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

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

WHY HIMAC Currently we have IEEE 802.11 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.

Performance Limitations in 802.11 CHANNEL STATE INDIFFERENCE DEMAND IGNORANCE

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

CHANNEL STATE INDIFFERENCE(2) In 802.11, 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

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 802.11b) is best only beyond 275 ft Hencle channel state awareness can significantly improve awareness

DEMAND IGNORANCE In 802.11,we multicast i.e. broadcast here irrespective of demand If node has already overheard data, still data is send to it.

Example to show the problem

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

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

Example showing effect of UCF signal on rate Ask mam

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

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

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

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

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

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)

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

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)

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

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

Impact of packet size

Impact of Network Load

Impact of Number of Recievers

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.