IPTV 서비스 품질 기술
이 철 희
연세대학교
채널 용량이 증대함에 따라 네트워크를 이용하여 새 로운 서비스 가능
¾ 멀티미디어 서비스 (VOD, MOD, 화상전화 등)
¾ IPTV
인터넷, 무선 통신 등이 주요 역할 기대.
네트워크를 이용한 멀티미디어 서비스
기존 방송
¾ 대역폭 보장됨
¾ 적절히 설치되면 일반적으로 품질 보장
¾ 전송에러 거의 없음
¾ 실시간 전송이 아무 문제 없음
네트워크를 이용한 멀티미디어 서비스 (IPTV 등)
¾ 대역폭 보장 어려움
¾ 데이터 폭주 시 품질 저하
¾ 실시간 전송을 보장하기 어려움
네트워크를 이용한 멀티미디어 vs 기존 방송 비교
기존 방송
¾ 시청료
¾ 광고수입
네트워크를 이용한 멀티미디어 서비스 (IPTV 등)
¾ 시청료
¾ 광고수입
¾ PPV (VOD, contents-based billing)
¾ 품질 보장 필요.
수익구조
통신망을 이용함으로 기존에 불가능했던 새로운 서 비스 가능.
¾ 개인 수요 맞춤형 서비스
¾ 무제한 프로그램 제공 가능
¾ 국경에 영향 받지 않음
¾ 이동 중에도 이용 가능
네트워크를 이용한 멀티미디어 서비스 장점
100% 품질 보장 불가능.
PPV에서는 품질 보장 필요.
열화 발생 시, 쌍방이 동의 할 수 있는 방법으로 요금 정산 필요
품질 모니터링은 중요한 문제로 부각.
품질 측정에 관한 국제 표준 필요.
Challenges of Multimedia Services over Networks
QoE Requirements for IPTV
¾ QoE for video
¾ Resolution , bit rate, application layer video encoding, encoder setting (GOP)
¾ Codec: MPEG-2, MPEG-4 AVC (MPEG-4 Part 10 or H.264), SMPTE VC-1
Video Requirements for IPTV: video
2.1 Mbps CBR / 10 Mbps SMPTE VC-1
2.1 Mbps CBR / 10 Mbps MPEG-4 AVC (Main profile at Level 3)
3.18 Mbps CBR / 15 Mbps MPEG-2 - Main profile at Main level (MP@ML)
Minimum Bit Rate (SD / HD) Video Codec
¾ QoE for audio
¾ channels: mono, stereo, 5.1 channels
¾ sampling rates: 16-48kHz
Audio Requirements for IPTV
128 Stereo
MP3 (MPEG-1, Layer 3)
96 for stereo Stereo
AAC
384 for 5.1 / 128 for stereo 5.1 if available, else
left/right stereo pair Dolby Digital (AC-3)
128 for stereo Mono or stereo
MPEG Layer II
Minimum Bit Rate (kbps) 채널수
오디오 코덱
45 ms maximum 15 ms maximum
Audio Lag Video Audio Lead Video
Audio – Video
Synchronization
¾ QoE for control functions
¾ 채널 변경시간
¾ VOD trick mode
¾ QoE for EPG
¾ 사용자 편의성
¾ 응답시간
¾ QoE for Metadata: Availability, Data size, Correctness
¾ QoE for Browser: Characteristics of a television set, TV-like display, 글자 크기, Navigation, Cookie
QoE Requirements for IPTV
¾ Traffic management
¾ Application layer reliability solutions
품질 보증을 위해 취할 수 있는 방법
Control plane
Data plane
Multicasting
Traffic Management for IPTV
Control Plane
¾ admission control (IETF RFC 2753)
¾ Admission control meets requirements for IPTV multicast/unicast services as negotiated in the SLA.
¾ The network needs to properly engineered to accommodate the number of subscribers.
¾ QoS routing (ITU-T Rec Y.129)
¾ This method is used to control network congestion and improve network utilization by selecting an appropriate path
¾ Resource management
¾ network traffic management according to the network information by means of data transmission between the network resource manager and the network nodes
Traffic Management for IPTV
Data Plane
¾ Traffic conditioning (required in access network)
• QoS provisioning per subscriber and per service
• Traffic classification based on multiple header fields (5-tuple, 6-tuple, and etc.)
