (BEB) algorithm to back off a random interval of time before retrying. In this each time a collision occurs the node doubles its maximum back-off windows.  The binary exponential back-off mechanism used in MACA might starves flows sometimes.  The problem is solved by MACAW. Chandra prakash, Lovely Professional University, Punjab
  42. 42. 42 MACA Protocol The MACA protocol. (a)A sending an RTS to B. (b) B responding with a CTS toA. Chandra prakash, Lovely Professional University, Punjab
  43. 43. MACA  Has Power control features :  Key characteristic of MACA is that it inhibits a transmitter when a CTS packet is overheard so as to temporarily limit power output .This allows geographic reuse of channels. For example,  If node A has been sending data packets to node B, after some time,A would know how much power it needs to reach B.  If node A overhears node B's response to an RTS (i.e., a CTS) from a downstream node C,A need not remain completely silent during this time.  By lowering its transmission power from the level used to reach node B, node A can communicate with other neighboring nodes (without interfering with node B) during that time with a lower power.43 Chandra prakash, Lovely Professional University, Punjab
  44. 44. 44  MACA avoids the problem of hidden terminals  A and C want to send to B  A sends RTS first  C waits after receiving CTS from B  MACA avoids the problem of exposed terminals  B wants to send to A, C to another terminal  now C does not have to wait for it cannot receive CTS fromA MACA examples A B C RTS CTSCTS A B C RTS CTS RTS Chandra prakash, Lovely Professional University, Punjab
  45. 45. MACA  There is no carrier sensing in MACA so Collision occurs during the RTS-CTS phase  Each mobile host adds a random amount of time to the minimum interval required to wait after overhearing an RTS or CTS control message.  In MACA, the slot time is the duration of an RTS packet.  If two or more stations transmit an RTS concurrently,resulting in a collision,these stations will wait for a randomly chosen interval and try again, doubling the average interval on every attempt.  The station that wins the competition will receive a CTS from its responder, thereby blocking other stations to allow the data communication session to proceed.  Compared to CSMA, MACA reduces the chances of data packet collisions. Since control messages (RTS and CTS) are much smaller in size compared to data packets, the chances of collision are also smaller45 Chandra prakash, Lovely Professional University, Punjab
  46. 46. MACAW (MACA wireless )  The binary exponential back-off mechanism used in MACA might starves flows sometimes.  The problem is solved by MACAW.  The packet header has current back-off counter value of transmitting node.  It implements per flow fairness as opposed to the per node fairness in MACA. 46 Chandra prakash, Lovely Professional University, Punjab
  47. 47. MACAW MACAW is proposed as a series of improvements to the basic MACA algorithm. 1. Suggest a less aggressive backoff algorithm:  a multiplicative increase and linear decrease(MILD) backoff mechanism is used.  Increasing BO by 1.5 after a timeout, and decreasing it by 1 after a successful RTS-CTS pair. 2. proposes that receivers should send an ACK to the sender after successfully receiving a data message. 3. Propose two related techniques for allowing transmitters to avoid contention more effectively:  Data sending (DS)  Request-for-request-to-send (RRTS) Concept 47 Chandra prakash, Lovely Professional University, Punjab
  48. 48. NPDU’s  DATA Sending (DS) Packets :  A DS packet should be sent after a successful RTS-CTS exchange, just before the data message itself.The idea is to explicitly announce that the RTS-CTS succeeded, so that if a node can hear an RTS but not the CTS response, it does not attempt to transmit a message during the subsequent data transfer period. In MACA , an exposed node can received only the RTS and not the CTS packet  READY for RTS (RRTS):  if a receiver hears an RTS while it is deferring any transmissions, at the end of the deferral period it replies with an RRTS (“ready for RTS”) packet, prompting the sender to resend the RTS. 48 Chandra prakash, Lovely Professional University, Punjab
  49. 49.  MACA : RTS-CTS-DATA exchange mechanism  MACAW : RTS-CTS-DS-DATA-ACK exchange mechanism49 Chandra prakash, Lovely Professional University, Punjab
  50. 50. 2. MACA-BI (By Invitation)  MACA-BI uses only a two-way handshake.  No RTS. , the CTS message is renamed as RTR (ReadyTo Receive).  Type Receiver initiated MAC Protocol  A node cannot transmit data unless it has received an invitation from the receiver.  Receiver node does not necessarily know that the source has data to transmit.  receiver needs to predict if node has data to transmit to it.  The timeliness of the invitation will affect communication performance. 50 Chandra prakash, Lovely Professional University, Punjab
  51. 51. MACA-BI (By Invitation) 51 Chandra prakash, Lovely Professional University, Punjab
  52. 52. MACA-BI (By Invitation)  Packet queue length and arrival rate information is piggyback into each data packet so that the receiver is aware of the transmitter's backlog.  For constant bit rate (CBR) traffic, the efficiency of MACA-BI will be high since the prediction scheme will work fine. However, will not perform well in case of bursty traffic.  To enhance the communication performance of MACA-BI under non-stationary traffic situations  a node may still transmit an RTS if the transmitter's queue length or packet delay exceeds a certain acceptable threshold before an RTR is issued.  MACA-BI now reverts back to MACA. 52 Chandra prakash, Lovely Professional University, Punjab
  53. 53. MACA Vs MACA-BI  As MACA-BI only uses a single control message, this turn around limitation is reduced (i.e., up to 25 microseconds).  MACA-BI is less likely to suffer from control packet collision since it uses half as many control packets as MACA 53 Chandra prakash, Lovely Professional University, Punjab
