Overview
IEC 61883-7:2003 - "Consumer audio/video equipment - Digital interface - Part 7: Transmission of ITU‑R BO.1294 System B" specifies packetization and transmission rules for ITU‑R BO.1294 System B (DSS/DirecTV) transport streams over the IEEE 1394 (FireWire) serial bus. First published in January 2003 (bilingual reissue 2012‑08 corresponding to the 2003 English edition), the standard defines how DSS transport stream packets are formed, timestamped, smoothed and carried in IEEE 1394 isochronous packets so receivers can reconstruct correct timing despite interface jitter.
Key topics and technical requirements
- Source packet structure: A DSS source packet is 140 bytes - a 130 B DSS transport stream packet plus a 10 B DSS packet header. A separate source packet header (4 B) containing timestamps is added for timing recovery.
- DSS packet header: Includes a System Clock Count (23‑bit field) and flags such as SIF (invalid flag) and EF (error flag). The clock count synchronizes to the MPEG system clock and assists bit‑stream recorders (e.g., D‑VHS) in clock recovery.
- Timing and timestamps: The source packet header carries cycle_count (13 bit) and cycle_offset (12 bit) fields derived from the IEEE 1394 CYCLE_TIME register. These timestamps indicate the intended delivery time at the receiver’s T‑STD (Transport Stream Target Decoder).
- Smoothing and jitter control: The standard describes use of a smoothing buffer to reduce bandwidth when program selection occurs; smoothing introduces time shifts that are compensated with timestamps. Receivers use a receiver buffer to absorb IEEE 1394 transmitter jitter.
- Isochronous/CIP packaging: DSS uses the IEEE 1394 isochronous transport with a two‑quadlet CIP header format. CIP fields defined include DBS (data block size), FN (fractions per source packet), DBC (data block counter rules), FMT (DSS format) and FDF (including TSF - timeshift flag).
- Fragmentation rules: Source packets are split into data blocks (fractions) of 9 quadlets and packed into isochronous packets; rules control DBC progression and alignment.
Applications and who uses it
- Implementers of set‑top boxes, satellite receivers (DSS/DirecTV) and consumer A/V devices using IEEE 1394 for packetized broadcast transport.
- Chipset and firmware developers building IEEE 1394 isochronous transmitters/receivers, CIP header handlers and timestamp logic.
- Recorders and playback devices (e.g., digital VCR/bit‑stream recorders) that need accurate system clock recovery and jitter compensation.
- System integrators and test labs validating conformance to packetization, timing and buffering requirements.
Related standards
- IEC 61883‑1 (General)
- ITU‑R BO.1294:1997 (DSS functional requirements)
- IEEE 1394:1995 and IEEE 1394a:2000 (High Performance Serial Bus)
Keywords: IEC 61883‑7, DSS, DirecTV, ITU‑R BO.1294, IEEE 1394, FireWire, transport stream, isochronous packets, CIP header, packetization, timestamps, jitter compensation.
Open preview (PDF)Consumer audio/video equipment - Digital interface - Part 7: Transmission of ITU-R BO.1294 System B
