.rs
.\" Troff code generated by TPS Convert from ITU Original Files
.\"                 Not Copyright ( c) 1991 
.\"
.\" Assumes tbl, eqn, MS macros, and lots of luck.
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.EN
.nr LL 40.5P
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.nr FM 6P
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.nr PD 9p
.po 4P

.rs
\v | 5i'
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\v'12P'
\s12PART\ II
\v'4P'
.RT
.ce 0
.sp 1P
.ce 1000
\fBSUPPLEMENTS\ TO\ SECTION\ 1\fR 
.ce 0
.sp 1P
.ce 1000
\fBOF\ THE\ SERIES\ G\ RECOMMENDATIONS\fR 
.ce 0
.sp 1P
.LP
.rs
.sp 28P
.ad r
Blanc
.ad b
.RT
.LP
.bp
.LP
\fBMONTAGE: PAGE PAIRE = PAGE BLANCHE\fR 
.sp 1P
.RT
.LP
.bp
.sp 2P
.LP
\fBSupplement\ No.\ 1\fR 
.RT
.sp 2P
.ce 1000
\fBCALCULATION\ OF\ THE\ STABILITY\ OF\ INTERNATIONAL\ CONNECTIONS\fR  |
\fBESTABLISHED\ IN\fR 
.EF '%	Fascicle\ III.1\ \(em\ Suppl.\ No.\ 1''
.OF '''Fascicle\ III.1\ \(em\ Suppl.\ No.\ 1	%'
.ce 0
.sp 1P
.ce 1000
\fBACCORDANCE\ WITH\ THE\ TRANSMISSION\ AND\ SWITCHING\ PLAN\fR 
.ce 0
.sp 1P
.ce 1000
(Referred to in Recommendation G.131; this Supplement is to be found
.sp 9p
.RT
.ce 0
.sp 1P
.ce 1000
on page 555 of Volume III.2 of the \fIGreen Book\fR , Geneva, 1973)
\v'1P'
.ce 0
.sp 1P
.sp 2P
.LP
\fBSupplement\ No.\ 2\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fBTALKER\ ECHO\ ON\ INTERNATIONAL\ CONNECTIONS\fR 
.EF '%	Fascicle\ III.1\ \(em\ Suppl.\ No.\ 2''
.OF '''Fascicle\ III.1\ \(em\ Suppl.\ No.\ 2	%'
.ce 0
.sp 1P
.ce 1000
\fI(Geneva, 1964; amended at Mar del Plata, 1968 and Geneva, 1976 and\fR 
\fI1980;\fR 
.sp 9p
.RT
.ce 0
.ce 1000
\fIMalaga\(hyTorremolinos, 1984; and Melbourne, 1988;\fR 
.ce 0
.sp 1P
.ce 1000
\fIreferred to in Recommendation\ G.131,\ \(sc\ 2)\fR 
.ce 0
.sp 1P
.PP
\fB1\fR The curves of Figure\ 2/G.131 may be used to determine
whether a given international connection requires an echo control device 
(echo suppressor or echo canceller). Alternatively they may be used to 
find what 
value of nominal overall loss shall be adopted for the 4\(hywire chain of a
complete connection so that an echo control device is not needed. Before the
curves can be used it must be decided what proportion of calls are to be
allowed to exhibit an objectionable echo and Recommendation\ G.131 gives
guidance on this matter.
.sp 1P
.RT
.PP
The coordinates of the graph represent two of the parameters of a telephone 
connection that govern echo, i.e.\ the overall loudness rating (OLR) of 
the echo path and the mean one\(hyway propagation time. By making certain 
assumptions (discussed below) these two parameters become the principal ones.
.PP
Each curve divides the coordinate plane into two portions and the
position, relative to the curve, of the point describing the connection
indicates whether an echo control device is needed, bearing in mind the
percentage of calls permitted to exhibit an objectionable echo.
.RT
.sp 2P
.LP
\fB2\fR 	\fBFactors governing echo\fR 
.sp 1P
.RT
.PP
The principal factors which must be considered in order to describe whether 
an echo control device is needed on a particular connection 
are:
.RT
.LP
	a)
	the number of echo paths;
.LP
	b)
	the time taken by the echo currents to traverse these paths;
.LP
	c)
	the OLRs of the echo path including the subscriber lines;
.LP
	d)
	the tolerance to echo exhibited by subscribers.
.PP
These factors are discussed in turn in the following.
.PP
When circuits are switched together 4\(hywire there is only one echo path, 
assuming negligible go\(hyto\(hyreturn crosstalk. This is also substantially 
true if the circuits are switched together 2\(hywire and good echo return 
losses are achieved at these connection points (e.g.\ a mean value of 27\ 
dB and a standard deviation of 3\ dB). The principal echo currents are 
those due to the relatively poor echo balance return losses at the ends 
of the two extreme 
4\(hywire circuits, where the connection is reduced to 2\(hywire.
.PP
The time taken to traverse the echo path is virtually dependent solely 
on the length of the 4\(hywire connection, because the main circuits of 
modern 
national and international networks are high\(hyvelocity circuits.
.bp
.PP
The OLR of the talker echo path for a symmetrical connection for
planning purposes is approximately given by the sum of:
.RT
.LP
	\(em
	twice the junction loudness rating (JLR) of the connection
between the 2\(hywire point in the talker's local terminal exchange and the
2\(hywire side of the 4\(hywire/2\(hywire terminating set at the
listener's end
.FS
According to Recommendation G.111, \(sc\ A.3.3 the Junction
Loudness Rating of 4\(hywire circuits should be taken as the 800 or 1000\ Hz
loss.
.FE
;
.LP
	\(em
	the echo balance return loss at the listener's end;
.LP
	\(em
	the sum of the sending LR and receiving LR
of the talker's telephone and subscriber line;
.PP
In general, values of sending LR and receiving LR corresponding
to low\(hyloss subscriber lines should be used.
.PP
The echo experienced by subscribers on lines with more loss will be
further attenuated. This is, therefore, a conservative assumption.
.PP
The data on tolerance to echo exhibited by subscribers given in
Table\ 1 are furnished by the American Telephone and Telegraph\ Co. and 
are based on a series of studies completed in 1971. These tests provided 
information on the overall loudness rating (EARS) of the echo path for 
echo, just detectable, as a function of echo\(hypath delay. In addition, 
ratings of quality on a 
five\(hypoint scale (excellent, good, fair, poor, unsatisfactory) were also
obtained. The values in terms of EARS loudness ratings (then used by AT&T) 
were subsequently translated to values of CCITT loudness ratings by adding 
1\ dB. 
Table\ 1 indicates the mean echo path loss for the threshold of detectability
and for ratings of unsatisfactory. These mean values are the loudness rating 
of the echo path for 50% detectability and 50% unsatisfactory. The standard 
deviation is also given.
.RT
.ce
\fBH.T. [T1.2]\fR 
.ce
TABLE\ 1
.ce
\fBResults of echo tolerance tests\fR 
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(60p) | cw(36p) sw(36p) sw(36p) sw(36p) , ^  | c s | c 
^  | c | c | c | c.
