/ NASA Technical Memorandum 107421 ,,

ATM Quality of Service Tests for Digitized Video

Using ATM Over Satellite: Laboratory Tests

William D. Ivancic

Lewis Research Center

Cleveland, Ohio

David E. Brooks and Brian D. Frantz

Sterling Software

Cleveland, Ohio

July 1997

National Aeronautics and

Space Administration
Trade names or manufacturers' names are used in this report for identification

only. This usage does not constitute an official endorsement, either expressed

or implied, by the National Aeronautics and Space Administration.
ATM Quality of Service Tests for Digitized Video Using ATM Over Satellite: Laboratory Tests

William D. Ivancic

National Aeronautics and Space Administration, Lewis Research Center, Cleveland, Ohio 44135

David E. Brooks and Brian D. Frantz

Sterling Software, Cleveland, Ohio 44135

ABSTRACT: A digitized video application was used to help

determine minimum quality of service parameters for asynchronous transfer mode (ATM) over satellite. For these tests, binomially distributed and other errors were digitally inserted in an

intermediate frequency link via a satellite modem and a commercial gaussian noise generator. In this paper, the relationship

between the ATM cell error and cell loss parameter specifications is discussed with regard to this application. In addition, the

video-encoding algorithms, test configurations, and results are

presented in detail.

Introduction

NASA Lewis Research Center is the lead center for commercial satellite communications and hybrid satellite/terrestrial

networks. As such, Lewis has been asked to assist the commercial satellite communications industry with hybrid satellite/

terrestrial networks and interoperability issues. One of the major

topics of interest is the satellite link requirements for asynchronous transfer mode (ATM) quality of service (which is application dependent). Voice quality may be acceptable with bit error

rates (BER's) of 10--6 or higher. For medical imaging, BER's of

10-7 may be acceptable. For file transfers that are not delay sensitive, high-level protocols will resolve many problems resulting

from transmission errors. Thus, the question to be resolved is

"What link quality will satellites have to provide in order to be

globally interoperable with terrestrial systems?"

Digitized Video

As an interim step in determining the satellite link quality

requirements, we chose to use FORE Systems' AVA-200 Video

[1,2] to digitize video over ATM since this equipment was

already available. Future tests will use MPEG-2 (Moving

Pictures Experts Group). The uncompressed digitized video

rate used in these tests was approximately 19 Mbps, giving a

"pseudocompression" ratio of approximately 20:1. Here,

pseudocompression refers to the lossy compression resulting

from encoder parameter settings such as video resolution, picture

size, and frame rate. For comparison, MPEG-2 can compress

video at ratios as high as 90:1 for quality videos, such as sports

and movies.

For the AVA-200 uncompressed video, the picture frame

was split into and transmitted as a sequence of tiles, where each

tile was an 8- by 8-pixei segment of a video frame. Figure i

shows the common part convergence sublayer (CPCS) packet.

Each asynchronous transfer mode adaptation layer 5 (AAL5)

frame consisted of an integral number of bytes of encoded pixel

data, a variable-length pad, a 2-byte tile trailer, and a 2-byte

AAL5 trailer. The pad ensured that the AAL5 protocol distribution unit (PDU) frame would be an integral number of cells

(48 bytes) in length. The tile trailer contained the coordinates of

the first tile in the tile dimension units and a 32-bit picture frame

number that stated which frame the tile belonged to. The AAL5

trailer contained a 2-byte pad, a 2-byte code, and a 4-byte cyclic

redundancy check (CRC) code. For the particular encoding

parameters used in these tests, the AAL5 CPCS packet consisted

of 66 ATM cells.

The following encoder parameters were used in our test,

resulting in a pseudocompression ratio of approximately 20:1, as

given by equations (1) and (2):

Packing factor (PF)

/

-?-": '_":-'i

¢ _----!--'-! .... !- "..- !"' "!"" '-:i

"----,=----_ .... I----I----I----1----i _,

/ i i i ! i i i i \

/ L.-i-.-.i.....L--i----i----i-.-.[ ".