  54. 54. 3. Power-Aware Multi-Access Protocol with Signaling (PAMAS)  PAMAS is based on the MACA protocol with the addition of a separate signalling channel.  2 channel interface  Signalling channel :  RTS-CTS dialogue exchanges occur over this channel.  Data channel  PAMAS conserves battery power by selectively powering off nodes that are not actively transmitting or receiving packets.  In PAMAS, nodes are required to shut themselves off if they are overhearing other transmissions not directed to them. 54 Chandra prakash, Lovely Professional University, Punjab
  55. 55. Power-Aware Multi-Access Protocol with Signaling (PAMAS) 55 Chandra prakash, Lovely Professional University, Punjab
  56. 56. Power-Aware Multi-Access Protocol with Signaling (PAMAS)  Each node makes an independent decision about whether to power off its transceiver.  The conditions that force a node to power off include:  If a node has no packets to transmit, it should power off if one of its neighboring nodes is transmitting.  If a node has packets to transmit, but at least one of the neighboring nodes is transmitting and another is receiving, then it should power off its transceiver.  Use of probing to detect when a node should appropriately power up. The duration of power-off is critical since it affects delay and throughput performance.  A node can selectively power down only its data interface and leave the signalling interface power on. 56 Chandra prakash, Lovely Professional University, Punjab
  57. 57. 4. Dual Busy Tone Multiple Access (DBTMA)  The single shared channel is further split into 2 sub channels :  Data Channel : Data packets are sent over the data channel  Control channels: control packets (such as RTS and CTS) are sent + busy tone (BTt (Transmit busy tone) and BTr (Receive busy tone))  One busy tone signifies transmit busy, while another signifies receive busy.  These two busy tones are spatially separated in frequency to avoid interference. 57 Chandra prakash, Lovely Professional University, Punjab
  58. 58. Dual Busy Tone Multiple Access (DBTMA)  Uses two busy tone on the control channel BTt (Transmit busy tone) and BTr (Receive busy tone) are used to notify neighboring nodes of any on-going transmission.  BT(t) used by the node that transmits data over the data channel  BT(r) used by the node receiving data 58 Chandra prakash, Lovely Professional University, Punjab
  59. 59. Dual Busy Tone Multiple Access (DBTMA) 59  BTMA was used to solve the hidden terminal problem  BTMA relies on a wireless last-hop network architecture, where centralized base station serves multiple mobile hosts.  When the base station receives packets from a specific mobile host, it sends out a busy tone signal to all other nodes within its radio cell. Hence, hidden terminals sense the busy tone and refrain from transmitting  Zygmunt Haas from Cornell applied this concept further for use in ad hoc wireless networks Chandra prakash, Lovely Professional University, Punjab
  60. 60. DBTMA (Cont…)  An ad hoc node wishing to transmit first sends out an RTS message.  When the receiver willing to accept the data, it sends out a receive busy tone message followed by a CTS message.  All neighboring nodes that hear the receive busy tone are prohibited from transmitting.  Upon receiving the CTS message, the source node sends out a transmit busy tone message to surrounding nodes prior to data transmission.  Neighboring nodes that hear the transmit busy tone, are prohibited from transmitting and will ignore any transmission received. 60 Chandra prakash, Lovely Professional University, Punjab
  61. 61. Dual Busy Tone Multiple Access (DBTMA) 61 Chandra prakash, Lovely Professional University, Punjab
  62. 62. 5. Media Access with Reduced Handshake: MARCH  MARCH exploits the overhearing characteristic associated with an ad hoc mobile network employing omni-directional antenna.  MARCH is a sender and receiver initiated protocol  MARCH supports fast data transfer over a multi-hop route  MARCH provides data flow control by using a sequence number contained inside the CTS packet  Improves communication throughput in wireless multi- hopAd-hoc networks by reducing the amount of control overhead. 62 Chandra prakash, Lovely Professional University, Punjab
  63. 63. MARCH: Media Access with Reduced Handshake 63 Chandra prakash, Lovely Professional University, Punjab
  64. 64. MARCH (cont…)  Exploits the broadcast characteristic of omni-directional antennas to reduce the number of required handshakes.  In MARCH, a node has knowledge of data packet arrivals at its neighboring nodes from the overheard CTS packets. It can then initiate an invitation for data to be relayed.  Node C will receive the CTS1 message sent by node B.  This characteristic implies that the overheard CTS1 packet can also be used to convey the information of a data packet arrival at node B to node C.  Subsequently, after the data packet has been received by node B, node C can invite node B to forward that data via the CTS2 packet. Hence, the RTS2 packet can be suppressed here.  RTS-CTS handshake is now reduced to a single CTS (CTS-only) handshake after the first hop. 64 Chandra prakash, Lovely Professional University, Punjab
  65. 65.  For an ad hoc route of n hops, the number of handshakes needed to send a data packet from the source to the destination is 2n is in MACA, n in MACA-BI, but only (n + 1) in MARCH.  If n is large, MARCH will have a very similar number of handshakes as in MACA-BI.  There are n – 1 intermediary nodes between the source and destination.  MARCH can be viewed as a request-first, pull-later protocol since the subsequent nodes in the path just need to send invitations to pull the data toward the destination node.  The RTS-CTS message in MARCH contains:  The MAC addresses of the sender and receiver  The route identification number (RTID)65 Chandra prakash, Lovely Professional University, Punjab
  66. 66. MARCH: Media Access with Reduced Handshake 66 Chandra prakash, Lovely Professional University, Punjab

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