 {
One\(hyway propagation time
(ms)
 }	 {
Overall loudness rating of the talker echo path
 }
	Threshold	Unsatisfactory	Mean (dB)	Standard deviation (dB)	Mean (dB)	Standard deviation (dB)
_
.T&
cw(60p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
\ 10	26	\( = 4	\ 9	\( = 6
.T&
cw(60p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
\ 20	35	\( = 4	16	\( = 6
.T&
cw(60p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
\ 30	40	\( = 4	20	\( = 6
.T&
cw(60p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
\ 40	45	\( = 4	23	\( = 6
.T&
cw(60p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
\ 50	50	\( = 4	25	\( = 6
.T&
cw(60p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
\ 75	\ \(em	\( = \(em	29	\( = 6
.T&
cw(60p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
100	\ \(em	\( = \(em	32	\( = 6
.T&
cw(60p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
150	\ \(em	\( = \(em	35	\( = 6
.T&
cw(60p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
200	\ \(em	\( = \(em	37	\( = 6
.T&
cw(60p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
300	\ \(em	\( = \(em	39	\( = 6
_
.TE
.nr PS 9
.RT
.ad r
\fBTABLE 1 [T1.2] p.\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 2P
.LP
\fB3\fR 	\fBConstruction of Figure 2/G.131\fR 
.sp 1P
.RT
.PP
The mean margin against poor or unsatisfactory echo performance is
given by:
\v'6p'
.RT
.sp 1P
.ce 1000
\fIM\fR \ =\ 2\fIT\fR \ +\ \fIB\fR \ \(em\ \fIE\fR \ +\ SLR\ +\ RLR
.ce 0
.sp 1P
.LP
.sp 1
where
.LP
	 \fIT\fR is the mean junction loudness rating of the connection between 
the 2\(hywire point in the talker's local terminal exchange and the 2\(hywire 
side of the 4\(hywire/2\(hywire terminating set at the listener's
end. The loudness rating is assumed to be the same in both directions of
transmission;
.LP
	\fIB\fR 	is the mean echo balance return loss at the listener end;
.LP
	\fIE\fR 	is the mean value of loudness rating of the echo path
required for an opinion rating of unsatisfactory
.FS
This corresponds to
the value of overall loudness rating of the echo path at which 50% of
the opinion ratings are unsatisfactory.
.FE
;
.LP
	SLR
	is the sending loudness rating at the 2\(hywire point in
the originating local exchange for short subscriber lines;
.LP
	RLR
	is the receiving loudness rating at the 2\(hywire point in
the originating local exchange for short subscriber lines.
.sp 2P
.LP
\fB4\fR 	\fBFully analogue connections\fR 
.sp 1P
.RT
.PP
The echo balance return loss is assumed to have a mean value of
not less than 11\ dB, with a standard deviation of 3\ dB expressed as a 
weighted mean\(hypower ratio (see Recommendation\ G.122). The mean value 
of the 
transmission loss is assumed to be uniform over this band and the standard
deviation of transmission loss for each 4\(hywire circuit is assumed to 
be 1\ dB 
for each direction of transmission. The correlation between the variations 
of loss of the two directions of transmission is assumed to be unity. 
.PP
The standard deviation of the margin is given by:
\v'6p'
.RT
.sp 1P
.ce 1000
\fIm\fR \u2\d\ =\ \fIn\fR  | \fIt\fR \u2\d\d1\u\ +\ 2\fIrt\fR\d1\u\fIt\fR\d2\u\ 
+ 
\fIt\fR \u2\d\d2\u)\ +\ \fIb\fR \u2\d\ +\ \fIe\fR \u2\d
.ce 0
.sp 1P
.LP
.sp 1
where
.LP
	\fIm\fR 	is the standard deviation of the margin;
.LP
	\fIt\fR\d1\u,\ \fIt\fR\d2\u	are the standard deviation of the transmission
loss in the two directions of transmission of one 4\(hywire circuit,
national or international;
.LP
	\fIb\fR 	is the standard deviation of echo balance return loss;
.LP
	 \fIe\fR is the standard deviation of the distribution of talker echo 
path loudness ratings required for opinion ratings 
of unsatisfactory;
.LP
	\fIr\fR 	is the correlation factor between\ \fIt\fR\d1\uand\ \fIt\fR\d2\u;
.LP
	\fIn\fR 	is the the number of 4\(hywire circuits in the 4\(hywire chain.
.PP
Inserting \fIt\fR\d1\u\ =\ \fIt\fR\d2\u\ =\ 1\ dB; \fIr\fR \ =\ 1; \fIb\fR 
\ =\ 3\ dB; \fIe\fR \ =\ 6\ dB gives \fIm\fR \u2\d\ =\ (4\fIn\fR \ +\ 45). 
.PP
In Recommendation\ G.131, \(sc\ 2.3, Rules\ A and\ E refer to 1% and 10%
probabilities of encountering unsatisfactory echo and for these cases nine
4\(hywire circuits are assumed (3\ national and 3\ international +\ 3\ 
national). 
For both the 1% and 10% curves therefore \fIm\fR \ =\ 9.0\ dB.
.PP
For 10% probability, the margin may fall to 1.28\ times the standard
deviation. The corresponding factor for the 1% curve is 2.33. Hence the
corresponding values of \fIM\fR \ are:
.RT
.LP
	\fIM\fR \ =\ 1.28\ \(mu\ 9.0\ dB\ =\ 11.5\ dB\ for\ 10%\ probability
.LP
\fIM\fR \ =\ 2.33\ \(mu\ 9.0\ dB\ =\ 21 |  \ dB\ for\ \ 1%\ probability.
.PP
Putting these values into \fIM\fR \ =\ 2\fIT\fR \ +\ \fIB\fR \ \(em\ \fIE\fR 
\ +\ SLR\ +\ RLR 
gives the following values for the mean talker echo attenuation,
2\fIT\fR \ +\ \fIB\fR \ +\ SLR\ +\ RLR:
.LP
	 2\fIT\fR \ +\ \fIB\fR \ +\ SLR\ +\ RLR\ =\ 11.5\ dB\ +\ \fIE\fR for\ 
10%\ probability 
.LP
2\fIT\fR \ +\ \fIB\fR \ +\ SLR\ +\ RLR\ =\ 21 |  \ dB\ +\ \fIE\fR for\ 
\ 1%\ probability. 
.bp
.PP
The values in Table\ 2 have been calculated (to the nearest whole
decibel) using these equations. The figures in the length of connection 
column have been calculated assuming a velocity of propagation of 160\ 
km/ms. 
.ce
\fBH.T. [T2.2]\fR 
.ce
TABLE\ 2
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(60p) | cw(60p) | cw(42p) sw(42p) , ^  | ^  | c | c.
 {
Mean one\(hyway
propagation time
(ms)
 }	Length of connection (km)	 {
Mean loudness rating
of the talker echo path
2\fIT\fR
+ \fIB\fR
+ SLR + RLR
(dB)
 }
		10% unsatisfactory	1% unsatisfactory
_
.T&
cw(60p) | cw(60p) | cw(42p) | cw(42p) .
\ 10	\ 1 | 00	21	30
.T&
cw(60p) | cw(60p) | cw(42p) | cw(42p) .
\ 20	\ 3 | 00	28	37
.T&
cw(60p) | cw(60p) | cw(42p) | cw(42p) .
\ 30	\ 4 | 00	32	41
.T&
cw(60p) | cw(60p) | cw(42p) | cw(42p) .
