





8.Recommendation G.738

       CHARACTERISTICS OF PRIMARY PCM MULTIPLEX EQUIPMENT
       OPERATING AT 2048 KBIT/S AND OFFERING SYNCHRONOUS
         DIGITAL ACCESS AT 320 KBIT/S AND/OR 64 KBIT/S

                       (Melbourne, 1988)
                                

       This Recommendation gives the characteristics of a  PCM  multiplex
equipment operating at 2048 kbit/s and providing one or  several  of  the
following internal digital access options:

       -      bidirectional   synchronous   64   kbit/s   channels   (see
            Figure 1a/G.738;

       -     unidirectional  synchronous   320   kbit/s   channels   (see
            Figure 1b/G.738.

       The 320 kbit/s channel is based on the allocation of 5 x 64  kbit/s  time
slots,  e.g.,   for   setting   up   sound-programme   circuits   according   to
Recommendations J.43 and J.44.

       Because these circuits are specified as unidirectional, the equipment for 
insertion/extraction has to be separated as shown in Figures 1b/G.738.

1.     General characteristics

1.1    Fundamental characteristics for voice channel encoding

       The encoding law used is the A-law as specified in Recommendation  G.711.
The sampling rate, load capacity  and  the  code  are  also  specified  in  that
Recommendation.

       The number of quantized values is 256.

Note - The inversion of bits 2, 4, 6 and 8 is covered by the encoding law and is 
applicable only to voice channel time slots.

1.2    Bit rate

       The nominal bit rate is 2 048 kbit/s. The tolerance on this rate is +  50
parts per million (ppm).

1.3    Timing signal

       It should be possible to derive the transmit timing signal  from  any  of
the following:

       a)   from the received 2084 kbit/s signal;

       b)   from an external source at 2 048 kHz (see  5);

       c)   from an internal oscillator.

Note - The provision of a timing signal output, available  for  the  purpose  of
synchronizing other equipments, is an option that might be required depending upon 
national synchronization arrangements.












1.4    Types of access

       a)    access  for  bidirectional  synchronous  64  kbit/s  channels  (see
            Figure 1a/G.738);

       b)   access for  unidirectional  synchronous  320  kbit/s  channels  (see
            Figure 1b/G.738).

Note - The synchronous insertion of a digital  sound  programme  signal  into  a
320 kbit/s channel requires the internal  regeneration  of  a  timing  signal  T
synchronized by the 2048 kbit/s signal I1. the timing signal is used for synchronizing 
the sampling frequency of the analogue/digital converters producing the  digital
sound programme signal.

2.     Frame structure and use of derived channel time slot

2.1    Frame structure of 2048 kbit/s signal

       Refer to  2.3 of Recommendation G.704. Bit 1 of the frame should be used 
in accordance with  2.3.3/6.706, i.e., for a CRC check bit procedure.

2.2    Use of derived channel time slots

2.2.1  Telephone channels

       It should be possible to assign channel time slots 1 to 15 and 17  to  31
to 30 telephone channels numbered from 1 to 30.

2.2.2  64 kbit/s access

       The number of accessible channel time slots should be at least  four  and
the equipment shall allow access to any of channel time slots 1 to 15 and 17  to
31.

Note - Equipment exists which provides access to  at  least  four  channel  time
slots in the following order to priority:

       6 - 22 - 14 - 30 - 2 - 18 - 10 - 26 - 4 - 20 - 12 - 28 - 8 - 24 -  5  -
       21 - 13 - 29 - 1 - 17 - 9 -  25  -  3  -  19  -  11  -  27  -  7  -  23
       - 15 - 31.

