SRP A Multimedia Protocol Introduce ourselves Purpose of SRP Stream multimedia over a network. Ken French George Oprica Mike Piecuch Advisor: Mark Claypool 11/9/2018

Multimedia Characteristics Loss Latency Undesirable for multimedia 2 key issues that SRP is designed to address Loss – Message lost in the network transmission of the stream Causes gaps in data that user can see Latency - Time from sender to receiver Causes delay in transmission Example: Satellite feed on TV Variance disrupts timing of playback 11/9/2018

Multimedia Over TCP Guaranteed delivery (No loss) Flow Control Unbounded delay Commonly used Guarantees no overall loss automatically retransmits for losses flow control exponential back-off slow retransmission rate in heavy traffic Cost is unbounded delay 11/9/2018

Multimedia Over UDP Best effort delivery (minimal latency) Unbounded loss No guarantee Small latency High loss 11/9/2018

Multimedia Over SRP Selective Retransmission Protocol Combination of TCP & UDP Retransmits a percentage of lost packets Application layer client/server protocol To remedy problems of multimedia transmission SRP - Selective Retransmission Protocol Balance between Latency of TCP and Loss of UDP Retransmits percentage of lost packets Application layer Client/Server Client requests retransmissions based on current loss/latency statistics 11/9/2018

SRP Implementation Algorithms Equal Loss Latency (ELL) Optimum Quality (OQ) Decision Algorithm Retransmit Give up ELL Equalize loss and latency OQ Minimize loss and latency 11/9/2018

Testing Approach UDP blaster Token bucket router 11/9/2018 Network Topology UDP Blaster Random traffic over network Token bucket router Modified Depth controls latency UDP blaster Token bucket router 11/9/2018

Sample Data 11/9/2018 Horizontal blue line is per packet latency y-axis Left hand scale (milliseconds) x-axis is packet number received Spikes are retransmissions Rising pink line is lost packets y-axis Right hand scale (packets) Rises every time there is a packet loss 11/9/2018

Low Loss, Low Latency 11/9/2018 Low Traffic 3% Loss 50ms Latency Average Latency Y-axis Average Loss X-axis Scales are normalized based on desired loss and latency 250ms latency 10% loss Arc is range of acceptable qualities Closer to the origin, the better the quality Origin is perfect quality TCP exponential back-off UDP some loss low latency OQ has no loss ELL did not perform as well as oq 11/9/2018

High Loss, High Latency 11/9/2018 High Traffic conditions 15% loss 275ms RTT TCP off the chart due to exponential back-off UDP Highest loss Lowest latency ELL better than UDP OQ within the acceptable quality range 11/9/2018

Conclusions SRP is a good balance Great potential Additional tuning SRP is good balance of High loss of UDP High latency of TCP Great potential for Controlling multimedia streams Tuning can increase performance of SRP in extreme network conditions tuning different parameters 11/9/2018

Future Work Flow control Loss detection Additional algorithms in the idea of TCP’s exponential back-off Loss detection how long to wait for packet? Additional algorithms Decision algorithms can be customized 11/9/2018