\ 40	\ 6 | 00	35	47
.T&
cw(60p) | cw(60p) | cw(42p) | cw(42p) .
\ 50	\ 8 | 00	37	46
.T&
cw(60p) | cw(60p) | cw(42p) | cw(42p) .
\ 75	12 | 00	41	50
.T&
cw(60p) | cw(60p) | cw(42p) | cw(42p) .
100	16 | 00	44	53
.T&
cw(60p) | cw(60p) | cw(42p) | cw(42p) .
150	24 | 00	47	56
.T&
cw(60p) | cw(60p) | cw(42p) | cw(42p) .
200	32 | 00	49	58
.T&
cw(60p) | cw(60p) | cw(42p) | cw(42p) .
300	48 | 00	51	60
_
.TE
.nr PS 9
.RT
.ad r
\fBTABLE 2 [T2.2] p.\fR 
.sp 1P
.RT
.ad b
.RT
.PP
The solid last line for \fIn\fR = \fIg\fR in Figure\ 2/G.131 has been
constructed from these values and similar values calculated for other values 
of \fIn\fR (analogue circuits). 
.sp 2P
.LP
\fB5\fR 	\fBFully digital connections with analogue 2\(hywire subscribers\fR 
\fBlines\fR (conform to Figure 2/G.111)
.sp 1P
.RT
.PP
The standard deviation of the margin is given by:
\v'6p'
.RT
.sp 1P
.ce 1000
\fIm\fR \u2\d = \fIn\fR (2\fIt\fR \u2\d
) + \fIb\fR \u2\d +
\fIe\fR \u2\d
.ce 0
.sp 1P
.LP
.sp 1
.LP
where
.LP
	\fIm\fR 	is the standard deviation of the margin;
.LP
	\fIn\fR 	is the number of coder/decoder pairs;
.LP
	 \fIt\fR is the standard deviation of the transmission loss in the two 
directions of transmission; 
.LP
	\fIb\fR 	is the standard deviation of the echo balance return loss;
.LP
	\fIe\fR 	is the standard deviation of the distribution of talker
echo path loudness ratings required for opinion ratings of unsatisfactory.
.PP
The term (2\fIt\fR \u2\d
) represents the loss variance of a coder/decoder pair, where \fIt\fR \ 
=\ 0.2\ dB. For a fully digital connection between 2\(hywire analogue subscribers 
lines there are 2\ coder/decoder pairs (i.e.\ one at the talker's local 
exchange and one at the listener's local exchange). 
.PP
Inserting \fIn\fR = 2, \fIt\fR = 0.2 dB, \fIe\fR = 6 dB and assuming \fIb\fR 
= 3\ dB 
gives \fIm\fR \u2\d = 45.2 and \fIm\fR = 6.7.
.PP
Hence the values of \fIm\fR are:
.RT
.LP
	\fIm\fR = 1.28 \(mu 6.7 dB = 8.6 dB for 10% probability
.LP
\fIm\fR = 2.33 \(mu 6.7 dB = 15.6 dB for 1% probability.
.bp
.PP
Putting these values into \fIM\fR = 2\fIT\fR + \fIB\fR \(em \fIE\fR + SLR + RLR
gives the following values for the mean talker echo path attenuation, 2\fIT\fR 
+ 
\fIB\fR + SLR + RLR:
.LP
	2\fIT\fR + \fIB\fR + SLR + RLR = \ 8.6\ dB + \fIE\fR  | for 10% probability
.LP
2\fIT\fR + \fIB\fR + SLR + RLR = 15.6 dB + \fIE\fR  | for 1% probability.
.PP
The values in Table 3 have been calculated using these equations.
.ce
\fBH.T. [T3.2]\fR 
.ce
TABLE\ 3
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(60p) | cw(60p) sw(60p) , ^  | c | c.
 {
Mean one\(hyway
propagation time
(ms)
 }	 {
Mean loudness rating of the talker echo path
2\fIT\fR
+ \fIB\fR
+ SLR + RLR
 }
	10% unsatisfactory (dB)	1% unsatisfactory (dB)
_
.T&
cw(60p) | cw(60p) | cw(60p) .
\ 10	17.6	24.6
.T&
cw(60p) | cw(60p) | cw(60p) .
\ 20	24.6	31.6
.T&
cw(60p) | cw(60p) | cw(60p) .
\ 30	28.6	35.6
.T&
cw(60p) | cw(60p) | cw(60p) .
\ 40	31.6	38.6
.T&
cw(60p) | cw(60p) | cw(60p) .
\ 50	33.6	40.6
.T&
cw(60p) | cw(60p) | cw(60p) .
\ 75	37.6	44.6
.T&
cw(60p) | cw(60p) | cw(60p) .
100	40.6	47.6
.T&
cw(60p) | cw(60p) | cw(60p) .
150	43.6	50.6
.T&
cw(60p) | cw(60p) | cw(60p) .
200	45.6	52.6
.T&
cw(60p) | cw(60p) | cw(60p) .
300	47.6	54.6
_
.TE
.nr PS 9
.RT
.ad r
\fBTable 3 [T3.2], p.\fR 
.sp 1P
.RT
.ad b
.RT
.PP
.sp 1
The dashed line in Figure 2/G.131 has been constructed from these values 
(fully digital connections). 
.sp 2P
.LP
\fB6\fR 	\fBFully digital connections with digital subscribers lines\fR 
(conform to Recommendation\ G.801)
.sp 1P
.RT
.PP
In this case there are no 2\(hywire points in the connection. However, 
there is an acoustical feed\(hyback path between the earpiece and mouthpiece 
of 
the telephone set. Therefore the echo balance return loss used above is now
represented by the loss of this acoustical path. Representative values 
of this acoustical loss are under wider study. The appendix to this supplement 
gives 
some information on this question.
.PP
It may be assumed that the standard deviation of the transmission loss 
of the coder/decoder pair equals the value given above for digital connections 
with 2\(hywire subscriber lines. The value of the equivalent of \fIT\fR 
should be 
taken as zero. The quantities SLR and RLR now refer to virtual analogue
4\(hywire points of 0\ dBr level.
.PP
If it can be assumed that the standard deviation of the acoustical
echo path loss equals 3\ dB and a normal distribution applies, then the 
values of Table\ 3 also apply to the digital subscriber line case and the 
dashed curve of Figure\ 2/G.131 may be used. 
.RT
.sp 2P
.LP
\fB7\fR 	\fBMixed analogue/digital connections\fR 
.sp 1P
.RT
.PP
This case is a combination of the cases given above and the
appropriate variables and their values should be taken from the above
information and an appropriate table can be constructed.
.PP
In general, if there are only two coder/decoder pairs in the
connection, the variability of the transmission loss of the codecs may be
ignored compared with the variability of the analogue circuits and the other
variabilities. For such connections the solid curve given in Figure\ 2/G.131 
for the number of analogue circuits in the connection may be used with 
good 
accuracy.
