Audiovisual QoS for communication over IP networks Trond Ulseth Telenor R&I E-mail: trond.ulseth@telenor.com Effect of transmission performance on Multimedia Quality of Service,
The path towards the Next Generation Network - NGN The telecommunication industry is moving from Circuit Switched technology to Packet Switched technology often called IP technology, An all purpose network, Simple creation of new applications and services, There is a cost element justifying the migration, Packet switched technology is a challenge for interactive real-time services.
NGN architecture Applications/ Content Service enabler/ Session engine Customer IPTV/Stream Audiovis. Voice Web Message IMS Aggregation/core IP Access Cellular WiMax WLAN xdsl Satellite Fibre
ETSI work on IP QoS TC TISPAN is responsible for standardising network QoS mechanisms, TC STQ is responsible for standardising end to end performance characteristics, The network mechanisms need to be aligned with the performance characteristics, QoS mechanisms that meet the needs of multimedia communication might be a challenge.
ETSI TC STQ roadmap on IP performance REG 101-1 QoS parameter definitions and measurements General REG 101-4 Internet Access DES 097 Audiovisual QoS DEG 100 Appl./Interact. Existing QoS standards DEG 104-2 QoS metrics and measurements Voice quality DTR 113 Framework for e2e quality assesm. DTR 118 Prov. Resiproveness Thresholds MM Appl. DEG 104-3 Network perf. metrics and measurements in IP networks REG 125 VoIP terminals transmission requirements (4 parts) DTS 130 Requirements at VoIP intercon. points DEG 104-1 General considerations QoS and netw. perf. petrics DTR 133 QoS implications of NGN arch. DEG YYY (104-4) Multimedia DTS MMM Quality parm. at interconn. points for WB/MM 2008 2010 2009
IP network characteristics determining perceived media quality Network Bandwidth Application Codec User perception Packet loss Packet loss Media quality Network delay E2E delay Jitter Jitter Buffer Terminal characteristcs
IP network performance IP communication no performance guarantee. Some information on Internet performance is available, QoS mechanisms may be implemented in the network. Effects on e2e performance is not known, There might be (are) bottlenecks affecting the perceived quality (e.g. the access network), It is not the task of ETSI TC STQ to describe network performance, but to describe effects on perceived quality. Information is required on Transmission bandwidth variations, Delay variations (jitter), Packet loss (Random vs. burst packet loss, burst length).
Access technologies There are several cellular options, 2G/EDGE. UMTS, UMTS/HSPA (HSDPA and/or HSUPA). The xdsl might be asymmetric (ADSL or VDSL) or symmetric (SDSL or SHDSL), IEEE 802.11 (a, b, g or n), WiMax fixed or mobile, Common for all technologies are bandwidth and delay variations depending on parameter choice and working conditions (e.g. number of users within a radio cell).
Audiovisual - Media Speech Oral production of information by a human being. Two groups of speech codecs, Narrowband (300 Hz 3400 Hz), Wideband (50 Hz 7000 Hz). Audio All signals that are audible to human beings. Bandwidth up to 20 khz, mono or stereo, a large range of bit rates. Video Moving image. Differential codecs. Bit rates is determined by the image characteristics as well as a number of codec parameters. Still image, fax, drawings (not considered in this presenation)
Audiovisual applications Real-time interactive. Videotelephony, videoconferencing. Delay sensitive. Broadcasting, streaming and download. IPTV, mobile TV, Audiovisual download (Podcast). As a principle delay un-sensitive, but large network delay may degrade the perceived quality. Download usually use the TCP protocol where retransmission repairs packet loss. Broadcasting and streaming are usually UDP based.
Speech (telephony) Standardised codecs are bit exact (i.e. both encoder and decoder are specified), MOS values in error free conditions are available, Effects of delay is well known, E-model (ITU-T Recommendation G.107) can be used to estimate perceived quality of narrowband speech, Effects of random and burst packet loss are included, but refinement might be required, There is work on E-model wideband extension. Amendment 1 to the Recommendation provides provisional impairment factor framework.
Audio Two groups of standardised codecs, Standardised by MPEG (MP3 and AAC). Several versions of the AAC codec. Standardised by 3GPP (AMR-WB+). Both support both mono and stereo, The MPEG codecs supports a wide range of bit rate; the 3GPP codec is designed for mobile applications, A limited amount of information describing the perceived quality as a function of bandwidth is available, A limit amount of information describing the effects of packet loss (random and burst) on perceived quality is available.
Effects of random packet loss on perceived audio quality (3GPP results) 100 MUSHR RA Rating 80 60 40 20 AMR-WB+ 24 AMR-WB+ 20 AMR-WB+ 40 Eaac+ 24 Eaac+ 32 Eaac+ 40 0 0 2 4 6 8 10 Packet Loss Rate (%)
Video (moving image) Required bandwidth depends on the codec algorithm and the content. Some information is available, more is needed, Encoding parameter choice influences both bandwidth requirements and perceived quality, There is a range of display sizes, from a mobile handset (2-3 ) up to TV screen more than 50. The effects of small displays on perceived video quality is not studied in detail. User environment might influence the acceptable quality, Effects of packet loss on perceived video quality need more investigation. Is it codec and content dependent? Packet loss duration and frequency are important, Other interruptions (e.g. re-buffering) has effect on the perceived quality.
Effects of packet loss on video quality (Example) rating MOS 5 4,5 4 3,5 3 2,5 2 1,5 1 0 5 10 15 20 256 kbit/s 50 kbit/s Packet loss (%)
Audio Video interaction The objective is to estimate the audiovisual quality based on audio and video quality. Current information identifies three possible groups 1. Delay insensitive applications presenting low motion video, 2. Delay insensitive applications presenting high motion video, 3. Delay sensitive (conversational) applications. MOS MOS MOS AV AV AV = α( MOS = αmos = αmos A V A * MOS V + βmos ) + C V ΘGD + C + γ ( MOS A * MOS V ) + C GD is the Global Delay expressed in seconds
Subjective evaluation resu ults (Diffgrade) Audio video Synchronization 0 C Undetectability plateau C' -0,5 B Detectability threshold B' -1-1,5 A Acceptability threshold A' Sound delay wrt vision Sound advanced wrt vision -2-200 -180-160 -140-120 -100-80 -60-40 Delay time (ms) -20 0 20 40 60 80 100
Conclusion The telecommunications industry is moving towards IP based communication, The IP technology introduces new opportunities and new challenges to operators and application providers, Effects of QoS mechanisms on network performance are not yet fully understood, More knowledge about effects of IP network bandwidth and network degradations on perceived media quality is required, The user preferred quality levels need to be identified for different media and usage scenarios, It is hardly possible to develop a single set of recommendations covering all applications and presentation formats.
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