• Minimum bandwidth guarantee
• Traffic shaping/policing
• Advanced packet queuing and scheduling
• Traffic marking (DSCP, 802.1p, and etc.)
Traffic Management for IPTV
Data Plane
¾ Transmission schedulers
¾ First-in, first-out scheduler
¾ Round-Robin Scheduler
¾ Priority scheduler
¾ Weighted Round-Robin scheduler
¾ Class-based schedule
¾ Buffer management
Traffic Management for IPTV
Multicasting
¾ Multicast replication point
Traffic Management for IPTV
Traffic Management for IPTV: Y.1541 – IP network QoS class
definitions and network performance objectives/Applications
Network QoS Classes
¾ ITU-T Recommendation Y.1541 (8 QoS classes) 등을 참고하여 IPTV 규격 논의 중
¾ IPTV 서비스를 5가지 경우로 분류
① Best Effort 서비스 (QoS class 5): content download 서비스, 정기적인 정보 제공, T-information, 이메일
② Low Loss 서비스 (QoS class 4): VOD, MOD, T-commerce, VOD 기반 T- learning
③ Interactive 서비스 (QoS class 2/3): 메신저, T-learning based on interactive
④ Real-Time Interactive 서비스 (QoS class 0/1): VOIP, 화상전화, 다자간 게임
⑤ Real-Time Multicase & Unicast 서비스 (QoS class 6/7): linear/broadcasting, multi angle, PPV, PVR
Traffic Management for IPTV
Cross-layer interaction for IPTV services
Traffic management capabilities:
core networks
Traffic management capabilities:
acces networks
Traffic management capabilities:
home networks
Traffic Management for IPTV
Application Layer Reliability
Solution for IPTV
전송 오류 복구 방법
¾ Retransmission
¾ FEC (Forward Error Correction)
¾ hybrid combinations of both
Application Layer Reliability Solution for IPTV
Retransmission
Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF)
[IETF RFC4585]
Real Time Protocol Control Protocol Extended Reports (RTCP XR)
[IETF RFC3611]
Real Time Control Protocol (RTCP) Attribute in Session Description Protocol (SDP)
[IETF RFC3605]
Session Description Protocol (SDP) Bandwidth Modifiers for RTP Control Protocol
[IETF RFC3556]
Real Time Protocol: A Transport Protocol for Real-Time Applications
[IETF RFC3550]
Title
Reference
Forward Error Correction (FEC) at the Application/Transport layers
Packet erasure correction techniques
FEC for Streaming Applications
¾ IETF RFC2733 [IETF RFC2733]
¾ 3GPP TS26.346 Multimedia Broadcast/Multicast: Protocols and Codecs [3GPP TS26.346]
¾ ETSI EN301 192 Digital Video Broadcasting: DVB Specification for Data Broadcasting [ETSI EN301 192]
¾ ETSI TS 102 034 1.3.1 Transport of MPEG 2 Transport Stream (TS) Based DVB Services over IP Based Networks [ETSI TS 102 034]
FEC (Forward Error Correction)
IETF RMT working group standardizes protocols for reliable file delivery over IP multicast.
FEC for Download Services
The Use of Forward Error Correction in Reliable Multicast [IETF RFC3453]
Forward Error Correction Building Block [IETF RFC3452]
Layered Coding Transport (LCT) Building Block [IETF RFC3451]
Asynchronous Layered Coding Protocol Instantiation [IETF RFC3450]
Author Guidelines for RMT Building Blocks and Protocol Instantiation Documents
[IETF RFC3269]
Reliable Multicast Transport Building Blocks for One-to-Many Bulk-Data Transfer
[IETF RFC3048]
The Reliable Multicast Design Space for Bulk Data Transfer [IETF RFC2887]
Title
Reference
Performance Monitoring for IPTV
현재 인터넷은 특성상 bandwidth 보장 어려움
품질은 전송상태에 따라 가변적임
필연적으로 발생하는 품질저하문제를 서비스 제공업 자 및 사용자가 동의할 수 있는 방법으로 해결 필요.