.bp
.RT
.ce 1000
APPENDIX\ I
.ce 0
.ce 1000
(to Supplement No. 2)
.sp 9p
.RT
.ce 0
.ce 1000
\fBEcho loss in 4\(hywire telephone sets\fR 
.sp 1P
.RT
.ce 0
.ce 1000
(Contribution by Norway)
.sp 9p
.RT
.ce 0
.LP
	\fIAbstract\fR 
.sp 1P
.RT
.PP
In a 4\(hywire telephone set, echo may arise both by electrical
crosstalk in the cord and by acoustical coupling between earpiece and
mouthpiece in the handset. The echo loss for these paths has been determined
for two analogue 2\(hywire telephone sets. This data is used to derive the echo
loss of a hypothetical 4\(hywire set having SLR\ +\ RLR\ =\ 3\ dB, and 
acoustical 
and electrical properties the same as the 2\(hywire telephone sets.
.RT
.sp 1P
.LP
I.1
	\fIIntroduction\fR 
.sp 9p
.RT
.PP
It has been pointed out in several contributions that the choice of LRs 
for digital telephone sets has to be made considering aspects of loudness 
and echo in a complete 4\(hywire connection. To enable a study of the risk 
of 
objectionable echo, Study Group\ XVI has asked Study Group\ XII to present
information on the subjective effect of talker echo as a function of delay,
overall LR and echo path loss.
.PP
In a digital 4\(hywire connection, including 4\(hywire subscriber lines 
and digital telephone sets, the main echo paths are found in the telephone 
set 
itself:
.RT
.LP
	\(em
	the acoustical coupling between earpiece and mouthpiece of
the handset, and
.LP
	\(em
	the electrical coupling in the flexible cord to the
handset.
.PP
In order to assess the echo performance of a 4\(hywire connection,
the echo loss of the 
digital telephone set
must be estimated.
.PP
As an example of what can be expected, measurements of these echo
paths have been made on two different 
analogue telephone sets
. These
results have been used to derive the echo loss between the receive and send
terminals of a hypothetical 4\(hywire telephone set having SLR\ =\ 6\ dB and
RLR\ =\ \(em3\ dB, and having the same electrical and acoustical properties 
as the 
measured sets.
.RT
.sp 1P
.LP
I.2
	\fIMeasurements\fR 
.sp 9p
.RT
.PP
Figure I\(hy1 shows a set\(hyup for measurement of the loss between the 
receive and send direction in an ordinary 2\(hywire telephone. Two telephone 
sets are used to separate the two directions of transmission. 
.PP
The 
acoustical path
is measured by replacing the 
cord of   the handset
by shielded wires and the electrical path is measured by
replacing the microphone by an appropriate resistor. When measuring the
acoustic coupling
, the handset was placed both in \*Qfree field\*U and held in a normal 
listening position. 
.PP
Two different Norwegian standard telephone sets were included in the measurements. 
Both sets are equipped with linear microphones. EB model 67 has a \*Qconventional\*U 
handset whereas Testafon is a \*Qmodern\*U set. 
.RT
.sp 1P
.LP
I.3
	\fIEcho loss results\fR 
.sp 9p
.RT
.PP
In order to enable comparison of the data obtained for the two
telephone sets, the measurements have been referred to a telephone set 
having SLR\ +\ RLR = 3\ dB. The echo loss, as defined in Recommendation\ 
G.122, 
\(sc\ 2.2, for this hypothetical telephone is shown in Table\ I\(hy1.
.RT
.PP
The acoustical conditions refer to:
.LP
	1)
	the handset held in a normal listening position, tightly
against the ear (\*Qreal ear\*U), and
.LP
	2)
	the handset held in \*Qfree field\*U.
.bp
.LP
.rs
.sp 33P
.ad r
\fBFigura I\(hy1, p.\fR 
.sp 1P
.RT
.ad b
.RT
.ce
\fBH.T. [T4.2]\fR 
.ce
TABLE\ I\(hy1
.ce
\fBEcho loss in dB of hypothetical telephone set\fR 
.ce
\fBhaving SLR + RLR = 3 dB\fR 
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(60p) | cw(30p) sw(30p) | cw(30p) sw(30p) , ^  | c | c | c | c.
Acoustical condition	EB model 67	Tastafon
	Free field	Real ear	Free field	Real ear
_
.T&
lw(60p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
Acoustical path	28.2	31.7	41.5	44.4
.T&
lw(60p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
Electrical path	32.2	32.2	37.0	37.0
_
.TE
.nr PS 9
.RT
.ad r
\fBCuadro I\(hy1 [T4.2], p.\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
I.4
	\fIDiscussion\fR 
.sp 9p
.RT
.PP
It should be noted that high echo loss has not been design
objective for either of the measured telephone sets. The results may therefore 
be considered as representative of what may be obtained when no special 
precautions are taken.
.PP
The echo loss of the acoustical path is apparently highly dependent on 
the physical design of the telephone handset and of the acoustical properties 
of the transducers. A difference of 13\ dB is obtained in Table\ I\(hy1 
between the two sets in the test. The effect of acoustical termination 
of the earphone, 
i.e.\ \*Qfree field\*U or \*Qreal ear\*U, is fairly small, approximately 
3\ dB for both sets. 
.PP
Table I\(hy1 shows that the electrical crosstalk in the flexible cord is 
an important echo source in both sets. For a given \fISLR\fR and \fIRLR\fR 
, the level of crosstalk will depend on the partitioning of the gain between 
the handset 
(i.e.\ the microphone) and the telephone apparatus. Increasing the gain 
in the handset (by increasing the microphone sensitivity or by placing 
the microphone amplifier in the handset) will increase the signal level 
in the cord and 
improve the signal\(hyto\(hycrosstalk level. The crosstalk may also be 
reduced by 
using 
shielded wires
. The electrical echo path may therefore be
eliminated by proper design, and the acoustical component may be considered 
as the lower limit for the echo loss. 
