SMPTE ST 2022: Moving Serial Interfaces (ASI & SDI) to IP. Thomas Edwards VP Engineering & Development FOX Networks Engineering & Operations

Transcription

1 SMPTE Standards Webcast Series SMPTE ST 2022: Moving Serial Interfaces (ASI & SDI) to IP Thomas Edwards VP Engineering & Development FOX Networks Engineering & Operations SMPTE Standards Update Webcasts Series of 90-minute, interactive webcasts covering select SMPTE standards and topics Free for everyone Sessions are recorded for on-demand viewing convenience SMPTE.ORG and YouTube

2 Your Host Joel E. Welch Director of Education SMPTE 3 Today s Guest Speaker Thomas Edwards Vice President, Engineering & Development FOX Network Engineering & Operations

3 Overview ST 2022-x standards take payloads from specialized electrical interfaces and puts them on IP using RTP The electrical interfaces are ASI and SDI The 2022-x standards are: Forward Error Correction for Real-Time Video/Audio Transport Over IP Networks Unidirectional Transport of Constant Bit Rate MPEG-2 Transport Streams on IP Networks Unidirectional Transport of Variable Bit Rate MPEG-2 Transport Streams on IP Networks Unidirectional Transport of Non-Piecewise Constant Variable Bit Rate MPEG-2 Streams on IP Networks Forward Error Correction for Transport of High Bit Rate Media Signals over IP Networks (HBRMT) Transport of High Bit Rate Media Signals over IP Networks (HBRMT) Seamless Protection Switching of SMPTE ST 2022 IP Datagrams MPEG Transport Stream (TS) ISO/IEC and ITU-T Rec. H Encapsulates packetized elementary streams (PES) Has error detection and stream synchronization packets (or 204 with Reed-Solomon FEC) Every has a Payload ID (PID) Over 75 of mappings into MPEG TS SMPTE Registration Authority, LLC is the registration authority for ISO/IEC Besides MPEG video: KLV Data, Dolby Vision, Camera Positioning Information, VC-1, VC-4, Dirac, AES3, Dolby TrueHD audio etc.

4 MPEG TS Logical View PID 0 Program Association Table (PAT) Program # 100 PMT PID 1025 Program # 200 PMT PID 1026 MPEG Transport Stream Program Video Audio 1 Audio 2 Program Map Table (PMT) Program # 100 Video PID 501 MPEG-2 Video Audio PID (English) 502 MPEG-2 Audio Audio PID (Spanish) 503 MPEG-2 Audio Program Video Audio Program Map Table (PMT) Program # 200 Video PID 601 AVC Video Audio PID (English) 602 AAC Audio MPEG TS Packet View 0x47 (sync) Flags Example Transport Stream Packet PID (Payload ID) Header More Flags 188 Bytes CC Adaptation Field Data Payload Example Transport Stream Flags: Transport Error Indicator Payload Unit Start Indicator Transport Priority Transport Scrambling Control Important PIDs: 0x0000 PAT PID 0x1FFF Null PID gives space for VBR Continuity Counter (CC) 4-bit per-pid sequence # Helps detect packet loss Adaptation Field (optional) Can carry range of other info PCR, splice point flags Transport of private data PID 0 CC 3 PAT Data PID 601 CC 11 PID 602 CC 7 PID 0x1FFF NULL PID 601 CC 12 PID 602 CC 8

