IP over VBI (ipvbi)

Status: Concluded December, 1999 
 Dan Zigmond 
Description of Working Group:
IP can be carried by many physical mechanisms. The vertical blanking
interval of analog television signals (or VBI) is one more of these
with the characteristic that it is unidirectional. It may therefore be
only suitable for UDP/IP or multicast applications at present or we may
build on this as other internet protocols are enhanced to allow
unidirectional operation. A number of companies have already enhanced
the functionality (in layers above the NABTS or WST, the two byte
encoding standards for VBI) to include FEC, conditional access,
encryption, file transfer etc, but each in a proprietary and
incompatible way. This is a disincentive for systems to grow, and for
the VBI to become widely used as a data transport mechanism.
The broadcast industry is turning to digital TV, which will offer many
Mbps broadcast data capacity, but this technology is in its infancy and
still not widely available at the right price.  VBI may therefore be
viewed as an intermediate system (using well known, low cost and
currently operating - for more than 10 years - technology) which will
serve the data broadcast industry for a few years yet and probably for
very many years in the less advanced countries - most countries
actually. Sure the data rate is lower, but so is the cost.  We already
have transmissions, test equipment, test software, decoding software
and chipsets. All we are talking of doing is upgrading the software to
do a bit more.
The reason for carrying IP is that it is a commonly available well
known format to build on. The data broadcast industry then does not
have to re-invent the wheel to use higher level protocols, but can
simply layer existing protocols on IP.  We expect IP and non-IP traffic
to co-exist on VBI initially, but as the higher levels of internet are
defined for broadcast use the IP traffic would dominate.
The IPVBI group will define a standard mechanism for transmitting IP
datagrams on top of both NABTS and WST VBI formats.  The standard will
include framing mechanisms, header compression, and an FEC system, all
based on existing IETF standards where possible.  Protocols above the
IP layer (like streaming media and broadcast file transfer) will not be
considered by IPVBI.

Request for Comments:

  • RFC2728 The Transmission of IP Over the Vertical Blanking Interval of a Television Signal (Proposed Standard)