1. High Throughput MAC layer Multicasting
HIMAC
High Throughput MAC layer Multicasting
Jaya Goyal
MSc. 1st Year

2. CONTENTS Why HIMAC Performance Limitations in IEEE 802.11 MAC protocol
* Channel State Indifference
* Demand Ignorance
Proposed solution is HIMAC
* UCF
* UNF
Working of HIMAC
Possible cases
Performance Evaluations
Conclusions

3. WHY HIMAC
Currently we have IEEE protocol to provide multicasting at MAC layer
It doesn’t have specific mechanism for it
Do so by broadcasting at BTR
Hence need a HIMAC as neither a specific mechanism nor do it have mechanism receive feedback from intended receivers.

4. Performance Limitations in 802.11
CHANNEL STATE INDIFFERENCE
DEMAND IGNORANCE

5. CHANNEL STATE INDIFFERENCE
Broadcasting (BTR) can be < highest acceptable rate for multicast neighbors
acceptable rate changes frequently as time varying channel
Hence best approach is to find rate before each transmission
Suppose R has acceptable rate of 11MBPS but S is sending at 1MBps

6. CHANNEL STATE INDIFFERENCE(2)
In , it will still send at 6 mbps though it’s a wastage as c still cant receive it due to interference as collision will occur

7. Experimental Result of Channel Aware Transmission
Each point is obtained by transmitting 1000 packets from one node to other
Graph shows that when all receivers are within 225ft from transmitting node, transmissions at 11mbps is best and 1mbps ( btr of b) is best only beyond 275 ft
Hencle channel state awareness can significantly improve awareness

8. DEMAND IGNORANCE
In ,we multicast i.e. broadcast here irrespective of demand
If node has already overheard data, still data is send to it.

9. Example to show the problem

10. SOLUTION PROPOSED HIMAC protocol Main focus is to improve throughput
It uses two mechanisms to handle it:
* Unary Channel Feedback(UCF)
* Unary Negative Feedback (UNF)
UCF FR CHANNEL STATE INDIFF
UCF + UNF FR DEMAND IGNORANCE
Y unary signals

11. UCF Before data transmission, find highest acceptable rate using UCF
S broadcasts RTS packet ( which contains MAC layer multicast addresses )
Each potential R will send UCF (encodes highest acceptable rate)
Hence rate selection before each data transmission
MAC layer multicast address – so that each receiver can determine whether need to respond with UCF or not.
encodes highest acceptable rate on basis of channel quality measuredafter receiving RTS

12. Example showing effect of UCF signal on rate
Ask mam

13. UCF mechanism properties
OVERHEADS
RTS
UCF Packets
BENEFITS
Sender knows there is at least one active receiver
Sender can use transmission rate higher than BTR
If receiving atleast one ucf than atleast one active receiver
Inc rate, inc speed of transmission, reduce latency, inc throughput

14. UNF Only needed in multihop network
Solution to demand ignorance along with UCF
In this basically, receiver respond with UNF if have overheard else UCF
Overhearing is possible only in multihop network

15. UNF handles two scenarios
1) no demand for packet  sender needs to drop packet 2) heavy interference  packet retransmission is attempted

16. Example Showing drop of packet
2 neighbours of sender have received packet by overhearing
Each receiver respond with unf on receiving rts
Hence no ucf so packet is dropped

17. Working Of HIMAC S broadcasts RTS before packet transmission
Receivers on receiving RTS, if overheard the packet respond with UNF else UCF(+ highest acceptable rate)
If S receives only UNF, drop packet
Else if even a single UCF, send data at rate received with UCF
COMBINING BOTH MECHANISMS

18. Possible Cases Case1: S receives both UCF and UNF:
Means some receivers have overheard some not
So will send data at lowest rate in UCF
Information of UNF is wasted
Case2: UCF received, no UNF:
same as above (all receivers want data)

19. Possible Cases(2) Case3: UCF not received , UNF received:
Means all receivers have overheard the packet
Drop it
Case4: both not received:
Means no overhearing (no UNF)
Receiver not in a position to receive packet(no UCF)
Retransmit later

20. Implementation of Unary Feedback
Sometimes it is difficult to extract the minm channel rate information from combined feedback
Hence here they use OFDM technology to receive feedback from multiple users without overlapping
( as signals may get cancel due to overlapping due to multi path effect,phase etc)

21. PERFORMANCE EVALUATION
End-to-end throughput of multicast sessions using MAODV can be inc up to 74%
Reduces end-to-end latency by factor of 56
Here we will see simulation results on packet size, network load and number of receivers due to space constraints.( on x axis)
Himac protocol at mac layer
Maodv at network layer

22. Metrics for Performance Evaluation
* End-to-end throughput : avg number of packets received by each receiver per second
* MAC Latency: avg latency of receivers receiving the packets at MAC layer
* End-to-end latency: avg latency of receivers receiving the packets at network layer

23. Impact of packet size

24. Impact of Network Load

25. Impact of Number of Recievers

26. Conclusions In IEEE 802.11, no provision of multicasting specifically
Hence a new protocol HIMAC to handle this issue.
It uses two unary signals UCF and UNF for the same
It has increased throughput and reduced latency.