WPCL 2BJ|x ` H   x|@  @8'@8' S  `  A <AP IX61E ASS  `  A <AP IX61E AS  (3202)   (3202)   11.HRecommendation G.763 -DIGITAL CIRCUIT MULTIPLICATION EQUIPMENT &USING A 32KBIT/S ADPLM AND DIGITAL SPEECH INTERPOLATION A 9(Melbourne, 1988) 1.HGeneral 1.1HScope  H HThis Recommendation is intended as an introduction to digital circuit multiplication equipment and systems, and as a base document for the specification of Digital Circuit Multiplication Equipment (DCME) and Digital Circuit Multiplication Systems (DCMS). HEssential facilities, interface conditions and overall performance requirements are given. Requirements for full compatibility and interoperability are under study (see Supplement No. 31). 1.2HAttributes HDigital Circuit Multiplication equipment (DCME) is utilized as a means of augmenting the capacity of digital transmission systems operating between several International Switching Centers (ISC). DCME has all of the following attributes: H  digital speech interpolation (DSI); H  low rate encoding (LRE); H dynamic load control (DLC) arrangement in association with interfacing; H capability to accomodate the following types of bearer service requirements: H speech H 3.1 kHz audio (data and speech) H 64 kbit/s unrestricted (transparent) H alternate speech/64 kbit/s unrestricted. HThe link between two DCMEs is generally one where a highly efficient traffic carrying capability is required, e.g., a longdistance link. 1.3HApplication HThis Recommendation is applicable to the design of digital circuit multiplication equipment intended for, but not limited to, use in an international digital circuit. Freedom is permitted in design details which are not covered in this Recommendation (Note). Note Several additional items yet to be fully considered include the evaluation of: H instantaneous 2 bit speech encoding on overloads (to avoid clipping), and voice band data rate discrimination (to permit rates less than or equal to 4800 bit/s to be coded at 32kbit/s only). H silence elimination techniques (to permit saving of bearer channel capacity during the inactive periods of halfduplex voice band data calls). 2.XHDefinitions relating to digital circuit multiplication equipment (DCME) 2.1HDigital circuit multiplication equipment (DCME) HA general class of equipment which permits concentration of a number of 64 kbit/s PCM encoded input trunk channels on a reduced number of transmission channels (see 2.7). 2.2HDigital circuit multiplication system (DCMS) HA telecommunications network comprised of two or more DCME terminals where each DCME terminal contains a transmit unit and a receive unit. 2.3HLow rate encoding (LRE) HA voice band signal encoding method, e.g., adaptive differential pulse code modulation (ADPCM), which results in a bit rate less than 64 kbit/s, e.g., 40 kbit/s, 32 kbit/s, or 24 kbit/s.  h Note 1 Conversion between speech signals encoded in PCM at 64 kbit/s and those encoded in ADPCM must be carried out by means of transcoding processes given in RecommendationsG.721 and G.723. 2.4HVariable bit rate (VBR) HThe capability of the encoding algorithm to dynamically switch between 32 and 24 kbit/s for speech traffic under control of the DCME. 2.5HDigital speech interpolation (DSI) H  A process which, when used in the transmit unit of a DCME, causes a trunk channel (see 2.9) to be connected to a bearer channel (see 2.8) only when activity is actually present on the trunk channel. This, by exploiting the probability of the Speech Activity Factor (see 2.14) of trunk channels being less than 1.0, enables the traffic from a number of trunk channels to be concentrated and carried by a lesser number of time shared bearer channels. The signals carried by a bearer channel therefore represent interleaved bursts of speech signals derived from a number of different trunk channels. Note A process complementary to DSI is required in the receive unit of a DCME, i.e., assignment of the interleaved bursts to their appropriate trunk channels. 2.6HDCME frame HA time interval, the beginning of which is identified by a "unique word" in the control channel. The DCME frame need not coincide with the multiframes defined in CCITT Recommendation G.704. The format specification of the DCME frame includes channel boundaries and bit position significance. 