無線與行動多媒體網路Wireless and Mobile MultimediaNetworks國立中山大學 電機系

許蒼嶺 教授

Multimedia Traffic Characteristics

Traffic Types Traditional Data Traffic Image Voice, High-Quality Sound Full Motion Video Interactive Multimedia

Data Traffic

Interactive Transactions Banking, Airline Reservation, Insurance Processing 30 Transactions per sec for 1000 Terminals Very Stable and Predictable Traffic Patterns

File Transfer From a Few Kbytes to Hundred Million Bytes Uniform, Regular Transmission of Data at a Constant Rate

Interactive LAN Data Traffic Interactive Response May be Relatively Sensitive to Network Delay

Real Issues for Data Traffic Flow/Congestion Control Error Recovery or Re-Transmission

IMAGE Traffic

Major Difference from Data Traffic Very Large Block Transfer Response Time Between 1 - 5 sec

Transporting Image Compression Ratio of 4 to 1 on Average Network Load can be Reduced

On-Line Books with Illustrations Consecutive Display of Many Images with 1 - 2 sec Apart Unplanned Load on Network

Voice and High-Quality Sound

Voice Traffic PCM Encoding Gives 64 Kbps Acceptable End-to-End Delay is about 90 msec Variable-Rate Coding

– Half Duplex– About 60% of One-Way Voice Conversation Consists of Silence

High-Quality Sound CD Quality Stereo (5 Channels) Involves Very High Bit Rate Continuous (Such as Film Soundtrack) Delay Does not Matter as Much as Voice

Full-Motion Video

A Sequence of Pictures or Frames NTSC ： 525 Lines at 30 Frames per sec PAL ： 625 Lines at 25 Frames per sec

High Compression Ratio Very Little Different From the Frame Before MPEG-2 ： I, B, and P Frames

Timing Considerations Jitter May Affect Presentation Quality

Network Considerations Sufficient Bandwidth via Reservation Acceptable End-to-End Delay

RTP Timestamps vs System Time

74

66652 us 6007=66744 us

66598 us

67152 us

VF-1

VF-2

VF-3

VF-4

6007

6007

System Time(sec)

System Time (usec)

RTP Timestamp (1/90K sec)

1204735165 901009 2097329347

1204735165 901059 2097329347

1204735165 967661 2097335354

1204735165 967702 2097335354

1204735166 34259 2097341361

1204735166 34299 2097341361

1204735166 34319 2097341361

1204735166 101411 2097347368

1204735166 101448 2097347368

1204735166 101470 2097347368

1204735166 101488 2097347368

VF-1

VF-2

VF-3

VF-4

RTP Header I-VOP(Part 1) RTP Header

Part N

……

Timestamp = αMarker = 0

UDP Header IP Header

Timestamp = αMarker = 1

MTU

I-VOP(Part N)

Start code in MPEG-4 header

A single I-VOP

Part 1

Start code in MPEG-4 header

IP Header UDP Header

I-VOP Encapsulation of MPEG-4

Start Code in MPEG-4 Header

RTP Payload Data

Frame Types

Start code Next 2 bits

0x000001B3 Don’t care

I

0x000001B6

00

01 P

10 B