Experiences with Multimedia Streaming over 2.5G and 3G Networks J. Chesterfield, R. Chakravorty, J. Crowcroft, P. Rodriguez, S. Banerjee Presented by Denny Iskandar

1. Introduction What? –Evaluates performance of multimedia streaming over wireless network. Why? –2.5G and 3G technologies are being deployed everywhere (Europe, America, and Asia) –Popularity of multimedia applications such as videoconferencing, Voice over IP, and audio/video broadcasting

1. Introduction Scope of experiment –Measurements from real networks: The effect of heterogeneity of network is captured by comparison across different network technologies: (GSM), GPRS, and UMTS. Describes the importance of cooperation between network and application using an application called vorbistreamer.

Roadmap 1.Introduction 2.Network measurements 3.Application measurements 4.Conclusions Application layer Presentation layer Session layer Transport layer Network layer Data link layer Physical layer

2. Network Measurements Multimedia traffic characterization –Assume layered organization of media –Bandwidth used ranges between a minimum and a maximum target rate.

Figure taken from paper. 2. Network Measurements 2.1Propagation delay and jitter

The figure is only an approximation. 2. Network Measurements 2.1Propagation delay and jitter

2. Network Measurements 2.1Propagation delay and jitter –Compare with ITU recommendation for voice communications: RTT ≤ 500 ms GSMGPRSUMTS Mean 1460 ms220 ms30 ms VarianceNot mentioned ms ms Note:For GPRS, disabling ARQ reduces jitter at the cost of higher packet loss rate (around 3%).

Figure taken from paper. 2. Network Measurements 2.2Capacity variation

Figure taken from paper. 2. Network Measurements 2.2Capacity variation

2. Network Measurements 2.3Summary –Propagation delay and delay jitter are reduced as link capacity increases. –GPRS should disable ARQ for multimedia application. –Sub-packet error detection [1] improves performance. [1]J. Chesterfield, R. Chakravorty, S. Banerjee, P. Rodriguez and I. Pratt. Transport Level Optimisations for Interactive Media Streaming Over Wide-Area Wireless Networks. In WiOpt ’04, 2004.

Figure taken from paper. 3. Application Measurements Use Vorbis codec –A layered codec, encodes data into a base layer and enhancement layers

3. Application Measurements Design of vorbistreamer –Implements IP-based data striping; this is used to aggregate channel bandwidth. –Uses RTP as transport protocol. –Supports interactivity constraints from fully interactive communication to one-way streaming. –Uses Vorbis codec.

3. Application Measurements Encoding techniques –For multimedia application, reliability is disabled –Needs to add redundancy to multimedia data to facilitate receiver-based repairs –Also involves interleaving of encoding blocks to reduce the effect of error burst

3. Application Measurements 3.1Intra-packet redundancy (UEP) HeaderBase layerEL 1 EL 2 EL n... Vorbis frame RLC packets FEC 1 FEC 2 frame 1 n-2 frames FEC blocks

3. Application Measurements Things to note: –This “bucketing” is done at application layer, the actual RLC packetization is done at link layer. –Multiple layers in one packet to minimize header overhead.

3. Application Measurements 3.2Inter-packet redundancy Cross-packet coding –Sends parity data in separate packets than the original data. original dataparity data d The greater d is: The more effective recovery The greater recovery delay

3. Application Measurements 3.2Inter-packet redundancy Cross-channel coding –From tests, it is more likely that error occurs to A and B than to B and C AB C channel 1 channel 2

3. Application Measurements 3.3Interleaving Intra-packet: change the order of frames in the same packet Inter-packet: change the order of packets in the same channel Inter-channel: 5 channel 1 channel

Tables taken from paper. 3. Application Measurements 3.4Comparison

4. Conclusions The need for cooperation between network and application. Encoding and organization of multimedia data is important. Benefits from aggregating independent channels. Benefits from sub-packet error detection.

5. Related works [1]J. Chesterfield, R. Chakravorty, S. Banerjee, P. Rodriguez and I. Pratt. Transport Level Optimisations for Interactive Media Streaming Over Wide-Area Wireless Networks. In WiOpt’04: Modelling and Optimization in Mobile, Ad Hoc and Wireless Networks, [2]R. Chakravorty, J. Chesterfield, P. Rodriguez and S. Banerjee. Measurement Approaches to Evaluate Performance Optimizations for Wide-Area Wireless Networks. In Passive and Active Network Measurement (PAM 2004) 5 th International Workshop, 2004.