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  • Good afternoon, every one. It is my honor to give a presentation in the department of computer science at Michigan State University. The title for my presentation is : coordinated multi-hop scheduling: a mechanism for efficient end-to-end service in wired and wireless networks. All materials related to my presentation are available from my homepage.
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    1. 1. VoIP on Wireless Meshes: Models, Algorithms and Evaluation A. Kashyap 1 S. Ganguly 2 S. Das 1 S. Banerjee 3 1. Department of Computer Science, Stony Brook University 2. NEC Lab, Princeton, NJ 3. Department of Computer Science, University of Wisconsin IEEE INFOCOM 2007 Presented by Chengzhi Li
    2. 2. Outline <ul><li>Background </li></ul><ul><li>Related Work </li></ul><ul><li>Main Results </li></ul><ul><ul><li>Modeling Capacity Utilization </li></ul></ul><ul><ul><ul><li>Interference Map </li></ul></ul></ul><ul><ul><ul><li>Traffic Offered Load </li></ul></ul></ul><ul><ul><ul><li>Capacity Utilization </li></ul></ul></ul><ul><ul><li>Route Computation </li></ul></ul><ul><li>Performance Evaluation </li></ul><ul><li>Final Remarks </li></ul>
    3. 3. Background <ul><li>VoIP is becoming more and more popular </li></ul><ul><ul><li>Already 3-7 million residential customers </li></ul></ul><ul><ul><li>By 2008, phone lines of Corporate will contain about 44% VoIP lines </li></ul></ul><ul><li>Providing VoIP service over WMNs is one of the most wanted items of ISP providers </li></ul><ul><li>Many new challenges for providing VoIP over WMNs </li></ul>2 Mbps Norminal Channel Capacity
    4. 4. Related Work by NEC Lab & Stony Brook University <ul><li>A practical framework for supporting VoIP over Wireless Mesh Networks </li></ul><ul><ul><li>VoIP packet aggregation and packet header compression </li></ul></ul><ul><ul><li>Efficient path selection technique to route VoIP traffic </li></ul></ul><ul><ul><li>A fast network layer handoff technique to support mobility </li></ul></ul><ul><ul><li>An efficient CAC to maintain QoS </li></ul></ul>“ Performance of VoIP in a 802.11 Wireless Mesh Network ”, D. Niculescu, S. Ganguly, K. Kim, R. Izmailov, (NEC Lab, Princeton, NJ), IEEE INFOCOM 2006 “ On Admission of VoIP Calls over Wireless Mesh Network ”, H. Wei, K. Kim, A. Kashyap D. Niculescu, S. Ganguly (NEC Lab, Princeton, NJ), IEEE ICC 2006 “ Performance Optimizations for Deploying VoIP Service in Mesh Networks ”, S. Ganguly, V. Navda, K. Kim, A. Kashyap, D. Niculescu, (NEC Lab, Princeton, NJ), JSAC, 2006 “ VoIP on Wireless Meshes: Models, Algorithms and Evaluation ”, A. Kashyap, S. Ganguly, S. Das, S. Banerjee, IEEE INFOCOM 2007
    5. 5. Main Results of This Paper <ul><li>A centralized architecture with five components to support VoIP </li></ul><ul><ul><li>Interference map </li></ul></ul><ul><ul><li>Offered traffic load estimation </li></ul></ul><ul><ul><li>Capacity utilization estimation </li></ul></ul><ul><ul><li>Polynomial time route selection algorithm </li></ul></ul><ul><ul><li>Measurement based call admission control algorithm </li></ul></ul><ul><li>When a VoIP call arriving </li></ul><ul><li>SIP authorization </li></ul><ul><li>Route computation </li></ul><ul><li>Admission control </li></ul><ul><li>Route setup </li></ul>
    6. 6. VoIP QoS Metric <ul><li>R-score for G.729a </li></ul><ul><li>R = 94.2 - 0.024*d -0.11*(d-177.3)*H(d-177.3) -11-40*log(1+10*e) </li></ul><ul><ul><li>One way delay: d = d encoder + d jitter_buffer + d network </li></ul></ul><ul><ul><ul><li>For G.729a encoder </li></ul></ul></ul><ul><ul><ul><ul><li>d encoder = 25 ms </li></ul></ul></ul></ul><ul><ul><ul><ul><li>d jitter_buffer = 50 ms </li></ul></ul></ul></ul><ul><ul><li>Total loss rate: e = e network + (1-e network )*e jitter </li></ul></ul><ul><ul><li>H(x) = 0 if x < 0 otherwise 1 </li></ul></ul><ul><li>Acceptable VoIP service quality : R > 70  d<200ms & e < 5% </li></ul>2-hop segment of a IEEE 802.11a based mesh testbed with 6 Mbps channels
    7. 7. Interference Map <ul><li>csf x y - carrier sense factor of sender x with respect to interferer y </li></ul><ul><ul><li>The ratio of actual transmission rate of x when both x and y attempt to transmit at their nominal rate, to transmission rate of x when x transmits alone at its nominal rate </li></ul></ul><ul><ul><li>csf x y = 0.5 if x and y are within carrier sensing range of each other and fairly share the medium </li></ul></ul><ul><ul><li>csf x y = 1 if x and y cannot hear each other </li></ul></ul><ul><li>csf x y for all node pairs (x,y) defines interference map </li></ul>