특히 화상전화, pay-per-view에서는 품질에 근거한 과금 필요
이를 위하여 체감 품질 모니터링 기술 필요
Performance Monitoring for IPTV
모니터링 파라미터
– Physical Layer Parameters
– IP Layer/Network Parameters – Transport Stream parameters – Service Line-Up parameters – Channel Attribute parameters – VOD Parameters
– Other Parameters
Performance Monitoring for IPTV
Physical Layer Parameters
① RF intergrity
② Available bandwidth
Performance Monitoring for IPTV
IP Layer/네트워크 파라미터
① Link IP layer used/available bandwidth
② End-to-end IP layer bandwidth
③ End-to-end IP layer available bandwidth
④ Loss run length distribution
⑤ Error-free interval distribution
⑥ Packet loss metrics and models
⑦ Streaming jitter
Performance Monitoring for IPTV
Service Line-Up parameters
¾ Video
¾ Audio
¾ Meta data
• Subtitles
• EPG
• Parental control
Performance Monitoring for IPTV
Service Line-Up parameters
Channel line up
Service meta-data (eg. EPG, subtitles, parental control, etc.)
Channel zap time
Correctness Rate
Channel Attribute parameters
Channel attributes
Video quality
Audio quality
Ancillary channel associated attributes (subtitles, closed captions, descriptive audio)
VOD Parameters
Performance Monitoring for IPTV
Monitoring Methods
Generalized monitoring method for multi-media data based on transmission packet loss
Bearer network monitoring
Network performance monitoring
IPTV service attribute monitoring
Video quality monitoring
Audio quality monitoring
Performance Monitoring for IPTV
•
Full Reference (전기준법)–
기준영상 제공
–
응용분야: Codec 성능 평가, 디지털 방송, 멀티미디어 장비 성능 평가
•
Reduced Reference (감소기준법)–
압축영상과 reference bit-stream 함께 전송
–
허용 reference bit-stream: 10Kb, 56Kb, 256Kb
–
응용분야: 무선 통신 멀티미디어 전송, 채널 상태에 대응하여
parameter 최적화
• No Reference (무기준법)
–
수신 동영상만으로 화질평가
–
상대적으로 신뢰도 저하
–
응용분야: 무선 통신 멀티미디어 전송, 채널 상태에 대응하여
parameter 최적화
객관적 화질 평가 방법 분류
객관적 화질 평가 시스템 구성도
Encoder Decoder
Digital Channel Video Source
FR FR
RR
RR Extracted Feature RRRR
Multimedia terminal
전송에러를 이용한 화질평가 방법 (J.242)
• 패킷을 사용한 비디오 전송에서는 전송에러정보를 이용하여 수 신 동영상 추정가능
• 대역폭 사용을 최소화하면서 수신측의 화질 모니터링 가능
• IPTV , 화상전화, VOD 등에 적용 가능
encoder transmitter decoder
transmission error detection unit received video
estimation unit
video quality evaluation unit source
video
Head-end (service provider)
Receiver
packetized video data
estimated received video
received video
Hybrid Perceptual/Bit-stream Models
decoder
channel PVS
Hybrid perceptual
bit-stream NR model bit-steam
analyzer
- codec parameters - bit rate
- FPS
- packet information if available - IP information
- transmission error information
(lost or delay packets, impaired block lost or delayed frames)
Hybrid Perceptual/Bit-stream Models
objective model compression
error encoder
SRC
MUX
decoder
channel PVS
Hybrid perceptual
bit-stream NR model bit-steam
analyzer
- codec parameters - bit rate
- FPS
- packet information if available - IP information
- transmission error information
(lost or delay packets, impaired block lost or delayed frames)
Streaming Server with Quality Monitoring and Optimization
encoder
SRC streaming
server channel receiver
• Development of streaming server with quality monitoring capability and optimization.
• Optimization of streaming technologies based on quality monitoring results (e.g., codec parameter, application layer reliability solutions).