5 Asynchronous Serial Interface (ASI) Asynchronous -> no clock line, just self-clocked data European Standard EN Annex B Bottom layers Fibre Channel physical & signaling interface (FC-PH) Data transmission rate 270 Mbps on 75Ω coax or fiber transmission rate permits a constant receiver clock. To restore the original clock rate, a PLL circuit can be used. Annex E gives some proposals for how such a circuit can be designed. The input of the required transmission facility accepts MPEG-2 bytes and the output delivers MPEG-2 bytes. While the Fibre-Channel (FC) supports single mode fibre, multi-mode fibre, coaxial cable and twisted pair media interfaces, this standard defines only two distinct forms of interfaces: coaxial cable and multi-mode fibre-optical cable using LED emitters. Instead of a transmission rate of 265,625 Mbit/s, as required in the ISO/IEC standard, in this document the transmission rate is 270,000 Mbit/s. B.1 ASI transmission system overview Figures B.1 and B.2 represent the primary components of the ASI transmission method over copper coaxial cable and fibre-optic cable, respectively. 8-bit data converted to 10-bit for transmission for DC-balance Don t have to use all 270 Layer-2 Layer-1 Mbps Comma 10-bit symbol Packet- 8B/10B Sync Byte inserted when no data Parallel/Serial Synchronous Coding (FC Comma) Conversion MPEG2 TS Insertion ready to transmit Ignored by receivers Allows any bit rate <270 Mbps Packet- Synchronous MPEG-2 TS 8B/10B Decoding Sync Byte (FC Comma) Deletion Clock/Data Recovery & Serial/Parallel Conversion Amplifier/ Buffer Amplifier/ Buffer Coupling/ Impedance Matching Coupling/ Impedance Matching Layer-0 Connector Connector Figure B.1 - Coaxial cable-based asynchronous serial transmission link (ASI type) Coaxial Cable IP Internet Protocol A protocol for packet network intercommunication IP version 4 (IPv4) is dominant protocol of the Internet IPv6 its successor is starting to be used IHL = Internet Header Length TOS = Type of Service (now Differentiated Services Code Point, DSCP, and Explicit Congestion Notification, ECN) If IP packet too large to fit down network pipe, it gets fragmented Identification: Groups fragments Flags: Don t Fragment / More Fragments Address: 32 bits, human-readble as A.B.C.D bytes IPv4 Header

6 UDP User Datagram Protocol RFC 768 Connectionless datagram Unreliable, TCP/IP stack provides no packet loss detection or fix Ports for source & destination provide multiplexing of different applications and flows Header: RTP Real-time Transport Protocol RFC 3550 Typically over UDP V Version P Padding at end X Header Extension CC #of CSRCs M Marker bit PT Payload Type Sequence # helps identify dropped packets Timestamp aids in sync SSRC = Synchronization Source, the source of RTP stream and timestamp CSRC = Contributing Source, sources that have contributed to a mixed stream (optional) Practically, 2022-x implementations use no CSRCs RTP Header

7 ST : Constant Bit Rate (CBR) TS over RTP References IETF RFC 2250 Constrains RTP header fields: Padding (P) bit = 0, Extension (X) bit = 0 Payload Type: 33 ( MP2T ) M bit: 0 (i.e. no timestamp discontinuities) Timestamp: 32-bit 90 KHz timestamp of target transmission time for 1st byte of payload Clock supposed synchronized with Program Clock Reference (PCR) or System Clock Reference (SCR) Which is not realistic for Multi-Program Transport Streams (MPTS) with multiple PCRs Either 1, 4, or 7 s in RTP Payload ST : Constant Bit Rate (CBR) TS over RTP Transport Stream IP HDR UDP HDR RTP HDR RTP Packet

8 Basics of Parity FEC Forward Error Correction (FEC) sends redundant information to allow recovery from (some) data loss Parity Operation is mathematically exclusive-or (XOR) (A XOR B) XOR B = A & (A XOR B) XOR A = B Send A, B, and A XOR B only need 2 to recover A & B Just XOR them to recover lost data example below loses & recovers packet B A B A XOR B Packet A Packet A A XOR B Recovered Packet B (A XOR B) XOR A Packet B A XOR B ST : Forward Error Correction XOR packet payloads across L columns and D rows of RTP packets First FEC stream (columns) and second FEC stream (rows)

9 ST : Forward Error Correction extends RFC 2733 Media packets sent to destination UDP port N Level A devices: FEC stream (XOR down columns) on port N+2 Level B devices: 2 FEC streams (XOR down columns & XOR across rows) on ports N+2, N+4 FEC streams have own RTP sequence numbering FEC data uses payload type 96 Column and Row FEC Coverage X X X X X X X First FEC stream (columns) handles burst losses up to length L Second FEC stream (rows) handles random losses