/

/ -,..

/ "%

/48 pixels_,--_8 pixels_-_8 pixels_,-_8 pixels_

2,

I

0 8 • •

7 15 • 2PF-1

I

I

i 8 pixels x 8 pixels x PF x PixelsEncoding Variable _, 16 bytes

I 0 I 1 I----I 2PF'll Pad Trailer

Integral number of 48-byte cells . -

Tile trailer

AAL5 t2iler

t

/

Reserved I y-tile Ix-tile

Sequence number

Pad Length

CRC

4 bytes

Figure 1 .i Video tile encoding.

NASA TM-107421 1
The AAL5 CPCS packet size PKS is given by equation (1): ATM Quality of Service Measurement Parameters

PKS bytcs/AAL5 - CPCS ----[PE bytes/tile(PF tiles/AAL5 - CPCS)]

+pad bytes/AAL5 - CPCS + trailer bytes/AAL5 - CPCS (1)

where PE is a pixel encoding of 24 rgb and 3 bytes and PF is a

packing factor of 64 tiles per AAL5 CPCS.

The video bit rate VBR can be determined from equation (2):

VBR bits/see = FR frames/see ( PS tiles/frame

_ PF tilcs/AAL5 - CPCS )

CPCS( 424 bits/ATM - Cell )

xPKS bytes/AAL5 - _ 48 bytes/ArM - C-_lJ

(2)

where FR is the frame rate and PS is the picture size.

No audio was used in these tests because it was not deemed

necessary at the time. In hindsight, it would have been useful to

have included the audio channels in these tests to see if they

degrade gracefully and at what point their degradation is

unacceptable.

Each of the following six parameters give a particular measure of the ATM quality of service:

• CER cell error ratio

• CLR cell loss ratio

• CDV cell delay variation

• SECBR severely errored cell block ratio

• CTD cell transfer delay

• CMR cell misinsertion rate

Cell error ratio, cell loss ratio, and cell delay variation are

the most important quality of service parameters to consider

when one is testing digital video applications over ATM. Cell

error rate and cell loss ratio are of greatest concern. With the test

setup and equipment on hand we were able to obtain reliable,

repeatable measurements for the cell error ratio and cell loss

ratio, as well as for the severely errored cell block ratio.

Severely errored cell block ratio measurements were readily

obtained but were not particularly meaningful for our tests. They

are used primarily as an availability measurement to identify

bursts of errors.

Digital video is not delay sensitive; therefore, the cell

transfer delay will not affect the ATM quality of service. For

instance, the round-trip delay for a geostationary satellite is

OC3c/ATM

OC3c/ATM

I I"' OC3c

I II

TAXI/ATM I TAXI

NTSC --- ATM (AAL5)

OC3c/ATM

II

ForeRunner ASX-200

ADTECH

SX/4000

ATM

Traffic

Generator/Analyzer

SVideo

Source

Adtech

SX/14 Data

Channel

Simulator

SUN SPARCstation 20

AVA-200 Control

Workstation

,r l OC3c/ATM

I II

ForeRunner ASX-200BX M

SVideo

Recorder

Silicon Graphics Onyx

AVA-200 Display Workstation

Figure 2.nBinomially distributed errors. (NTSC, National Television System Committee Video; TAXI, transparent

asynchronous transceiver/receiver interface; OC3c, optical carder 3c.)

NASA TM-107421 2
approximately 250msec.Thisdelayhasnoeffectonthevideo

qualityseenatthereceivingnode.Thus,thecelltransferdelay

didnotaffectthevideoquality.

Celldelayvariation(jitter)wasnotmeasuredduringthese

testsbecauseoftestequipment limitations. Theonlywaywe

couldhaveproducedjittereffectswiththeequipment onhand

wouldhavebeentoinsertadditional ATMtrafficintotheATM

switch. We believe that such a test would have been valid for

only the specific traffic scenario implemented.