2.2.3  320 kbit/s access

       The time slot allocation for digital channels with bit  rate  at
320 kbit/s is given in the following table:

                                   кФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФТФФФФФФФФФФФП
                                   Г               320 kbit/s channels (Note 1)                Г   DSP     Г
                                   УФФФФФФФФФТФФФФФФФФФТФФФФФФФФФТФФФФФФФФФТФФФФФФФФФТФФФФФФФФФД  ACCESS   Г
                                   Г    A    Г    B    Г    C    Г    D    Г    E    Г    F    Г  POINTS   Г
                                   УФФФФФФФФФХФФФФФФФФФХФФФФФФФФФХФФФФФФФФФХФФФФФФФФФХФФФФФФФФФХФФФФФФФФФФФД
                                   Г 1 - 2 - Г 6 - 7 - Г 11 - 12 Г 17 - 18 Г 22 - 23 Г 27 - 28 Г I3, T, E3 Г
                                   Г 3 - 4 - Г 8 - 9 - Г - 13 -  Г - 19 -  Г - 24 -  Г - 29 -  Г  Figure   Г
                                   Г 5       Г 10      Г 14 - 15 Г 20 - 21 Г 25 - 26 Г 30 - 31 Г 1b/G.738  Г
                                   РФФФФФФФФФСФФФФФФФФФСФФФФФФФФФСФФФФФФФФФСФФФФФФФФФСФФФФФФФФФСФФФФФФФФФФФй

Note 1 - The six possible 320 kbit/s channels in a 2048 kbit/s  stream  are
numbered A to F. Preferably the channel pairs A-B, C-D, and E-F  should  be
used for stereophonic transmission.







Note 2 - If the channel time slot 16 which is assigned to signalling  as  covered
in  5 below is not needed for signalling, it may be used for purposes other than 
a voice channel encoded within the PCM multiplex equipment.















       a)   Bidirectional synchronous  insertion/extraction  of  64  kbit/s  data
            channels














       b)   Unidirectional synchronous insertion and extraction of digital sound-programme (DSP) into/out of a 320 kbit/s channel


       I,E:   insertion side; extraction side

       I1,E1: 2048 kbit/s interface

       I2,E2  64 kbit/s interface

       I3,E3: synchronous; digital sound programme signal access

       T:     timing signal


                                 FIGURE 1/G.738
                                        
                PCM multiplex equipment operating at 2048 kbit/s
             and offering access to digital sound-programme signals
                 and/or to synchronous 64 kbit/s data channels

3.     Frame alignment and CRC procedures

       (An illustration of the procedure is given in Figure 2/G.706.)












3.1    Loss of frame alignment

       Refer to  4.1.1. of Recommendation G.706.

3.2    Recovery of frame alignment

       Refer to  4.1.2 of Recommendation G.706.

3.3    CRC multiframe alignment in TSO

       Refer to  4.2 of Recommendation G.706.

3.4    CRC bit monitoring

       Refer to  4.3 of Recommendation G.706.

4.     Fault conditions and consequent actions

4.1    Fault conditions

       The PMC multiplex equipment should detect the following conditions:

4.1.1  Failure of power supply.

4.1.2  Failure of codec (except when using single channel codecs).

       As a minimum requirement, this fault condition should be  recognized  when
for at least one signal level in  the  range  -21  to  -6  dBmO,  the  signal-to-
quantizing noise ration performance of the local codec is 18 dB or more below the level 
recommended in Recommendation G.712.

4.1.3  Loss of incoming signals at the 64 kbit/s and 320 kbit/s  tributary  input
ports.

Note 1 - This detection is not mandatory when  contradirectional  interfaces  are
used.

Note 2 - The detection of this fault condition is not mandatory for channel  time
slot 16 when channel associated signalling is used and the  signalling  multiplex
equipment is situated within a few metres of the PCM multiplex equipment.

4.1.4  Loss of the incoming signal at 2048 kbit/s.

Note 1 - The detection of this fault condition is required only when it does  not
result in an indication of loss of frame alignment.

Note 2 - Where separate circuits are used for the digital signal and  the  timing
signal, the loss of either or both should constitute loss of the incoming signal.

4.1.5  Loss of frame alignment.

4.1.6  Excessive bit error ratio  detected  by  monitoring  the  frame  alignment
signal.

4.1.6.1     With a random bit error ratio of < 10-4, the probability  of  activating
the indication of fault condition in a few seconds should be less than 10-6.

       With a random bit error ratio of > 10-3, the probability  of  activating  the
indication of fault condition in a few seconds should be higher than 0.95.