2.7HTransmission channel HA 64 kbit/s time slot within a DCME frame. )Ԍ 2.8HBearer channel (BC) HA bearer channel is a unidirectional, digital, transmission path from the transmit unit of one DCME to the receive unit of a second associated DCME used to carry concentrated traffic between the two DCMEs. Note 1 A number of bearer channels in each direction of transmission form the bothway link required between two DCMEs. This link may be, for example, a 2048kbit/s system. Note 2 A bearer channel may have any of the following instantaneous bit rates: 24, 32, 40 and 64 kbit/s. 2.9HTrunk channel (TC) HA unidirectional, digital transmission path (generally short distance) used for carrying traffic and which connects a DCME to other equipment e.g., an International Switching Centre (ISC). Two such trunk channels (transmit and receive) are needed by 4 wire telephone circuits and constitute a trunk circuit. Note 1 Signals carried by a trunk channel will be transmitted at a bit rate of 64 kbit/s. Note 2 A number of trunk channels in each direction of transmission are required between a DCME and, for instance, an ISC. These trunk channels may be carried by a number of 1544 or 2048 kbit/s systems. 2.10HAssignment message HThe message specifying the interconnections required between trunk channels and bearer channels. 2.11HAssignment map HA record, held in a memory of a DCME, of the interconnections required between trunk channels and bearer channels. This record is dynamically updated in real time in accordance with the traffic demands made on the DCME. 2.12HControl channel HA unidirectional transmission path from the transmit unit of one DCME to the receive unit of one or more associated DCMEs which is dedicated primarily to carrying channel assignment messages. In addition, the control channel transmits other messages such as idle noise levels, dynamic load control, and alarm messages. Note An alternative name for "control channel" is "assignment channel". 2.13HEnsemble activity HThe ratio of the time active signals and their corresponding hangover time and front end delay occupy the trunk channels to the total measuring time, averaged over the total number of trunk channels included in the measurement. 2.14HSpeech activity factor HThe ratio of the time speech signals with their corresponding hangover time and front end delay occupy a trunk channel to the total measuring time, averaged over the total number of trunk channels carrying speech. 2.15HVoice band data ratio HThe ratio of the number of trunk channels carrying voice band data signals to the total number of trunk channels averaged over a fixed interval of time. 2.16H64 kbit/s unrestricted digital data ratio HThe ratio of the number of trunk channels carrying 64 kbit/s unrestricted digital data signals to the total number of trunk channels averaged over a fixed interval of time. 2.17HDCME overload (mode) HThe condition when the number of input trunk channels instantaneously active carrying speech exceeds the number of 32 kbit/s channels available for interpolation. 2.18HOverload channels HThe additional bearer channel capacity which is generated using variable bit rate (VBR) encoding to minimize or eliminate DSI competitive clipping. 2.19HAverage bits per sample HThe average number of encoding bits per sample computed over a given time window for the ensemble of active interpolated bearer channels within a given interpolation pool. Only bearer channels carrying speech are included in this calculation. 2.20HTransmission overload HThe condition when the average bits per sample goes beyond the value set in accordance with speech quality requirements. 2.21HFreezeout HThe condition when a trunk channel becomes active and cannot immediately be assigned to a bearer channel, due to lack of available transmission capacity. 2.22HFreezeout fraction (FOF) HThe ratio of the total time that the individual channels experience the freezeout condition to the total time of the active intervals and their corresponding hangover times and front end delays, for all trunks over a fixed interval of time, e.g., one minute. 8I(3202) CCITT\APIX\DOC\061E4.TXS 88I(3202) CCITT\APIX\DOC\061E4.TXS 8  8R 8R 8R 8LTABLE 1/G.763 8R 8R  p        Synchronization  Buffer  Slip  Location  Figure   Type  Size  Size   No.   Note 3  Note 1  Note 2  Note 4    1. No Buffering             A Asynch No buffer   I 1/G.763         B Synch No buffer   I 2/G.763 I 15/G.763      I 12/G.763   C Synch       Analogue to No buffer   I 5/G.763   Digital       2. Plesiochronous/       Buffering             A Asynch  0.5 ms 2 frames Trunk side I 3/G.763         B Synch  0.5 ms 2 frames Bearer side I 4/G.763      I 13/G.763      I 16/G.763   3. Plesiochronous/       Doppler Buffering             A Synch  1.7 ms 2 frames Bearer side I 6/G.763      I 11/G.763 I 17/G.763      I 14/G.763 I 19/G.763         B Synch  2.4 &  Bearer side & I 7/G.763    1.7 ms  Trunk side          C Asynch  1.7 ms 2 frames Trunk side I 9/G.763         D Synch  2.4 &  Trunk side I 8/G.763    1.7 ms            E Synch  1.7 ms 2 frames Trunk side I 10/G.763      I 18/G.763