1、CCITT FASCICLE 1V.L * W 48b25L - 05053b5 4 I! Recommendation M.475 SETTING UP AND LINING UP MIXED ANALOGUE/DIGITAL CHANNELS FOR INTERNATIONAL, TELECOMMUNICATION SERVICES 1 Check of FDM multiplex or transmultiplexer equipment The FDM multiplex or transmultiplexer equipment, before it is connected to
2、a group or supergroup link, must be checked to ensure that it meets CCITT Recommendations and the other relevant specifications. The check should include a general visual inspection and vibration tests, if applicable. This is of particular importance if the equipment has remained unused since accept
3、ance tests were carried out after installation. 2 Setting up and lining up mixed analogueldigital channels The definition of a mixed analogue/digital channel is given in Recommendation M.300. When these channels are used for international telephone circuits, the required circuit transmission loss wi
4、ll in many cases be established through the use of variable loss pads in the transmultiplexer. For these mixed analogue/digital channel applications, Administrations may, through bilateral agreement, defer the separate channel line-up procedures contained in this Recommendation, and perform, instead
5、, the appropriate circuit section and circuit line-up procedures of Recommendation M.580. As a prerequisite to setting up and lining up channels using the procedures in this Recommendation, the involved group and supergroup links shall have been set up and lined up in accordance with Recommenda- tio
6、n M.460. 2.1 Measurement and adjustment of levels Depending upon the type of test equipment used, and the access features of the transmultiplexer, the following procedures may require taking an entire transmultiplexer out of service while each channel is being lined up. Careful consideration should
7、be given to procedures for removing transmultiplexers from service, and for restoring them to service, especially where the group links which terminate on the transmultiplexer are not co-terminous, or where international leased circuits are provided on transmultiplexers. 2.1.1 Transmultiplexers at e
8、ach end of the group or supergroup link Note - These configurations are shown in a) and b) of Figure 1/M.475. After the group or supergroup links have been set up, and the transmultiplexing equipments at the ends of the group or supergroup links have been checked and connected, the channels are adju
9、sted as follows. At the transmitting end, a bit sequence corresponding to 1020 Hz) test tone at a level of - 10 dBmO is applied to the 64 kbit/s time slot appearance of each channel in turn, at the digital path access point associated with the input to the transmultiplexer, using appropriate digital
10、 test equipment. At the receiving end, the 64 kbit/s time slot appearance of each channel is monitored in turn at the digital path access point associated with the output of the transmultiplexer, using appropriate digital test equipment, and each channel is adjusted as near as possible to its nomina
11、l level. 2.1.2 24-channel transmultiplexer at one end of the group links, with channel translating equipment ad the ofher end Note - This configuration is shown in c) of Figure WM.475. After the group links have been set up, and the transmultiplexing and channel translating equipments at the ends of
12、 the group links have been checked and connected, the channels are adjusted as follows. Transmitting from the channel translating equipment towards the transmultiplexer, an 1020 Hz 1) test signal is sent over each channel in turn at a level of - 10 dBmO. The channel translating equipment is adjusted
13、 so that the sideband level on each channel is as near to the nominal level as possible. At the receiving end, the 64 kbit/s time slot corresponding to each channel is monitored in turn at the digital path access point associated with the output of the transmultiplexer, and each channel is adjusted
14、to obtain the bit sequence corresponding to the nominal level of the received test signal. i) For further information about the choice of the test signal frequency, refer to Recommendation 0.6 i. r I 286 Fascicle IV.l - Rec. M.475 j CCITT FASCICLE IV-L * 4862593 O505366 6 60 channel transmultiplexer
15、 . 50 channel transmultiplexer - 2048 kbit/s 1 paths 1544 kbit/s paths 1544 -0-b -0-* Supergroup link a) Example of supergroup link with transmultiplexers at both ends 24 channel transmultiplexer 1 24 channel transmultiplexer . . 2048 kbit/s paths Group link 1544 kbit/s paths U U b) Example of group
16、 link with transmultiplexers at both ends 1-04 kbit/s paths 1 Channel 24 channel transrnultiplexer translating equipment n “ i L n F “ n “ A n Audio inputs and outputs -o - 1 1 -* 12 * Group link 1 t 12 . Channel translating cl Examaie of grc CCITT- 71 121 d) Example of supergroup link with transmul
17、tiplexer and group and channel translating equipment _o_ Distribution frame (o-r equivalent) -0- Digital path access point FIGURE 1/M.475 Fascicle IV.l - Rec. M.475 CCITT FASCICLE 1V.L * 9Bb257L - 05053b7 8 -I Transmitting from the transmultiplexer towards the channel translating equipments, a bit s
18、equence corresponding to 1020 Hz2) test tone at a level of -10 dBmO is applied to the 64 kbit/s time slot of each channel in turn, at the digital path access point associated with the digital input to the transmultiplexer, using appropriate digital test equipment. At the receiving end, the channel t
19、ranslating equipment should then be adjusted to bring the received level on each channel as near as possible to its nominal value. 2.1.3 60-channel transmultiplexer at one end of a supergroup link, with group and channel translating equipments at the other end Note - This configuration is shown in d
20、) of Figure WM.475. After the supergroup link and group links have been set up, and the transmultiplexing, group translating, and channel translating equipments at the ends of the supergroup link and group links have been checked and connected, the channels are adjusted by the following procedures i
21、n 0 2.1.2 above. 3 Check level of line signalling In the case of groups which are intended to be used for telephone circuits employing Signalling System R2, the checks of signalling level stipulated in the Specifications of Signalling System R2 should be made 2. For other signalling systems, the che
22、ck of signalling level should be carried out at the circuit line-up stage (see the Recommendation M.580). References CCITT Recommendation I020 Hz reference test frequency, Vol. IV, Rec. 0.6 CCITT Recommendations Specz3cations of Signalling System R2, Vol. VI, Recs. 4.400 to 4.490. i 2 2.4 Planned ou
23、tages and restoration of transmission systems Recommendation M.490 EXCHANGE OF INFORMATION FOR PLANNED OUTAGES OF TRANSMISSION SYSTEMS 1 Gen er a 1 Planned outages of transmission systems. are required to allow planned work to be done with the minimum impairment to the service concerned. All tests,
24、measurements, rearrangements, etc., which are not attributed directly to a failure - and are known in advance - are considered to be planned work Such work will include installation of new equipment, routine maintenance, work on power supply equipment and in some cases, work for the clearance of fau
25、lts which at first could only be remedied provisionally (mainly cable faults). In the event of planned work which results in the complete or partial interruption in a transmission system, efforts are at first made to reroute the telecommunication traffic as required. If special restoration plans exi
26、st for cases of faults, these plans can also be used in the event of planned outages. Should rerouting be impossible, planned work is generally carried out during periods of light traffic, e.g. at night. To allow appropriate measures to be taken, all stations affected by the planned outage must be informed in good time. *) For further information about the choice of the test signal frequency, refer to Recommendation 0.6 i. 288 Fascicle IV.l - Rec. M.490 I