4.1.6.2     With a random bit error ratio of > 10-3, the probability of deactivating 
the indication of fault condition in a few seconds should be almost 0.

       With a random bit error ratio of < 10-4, the probability of deactivating  the
indication of fault condition in a few seconds should be higher than 0.95.

Note - The activating and deactivating  period  specified  as  "a  few  seconds"  is
intended to be in the order of 4 to 5 seconds.

4.1.7  Alarm indication received  from  the  remote  PCM  multiplex  equipment  (see
 4.2.3).

4.2    Consequent actions

       Further to the detection of a fault condition, appropriate actions should  be
taken as specified in Table 1/G.738. The consequent actions are as follows:

4.2.1  Service alarm indication generated to signify that the  service  provided  by
the PCM multiplex is no longer available. This indication should be forwarded at least 
to  the  switching  and/or  signalling  multiplex  equipment  depending   upon   the
arrangements provided. The indication should be given as soon as possible and not later than 
2 ms after detection of the relevant fault condition.

       This specification, taking into account the specification given in  2.5,  is
equivalent to recommending that the average time to detect a loss of frame alignment 
or a loss of the incoming 2048 kbit/s signal and to  give  the  relevant  indication
should not be greater than 3 ms.

       When using common channel signalling the indication should  be  forwarded  to
the switching equipment by means of  a  separate  interface  on  the  PCM  multiplex
equipment.

4.2.2  Prompt maintenance alarm indication generated to signify that performance  is
below acceptable standards and maintenance attention is required locally.  When  the
AIS (see general note below to  4.2) at 2048 kbit/s input is  detected  the  prompt
maintenance alarm indication, associated with loss of frame alignment (see  4.1.5) and 
excessive error rate (see  4.1.6), should be  inhibited,  while  the  rest  of  the
consequent actions are in accordance with those associated in Table 1/G.738 with the two 
fault conditions.

Note - The location and provision of any visual and/or audible  alarm  activated  by
the alarm indications given in  4.2.1 and  4.2.2, is left to the discretion of each 
administration.

4.2.3  Alarm indication to the remote end transmitted by changing bit 3  of  channel
time slot 0 from the state 0 to the state 1 in those frames not containing the frame 
alignment signal. This should be effected as soon as possible.

4.2.4  Transmission suppressed at the analogue voice-frequency outputs

4.2.5  AIS applied to all 64 kbit/s and 320 kbit/s outputs (see general  note  below
to  4.2). For 64 kbit/s outputs this action should be taken as soon as possible and 
not later than 2 ms after the detection of the fault condition.

4.2.6  AIS applied to relevant time slots in the composite 2048 kbit/s output signal 
(if suspension of incoming 64 kbit/s and 320 kbit/s signals is provided).

Notes to  4.2












Note 1 - The equivalent binary content of the alarm indication  signal  (AIS)  is  a
continuous stream of binary 1s. The strategy for detecting the presence of  the  AIS
should be such that with a high probability the AIS is detectable even in the presence of 
random errors having a mean error rate of 1 in 103. Nevertheless, a signal in  which
all the binary elements, with the exception of the frame alignment signal, are in the 
state 1, should not be taken as an AIS.

Note 2 - All timing requirements quoted apply equally to restoration, subsequent  to
the fault condition clearing.

5.     Signalling

       Text as in Recommendation G.732.

6.     Interfaces

6.1    Audio frequency interface

       The  analogue  audio  frequency  interfaces  should  be  in  accordance  with
Recommendations G.712, G.713, G.714 and G.715.

6.2    Digital interfaces

       The  digital  interfaces  at  2048  kbit/s  should  be  in  accordance   with
Recommendation G.703.

       The digital interfaces at 64 kbit/s should be of either the codirectional  or
the contradirectional type specified in Recommendation G.703. The specification  for
64 kbit/s interfaces are  not  mandatory  for  channel  associated  signalling.  The
interface for external synchronization of the transmitting timing signal should be in 
accordance with Recommendation G.703.

       The need to define a digital interface  operating  at  320  kbit/s  is  under
study.

