1. “On the Integration of MPEG-4 streams Pulled Out of High Performance Mobile Devices and Data Traffic over a Wireless Network” Spyros Psychis, Polychronis Koutsakis and Michael Paterakis Electronics & Computer Engrg. Dept. & Telecommunication Systems Institute Technical University of Crete Chania, Greece

2. Introduction Wireless Networks: currently allow users to experience services that until now only the wire-line networks provided. The main concern remains: how to extend the broadband frontier to the end user given the constraints of the wireless media.

3. Introduction (cont.) Well designed MAC protocols are needed in order to: –Maximize system’s capacity –Integrate the different classes of traffic –Satisfy the diverse and sometimes contradictory QoS requirements of each traffic class

4. Concept We envision a system where the Mobile Terminals are high performance devices with extended storage capabilities which can act like cache memories streaming multimedia material. We focus on the uplink channel and we investigate the system’s performance under a variety of possible loads which consist of actual MPEG-4 streams and Data Traffic.

5. Channel Structure Uplink channel time is divided into time frames of equal length. Each frame consists of a request interval and an information interval.

6. Channel Structure (cont.) The request intervals consist of slots, which are subdivided into two mini-slots, and each mini-slot accommodates exactly one, fixed length, request packet. The size of the request interval was chosen to be equal to 10 slots (20 minislots). Video and data terminals share the request slots.

7. BS Scheduling and Terminal Actions We require Video terminals to contend in order to reserve information slots since we are dealing with high quality stored video content which corresponds to highly bursty information. When the Video contention period is over, Data Terminals that require information slots begin their contention process. The two-cell stack RRA and the two cell stack blocked access CRA are used to resolve the collisions, among video request packets and data request packets, respectively.

8. BS scheduling and Terminal Actions (cont.) At the end of the request interval BS allocates resources. Video Terminals have higher priority. If a full allocation is impossible, the BS proceeds to partial allocations. Data Terminals can reserve only one slot per frame. No preemption of data reservations is used.

9. BS scheduling and Terminal actions (cont.) When a Video Terminal decreases its bitrate it releases the slots that were previously allocated to it and are not needed anymore. –The BS realizes the change in the bit rate when the first currently unnecessary reserved slot is released by the video terminal. When the bit rate of a Video Terminal increases the terminal re-enters the contention process. It releases all of its currently reserved information slots before entering contention.

10. Data Traffic Data traffic model is based on statistics collected on email usage from a University and Research Network. The pdf for the length of the data msgs was found to be well approximated by the Cauchy (0.8,1) distribution. The msg inter-arrival time distribution is exponential. An upper bound on the average data msg delay equal to 2 secs is assumed (tolerable delay for email msg transmission).

11. Video Terminals Video Terminals are streaming actual MPEG-4 streams encoded @ 25 fps (one Video Frame every 40 ms). Video content is delivered to the network in the initial form that was encoded. No shaping mechanisms were used. Maximum transmission delay for Video Packets is assumed to be equal to 40 ms. Maximum Pdrop = 0,0001

12. Video Streams Movie Name Mean Bit rate (Kbps) Peak Bit rate (Kbps) News7203400 Parking Lot Cam 7902800 Silence of the Lambs 5804400 The Simpsons 13008800 Soccer11003600 Star Wars2801900

13. Performance Evaluation - Simulations We simulated the system under all possible movie loads from 1 to 6 movies. For each load, all different combinations were examined (63 in total), from 5 times each (Monte Carlo method). Each run simulated one hour of network activity (300005 channel frames).

14. Simulations (cont.) Single Movie Scenario Movieλ Throughput % ANews5.186.47 B Parking Lot Cam 4.8583.91 C Silence of the Lambs 4.7879.12 D The Simpsons 3.168.67 ESoccer5.0592.85 F Star Wars 5.8588.76 Average4.7883.29

15. Simulations (cont.) System Load Average λ Average Throughput % 1 Movie4.78833383.29986 2 Movies3.836683.97877 3 Movies2.9685.90973 4 Movies2.262591.91385 5 Movies1.26666797.34089 6 Movies0.3194.18723 The average data messages delays were found to be roughly constant and approximately equal to 960 msecs (80 packets per message * 12 msecs per frame).

16. Conclusions and Contributions of this Work The goal was to design efficient MAC scheduling mechanisms in order to satisfy the diverse nature of the traffic types that the network must accommodate and the contradictory QoS requirements of each traffic type. Simulation results show that the proposed mechanism achieves high aggregate channel throughput in all cases of traffic load, while preserving the Quality of Service (QoS) requirements of each traffic type.

17. Ideas for Future Work The evaluation of the proposed mechanisms when used over a wireless error prone channel. Investigating the case in which different media encoding techniques together with less strict QoS requirements for the time sensitive traffic are used. Incorporating the proposed mechanisms in a wider system framework (MAC and BS scheduling schemes together with a content placement scheme throughout the wireless and wireline network).