CIS679: Prioritized Delivery in UDP and TCP - PowerPoint PPT Presentation

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CIS679: Prioritized Delivery in UDP and TCP

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Prioritized Delivery on Transport-layer Protocols. Cyclic ... HPF = Heterogeneous Packet Flows. If TCP congestion/flow control is so good, why not retain it? ... – PowerPoint PPT presentation

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Title: CIS679: Prioritized Delivery in UDP and TCP


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
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