.RT
.LP
.sp 2P
.LP
\fBSupplement\ No.\ 3\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fBEVALUATION\ OF\ ECHO\ CONTROL\ DEVICES\fR 
.EF '%	Fascicle\ III.1\ \(em\ Suppl.\ No.\ 3''
.OF '''Fascicle\ III.1\ \(em\ Suppl.\ No.\ 3	%'
.ce 0
.sp 1P
.ce 1000
(Referred to in Recommendation G.161; this Supplement is to be found
.sp 9p
.RT
.ce 0
.sp 1P
.ce 1000
on page\ 559 of Volume\ III.2 of the \fIGreen Book\fR , Geneva,\ 1973)
.ce 0
.sp 1P
.sp 2P
.LP
\fBSupplement\ No.\ 10\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fBAPPLICATION\ OF\ RECOMMENDATION\ B.4\fR  |
\fBCONCERNING\ THE\ USE\ OF\ DECIBEL\fR 
.EF '%	Fascicle\ III.1\ \(em\ Suppl.\ No.\ 10''
.OF '''Fascicle\ III.1\ \(em\ Suppl.\ No.\ 10	%'
.ce 0
.sp 1P
.ce 1000
(This Supplement is to be found on page 598 of Volume III.2 of
.sp 9p
.RT
.ce 0
.sp 1P
.ce 1000
the \fIGreen Book\fR , Geneva, 1973)
.ce 0
.sp 1P
.sp 2P
.LP
\fBSupplement\ No.\ 20\fR 
.RT
.sp 2P
.ce 1000
\fBPOSSIBLE\ COMBINATIONS\ OF\ BASIC\ TRANSMISSION\ IMPAIRMENTS\fR 
.EF '%	Fascicle\ III.1\ \(em\ Suppl.\ No.\ 20''
.OF '''Fascicle\ III.1\ \(em\ Suppl.\ No.\ 20	%'
.ce 0
.sp 1P
.ce 1000
\fBIN\ HYPOTHETICAL\ REFERENCE\ CONNECTIONS\fR 
.ce 0
.sp 1P
.ce 1000
(Referred to in Recommendation G.103; this Supplement is to be found
.sp 9p
.RT
.ce 0
.LP
on page\ 319 of Fascicle\ III.1 of the \fIRed Book\fR , Geneva,\ 1985)
.bp
.sp 1P
.ce 1000
.ce 0
.sp 1P
.sp 2P
.LP
\fBSupplement\ No.\ 21\fR 
.RT
.sp 2P
.ce 1000
\fBTHE\ USE\ OF\ QUANTIZING\ DISTORTION\ UNITS\ IN\ THE\ PLANNING\fR 
.EF '%	Fascicle\ III.1\ \(em\ Suppl.\ No.\ 21''
.OF '''Fascicle\ III.1\ \(em\ Suppl.\ No.\ 21	%'
.ce 0
.sp 1P
.ce 1000
\fBOF\ INTERNATIONAL\ CONNECTIONS\fR 
.ce 0
.sp 1P
.ce 1000
\fI(Contribution of Bell\(hyNorthern Research)\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.ce 1000
(Referred to in Recommendation G.113; this Supplement is to be found
.sp 9p
.RT
.ce 0
.sp 1P
.ce 1000
on page 326 of Fascicle\ III.1 of the \fIRed Book\fR , Geneva, 1985)
\v'1P'
.ce 0
.sp 1P
.sp 2P
.LP
\fBSupplement\ No.\ 24\fR 
.RT
.sp 2P
.ce 1000
\fBCONSIDERATION\ CONCERNING\ QUANTIZING\ DISTORSION\ UNITS\fR 
.EF '%	Fascicle\ III.1\ \(em\ Suppl.\ No.\ 20''
.OF '''Fascicle\ III.1\ \(em\ Suppl.\ No.\ 20	%'
.ce 0
.sp 1P
.ce 1000
\fBOF\ SOME\ DIGITAL\ DEVICES\ THAT\ PROCESS\ ENCODED\ SIGNALS\fR 
.ce 0
.sp 1P
.ce 1000
(Referred to in Recommendation G.113; this Supplement is to be found
.sp 9p
.RT
.ce 0
.sp 1P
.ce 1000
on page 333 of Fascicle\ III.1 of the \fIRed Book\fR , Geneva, 1985)
\v'1P'
.ce 0
.sp 1P
.sp 2P
.LP
\fBSupplement\ No.\ 25\fR 
.RT
.sp 2P
.ce 1000
\fBGUIDELINES\ FOR\ PLACEMENT\ OF\ MICROPHONES\ AND\ LOUDSPEAKERS\fR 
.EF '%	Fascicle\ III.1\ \(em\ Suppl.\ No.\ 25''
.OF '''Fascicle\ III.1\ \(em\ Suppl.\ No.\ 25	%'
.ce 0
.sp 1P
.ce 1000
\fBIN\ TELEPHONE\ CONFERENCE\ ROOM\fR 
.ce 0
.sp 1P
.ce 1000
(Referred to in Recommendation G.172; this Supplement is to be found
.sp 9p
.RT
.ce 0
.sp 1P
.ce 1000
on page\ 335 of Fascicle\ III.1 of the \fIRed Book\fR , Geneva,\ 1985)
\v'1P'
.ce 0
.sp 1P
.sp 2P
.LP
\fBSupplement No.\ 29\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fBOBJECTIVE\ FOR\ THE\ MIXED\ ANALOGUE/DIGITAL\ CHAIN\ OF | fR \fB4\(hyWIRE\ 
CIRCUITS\fR 
.EF '%	Fascicle\ III.1\ \(em\ Suppl.\ No.\ 29''
.OF '''Fascicle\ III.1\ \(em\ Suppl.\ No.\ 29	%'
.ce 0
.sp 1P
.ce 1000
Draft Recommendation G.136
.sp 9p
.RT
.ce 0
.sp 1P
.PP
(This Supplement is proposed for further study during the present study 
period with the aim to convert the supplement into a Recommendation.) 
.sp 1P
.RT
.sp 2P
.LP
\fB1\fR 	\fBGeneral\fR 
.sp 1P
.RT
.PP
In the period of transition from a fully analogue to a fully
digital network, there will be, on international and national networks, 
mixed type chain of 4\(hywire telephone circuits (see Recommendation\ G.101, 
\(sc\ 4.2), 
some
sections of which can be made with analogue or digital transmission systems.
.bp
.PP
Considering the fact that the transition period may last for a fairly prolonged 
time, and also considering the need for guaranteeing a certain 
quality of transmission on mixed chain of circuits, the CCITT recommends
observance of some principles for the composition of mixed chain of circuits 
as set forth below and some objectives for their parameters. 
.PP
The main principle in the standardization of mixed circuits lies in
the retaining of the standards adopted for the FDM circuits. This would have
resulted in retaining the transmission quality over the 4\(hywire chain 
formed by the international circuits and national extension circuits. 
.PP
For some parameters this can be achieved, but as far as some other
parameters are concerned due to analogue/digital conversions and errors in
digital sections there are some considerable differences in standards and
measuring methods.
.PP
Objectives for some mixed circuit parameters are contained in a number 
of\ G\(hy,\ Q\(hy, and M\(hyseries Recommendations. However, these objectives 
do not take due account of the addition laws for distortions based on the 
multitude of 
mixed circuit structures and specific features of the measuring methods
involved.
.PP
Considering the importance of retaining the transmission quality
during the transition period and attaching great importance to the
standardization of mixed analogue/digital circuits the multitudinous types 
of which emerge while using various kinds of analogue\(hyto\(hydigital 
conversions, 
CCITT thinks it worth while to have a specific Recommendation on objectives 
for mixed analogue/digital circuits and 4\(hywire chains including both 
analogue and digital circuits. 
.PP
The present Recommendation related to mixed 4\(hywire chain of circuits 
and the analogue/digital mixed connections dealt with in this Recommendation 
are those with analogue telephone sets at both ends.
.PP
It is based on the existing Recommendations for FDM channel equipment G.232, 
for PCM channel equipment G.712, for analogue switching centres\ Q.45, 
Q.45 | fIbis\fR , for digital switching centres\ Q.551 to Q.554, and takes 
account of other existing Recommendations of\ G\(hy and M\(hyseries. 
.PP
Later on in accordance with the study results of Question\ 26/XII the present 
Recommendation will have to be supplimented by objectives for mixed 
chain of circuits formed with the help of various methods of
analogue\(hyto\(hydigital conversion such as transmultiplexers
(Recommendations\ G.793,\ G.794), modems (Recommendations\ G.941,\ V.37),
transcoders (Recommendation\ G.761), group codecs (Recommendation\ G.795), 
DCME, as well as connections with a digital telephone at one end and an 
analogue 
telephone at the other end.