Cell misinsertion also was not measured during these tests

because this measurement is only significant for complex, fully

loaded networks. Even then, the probability of misinserted cells

is quite rare.

Test Configurations

Two test configurations were used. The first (Fig. 2) provided for fixed delay and random, binomially distributed errors

inserted digitally with an Adtech SX/14 Data Channel Simulator

as the satellite link. This test shows digitized video versus BER.

The second configuration (Fig. 3) used the EFData SDM-9000

modem and the Hewlett Packard HP 3708A noise test set to

simulate the satellite; the Adtech SX/14 provided a fixed delay

only. This test shows digitized video as a function of the

energy-per-bit to normalized-noise-power ratio EjN o.

Results

Figure 4 uses GIF pictures to visually show the results of

the digitized video testing. The digitally generated noise test is

relative to the BER. When an actual quadrature phase shift keying (QPSK) modem was used at a 44.736 Mbps transmission

rate, the test results for analog generated noise were relative to

the EjN o. The digitized video parameters were set to provide a

digital video data stream at approximately 19 Mbps. Video clips

of these tests have been stored as MPEG-1 files and are available on the World Wide Web at NASA Lewis' Satellite Networks and Architectures Branch site [3]. Also a short, 8-min

video is available upon request.

Table I shows the relative range of readings obtained from

the FORE ATM network interface card at the video sink. The

output measurements for AAL5 packets provided from this card

were the number of CRC errors, the number of congested packets, and the number of dropped packets. The update rate was set

for 1-sec intervals. For this test, each AAL5 CPCS packet contained 66 ATM cells. The results for the digitally generated

errors show that the number of cells dropped was an integral

multiple of the AAL5 CPCS packet except for extremely high

BER's of 10-5. At this point, the AAL5 CPCS packets contained

enough errors that the measurement circuitry considered the packets lost because of congestion. This was even more apparent for

DS3c/ATM

EFData

DS3c/ATM SDM-9000

SVideo Source I

ForeRunner ASX-200

I ,_Jl i

DS3c

NTSC ---- ATM

ADTECH _1

SX/4000

ATM

Traffic

Generator/Analyzer

IF 70 MHz

Adtech

SX/14 Data

Channel

Simulator

SUN SPARCstation 20

AVA-200 Control

Workstation

HP3708A I

noise test

set

IOC3c/ATM

OC3c

I II

ForeRunner ASX-200BX |OC3c/ATM

SVideo

Recorder

NTSC

Silicon Graphics Onyx

AVA-200 Display Workstation

Figure 3.mErrors inserted by using average white gaussian noise. (NTSC, National Television System Committee

Video; TAXI, transparent asynchronous transceiver/receiver interface; OC3c, optical carder 3c.)

NASA TM-107421 3
Figure 4.--Digitally generated noise. (a) Bit error rate,

10--8. (b) Bit error rate, 10-5. (c) Signal-to-noise ratio,

Eb/N O,8.2 dB. (d) Signal-to-noise ratio, Eb/No, 6.0 dB.

TABLE I.--RANGE OF READINGS FROM FORE ATM

NETWORK INTERFACE CARD

Bit error rate

(BER)

10 -9

10 -8

10 7

10 -6

10 -5

Signal-to-noise ratio,

E b/N 0,

dB

82

7_5

6.0

AAL5 CPCS

packets with

CRC errors,

range

0

0

(l to2

occasionally)

I to7

15 to 30

80 to 120

AAL5 CPCS

packets with

CRC errors,

range

Oto 1

0to3

50 to 120

Congested

packets,

range

0

0

Oto 1

Congested

packets,

range

0

0

9 to 29

Dropped cells,

range

0

0

(66 to 132

occasionally)

66 to 462

990 to 1980

5200 to 12 500

Dropped cells,

range

0 to 66

0 to 198

5500 to 7000

the Eb/N Otest at a low Eb/No. Most likely, this was due to the

bursty nature of the errors associated with the intermediate data

rate 0DR) modem [4,5]. From the measurements in Table I, it is

apparent that an Eb/N Osetting of 6.0 dB corresponds closely to a

BER of approximately 10-5, whereas an Eb/N Osetting of 8.2 dB

corresponds to a BER of 10-8 or better.

