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Comparison of Two Synchronization Mechanism. Amy, Mei-Hsuan Lu CML/CSIE/NTU Mar. 27 ,1999. Synchronization. For Master Stream ET i (n) = MAX(D i + TS i (n) - TS i (1), A i (n)) D i is initialized as (lower-bounded by) initial delay Increase/Decrease D i dynamically Pure Time Control

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Comparison of two synchronization mechanism

Comparison of Two Synchronization Mechanism

Amy, Mei-Hsuan Lu

CML/CSIE/NTU

Mar. 27 ,1999


Synchronization
Synchronization

  • For Master Stream

    • ETi(n) = MAX(Di + TSi(n) - TSi(1), Ai(n))

    • Di is initialized as (lower-bounded by) initial delay

    • Increase/Decrease Di dynamically

      • Pure Time Control

      • Buffer Level Control

  • For Slave Stream

    • ETi(n) = MAX(DM + TSi(n) - TSi(1), Ai(n))


Pure time control
Pure Time Control

  • Decrease DMwhen DM + TSM (n) - TSM (1) > Th1 + AM (n) + PM (n)

  • Increase DMwhen DM + TSM (n) - TSM (1) + Th2 < AM (n) + PM (n)

  • Pi(n) = MAXS((AM (n)-AS (m))-(TSM (n)-TSS (m)))


Buffer level control
Buffer Level Control

  • Increase DMwhen buffer level of some stream is smaller than Th3

  • Decrease DMwhenbuffer level of all streams is larger than Th4


Comparison 1 2
Comparison (1/2)

  • No Loss and Jitter < Initial Delay : Same

  • BLC can not recognize the following two scenario

    • Packet Delay too much or Sampling Rate Changes

    • Packet Loss

    • Application have to send silence frames even during a long period of silence.


Packet loss in blc
Packet Loss in BLC

Increase D

Decrease D

Th3 = 2 packets

D = 90ms

D = 60ms

D = 60ms

1

270

Audio Frame

60

90

120

150

300

MasterStream

0

30

60

90

180

210

240

1

2

3

2

2

120

150

180

210

240

270

300

Time (ms)

0

30

60

90


Packet loss in ptc
Packet Loss in PTC

Th2 = 2 packets

?

DM + TSM (n) - TSM (1) + Th2 < AM (n) + PM (n)

D = 60ms

1

270

240

Audio Frame

60

90

120

150

300

Master Stream

0

30

60

90

180

210

240

120

150

180

210

240

270

300

Time (ms)

0

30

60

90


Comparison 2 2
Comparison (2/2)

  • BLC has to adjust Th3/Th4 when sampling rate changes

  • PTC keeps more parameters (e.g. Ai(n))

  • BLC : when CPU is not fast enough, packets will accumulate not because of delay increase


Flow control
Flow Control

  • Goal

    • Maintain equal encoding and decoding rate

    • Dynamic adjust transmit rate to utilize available resource

  • Mechanism

    • Buffer Control (Large Jitter)

    • A/V Eligible Time Control

    • Loss Rate Control


State Transition Diagram

Loss Rate > Hi-TH, Dec. Enc. Rate

1.Recv. SpeedUp Req. Send SpeedUp Cfm. Inc. Encoding Rate

2. Recv. SlowDown Req. Dec. Enc. Rate

Send SlowDwon Cfm

3. Loss Rate < Low-TH (Initial State)

Network Bound1

Loss Rate < Low-TH

(Initial State)

Slave Initial State

VideoIn Buf > Hi-TH, Dec. Enc. Rate, Send SlowDown Req.

Master Initial State

Loss Rate > Hi-TH

Dec. Enc. Rate

Loss Rate > Hi-TH

Dec. Enc. Rate

1.Recv. SlowDown Req., Dec. Enc. Rate, Send SlowDown Cfm

2. Recv. SpeedUp Req. Inc. Enc. Rate, Send SpeedUp Cfm.

Recv. SlowDown Req.

Dec. Enc. Rate

Remote Bound2

Local Bound3

HOL pkt ET pkts too small, Dec. Enc. Rate, Send SlowDown Req.

HOL pkt ET pkts too small, Dec. Enc. Rate, Send SlowDown req.

Recv. SpeedUp Cfm, Inc. Enc. Rate

1.Recv. SlowDown Cfm

2. Recv. SlowDown Req. & Req. Rate higher, Dec. Enc. Rate, Send SlowDown Cfm.

CPU fast enough for a period, Send SpeedUp Req.

Recv. SlowDown Cfm

1.Recv. SpeedUp Req

2. Recv. SlowDown Req. & Req. Rate lower

WFSDC4

WFSUC5

Recv. SlowDown Req., Dec. Enc. Rate, Send SlowDown Cfm


How to decrease rate
How to Decrease Rate ?

  • Reduce encode rate (frame rate v.s. bit rate)

  • Packetize multiple audio frames in one packet

  • Send audio/video mixed in one packet

  • Turn off video


Audio Packetization

  • Tradeoff between Delay and Bandwidth Efficiency

    • Header Overhead : 14(Ethernet) + 20(IP) + 8(UDP) + 12(RTP) = 54

    • Audio/Video mixed in one packet


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