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

2. 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

3. Prioritized Delivery for JPEG Data

4. Prioritized Delivery for MPEG Data

5. Prioritized Delivery for Audio Data

6. Playback Jitter

7. Prioritized Delivery on Transport-layer Protocols
Cyclic-UDP
HPF

8. 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.

9. 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

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

11. 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

12. 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.

13. 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

14. 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

15. HPF Architecture*

16. HPF*

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

18. 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*