10 ST FEC Header SNBase low bits: First sequence # of packets associated w. FEC packet (low 16 bits) Length, PT, and TS Recovery: XOR of packet lengths, Payload Types (PT), timestamps (TS) to enable recovery of these fields if missing packet E=1 indicating extended header, Mask not used, N=0, Type=0, Index=0 D=0 for 1st (column) FEC stream, D=1 for 2nd (row) FEC stream Offset offset between packets use for FEC: L for 1st FEC stream, 1 for 2nd FEC stream NA - # of packets associated w. FEC packet: D for 1st FEC stream, L for 2nd FEC stream SNBase ext bits If needed, high 8 bits of first sequence # associated with FEC packet RTP sequence # s are 16-bit, so should never be required ST :2007 FEC traffic shaping issues Interleave media & FEC packets to avoid large TX rate changes Row FEC sent 0-L packets after last media packet protected Column FEC sent >L packets after last media packet protected (to avoid burst loss) Column FEC sent < LxD packets after last media packet protected (to constrain RX buffer)

11 ST Block Aligned vs. Non- Block Aligned FEC FEC Pkt SNBase F1 0 F2 1 F FEC Pkt SNBase F1 0 F2 4 F3 8 SNBase fields in header is first sequence number in FEC packet Non-block aligned FEC reduces TX buffer requirements for smooth FEC emission FEC Latency Delay

12 ST Variable Bit Rate TS over RTP Real-time piecewise constant variable bit rate (VBR) Piecewise constant VBR means rate only changes at PCR-labeled packets of the program A max of 1, 4, or 7 s per RTP packet per session (Packet_per_Datagram_max) Mode 1 RTP packets always have Packet_per_Datagram_max TS packets. RTP packet send rate varies for VBR. Also has maximum_latency and maximum_bitrate. Mode 2 RTP packets sent at constant rate, # of s per RTP packet varies for VBR ST Mode 1 vs. Mode 2 Mode 1 Mode 2

13 ST FEC Rules for Mode 1 Only block-aligned FEC maximum_latency limits FEC matrix latency, partially filled packets moved to next FEC matrix ST Mode 1 FEC Header Like FEC header except N=1 indicating ST Mode 1 FEC Maximum_latency - 10-bit number defining the multiplier of 10 ms (up to seconds) Maximum_bit_rate - 10-bit number, first seven bits mantissa value and last 3 bits exponent value defining the multiplier of 10 Kbps (up to 1,280 Gbps)

14 ST : Non-Piecewise Constant Variable Bit Rate TS Non-piecewise constant VBR when the bit rate varies between PCRs Timing would be clear in 270 Mbps ASI, but since IP networks are non-isochronous, timing relationship between s lost in RTP transport signals inter-packet TS timing in RTP payload Number of s per RTP packet shall not vary (i.e. always Packet_per_Datagram_max) ST RTP Payload Structure 1,0 Bits are set to 0b10 as a flag to signal end of s (0x47=0b ) TDD Timing Data Descriptor, describes contents of Packet Timing Data Fields 0b001 = running counter, 0b010 = 27 MHz clock PTD # Number of Packet Timing Data Fields in payload In counter mode, null s are discarded but noted in counter

15 SDI Serial Digital Interface 75Ω coax or fiber ST 259 ( SD-SDI ) Generally 270 Mbps, rarely 360 Mbps for widescreen SD-SDI is polarity insensitive, ASI is polarity sensitive ST ( HD-SDI ) 1.5 Gb/s, actually or 1.485/1.001 Gbps ST ( 3G-SDI ) 2.97 or 2.97/1.001 Gbps Often used for 1080p50/60 Can carry ST Ancillary Data for Embedded Audio, CC, Timecode, etc. HD-SDI Raster Vertical ANC (VANC) space Horizontal ANC space (HANC) Active Video

