CIS679: Prioritized Delivery in UDP and TCP Review of last lecture Prioritized Delivery in UDP and TCP

Review of Last Lecture UDP can be tuned to better support multimedia applications. UDP-based applications should do end-to-end congestion control TCP-friendly Rate-based adaptation Packet-pair Hop-by-hop control

Prioritized Delivery for JPEG Data

Prioritized Delivery for MPEG Data

Prioritized Delivery for Audio Data

Playback Jitter

Prioritized Delivery on Transport-layer Protocols Cyclic-UDP HPF

Cyclic UDP Developed at UC Berkeley Notion of rounds -- data sent in a fixed size time units Retransmit data within the round Move on to next round if data not received within round Apply flow control within the round.

Prioritization in Cyclic UDP Prioritize packets within round Order higher priority packets in front CUDP improves chances of delivery of higher priority packets -- retransmissions have higher priority NACK - indicate not received packets so far on each packet reception

Congestion Control in Cyclic UDP Rounds allow timely delivery Uses delay and packet losses for determining available BW Adapt to congestion

Issues in Cyclic UDP Assumes all available BW can be used Not clear what happens to competing TCP applications Results indicate multiple CUDP flows share available BW

HPF HPF = Heterogeneous Packet Flows If TCP congestion/flow control is so good, why not retain it? Easy to show that “TCP-friendly” Get rid of reliable/in-order delivery mechanisms that get in the way.

Prioritization in HPF Allows marking packets high/low priority Provides In-order reliable delivery of high priority packets Allows low priority packets to be delivered when enough BW available If routers support priority, can drop low priority packets ahead of high priority packets

HPF Layers* Application Framing (AF) -- convert frames into packets, packets into frames Windowing, Reliability, Timing and Flow-control (WRTF) -- window management, flow control, reliability, deadlines Congestion Control (CC) -- congestion response, estimation of RTTs

HPF Architecture*

HPF*

HPF vs TCP* Separate the reliable delivery from windowing mechanisms. Multiplicative Decrease/Additive Increase

Conclusion CUDP Allows Timely Delivery and discard of expired packets, prioritization Not clear if more aggressive than TCP Not a multiplicative decrease response HPF UDP-based delivery puts application in charge to do flow control, congestion response etc. Tedious for every application to implement all the basic mechanisms* Separate ALF policies and implementation -HPF does this and follows TCP based congestion response*