Note 1 - It should be noted that, according  to  the  principle  of  minimizing  the
number of different types of interfaces, the information rate of 320 kbit/s will  be
offered to customers at the user/network interface level using the 2048 kbit/s interface as 
defined in Recommendation I.431 and Recommendation G.703.

Note 2 - In the case of the 64 kbit/s codirectional interface,  the  design  of  the
input ports should take into account the need to provide octet alignment,  to  allow
controlled slips when the tributary timing and that of the multiplexer timing source are 
plesiochronous, and  to  absorb  jitter  and  wander  up  to  the  limits  given  in
Recommendation G.823.








                                   TABLE 1/G.738
                                          
      Fault conditions and consequent actions for the PCM multiplex equipment
                                          

 кФФФФФФФФФФФФФФФТФФФФФФФФФФФФФФФТФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФП
 Г Equipment     Г Fault         Г                                 Consequent actions (see  3.2)                                Г
 Г part          Г conditions    УФФФФФФФФФФФФФФФТФФФФФФФФФФФФФФФТФФФФФФФФФФФФФФФТФФФФФФФФФФФФФФФТФФФФФФФФФФФФФФФТФФФФФФФФФФФФФФФД
 Г               Г (see  4.1)   Г Service       Г Prompt        Г Alarm         Г Transmission  Г AIS applied   Г AIS applied   Г
 Г               Г               Г alarm         Г maintenance   Г indication    Г suppressed at Г to 64 kbit/s  Г to the        Г
 Г               Г               Г indication    Г alarm         Г remote end    Г the analogue  Г and 320 kbit/sГ relevant time Г
 Г               Г               Г generated     Г indication    Г transmitted   Г voice-        Г outputs       Г slot of the   Г
 Г               Г               Г               Г               Г               Г frequency     Г               Г 2048 kbit/s   Г
 Г               Г               Г               Г               Г               Г outputs       Г               Г composite     Г
 Г               Г               Г               Г               Г               Г               Г               Г signal        Г
 УФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФД
 Г               Г Failure of    Г Yes           Г Yes           Г Yes (if       Г Yes (if       Г Yes (if       Г Yes (if       Г
 Г Multiplexer   Г power supply  Г               Г               Г practicable)  Г practicable)  Г practicable)  Г practicable)  Г
 Г and           УФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФД
 Г demultiplexer Г Failure of    Г Yes           Г Yes           Г Yes           Г Yes           Г               Г               Г
 Г               Г codec         Г               Г               Г               Г               Г               Г               Г
 УФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФД
 Г Multiplexer   Г Loss of       Г               Г Yes           Г               Г               Г               Г Yes           Г
 Г only          Г incoming      Г               Г               Г               Г               Г               Г               Г
 Г               Г signal at     Г               Г               Г               Г               Г               Г               Г
 Г               Г 64 kbit/s     Г               Г               Г               Г               Г               Г               Г
 Г               Г and/or        Г               Г               Г               Г               Г               Г               Г
 Г               Г 320 kbit/s    Г               Г               Г               Г               Г               Г               Г
 Г               Г inputs (see   Г               Г               Г               Г               Г               Г               Г
 Г               Г note under    Г               Г               Г               Г               Г               Г               Г
 Г               Г  4.1.3)      Г               Г               Г               Г               Г               Г               Г
 РФФФФФФФФФФФФФФФСФФФФФФФФФФФФФФФСФФФФФФФФФФФФФФФСФФФФФФФФФФФФФФФСФФФФФФФФФФФФФФФСФФФФФФФФФФФФФФФСФФФФФФФФФФФФФФФСФФФФФФФФФФФФФФФй


                             TABLE 1/G.738 (continued)


 кФФФФФФФФФФФФФФФТФФФФФФФФФФФФФФФТФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФП











