1. Safe Video Contribution & Distribution over IP Networks Philippe LEMONNIER

2. Compressed realtime Video over IP > High bandwidth IP networks bring new opportunities for transport of audiovisual contents. > IETF has defined a basic set of RFCs so as to standardize Video transport over IP. Application Network Process to Application Presentation Data Representation & Encryption Session Interhost Communication Transport End-to-End Connection Reliability Data Link MAC & LLC (physical addressing) Physical Media, signal & Binary Transmission Network Path Determination/Logical Addressing OSI model MPEG compressed A/V contents mapped over IP with the IETF toolbox IP (RFC791) UDP (RFC768) RTP (RFC1889) IGMP (RFC2236) MPEG2 A/V MPEG2-TS RFC2250 Media layers Host layers

3. MPEG-TS mapping over IP & Ethernet 188 bytes MPEG Transport Stream packets MPEG-TS payloadRTP header RTP encapsulation (optional) 12 bytes MPEG-TS payloadRTP header UDP header UDP encapsulation 8 bytes MPEG-TS payloadRTP headerUDP headerIP header IP encapsulation 20 bytes MPEG-TS payloadRTP headerUDP headerIP header Ethernet header Mapping over Ethernet Ethernet CRC IEEE802.3 Ethernet MTU (Max. Transfer Unit) of 1500 bytes ✳, restricts the blocking factor (number of grouped TS packets) to 7. ✳ Jumbo frames with bigger MTU exist, but would lead to IP fragmentation in the networks. 14 bytes 4 bytes

4. IP networks main drawbacks Time transparency IP packet delay variation (IPDV) in the network is very high : 50ms as per ITU-T Rec. Y.1541, for Service Class 0 and 1 networks … to put in perspective of 3ms ATM Cell Delay Variation around the globe, as per ITU-T Rec. I.356. Information transparency Technologies used for IP transport (OSI level 2) don’t lose bits :  they drop full frames (eg. up to ~1500 bytes chunks for Ethernet)  Up to 7 MPEG-TS packets can be lost at once.  The impact of an IP datagram loss is getting even worse as compression ratios rise (MPEG4…)

5. Origin of network errors At OSI levels 1 and 2  Bits may get twisted for electrical reasons (impulse noise, crosstalk, etc) during their trip along cable runs.  IP header processing principle in all hosts relies on header coherency.  Therefore, all technologies used to carry IP datagrams use some form of signature to ensure that the received frames carry datagrams that are safe to pass to IP level.  Dubious frames are silently discarded upon reception. At OSI levels 2 and 3  IP networks are heterogeneous by nature. Hopping across network segments implies crossing switches (level 2) and routers (level 3).  Poor traffic engineering, network misuse or equipment problems can lead to congestion in these nodes.  Router / switch policy when facing congestion will lead to frames drop. Received frame Medium impairment CRC OK ? Yes Proceed to MAC, and upper to IP No Port 1 (in) Port 2 (in) Port 3 (out) Bridge / Router FIFO Payload burst Port 1 (in) Port 2 (in) Bridge / Router FIFO FIFO is full Incoming data dropped

6. Pro-MPEG Forum WAN Group Objectives Provide a forum for manufacturers, end-users and service providers to co- operatively develop interoperable systems for real-time delivery of high- quality program material over Wide Area Networks Outcome Code Of Practice #3r2 ✳ (July ’04) > professional MPEG-2 Transport Streams over IP networks > contribution and primary distribution applications > Addresses: > Encapsulation Protocol > Network Requirement ✳ http://www.pro-mpeg.org/publications/pdf/Vid-on-IP-CoP3-r2.pdf

7. Pro-MPEG Forum FEC scheme > Based on Generic Forward Error Correction RFC2733 > Deployed at RTP level to cope with lost IP datagrams > FEC protection data is embedded in regular RTP packets with a specific payload type > Relies on simple XOR ( ⊕ ) arithmetics : If P=A⊕B⊕C, then one with only A,B,P can retrieve C with C=A⊕B⊕P

8. Fundamentals : Row FEC principle Most simple FEC Low latency mechanism  Can only protect from single packet loss Pkt 2 Pkt n+2 Pkt 1 Pkt n+3Pkt n+1Pkt n Pkt 5Pkt 4Pkt 3Pkt 2Pkt 1Pkt 3 FEC 1 FEC (n+2)/3 RTP stream to protect Pkt 5Pkt 4FEC 1Pkt n+2Pkt n+1Pkt n FEC (n+2)/3 RTP stream with embedded FEC Pkt 2Pkt 1Pkt 3

9. 1D column FEC overview (D-1)LDL-1 ( D-1)L+2 10L-1 2 L+1L2L-1L+2 2L+12L3L-12L+2 Pkt 3L+13L4L-13L+2 (D-1)L+1 FEC C 0 FEC C 2 FEC C 1 FEC C L-1 RTP & RTP-FEC combiner RTP stream to protect D rows L Columns