.RT
.sp 2P
.LP
\fB2\fR 	\fBStructure of a mixed analogue/digital voice frequence chain of
4\(hywire circuit\fR 
.sp 1P
.RT
.PP
The parameters of a mixed 4\(hywire chain are essentially dependent on 
the number of analogue sections and on the number of analogue/digital 
conversions in the chain.
.PP
According to Recommendation G.103 the total number of 4\(hywire circuits 
in a 4\(hywire chain of the maximum length is\ 12 in exceptional cases 
(Table\ 2/G.101) so that it may be assumed that the number of circuits 
will not exceed\ 12. The worst cases in terms of distortions occur when: 
.RT
.LP
	\(em
	all switching centres are digital, and the circuit sections
from and to the centres are set up on analogue transmission
systems. The number of analogue/digital conversions is then\ 11,
the number of analogue sections is\ 12;
.LP
	\(em
	all switching centres are analogue, and the circuit sections
from and to the centres are set up on digital systems. The
number of analogue/digital conversions is\ 12 in this case, the
number of digital sections is\ 12.
.PP
Such cases are very rare. More representative is considered to be a case 
where the number of analogue/digital conversions makes one half of the 
maximum number (Recommendation\ G.103, Annex\ B), that is\ 6, and digital 
islands are available. The structure of such a 4\(hywire chain is presented 
in Figure\ 1. The number of analogue sections is\ 6, the number of digital 
sections is also\ 6. Other structures of mixed 4\(hywire chain come into 
the picture when connection of the sections is realized without a switching 
equipment. These structures are 
considered in Recommendation\ M.562 (\(sc\ 3.2). The worst case for a circuit 
of 
12\ sections without switching centres occurs when digital and analogue 
sections alternate (see Figure\ 2), the number of analogue\(hydigital conversions 
being 
equal to\ 6, the number of digital sections to\ 6, and the number of analogue
sections also to\ 6.
.bp
.LP
.rs
.sp 6P
.ad r
\fBFigure 1, p.\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 6P
.ad r
\fBFigure 2, p.\fR 
.sp 1P
.RT
.ad b
.RT
.PP
Thus, the examination of various structures of mixed
analogue/digital voice\(hyfrequency chain of circuits shows that for a 
4\(hywire 
chain of maximum length having 12\ sections, it is advisable to establish
objectives of distortions based on 6\ analogue/digital conversions, 6\ 
analogue and 6\ digital sections. 
.PP
Intermediate variants for combinations of analogue, digital sections and 
analogue\(hyto\(hydigital conversions will be: 
.RT
.ce 1000
11 analogue sections + 1 a/d conversion
.ce 0
.sp 1P
.ce 1000
(1 digital section) = 12
.ce 0
.sp 1P
.ce 1000
.ce 0
.sp 1P
.ce 1000
6 analogue sections + 6 a/d conversions
.ce 0
.sp 1P
.ce 1000
(6 digital sections) = 12
.ce 0
.sp 1P
.PP
It should be borne in mind that the chains may most frequently
consist of less than 12\ sections. The contribution of switching centres to
distortion is negligible, if they do not contain analogue/digital conversions.
.sp 2P
.LP
\fB3\fR 	\fBObjectives for parameters of mixed analogue/digital circuits\fR 
.sp 1P
.RT
.PP
3.1
The nominal value of the input/output impedance of the analogue
and digital sections and of a switching equipment should be 600\ ohms.
.sp 9p
.RT
.PP
3.2
Return loss of the input/output impedance referred to the
nominal
value of the analogue and digital sections and of a switching equipment 
should preferably be not less than 20\ dB in the 300\(hy3400\ Hz band. 
.sp 9p
.RT
.PP
\fINote\fR \ \(em\ For a switching centre and channel FDM equipment, the
value of 15\ dB is permissible in the 
300\(hy600\ Hz band (see
Recommendation\ Q.45, \(sc\ 6.3 and Recommendation\ G.232, \(sc\ 7).
.sp 1P
.LP
3.3
	\fIUnbalance loss in respect to earth\fR 
.sp 9p
.RT
.PP
The existing Recommendations for switching centres (Q.45,\ Q.553)
and channel FDM equipment (G.712) standardize the unbalance loss in respect 
to the earth in different ways. There are differences in the measuring 
methods as well. The Recommendation for the FDM\(hychannel equipment (G.232), 
does not 
specify this parameter. The question of standardization and methods of
measuring this parameter for mixed circuits channels is under study.
.bp
.PP
Pending the establishment of unified objectives and measuring methods, 
Recommendation\ K.10 on the unbalance loss of communication equipment should 
be referred to in general guidelines in the case of mixed chain of 4\(hywire 
circuits.
.RT
.sp 1P
.LP
3.4
	\fINominal relative level\fR 
.sp 9p
.RT
.PP
The nominal relative level on the transmit side of each section
(analogue and digital) is \(em14 (\(em16) dBr. The nominal relative level 
on the 
receive side of each section (analogue and digital) is +4 (+7) dBr 
(see
Recommendations \ G.232, \(sc\ 11,\ G.712, \(sc\ 14, Q.45, \(sc\ 3 and 
Q.553 \(sc\ 2.2) 
.PP
The nominal relative level at the virtual analogue switching point
is
.RT
.LP
	\(em
	sending:
	\(em3.5 dBr
.LP
	\(em
	receiving:
	\(em4.0 dBr for analogue
.LP
\(em3.5 dBr for digital
.LP
(See Recommendation G.101, \(sc 5.2.)
.PP
The nominal relative value in a mixed circuit is defined for a
frequency which is not a subharmonic of the sampling frequency. The recommended 
tentative value for the frequency is 1020\ Hz. 
.sp 1P
.LP
3.5
	\fIVariations of transmission loss with time\fR 
.sp 9p
.RT
.PP
The standard deviation of the transmission loss should not exceed   1\ dB.
.PP
The difference between mean and nominal value of the transmission loss 
should not exceed 0.5\ dB. 
.PP
\fINote\fR \ \(em\ The indicated values are defined in Recommendation\ 
G.151, \(sc\ 3 for a fully analogue circuit under the condition that the 
channels are part of a single group equipped with automatic regulation. 
.PP
For mixed chains the stability conditions improve on the one hand
because of the existence of digital sections which have a higher stability
than analogue ones; but on the other hand in the mixed circuits there is no
possibility of a transit automatic regulation of analogue sections, which
deteriorates the overall stability. That is why the indicated values should 
be considered as tentative and are to be confirmed. 
.RT
.sp 1P
.LP
3.6
	\fIAttenuation/frequency distortion\fR 
.sp 9p
.RT
.PP
Attenuation/frequency distortion for the whole 4\(hywire chain should not 
exceed the values given in Figure\ 1/G.132. 
.PP
For mixed chains (without consideration of switching centre
distortions) the accumulation law of attenuation/frequency distortions is
expressed by the following formula:
\v'6p'
.RT
.ad r
.ad b
.RT
.LP
with
.LP
	\fIn\fR\d1\u | 
	number of analogue sections;
.LP
	\fIn\fR\d2\u | 
	number of analogue/digital conversions;
.LP
	a\dF\\dD\u\dM\u | 
	average value (determined
component) of attenuation/frequency distortions of the
analogue sections;
.LP
	\(*s\dF\\dD\u\dM\u | 
	r.m.s. deviation of attenuation/frequency
distortions of analogue sections;
.LP
	\fIa\fR\dP\\dC\\dM\u | 
	attenuation/frequency characteristics of
analogue/digital equipment;
.PP
K = 1, 2 or 3: factor defining the probability of maximum/minimum
value of attenuation/frequency distortions.