16 HD-SDI ANC Space Data Line # Time Code EAV Embedded Audio SAV Closed Captions ST : SDI over RTP RTP items Marker bit indicates last datagram in frame PT=98 for , =99 for FEC 27 MHz RTP timestamp clock Video payload is always 1376 octets One datagram often has data from two lines Sometimes a pixel or even a sample could be split between datagrams Last datagram in frame is padded with zeros to fill out 1376 octets

17 Packet Boundaries for 720p Example packet coverage Note last packet needs zero padding to be 1376 octets ST Payload Header Ext header extended by Ext x 4 octets F Is the video format present? 1=Yes VSID 0=primary, 1=protect FRCount Frame Count R Reference for video timestamp 0b00=not locked, 0b10=UTC, 0b11=private reference S Scrambling, 0=not scrambled FEC 0b000=none, 0b001=column, 0b010=row & column

18 Downloaded at Fox on from IP SMPTE Standards Update ST Payload Header cont. CF Clock Frequency 0000 = No time stamp 0001 = 27 MHz 0010 = MHz 0011 = /1.001 MHz 0100 = 297 MHz 0101 = 297/1.001MHz MAP 0=normal SDI or Level A, 1=Level B-DL, 2=Level B-DS FRAME Active picture size code FRATE Frame rate code SAMPLE Sampling type code (e.g. 0b01=4:2:2 10-bit) Video Timestamp At rate based on CF Header Extension TLV value (not defined to date) FEC for SMPTE ST : E R P X CC M PT Recovery SN Base TS Recovery Length Recovery Reserved Offset Reserved NA Reserved Figure 4 Definition of the FEC Header defines row/column XOR FEC much like Header similar to but slightly different Extension flag (E) 1 bit: Added XORed be set to 0. recovery field for Padding (P), Extension (X), CSRC Count (CC), Marker Bit (M) The E bit is the extension flag reserved to indicate any future extension to this specification. It shall Reserved (R) 1 bit: Shall be set to zero by the sender. Padding Recovery field (P) 1 bit: The Padding Recovery field shall be computed via the XOR operation applied to the corresponding P values from the RTP headers of the Media Datagrams Associated with the FEC Datagram. Extension Recovery field (X) 1 bit: The Extension Recovery field shall be computed via the XOR operation applied to the corresponding X values from the RTP headers of the Media Datagrams Associated with the FEC Datagram. CSRC Count Recovery field (CC) 4 bits:

19 Constraints on FEC L & D constraints Column Only FEC 1 L 1020, 4 D 255 Column and Row FEC 4 L 1020, 4 D 255 L x D constraints SD (270 Mb/s) L x D 1500, max 33 ms protection HD (1.485 Mb/s) L x D 3000, max 6 ms protection 3G (2.97 Gb/s) L x D 6000, max 3 ms protection ST : Seamless Protection Switching RTP packets replicated for transmission on multiple diverse paths Recoverable if at least one copy makes it through one path, within receiver buffer limitations

20 Seamless Reconstruction Timing P n instantaneous latency from TX to RX on path n inclusive of network jitter EA earliest time packet could reach RX for seamless reconstruction PT latency from TX to reconstructed output & latest time pkt can reach RX to be included in reconstructed output MD max differential, difference of PT and EA. PD instantaneous path differential, Reconstruction possible from paths with P n such that EA < P n < PT ST : Receiver Classes Receiver Classification Use Case (example) SBR Streams < 270 Mbps HBR Streams > 270 Mbps Class A: Low-Skew Intra-Facility Links PD <= 10ms PD <= 10ms Class B: Moderate-Skew Short-Haul Links PD <= 50ms PD <= 50ms Class C: High-Skew Long-Haul or special circumstance Links PD <= 450ms PD <= 150ms (Proposed) Class D: Ultra Low-Skew Physical Layer LAN Redundancy PD <= 150µsec PD <= 150µsec

21 Using Wireshark for Right-click decode as and choose RTP Using Wireshark for You ll need a dissector :

22 Questions?