 Г Equipment     Г Fault         Г                                 Consequent actions (see  3.2)                                Г
 Г part          Г conditions    УФФФФФФФФФФФФФФФТФФФФФФФФФФФФФФФТФФФФФФФФФФФФФФФТФФФФФФФФФФФФФФФТФФФФФФФФФФФФФФФТФФФФФФФФФФФФФФФД
 Г               Г (see  4.1)   Г Service       Г Prompt        Г Alarm         Г Transmission  Г AIS applied   Г AIS applied   Г
 Г               Г               Г alarm         Г maintenance   Г indication    Г suppressed at Г to 64 kbit/s  Г to the        Г
 Г               Г               Г indication    Г alarm         Г remote end    Г the analogue  Г and 320 kbit/sГ relevant time Г
 Г               Г               Г generated     Г indication    Г transmitted   Г voice-        Г outputs       Г slot of the   Г
 Г               Г               Г               Г               Г               Г frequency     Г               Г 2048 kbit/s   Г
 Г               Г               Г               Г               Г               Г outputs       Г               Г composite     Г
 Г               Г               Г               Г               Г               Г               Г               Г signal        Г
 УФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФД
 Г               Г Loss of       Г Yes           Г Yes           Г Yes           Г Yes           Г Yes           Г               Г
 Г               Г incoming      Г               Г               Г               Г               Г               Г               Г
 Г               Г signal at     Г               Г               Г               Г               Г               Г               Г
 Г               Г 2048 kbit/s   Г               Г               Г               Г               Г               Г               Г
 Г               УФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФД
 Г               Г Loss of frame Г Yes           Г Yes (see      Г Yes           Г Yes           Г Yes           Г               Г
 Г               Г alignment     Г               Г  4.2.2)      Г               Г               Г               Г               Г
 Г               Г (see Note 2   Г               Г               Г               Г               Г               Г               Г
 Г               Г 4.2/G.706)    Г               Г               Г               Г               Г               Г               Г
 Г Demultiplexer УФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФД
 Г only          Г Error ratio   Г Yes           Г Yes (see      Г Yes           Г Yes           Г Yes           Г               Г
 Г               Г 1 10-3        Г               Г  4.2.2)      Г               Г               Г               Г               Г
 Г               Г alignment     Г               Г               Г               Г               Г               Г               Г
 Г               Г signal        Г               Г               Г               Г               Г               Г               Г
 Г               УФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФХФФФФФФФФФФФФФФФД
 Г               Г Alarm         Г Yes           Г               Г               Г               Г               Г               Г
 Г               Г indication    Г               Г               Г               Г               Г               Г               Г
 Г               Г received from Г               Г               Г               Г               Г               Г               Г
 Г               Г the remote endГ               Г               Г               Г               Г               Г               Г
 РФФФФФФФФФФФФФФФСФФФФФФФФФФФФФФФСФФФФФФФФФФФФФФФСФФФФФФФФФФФФФФФСФФФФФФФФФФФФФФФСФФФФФФФФФФФФФФФСФФФФФФФФФФФФФФФСФФФФФФФФФФФФФФФй

Note to Table 1/G.738 - A "Yes" in the table signifies that an action  should  be
taken as a consequence of the relevant fault condition.  An  open  space  in  the
table signifies that the relevant action should not be taken as a consequence of the 
relevant fault condition, if this condition is the only one present. If more than 
one fault condition is simultaneously present, the relevant action should be taken 
if, for at least one of the conditions, a "Yes" is defined in  relation  to  this
action.

7.     Jitter

7.1    Jitter at 2048 kbit/s output (see Figure 2/G.823)

7.1.1  In the case where the  transmitting  timing  signal  is  derived  from  an
internal oscillator, the peak-to-peak jitter at the 2048 kbit/s output should not exceed 
0.05 UI when it is measured within the frequency range from f1 = 20 Hz to f4 = 100 
kHz.

7.1.2  In the case where the  transmitting  timing  signal  is  derived  from  an
external source having no jitter, the peak-to-peak jitter at the 2048 kbit/s output 
should not exceed 0.05 UI when it is measured within  the  frequency  range  from
f1 = 20 Hz to f4 = 100 kHz.

7.1.3  In the case where the transmitting  timing  signal  is  derived  from  the
incoming 2048 kbit/s signal having no jitter,  the  peak-to-peak  jitter  at  the
2048 kbit/s output should not exceed 0.10 UI when it is measured within the frequency range 
from f1 = 20 Hz to f4 = 100 kHz. The equivalent binary content of the test signal 
applied at the 2048 kbit/s input shall be a pseudo-random bit sequence of  length
215-1 as specified in Recommendation 0.151.







