Yi Liang Aug. 2, 01 Low-latency Internet media streaming using packet path diversity - prior and future work.

Yi Liang Aug. 2, 01

Low-latency Internet media streaming using packet path diversity - prior and future work

HP Labs Project Meeting Yi Liang

Outline

What we have done UDP with path diversity for real-time voice Path diversity augmented TCP for file transfer and

streaming multimedia Proposed work and open problems

Source/channel coding adapted to channel conditions Retransmission on the transport layer

HP Labs Project Meeting Yi Liang

Outline

What we have done UDP with path diversity for real-time voice Path diversity augmented TCP for file transfer and

streaming multimedia Proposed work and open problems

Source/channel coding adapted to channel conditions Retransmission on the transport layer

HP Labs Project Meeting Yi Liang

Real-time Voice Communication

Best-effort services vs. strict QoS requirements of real-time speech communication.

Low data rate of the voice stream

Why alternative path/multi-path? Exists a superior alt. path in

30-80% cases [Savage, 99’] Path diversity – network

behavior averaged; burst loss converted to isolated loss; outage probability decreased [Apostolopoulos, 01’]

Multi-path – independent delay jitter characteristics

Realization: explicitly path selection using relay servers

D

S

RelayRelay1 2

Datatraffic

Datatraffic

The bottleneck

Voice traffic

[Liang, Steinbach, Girod, ACM MM 01’]

HP Labs Project Meeting Yi Liang

Delay Traces Measured over the Internet

Playout of packets from multiple streams

HP Labs Project Meeting Yi Liang

Multi-stream with MDCStream 1:

Even samples: quantized in finer resolution (PCM, 8-bit) Odd/even samples: quantized in coarser resolution (ADPCM, 2-bit)Stream 2: the opposite way [Jiang, 00’]

MDC over Multiple Streams

Es1

s2

O-E

OE-O Packets in multi-streams

Multiple description coding (MDC): generates multiple descriptions of equal importance for the same source signal

E O-E E O-E E O-E

OE-O OE-O

HP Labs Project Meeting Yi Liang

Adaptive Playout Scheduling for Multiple Streams

To minimize the Lagrange cost functionC = delay + 1 p (packet from both streams lost)

+ 2 p (one packet lost)

= d + 1 lp1 • lp2 + 2 [lp1 (1- lp2)+lp2 (1- lp1)]

Stream 1 ds1

lp1

lp2

dFreq

Maintaining history for both streams; loss probability determined by delay and past history (order statistics)

Stream 2 ds2

HP Labs Project Meeting Yi Liang

Experiments over the Internet

Path 1 (direct): Netergy – MITPath 2 (alternative): Netergy – Harvard – MIT

Direct path: 30ms UDP packets sent from source to dest.; routes determined by routing algorithm

Alt. path: packets sent from source to relay server, then forwarded to dest.

Exodus

Comm.

Exodus

Comm.

BBN PlanetBBN Planet

QwestQwest

Netergy networks

192.84.16.176

MIT18.184.0.5

0

Harvard140.247.62.110

(5) (45)

(40) (5)

(5)

HP Labs Project Meeting Yi Liang

Results – Improved Delay-loss Tradeoff

Delay – loss curve obtained by varying 1 while keeping 2 small and fixed.

Observed significant reduction in delay and loss rate by using multiple streams.

Total/burst loss rate greatly reduced since jitter averaged.

Path 1 (direct): Netergy – MITPath 2 (alt): Netergy – Harvard -

MIT

HP Labs Project Meeting Yi Liang

Results – Improved Speech Quality

PESQ (perceptual evaluation of speech quality): an objective measure in ITU-T P.862

Results obtained by varying 2 and 1 while keeping ratio fixed

With higher delay: better chances to play both descriptions and lower erasure rate

HP Labs Project Meeting Yi Liang

Outline

What we have done UDP with path diversity for real-time voice Path diversity augmented TCP for file transfer and

streaming multimedia Proposed work and open problems

Source/channel coding adapted to channel conditions Retransmission on the transport layer

HP Labs Project Meeting Yi Liang

TCP File Transfer and Media Transport

[Steinbach, Liang, Girod, submitted to INFOCOM 02’]

Packet path diversified TCP (PPD-TCP)

DS

PPD node TCP client

Path 1…

PPD nodeTCP server…

Path 2

HP Labs Project Meeting Yi Liang

PPD-TCP Variants Studied

PPD-TCP1

PPD-TCP2

PPD-TCP3

HP Labs Project Meeting Yi Liang

Simulation Topology

H8H6H5

H4H2H1

TCP server

H3

H7

PPDnode

TCP client/PPD node

Simulation parameters 20 TCP/UDP sources attached to each intermediate hop as

background traffic; avg load is varied All links 10Mbps Transfer 1000 bytes x 100 packet

HP Labs Project Meeting Yi Liang

Results – Transmission time

Identical avg load on two paths One path has avg load 20% lower

HP Labs Project Meeting Yi Liang

Results – Media Throughput

Identical avg load on two pathsLoad = 0.94

One path has lower avg loadLoad = 0.94/0.85

HP Labs Project Meeting Yi Liang

Outline

What we have done UDP with path diversity for real-time voice Path diversity augmented TCP for file transfer and

streaming multimedia Proposed work and open problems

Source/channel coding adapted to channel conditions Retransmission on the transport layer

HP Labs Project Meeting Yi Liang

Multiple Description Video Coding

1 3

0 2

5

4

7

6

9

8

[Apostolopoulos, Wee, ICIP 01’]

1 3

0

5

4

7 9

8

Balanced coding

Unbalanced coding

HP Labs Project Meeting Yi Liang

Layered Coding

Priority encoding transmission (PET) with FEC [Albanese et al. 96’]

Prioritized coding -> non-prioritized coding:

L0 L1 L2 Lm

FEC FEC FEC

…

MR layers

r0 r1 r2 rm

Packet

MD

k

n

RS(n,k)

HP Labs Project Meeting Yi Liang

Scalable Video Codec Spatial/temporal scalability

[Girod et al. VCIP 99’]

Temporal scalability [Leicher et al. 94’]

Progressive texture coding [Stockhammer et al.] [Puri, Ramchandran et al.]

Optimal rate allocation for different priority layers – adapted to varying conditions of multiple channels

Selection of the appropriate video codec: rate must be adjustable with enough flexibility

BL EL

FEC FEC

MR layers

r0 r1

Packetk

n

RS(n,k)

I P

FEC FEC

r0 r1

Packetk

n

RS(n,k)

B

r2

HP Labs Project Meeting Yi Liang

The Channel Model Channel loss rate (with

memory) The Gilbert model for one

network path [Girod et al. VCIP 99’]

Two network paths:4 states

Other (unbalanced) channel conditions: Delay BW

G B

pGB

pBG

GG GB

BG BB

HP Labs Project Meeting Yi Liang

Communication with the Transport Layer

Conditions of multiple paths can be estimated and recorded on transport layer: delay, BW, loss rate

The selection of channel/bit allocation can be based on recorded history of channel conditions

Optimize FEC vs. retransmission

Need to model ARQ The cost function:

Delay (on the order of rtt) Distortion Rate (constrained)

L0 L1 L2 Lm

FEC FEC FEC

…

MR layers

r0 r1 r2 rm

Packet

k

n

RS(n,k)

HP Labs Project Meeting Yi Liang

Work Plan

AugSep

OctNovDec

JanFebMar

AprMayJun

Video codec

Transport layer;channel modeling

Optimization

Simulation &experiment