10. Example of correction hits 1 and at most 1 data packet per column 0 6 18 24 30 1 7 19 25 31 2 8 14 20 32 3 9 15 21 27 33 4 10 16 22 28 34 11 17 23 29 35 FEC 0 FEC 1 FEC 2 FEC 4 FEC 5 burst of L consecutive data packets 0 6 18 24 30 1 7 19 25 31 2 8 20 26 32 3 9 21 27 33 4 16 22 28 34 5 17 23 29 35 FEC 0 FEC 1 FEC 2 FEC 3 FEC 4 FEC 5

11. Example of correction failures 0 6 12 18 24 30 1 7 13 19 25 31 2 8 20 32 3 9 15 21 27 33 4 10 16 22 28 34 5 11 17 23 29 35 FEC 0 FEC 1 FEC 2 FEC 3 FEC 4 FEC 5 2 data packets on the same column ? ? 0 6 12 18 24 30 1 7 13 19 25 31 2 8 14 20 26 32 3 9 21 27 33 4 10 16 22 28 34 5 11 17 23 29 35 FEC 0 FEC 1 FEC 2 FEC 4 FEC 5 1 data packet and its associated FEC packet ?

12. 2D – FEC scheme overview (D-1)LDL-1 ( D-1)L+2 10L-1 2 L+1L2L-1L+2 2L+12L3L-12L+2 Pkt 3L+13L4L-13L+2 (D-1)L+1 FEC C 0 FEC C 2 FEC C 1 FEC C L-1 RTP stream to protect D rows L Columns RTP & RTP-FEC combiner FEC R D-1 FEC R 0 FEC R 1 FEC R 2 FEC R 3

13. Sample correction hit 0 6 12 18 24 7 13 19 31 2 14 20 26 32 9 15 27 4 10 16 22 34 5 11 17 23 35 FEC’ 0 FEC’ 1 FEC’ 3 FEC’ 4 FEC’ 5 FEC 0 FEC 1 FEC 2 FEC 3 FEC 4 FEC 5 FEC’ 1 8 FEC’ 3 21 FEC 0 30 FEC 1 25 FEC 4 28 FEC’ 5 33 FEC’ 4 29 8 21 3033 FEC 3 3 3 FEC’ 0 1 1 252829 The 9 missing data packets are successfully recovered !!! 6x6 data matrix with 9 data packets lost and 1 FEC packet lost

14. Sample correction failures 0 6 12 18 24 30 1 7 13 19 25 31 2 8 14 20 26 32 3 9 21 27 33 4 10 16 22 28 34 5 11 17 23 29 35 FEC’ 0 FEC’ 1 FEC’ 3 FEC’ 4 FEC’ 5 FEC 0 FEC 1 FEC 2 FEC 4 FEC 5 1 data packet and its 2 associated FEC packets ? 0 6 12 18 24 30 1 7 13 19 25 31 2 8 14 20 26 32 3 9 27 33 4 10 28 34 5 11 17 23 29 35 FEC’ 0 FEC’ 1 FEC’ 3 FEC’ 4 FEC’ 5 FEC’ 2 FEC 0 FEC 1 FEC 2 FEC 3 FEC 4 FEC 5 4 data packets positioned on exactly 2 rows and 2 columns ?

15. Video & FEC data & streams > Elegant, does not break the original AV stream > A receiving party can use : > Just the original encapsulated A/V stream it is not FEC-capable > Use the row or column FEC data if only 1D-FEC capable > Use both row & column FEC streams if 2D-FEC capable IP UDP RTP MPEG-TS packets IP UDP RTP Column FEC packets IP UDP RTP Row FEC packets Media Same destination IP address (unicast node or multicast group) UDP Port n UDP Port n+4 UDP Port n+2

16. Typical performance 2D FEC Row only 1D FEC Column only 1D FEC Reference : Video at 4Mb/s transported with 7 MPEG-2 TS packets per RTP/IP datagram Legend: L : matrix row length D : matrix column depth I : Interleaving depth used in FEC packets sequencing PLR : Network Packet Loss Ratio MTBE : Mean Time Between Errors Error distribution: random/uniform In secondsIn days !

17. Status > First complete 2D FEC unveiled at IBC’04 by Thomson/Grass Valley > Interop session held at the joint Vidtrans/SMPTE conference (On January 30..Feb 2, 2005 in Atlanta, GA), showed full interop of 1D FEC between manufacturers. > CoP#3 adopted by Video Services Forum (VSF) Pro-MPEG CoP#3 FEC is widely accepted as the recommended solution for high quality video contribution on IP

18. Perspectives > FEC on the access network, down to the STBs (under consideration by DVB-IP) > Further work in the uncompressed world Proposed Pro-MPEG Forum CoP#4, still leaves room for improvements (latency, etc)

19. Thank you for your attention ! philippe.lemonnier@thomson.net http://www.thomsongrassvalley.com/