FORE Systems' AVA-200 uncompressed digital video is

very robust in that it continues to operate in the presence of errors.

Even extremely errored video is tolerable, and the video decoder

does not lose synchronization. This is due mainly to the nature of

the encoding and decoding algorithms. If a tile is in error, that

tile's information is ignored and the information from the previous

frame's file is retained.

Video degradation is perceived at a BER of 10-7 and is

unacceptable at BER's of 10-6 and above. AT&T demonstrated

similar results with a JPEG (Joint Photographic Experts Group)

video that was set to operate at a quality level of 50, producing a

video bit rate signal from 10 to 20 Mbps [6].

Conclusions

Test results indicate that satellite link quality with a bit

error rate of at least 10-8 should be maintained for stringent

asynchronous transfer mode (ATM) applications. Occasional,

very short term link degradations that provide bit error rates of

10-7 or 10-6 may be acceptable for some robust video-encoding

schemes.

Quality of service tests for highly compressed data applications are expected to produce more stringent link quality

requirements. Applications such as MPEG-2 (Moving Pictures

Experts Group) should provide additional input to better identify the necessary quality of service parameters.

References

1. FORE Systems. WWW information: http://

www.nemesys.co.uk/ava200.html (Apr. 1997).

NASA TM-107421 4
2. FORESystemsAVA-200User'sManual,Rev.A,Mar.

995.

3.SatelliteNetworksandArchitectures Branch,CommunicationTechnologyDivision,NASALewisResearchCenter.

WWWinformation: http://sulu.lerc.nasa.gov15610/

f5610.html (Apr.1997).

4.Bronnimann, R.:ATMOverSatellite--Analysis andExperimentalResults, Telecom95TechnologySummit,Session

4.1.

5. Ivancic,W.D.;andBobinsky, E.A.:ATMQualityofService

Parameters at45 Mbps Using a Satellite Emulator: Laboratory Measurements. Globecom '97. (Also NASA

TM-107345, 1997.)

6. AT&T and Telstra: QOS Measurement Results of ATM

Applications Over an IDR Satellite Link, Liaison Statement

to ITU-T Study Group 13, WP 4/13, [4B/33] Report of the

Seventh of WP 4B, Rio de Janeiro, Brazil, Sept. 23-27,

1996.

NASA TM-107421 5
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July 1997 Technical Memorandum

4. TITLE AND SUBTITLE

ATM Quality of Service Tests for Digitized Video Using ATM Over Satellite:

Laboratory Tests

6. AUTHOR(S)

William D. Ivancic, David E. Brooks, and Brian D. Frantz

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Lewis Research Center

Cleveland, Ohio 44135-3191

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

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REPORT NUMBER

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10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

NASA TM- 107421

11. SUPPLEMENTARY NOTES

William D. lvancic, NASA Lewis Research Center; David E. Brooks and Brian D. Frantz, Sterling Software, 21000

Brookpark Road, Cleveland, Ohio 44135. Responsible person, William D. Ivancic, organization code 5610, (216)

433-3494.

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13. ABSTRACT (Maximum 200 words)

A digitized video application was used to help determine minimum quality of service parameters for asynchronous

transfer mode (ATM) over satellite. For these tests, binomially distributed and other errors were digitally inserted in an

intermediate frequency link via a satellite modem and a commercial gaussian noise generator. In this paper, the relationship between the ATM cell error and cell loss parameter specifications is discussed with regard to this application. In

addition, the video-encoding algorithms, test configurations, and results are presented in detail.

14. SUBJECT TERMS

ATM; Quality of service; Satellite communication; Digital video

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