DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

CENELEC EN 50083-9, Cabled
distribution systems for television,
sound and interactive multimedia
signals – Part 9: Interfaces for
CATV/SMATV headends and similar
professional equipment for
DVB/MPEG-2 transport streams.
SMPTE 310M, Synchronous
Serial Interface for MPEG-2
Digital Transport Stream.
IEEE 1394, Standard for a High
Performance Serial Bus.
DVB ASI and SMPTE SSI
The DVB organization has standardized a high-speed
serial interface for an MPEG-2 transport stream – the
asynchronous serial interface (ASI). MPEG-2 transport
packets of 188 bytes are subject to 8b–10b coding,
then serialized. (Optionally, packets that have been
subject to Reed-Solomon encoding can be conveyed;
these packets have 204 bytes each.) The 8b–10b
coding is that of the FiberChannel standard. The link
operates at the SDI rate of 270 Mb/s; synchronization
(filler) codes are sent while the channel is not occupied
by MPEG-2 data. The standard specifies an electrical
interface whose physical and electrical parameters are
drawn from the SMPTE SDI standard; the standard also
specifies a fiber-optic interface.
A functional alternative to DVB-ASI is the synchronous
serial interface (SSI), which is designed for use in environments
with high RF fields. SSI is standardized in
SMPTE 310M. As I write this, it is not very popular,
except for interconnection of ATSC bitstreams to 8-VSB
modulators.
IEEE 1394 (FireWire, i.LINK)
In 1995, the IEEE standardized a general-purpose highspeed
serial bus capable of connecting up to 63 devices
in a tree-shaped network through point-to-point
connections. The link conveys data across two shielded
twisted pairs (STP), and operates at 100 Mb/s,
200 Mb/s, or 400 Mb/s. Each point-to-point segment is
limited to 4.5 m; there is a limit of 72 m across the
breadth of a network. Asynchronous and isochronous
modes are provided; the latter accommodates realtime
traffic. Apple computer refers to the interface by their
trademark FireWire. Sony’s trademark is i.LINK, though
Sony commonly uses a 4-pin connector not strictly
compliant with the IEEE standard. (The 6-pin IEEE
connector provides power for a peripheral device;
power is absent from Sony’s 4-pin connector. A node
may have either 4-pin or 6-pin connectors.)
As I write in 2002, agreement upon IEEE 1394B
(“Gigabit 1394”) is imminent. For STP media at
a distance of 4.5 m per link, this extends the data rate
CHAPTER 15 DIGITAL VIDEO INTERFACES 133