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1991-12-30
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Draft Recommendation N.xx (N.86)
LINE-UP AND SERVICE COMMISSIONING OF INTERNATIONAL
VIDEOCONFERENCE SYSTEMS OPERATING AT TRANSMISSION BIT RATES
OF 1544 AND 2048 KBIT/S
1. General
This Recommendation deals with the line-up and service commissioning of
international videoconference systems routed over transmission paths operating
at transmission bit rates of 2048 and 1544 kbit/s. In this context an
international videoconference system comprises the international videoconference connection
and the videoconference rooms which are interconnected.
Figure l/N.xx shows the constituent parts of an international
videoconference connection. Recommendation H.110 describes hypothetical reference
connections for videoconferencing.
VS = Videoconference studio
IVC = International videoconference centre
FIGURE l/N.xx
The constituent parts
of an international videoconference connection
The video codecs are normally located within the videoconference studios
but in some circumstances are located elsewhere so that the local tail serving
the videoconference studio may be provided on wideband analogue (e.g. 5.5 MHz) or
higher order digital transmission systems (e.g. 140 Mbit/s). Codecs are described
in Recommendation H.120.
The location of any 2048/1544 kbit/s remultiplexers which may be involved
will be as agreed between the administrations.
Supplement No. 5.2 gives guidance on the setting up and testing
arrangements for videoconference studios.
The international videoconference centre provides the interconnection
point of the national videoconference circuit and the international link. This
interconnection may be made manually or by automatic means.
Normally the international videoconference link will be common for all
videoconference calls between the two administrations concerned whereas the
national videoconference circuits will vary from call to call. Thus, in addition to the
setting up and lining up of the constituent parts of the international
videoconference connection, service commissioning tests are made between videoconference
studios prior to the opening of an international videoconference service to ensure
that a service can be satisfactorily sustained.
2. Setting up and lining up the constituent parts of the connection
2.1 National videoconference circuits
The national videoconference circuits should be set up and tested in
accordance with the national procedures of the administration concerned. This will
include the line up of any sections which may not be provided as 2048 or 1544
kbit/s digital paths. The 2048 and 1544 kbit/s data performance limits to be met are
given in Table l/N.xx and it is recommended that two data tests should be made,
each of one hour's duration, on different days and at times that cover the peak
traffic periods on the route concerned.
2.2 International link
The international videoconference link will only need to be set up and
tested when establishing the first service between two administrations. The
procedures of Recommendation M.465 should apply.
A data test should be made of five hours duration and should be scheduled
so as to include the peak traffic period on the route concerned. The test results
should meet the data performance limits given in Table l/N.xx.
3. Performance check codec to codec
The constituent parts of the connection having been satisfactorily lined
up and connected together at the international videoconference centres, three
data tests (each of one hour's duration) should be made between the codecs. The
tests should be made on different days and at times to cover the peak traffic
periods for the route. The testers should be connected at the digital line side of the
codecs, as close to the codecs as possible. Each test should meet the data
performance limits given in Table l/N.xx.
Where loop facilities exist, loop measurements may be made in order to
obtain reference measurements for subsequent maintenance. Care must be taken to
avoid simultaneous operation of loop facilities.
4. Digital test equipment
The data tester required for the above tests shall be capable of
transmitting and receiving a test pattern within a signal structured in accordance with
CCITT Recommendation G.732 for 2048 kbit/s interfaces or Recommendation G.733 for
1544 kbit/s interfaces. The nature of the test pattern is undefined but should be
the subject of further study.
When working through a 2048/1544 kbit/s remultiplexer, the test signal
should be restricted to time slots 1-24 with time slots 25-31 being vacated.
If compatible testers are not available at both ends of the link or
connection under test then one tester should be used to transmit and receive with a
loop being provided at the other end.
TABLE 1/N.xx
Data test limit
(The limits are provisional and subject to further study)
┌───────────────────┬──────────┬────────────┬──────────┬──────────┬────────────┐ │ │ Nominal*│ Bit │ Max │ Severely │ Min %
│ │ │ Data │ Error │ errors │ Errored │ error │
│ │ Rate │ Ratio │ in │ Events** │ free │ │
│ (kbit/s)│ │ 1 hour │ in 1 hour│ sec │
├───────────────────┼──────────┼────────────┼──────────┼──────────┼────────────┤
│National │ 2048 │ 1 x 10-6 │ 7142 │ 0 │ 92 │
│Videoconference ├──────────┼────────────┼──────────┼──────────┼────────────┤
│Circuit │ 1544 │ 1 x 10-6 │ 5530 │ 0 │ 92 │
├───────────────────┼──────────┼────────────┼──────────┼──────────┼────────────┤
│International │ 2048 │ 1 x 10-6 │ 7142 │ 2 │ 92 │
│Videoconference ├──────────┼────────────┼──────────┼──────────┼────────────┤
│Link │ 1544 │ 1 x 10-6 │ 5530 │ 2 │ 92 │
├───────────────────┼──────────┼────────────┼──────────┼──────────┼────────────┤
│International │ 2048 │ 3 x 10-6 │ 21427 │ 2 │ 92 │
│Videoconference ├──────────┼────────────┼──────────┼──────────┼────────────┤
│Connection │ 1544 │ 3 x 10-6 │ 16589 │ 2 │ 92 │
└───────────────────┴──────────┴────────────┴──────────┴──────────┴────────────┘
* Structured formatting required with consequent reduction in actual test data
rate as follows:
At 2048 kbit/s, test data rate = 1984 kbit/s (time slots 1-31 only).
At 1544 kbit/s, test data rate = 1536 kbit/s (8 bits used for frame
alignment).
** Severely errored events are defined by the particular data tester used,
e.g. 20,000 errors in 100 000 bits. A continuous period of up to 10 seconds,
during which severely errored transmission persists, will be considered a
single severely errored event.
Note 1 - In addition to the above limits the BER shall be no worse than 1x10-5
over any 5 minute period during the tests (5952 errors at 2048 kbit/s and
4608 errors at l544 kbit/s). If this test fails then corrective action shall be taken on
the offending section.
Note 2 - For loop-tests the above limits should be doubled (92% EFS becoming
84% EFS).
5. Videoconference studios
All videoconference studios that will be used for international
videoconference calls should comply with agreed design standards. Providers and operators
of such studios are encouraged to adopt the provisions of Supplement 5.2 until
CCITT Recommendations are specified. The adoption of common standards facilitates
the interworking between any pair of studios in different countries with pre-call
adjustments reduced to a minimum.
6. Service commissioning tests
6.1 General
The international videoconference connection having been satisfactorily
tested, functional video and audio service commissioning tests should be
undertaken between the videoconference studios.
6.2 Test videoconference studios
The videoconference studio chosen by an administration for commissioning
tests should be typical (with regard to the parameters of Supplement 5.2) of all
the other studios to be used for the service. This studio should then serve as a
reference studio for any future tests between videoconference studios with other
administrations.
The reference studio for each administration should be identified to all
other administrations. The parameters of this studio should also be shared with
all other administrations.
6.3 Commissioning test
The end-to-end commissioning tests between videoconference studios are
described in Supplement 5.2. The purpose of the tests is to demonstrate that the
international videoconference system performs adequately when the constituent parts
are connected together. The tests include a subjective assessment of the main
functions of each videoconference studio and selected objective tests. The tests are
not intended to be exhaustive but should serve as sample checks in compliance
with the standards and as a confidence indicator to both administrations before the
opening of an international videoconference service.