


                                
                            AP IX-61-E
                                

11.    Recommendation G.763

            DIGITAL CIRCUIT MULTIPLICATION EQUIPMENT
    USING A 32 KBIT/S ADPLM AND DIGITAL SPEECH INTERPOLATION
                                
                       (Melbourne, 1988)


1.     General

1.1    Scope

       This 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).

       Essential facilities,  interface  conditions  and  overall  performance
requirements are given. Requirements for full compatibility and interoperability 
are under study (see Supplement No. 31).

1.2    Attributes

       Digital 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: 

       -    digital speech interpolation (DSI);
            -    low rate encoding (LRE);

       -     dynamic  load  control  (DLC)  arrangement  in  association  with
            interfacing; 
       -    capability to accomodate the following  types  of  bearer  service
            requirements:

                 speech
                 3.1 kHz audio (data and speech)
                 64 kbit/s unrestricted (transparent)
                 alternate speech/64 kbit/s unrestricted.

       The link between two DCMEs is generally one where  a  highly  efficient
traffic carrying capability is required, e.g., a long-distance link.

1.3    Application

       This 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:

       -    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 32 kbit/s only).




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       -    silence elimination techniques (to permit saving of bearer channel 
            capacity during the inactive periods of half-duplex voice band data 
            calls).

2.     Definitions relating to digital circuit multiplication equipment (DCME)

2.1    Digital circuit multiplication equipment (DCME)

       A 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).

2.2    Digital circuit multiplication system (DCMS)

       A telecommunications network comprised of two or  more  DCME  terminals
where each DCME terminal contains a transmit unit and a receive unit.

2.3    Low rate encoding (LRE)

       A 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.

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
Recommendations G.721 and G.723.

2.4    Variable bit rate (VBR)

       The capability of the encoding algorithm to dynamically switch
between 32 and 24 kbit/s for speech traffic under control of the DCME.

2.5    Digital speech interpolation (DSI)
            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.

2.6    DCME frame

       A time interval, the beginning of which is identified by a "unique word" in 
the control channel. The DCME frame need not coincide with the multi-frames defined 
in CCITT Recommendation G.704. The format specification of the DCME frame includes 
channel boundaries and bit position significance.

2.7    Transmission channel

       A 64 kbit/s time slot within a DCME frame.

2.8    Bearer channel (BC)




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                            AP IX-61-E
                                

       A 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
both-way link required between two  DCMEs.  This  link  may  be,  for  example,  a
2048 kbit/s system.

Note 2 - A bearer channel may have any of the following instantaneous  bit  rates:
24, 32, 40 and 64 kbit/s.

2.9    Trunk channel (TC)

       A 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.

2.10   Assignment message

       The message specifying the interconnections required between trunk channels 
and bearer channels.

2.11   Assignment map

       A 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. 

2.12   Control channel

       A 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".

2.13   Ensemble activity

       The 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.











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                            AP IX-61-E
                                

2.14   Speech activity factor

       The 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.

2.15   Voice band data ratio

       The 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.

2.16   64 kbit/s unrestricted digital data ratio

       The 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.

2.17   DCME overload (mode)

       The condition when the  number  of  input  trunk  channels  instantaneously
active carrying speech exceeds the number of  32  kbit/s  channels  available  for
interpolation.

2.18   Overload channels

       The additional bearer channel capacity which is  generated  using  variable
bit rate (VBR) encoding to minimize or eliminate DSI competitive clipping.

2.19   Average bits per sample

       The 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.

2.20   Transmission overload

       The condition when the average bits per sample goes beyond the value set in 
accordance with speech quality requirements.

2.21   Freeze-out

       The condition when a trunk channel becomes active and cannot immediately be 
assigned to a bearer channel, due to lack of available transmission capacity.

2.22   Freeze-out fraction (FOF)

       The ratio of the total time that the  individual  channels  experience  the
freeze-out 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.










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                            AP IX-61-E
                                

                                         
                                         
                                         
                                  TABLE 1/G.763
                                         
                                         
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Г   Synchronization  Г Buffer  Г  Slip  Г Location    Г         Figure          Г
Г        Type        Г  Size   Г  Size  Г             Г           No.           Г
Г       Note 3       Г Note 1  Г Note 2 Г  Note 4     Г                         Г
УФФФФФФФФФФФФФФФФФФФФХФФФФФФФФФХФФФФФФФФХФФФФФФФФФФФФФХФФФФФФФФФФФФФФФФФФФФФФФФФД
Г1. No Buffering     Г         Г        Г             Г                         Г
Г                    Г         Г        Г             Г                         Г
Г   A    Asynch      ГNo bufferГ   -    Г    -        ГI  1/G.763               Г
Г                    Г         Г        Г             Г                         Г
Г   B    Synch       ГNo bufferГ   -    Г    -        ГI  2/G.763  I 15/G.763   Г
Г                    Г         Г        Г             ГI 12/G.763               Г
Г   C    Synch       Г         Г        Г             Г                         Г
Г        Analogue to ГNo bufferГ   -    Г    -        ГI  5/G.763               Г
Г        Digital     Г         Г        Г             Г                         Г
УФФФФФФФФФФФФФФФФФФФФХФФФФФФФФФХФФФФФФФФХФФФФФФФФФФФФФХФФФФФФФФФФФФФФФФФФФФФФФФФД
Г2. Plesiochronous/  Г         Г        Г             Г                         Г
Г   Buffering        Г         Г        Г             Г                         Г
Г                    Г         Г        Г             Г                         Г
Г   A    Asynch      Г 0.5 ms  Г2 framesГTrunk side   ГI  3/G.763               Г
Г                    Г         Г        Г             Г                         Г
Г   B    Synch       Г 0.5 ms  Г2 framesГBearer side  ГI  4/G.763               Г
Г                    Г         Г        Г             ГI 13/G.763               Г
Г                    Г         Г        Г             ГI 16/G.763               Г
УФФФФФФФФФФФФФФФФФФФФХФФФФФФФФФХФФФФФФФФХФФФФФФФФФФФФФХФФФФФФФФФФФФФФФФФФФФФФФФФД
Г3. Plesiochronous/  Г         Г        Г             Г                         Г
Г   Doppler BufferingГ         Г        Г             Г                         Г
Г                    Г         Г        Г             Г                         Г
Г   A    Synch       Г 1.7 ms  Г2 framesГBearer side  ГI  6/G.763               Г
Г                    Г         Г        Г             ГI 11/G.763  I 17/G.763   Г
Г                    Г         Г        Г             ГI 14/G.763  I 19/G.763   Г
Г                    Г         Г        Г             Г                         Г
Г   B    Synch       Г 2.4 &   Г        ГBearer side &ГI  7/G.763               Г
Г                    Г 1.7 ms  Г        ГTrunk side   Г                         Г
Г                    Г         Г        Г             Г                         Г
Г   C    Asynch      Г 1.7 ms  Г2 framesГTrunk side   ГI  9/G.763               Г
Г                    Г         Г        Г             Г                         Г
Г   D    Synch       Г 2.4 &   Г        ГTrunk side   ГI  8/G.763               Г
Г                    Г 1.7 ms  Г        Г             Г                         Г
Г                    Г         Г        Г             Г                         Г
Г   E    Synch       Г 1.7 ms  Г2 framesГTrunk side   ГI 10/G.763               Г
Г                    Г         Г        Г             ГI 18/G.763               Г
РФФФФФФФФФФФФФФФФФФФФСФФФФФФФФФСФФФФФФФФСФФФФФФФФФФФФФСФФФФФФФФФФФФФФФФФФФФФФФФФй













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