.PP
\*QK\*U is usually taken as equal to 3. The justification of the choice
for K\ =\ 3 depending on a given probability can be found in [1,\ 2].
.bp
.PP
\fINote\ 1\fR \ \(em\ Attenuation/frequency characteristics of analogue/digital 
equipment of the same type are similar. That is why, if in a mixed/chain 
of 
circuits analogue/digital equipment of the same type is used, in the sum
formula\ (1)
\v'6p'
.RT
.sp 1P
.ce 1000
@ pile { fIn\fR\d2\uabove~sum above \fIi\fR~=1 } @\fIa\fR\d\fIi\fR\u\dPCM
\u
.ce 0
.sp 1P
.LP
.sp 1
can be replaced by a product \fIn\fR\d2\u\fIa\fR\dP\\dC\\dM\u.
.PP
\fINote\ 2\fR \ \(em\ The analogue\(hydigital equipment distortion limits
recommended in Recommendation\ G.712 
(\(sc\ 1, Figure\ 1) and the FDM\(hychannel
equipment distortion limits recommended in Recommendation\ G.232 
(\(sc\ 1,
Figure\ 1)
meet the limits indicated in Recommendation\ G.132 for mixed circuits in 
which the number of sections does not exceed\ 4. 
.PP
When composing mixed chains with a greater number of sections, it is advisable 
to utilize modern channel equipment the attenuation/frequency 
distortions of which are considerably lower than those indicated in
Recommendations\ G.232 and\ G.712.
.PP
\fINote\ 3\fR \ \(em\ Attenuation/frequency distortions are measured relative 
to the reference frequency of 1020 (1000)\ Hz. 
.PP
\fINote\ 4\fR \ \(em\ See Recommendation Q.45 (\(sc\ 3.4 and\ Q.553) to 
take account of the switching equipment distortions. 
.RT
.sp 1P
.LP
3.7
	\fIGroup delay distortions\fR 
.sp 9p
.RT
.PP
Group delay distortions should not exceed the values indicated in Recommendation\ 
G.133 for the 4\(hywire chain. 
.PP
The law of imposition of group delay distortions is expressed by the following 
formula: 
\v'6p'
.RT
.ad r
.ad b
.RT
.LP
where
.LP
	\fIn\fR\d1\u	the number of analogue sections,
.LP
	\fIn\fR\d2\u	the number of analogue/digital conversions.
.PP
\fINote\ 1\fR \ \(em\ If, in a mixed chain, analogue/digital equipment 
of the same type is used, then the sum 
\v'6p'
.sp 1P
.ce 1000
@ pile { fIn\fR\d2\uabove~sum above \fIi\fR~=1 } @ \(*t\fI\fI\d\fIi\fR\u\dPCM
\u
.ce 0
.sp 1P
.LP
.sp 1
is substituted by a product \fIn\fR\d2\u | (mu | (*t\dP\\dC\\dM\u.
.PP
\fINote\ 2\fR \ \(em\ It is expected that the group delay distortion in 
mixed chains will be less than that of a fully analogue link for any combination 
of analogue and digital sections. But nevertheless the characteristics 
of 
distortion (symmetry) can change considerably. This should be taken into
account when transmitting data on mixed circuits containing group delay
equalizers.
.PP
\fINote\ 3\fR \ \(em\ Group delay distortions are measured with reference to a
frequency situated at the lower band end of the analogue channel,
i.e.\ 190\(hy200\ Hz.
.PP
\fINote\ 4\fR \ \(em\ Switching centre distortions are negligible and can be
ignored.
.bp
.RT
.sp 1P
.LP
3.8
	\fIIntelligible crosstalk\fR 
.sp 9p
.RT
.PP
Near\(hyend and far\(hyend signal\(hyto\(hyintelligible crosstalk ratios
between circuits and between send and receive directions should satisfy
Recommendation\ G.151 (\(sc\ 4).
.PP
\fINote\ 1\fR \ \(em\ It is expected that the values indicated in
Recommendation\ G.151, will be maintained and even better for mixed chains 
for any combination of analogue and digital sections, due to higher values 
achieved in the analogue/digital conversion equipment. 
.PP
\fINote\ 2\fR \ \(em\ Measurement of the signal\(hyto\(hycrosstalk ratio 
between 
circuits can be performed without feeding an auxiliary signal into a channel
affected by crosstalk (unlike that provided for in the note to point\ 11 of
Recommendation\ G.712). This can be explained by the fact that in a mixed
circuit, as a rule, and in an analogue circuit noise will be present at the
input of analogue/digital converters in a mixed chain.
.RT
.sp 1P
.LP
3.9
	\fINon\(hylinear distortions\fR 
.sp 9p
.RT
.PP
The existing Recommendations for analogue circuits (M.1020,
\(sc\ 2.11), for switching equipment 
(Q.45,\ \(sc\ 6.1) and Recommendation\ G.712 for analogue/digital equipment 
contain different specifications for non\(hylinear 
distortions, the methods of their measurement differ too. The Recommendations 
for digital centres (Q.551 to\ Q.554) do not contain specifications for 
non\(hylinear distortions.
.PP
At present it is not possible to recommend permissible values of
non\(hylinear distortions and a method for measuring mixed chains of circuits.
This question needs to be studied.
.RT
.sp 1P
.LP
3.10
	\fINoise (total distortions)\fR 
.sp 9p
.RT
.PP
The notion of noise in mixed chains of circuits due to
analogue\(hyto\(hydigital conversions producing quantization distortions which
accompany the signal has lost its initial meaning and therefore instead 
of the term \*Qnoise\*U applicable to mixed chain of circuits the term 
\*Qtotal distortions\*U is used very often. This is stipulated by the fact 
that the measurement of 
quantization distortions (Recommendation\ Q.132) includes part of non\(hylinear
distortions and single\(hyfrequency interferences.
.PP
From this view point the total distortions in mixed chains include
analogue section noise which depends on the length of the sections in case 
of terrestrial transmission systems and on the quantization distortion 
which are determined by the number and type of analogue\(hyto\(hydigital 
conversions. 
.PP
The addition law of total distortions is expressed by the following
formula:
\v'6p'
.RT
.ce 1000
P = 10 log\d1\\d0\u
@ left { 10\uD\dlF261\u9\d | (mu | ~\dFDM~\u~+~10~\u~0.1 left [ S~\(em~ left ( (S/N) \(em~10~log~\(*y\d2\uqdu right )  right ] \d right } @ 
.ce 0
.ad r
(3)
.ad b
.RT
.LP
.sp 1
.LP
where
.LP
	\(em
	W\dF\\dD\u\dM\u	noise power of analogue sections (pWp0)
.LP
	\(em
	W\dF\\dD\u\dM\u	= W\do\u
@ { Wp0 } over { m } @  L km
.LP
(for a section provided by a satellite the terrestrial length is taken to be
equal to 2500\ km).
.LP
	\(em
	S/N
	signal\(hyto\(hyquantization distortion ratio of one
analogue\(hyto\(hydigital conversion.
