1 Type of Question
Task-oriented Question that should result in one or more
Recommendations and in liaison statements to the appropriate
ITU-T and ITU-R Study Groups.
2 Motivation
ITU-T has issued a comprehensive set of Recommendations defining the form and
structure of digital signals carried in plesiochronous networks, on the
synchronous digital hierarchy (SDH), and on Broadband Integrated Services
Digital Networks, in which the signals are transported in an Asynchronous
Transfer Mode (ATM).
Both sound-programme and television signals can be carried on such digital
networks. It now remains to specify the requirements for the transmission of
MPEG-2 multiplexes of television and sound programme signals carried on PDH and
SDH links. In course of the conversion of TV broadcasting distributive networks
to the digital mode of operation a question is frequently raised on how to
organize MPEG-2 signals transmission over PDH/SDH networks. ITU-T has approved
Recommendations J.131 and J.132, containing the description of procedures needed
for MPEG-2 signals conversion into PDH and SDH formats correspondingly based on
ATM technology. Meanwhile, certain problems the solution for which is not
covered by the said Recommendations arise in countries where there is no
dedicated specialized network for distributing TV broadcasting programs (e.g., a
digital satellite or cable distributive TV network for MPEG-2). This leads to
the necessity to include digital TV programs signals into multiplex PDH/SDH
digital streams, which besides TV signals contain also multichannel digital
telephony and data signals. In short, the abovementioned problems arise when a
TV distributive network is based on an extensive terrestrial PDH/SDH network
including digital radio relay lines and fiber-optic lines covering thousands of
kilometers.
The problem mentioned before may be solved by forming and transmitting TV
signal in an Nx2,048 (N = 4 to 16) format, i.e., as a set of standard digital
2,048 Mbps E1 PDH streams. In such a case, e.g., an 8,448 Mbps E2 TV signal will
be transmitted as four 2,048 Mbps E1 streams. Presently existing PDH networks
are as a common practice using 16xE1 multiplexer (in most cases to combine 2,048
Mbps E1 multichannel telephony digital streams). A format for digital
transmission of a Nx2,048 (N = 4 to 16) Mbps TV signal will allow joint digital
transmission of TV and multichannel telephony on the basis of this unified
multiplexer without any additional hardware.
3 Questions
• What are the network characteristics required for carrying digital
sound-programme and television signals on PDH and SDH networks for purposes
of programme contribution or primary distribution?
• What are the service and performance requirements applicable to the
transmission of MPEG-2 multiplexes of television and sound programme signals
in the NxE1 PDH (N = 4 to 16) format over PDH and SDH networks?
• What Application Programming Interfaces (APIs) should be foreseen for
the software-based solution of MPEG-2/PDH (MPEG-2/SDH) conversion in TV
coders and decoders?
• What benefits and constraints would be offered by ATM techniques when
applied to digital sound-programme and television signals?
• How could a coded digital sound-programme or television signal be
most effectively adapted to and from the ATM?
4 Expected results and anticipated target dates
Studies will be presented in the form of Recommendations, to be adopted,
depending on incoming contributions, by the year 2003 and beyond.
5 Relationships
The work must be carried out in close cooperation with ITU-T Study Group 15,
which has responsibilities for Recommendations on PDH (e.g. G.730, 740,
750-series), SDH (e.g. G.707, G.780-series) and the associated source
signal mappings, including those for sound-programme and television broadcasting
Liaison with ITU-R Study Group 6, is also necessary in the study of this
Question.
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