CIS679: Prioritized Delivery in UDP and TCP

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CIS679 Prioritized Delivery in UDP and TCP

• Review of last lecture
• Prioritized Delivery in UDP and TCP

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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

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Prioritized Delivery for JPEG Data
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Prioritized Delivery for MPEG Data
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Prioritized Delivery for Audio Data
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Playback Jitter
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Prioritized Delivery on Transport-layer Protocols

• Cyclic-UDP
• HPF

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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.

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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

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Congestion Control in Cyclic UDP

• Rounds allow timely delivery
• Uses delay and packet losses for determining
  available BW
• Adapt to congestion

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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

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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.

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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

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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

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HPF Architecture
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HPF
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HPF vs TCP

• Separate the reliable delivery from windowing
  mechanisms.
• Multiplicative Decrease/Additive Increase

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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