Note - It may be necessary to include a frame alignment signal in the test signal 
to enable the measurement to be carried out.

7.2    Jitter at tributary outputs

7.2.1  Jitter at 64 kbit/s output

       In the case where the incoming 2048 kbit/s signal has no jitter, the peak-to-peak jitter at the 64 kbit/s output should not exceed 0.025 UI when it is 
measured within the frequency range from f1 = 20 Hz to f4 = 10 kHz. The equivalent 
binary content of the test signal applied to the 2048 kbit/s input shall be a pseudo-random bit sequence of length 215-1 as specified in Recommendation 0.151.

Note - In order to carry  out  this  measurement  without  invoking  AIS  at  the
64 kbit/s output it will normally be necessary to include a frame alignment signal in the 
test signal.

7.2.2  Jitter at 320 kbit/s output

       Since  the  physical  and  electrical  characteristics  of  a  320  kbit/s
interface are identical to those of the 2048 kbit/s interface, the specification of this 
parameter is the same as that given in  7.1.3 above.

7.3    Jitter transfer functions

7.3.1   The  jitter  transfer  function  between   the   2048   kbit/s   external
synchronization signal and the 2048 kbit/s output signal should not exceed the gain/frequency 
limits given in Figure 2/G.738. The 2 048 kHz  signal  shall  be  modulated  with
sinusoidal jitter.

       Some  administrations  require  that  equipment  is  fitted  with   jitter
reducers. In this case, the jitter transfer function should not exceed the gain/frequency 
limits given in Figure 3/G.738.

7.3.2  In the case where the transmitting timing is  derived  from  the  incoming
signal the jitter transfer function between the 2048 kbit/s input and the 2048 kbit/s 
output shall be as specified in  7.3.1.

Note 1 - The 2048 kbit/s test signal shall be modulated by sinusoidal jitter. The 
equivalent binary content of the test signal shall be 1000.

Note 2 - It may be necessary to include a frame  alignment  signal  in  the  test
signal to enable the measurement to be carried out.








































Note 1 - The frequency f0 should be less than 20 Hz and as low as possible (e.g., 
10 Hz), taking into account the limitations of measuring equipment.

Note 2 - To achieve accurate measurements, the  use  of  a  selective  method  is
recommended with a bandwidth sufficiently small referred to the relevant measurement 
frequency but not wider that 40 Hz.

Note 3 - For interfaces within national boundaries, this  characteristic  may  be
used.


                                 FIGURE 2/G.738

























Note 1 - The frequency f0 should be less than 20 Hz and as low as possible (e.g., 
10 Hz), taking into account the limitations of measuring equipment.

Note 2 - To achieve accurate measurement,  the  use  of  a  selective  method  is
recommended with a bandwidth sufficiently small referred to the relevant measurement 
frequency but not wider than 40 Hz.


                                 FIGURE 3/G.738








7.3.3  The jitter transfer  function  between  the  2048  kbit/s  input  and  the
64 kbit/s output should not exceed -29.6 dB when measured over the frequency range f0 to 
10 kHz. The frequency f0 should be less than 20 Hz and as low as possible  (e.g.,
10 Hz), taking into account the limitations of measuring equipment.

Note 1 - The 2048 kbit/s test signal shall be modulated by sinusoidal jitter. The 
equivalent binary content of the test signal shall be 1000.

Note 2 - In order to carry out this  measurement  without  invoking  AIS  at  the
64 kbit/s output it will normally be necessary to include a frame alignment signal in 
the test signal.

Note 3 - The jitter reduction of 1/32 due  to  demultiplexing  is  equivalent  to
-30.1 dB.

7.3.4  Since  the  physical  and  electrical  characteristics  of  a  320  kbit/s
interface are identical to those of 2048 kbit/s interface, the jitter transfer function 
between 2048 kbit/s input and 320 kbit/s output is the same as that given in 7.3.1 
and 7.3.2 above.