    8. 8. Normalized Traffic Load <ul><li>Normalized traffic offered load l i at node i </li></ul><ul><ul><li>For IEEE 802.11a with 6 Mbps channel and two-way G.729a VoIP calls </li></ul></ul><ul><ul><ul><li>l i = 1/84 if node i is source or destination </li></ul></ul></ul><ul><ul><ul><li>l i = 2/84 otherwise </li></ul></ul></ul><ul><li>Normalized actual traffic load t i at node i (retransmission<=1) </li></ul><ul><ul><li>Where l i,k denotes the normalized amount of traffic send by node i to node k </li></ul></ul><ul><li>Normalized overheard traffic o i by node i </li></ul>
    9. 9. Normalized Capacity Utilization <ul><li>Normalized capacity utilization c i of node i </li></ul><ul><ul><li>The total bit/sec traffic transmitted, received, and overheard by node i normalized to nominal channel capacity </li></ul></ul><ul><li>Determining c i </li></ul><ul><ul><li>Solve c i from 1 = t i + o i + r i </li></ul></ul><ul><ul><ul><li>where </li></ul></ul></ul>
    10. 10. Route Computation (1) <ul><li>Goal: </li></ul><ul><ul><li>Select feasible paths </li></ul></ul><ul><ul><ul><li>Increase number of supported VoIP callls </li></ul></ul></ul><ul><ul><ul><li>Minimize future call rejections </li></ul></ul></ul><ul><li>Techniques </li></ul><ul><ul><li>Select feasible path segments that consist of more than one links </li></ul></ul><ul><ul><li>Paths that consist of feasible path segments are feasible </li></ul></ul><ul><li>Fast heuristic algorithm </li></ul><ul><ul><li>Carrier sense range = transmission range </li></ul></ul><ul><ul><li>Length of path segment = 2 </li></ul></ul><ul><li>Two algorithms </li></ul><ul><ul><li>Shortest feasible path </li></ul></ul><ul><ul><li>Max residual feasible path </li></ul></ul>
    11. 11. Route Computation (2) <ul><li>Select path using call statistics to minimize future call rejections </li></ul><ul><ul><li>p(a, b): probability of (a,b) to be source & destination of new call </li></ul></ul><ul><ul><li>C(a,b): a critical set of links for a node pair (a, b) </li></ul></ul><ul><ul><ul><li>Any links in any one of min-cut for (a, b) </li></ul></ul></ul><ul><ul><ul><li>Any links that interferes with links in any one of min-cut for (a, b) </li></ul></ul></ul><ul><ul><li>Assign weights to link l </li></ul></ul>
    12. 12. Performance Evaluation (1) <ul><li>Experimental test-bed for capacity utilization model and CAC evaluation </li></ul><ul><ul><li>IEEE 802.11a with 6 Mbps norminal channel capacity </li></ul></ul><ul><ul><li>Located in one floor of NEC Labs building </li></ul></ul><ul><ul><li>Calls are generated as a Poison process with mean rate  calls/s </li></ul></ul><ul><ul><li> verage call duration is exponentially distributed with mean rate  </li></ul></ul><ul><ul><li> verage mean number of calls in any time  </li></ul></ul><ul><ul><li> calls are used for each experiments </li></ul></ul>
    13. 13. <ul><li>qq </li></ul>
    14. 14. Performance Evaluation (2) <ul><li>ns-2 simulator for evaluation of path selection algorithms </li></ul><ul><ul><li>IEEE 802.11b with 11 Mbps channels </li></ul></ul><ul><ul><li>Two-ray ground reflection large scale path loss model </li></ul></ul><ul><ul><li>Ricean model for small scale fading </li></ul></ul><ul><ul><li>Transmission range = 250 meters </li></ul></ul><ul><ul><li>Carrier sense range = 550 meters </li></ul></ul><ul><ul><li>Two topologies </li></ul></ul><ul><ul><ul><li>13 X 13 grid in 4000 X 4000 square meter area </li></ul></ul></ul><ul><ul><ul><li>169 nodes randomly distributed in 2000 X 2000 square meter area </li></ul></ul></ul><ul><ul><li>Calls are generated as a Poison process with mean rate  calls/s </li></ul></ul><ul><ul><li>R-scores are checked for all active calls for every 5 seconds </li></ul></ul><ul><ul><li>Call with R-score less than 70 is dropped </li></ul></ul><ul><ul><li>A single long simulation is run utill 200 calls have been completed </li></ul></ul>
    15. 17. Final Remarks <ul><li>A practical framework for supporting VoIP over WMNs </li></ul><ul><li>Does average performance metric work well for real-time traffic? </li></ul><ul><li>Is inference map accurate? </li></ul><ul><li>How to extend the results to multi-radio/multi-channel WMNs? </li></ul>
    16. 18. Call Admission Decision