.LP
	\(em
	\(*y\d2\u\ qdu
	total number of quantization distortion units
of analogue\(hyto\(hydigital conversions.
.PP
To determine S/N and the total number of qdu's one should
refer to Recommendation\ G.113.
.LP
	\(em
	S 
	signal level at which general distortions are
measured.
.PP
To eliminate any effect of non\(hylinear distortion the value of S
should be no more than \(em10\ dBm0.
.PP
The permissible value of P is to be determined in the studies in
Study Group\ XII.
.PP
The value of \(em36 dBm0 (with S = \(em10 dBm0), i.e.\ signal\(hyto\(hytotal
distortions ratio 26\ dB, can be indicated as a premilinary value.
.bp
.PP
The noise in an idle channel should comply with Recommendations\ G.123 
and\ G.153, \(sc\ 1. 
.PP
\fINote\ 1\fR \ \(em\ Total distortions also include a component determined by
errors in digital sections. It is assumed that if BER at each digital section 
is 10\uD\dlF261\u6\d (with the bit rate of 64\ kbit/s) the respective component 
can be omitted. 
.PP
\fINote\ 2\fR \ \(em\ The values of total distortions for various length of
analogue sections and various numbers of qdu's mixed chains are available in
Tables\ 5/M.580 and\ 6/M.580 of Annex\ A to this Recommendation.
.RT
.sp 1P
.LP
3.11
	\fISingle tone interference\fR 
.sp 9p
.RT
.PP
The level of any single tone signal should not exceed \(em73\ dBm0
(see Recommendation\ G.151, \(sc\ 8). The indicated value does not relate 
to the 
interfering signal at the sampling frequency.
.PP
The level of the interference at the sampling frequency should not
exceed the value of \(em50\ +\ 10\ log \fIn\fR\d2\uwhere\ \fIn\fR\d2\uis 
the number of 
analogue/digital conversions in a mixed circuit. The indicated value is
tentative and needs to be confirmed by study results in Study Group\ XII.
.RT
.sp 1P
.LP
3.12
	\fIProducts of unwanted modulation\fR 
.sp 9p
.RT
.PP
Product levels of unwanted modulation caused by power sources
should not exceed \(em45\ dB (see Recommendation\ G.151, \(sc\ 7).
.RT
.sp 1P
.LP
3.13
	\fIImpulse noise\fR 
.sp 9p
.RT
.PP
Impulse noise is specified for analogue circuits used for data
transmission (Recommendations\ M.1020 and\ M.1025) and for switching equipment
(Recommendation\ Q.45, \(sc\ 5.2 and\ Q.553). For voice\(hyfrequency circuits 
in PCM 
transmission systems the impulsive noise is not specified because it is
supposed that it should not be there at all. In practice, it has been noticed, 
however, that with accumulation of errors, impulse noise can appear in 
a 
voice\(hyfrequency circuit which leads to interference in the transmisison 
of data signals. (Preliminary results on the effect of digital link errors 
on impulse noise in idle PCM voice\(hyfrequency channels is given in\ [4].) 
.PP
The effect of impulsive noise appearing in digital sections on the
overall value of interference in a mixed 4\(hywire chain is subject of study.
.RT
.sp 1P
.LP
3.14
	\fIShort\(hytime interruptions, phase jitter, amplitude and phase hits\fR 
.sp 9p
.RT
.PP
These parameters strongly influence data transmission. For analogue circuits 
they are specified in Recommendations\ M.1020, M.1060 and\ M.910. For 
voice\(hyfrequency circuits set up on PCM systems, objectives are not available. 
It can be tentatively presumed that in mixed chains of circuits the presence 
of digital sections does not have a considerable effect. However, the question 
needs to be studied.
.RT
.sp 1P
.LP
3.15
	\fIError performance\fR 
.sp 9p
.RT
.PP
Further study.
.RT
.sp 2P
.LP
	\fBReferences\fR 
.sp 1P
.RT
.LP
[1]
	 Moskvitin (V. | .): Opredelenije trebovanij k chastotnym kharakteristikam 
zvenjev sostavnykh kanalov i traktov. (Specification of requirements for 
attenuation frequency distortions in sections of composite circuits and 
links). \*QElektroviaz\*U,\ 1969, No.\ 11. 
.LP
[2]
	 Moskvitin (V. | .): Nozmirovanije chastotnykh kharakteristik ostatochnogo 
zatuhanija kanalov. (Frequency distortion objectives for transmission loss.) 
\*QElektrosviaz,\ 1970, No.\ 1.
.LP
[3]
	COM XII\(hy19 (period 1985\(hy1988), USSR Attenuation/frequency distortions
and delay distortions of mixed audiofrequency analogue/digital circuits.
.LP
[4]
	 COM XII\(hy188 (period 1985\(hy1988), USSR Interrelation between errors 
of a digital line and impulse noise in voice\(hyfrequency channels of the 
PCM System. 
.bp
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to draft Recommendation G.136)
.sp 9p
.RT
.ce 0
.ce
\fBH.T. [T1.29]\fR 
.ce
TABLE\ 5/M.580
.ce
\fBSignal\(hyto\(hytotal distortion ratio for public telephone circuit\fR 
.ce
\fBmaintenance\fR 
.ce
\fBusing a test frequency level of \(em10 dBm0\fR 
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(36p) | cw(36p) | cw(30p) | cw(18p) sw(18p) sw(18p) sw(18p) sw(18p) sw(18p) sw(18p) , ^  | ^  | ^  | c | c | c | c | c | c | c.
Type of circuit	Number of QDUs (Note 1)	Unit	 {
Distance in analogue transmission (Note 3)
(km)
 }
			< 320   \ \   \ \ \ 	321  to  640	641  to  1600	1601  to  2500	2501  to  5000	5001  to  10000 	10 | 01  to  20 | 00
_
.T&
lw(36p) | cw(36p) | cw(30p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) .
Analogue	0 |    (Note 2)	dB	45	43	41	39	36	33	30
_
.T&
lw(36p) | cw(36p) | cw(30p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) , ^  | c | c | c | c | c | c | c | c | c 
^  | c | c | c | c | c | c | c | c | c 
^  | c | c | c | c | c | c | c | c | c 
^  | c | c | c | c | c | c | c | c | c 
^  | c | c | c | c | c | c | c | c | c.
Composite circuit	0.5	dB	35	35	34	34	33	31	29
	1 |  	dB	33	33	32	32	31	30	28	2 |  	dB	30	30	30	29	29	28	27	3 |  	dB	28	28	28	28	28	27	26	3.5	dB	27	27	27	27	27	26	26	4 |  	dB	27	27	27	27	26	26	25
.TE
.LP
\fINote\ 1\fR
\ \(em\ The number of QDUs contributed by various processes are given in
Table 1/G.113 [8].
.LP
\fINote\ 2\fR
\ \(em\ The values are idle noise terminated with a nominal impedance
of 600 ?73.
.LP
\fINote\ 3\fR
\ \(em\ The section of the circuit provided by satellite (between
earth stations), employing FDM\ techniques, contributes approximately
10 | 00\ pWp (\(em50\ dBm0p) of noise. Therefore, for the purpose of
determining the total distortion limits for international public
telephony circuits, the length of this section may be
considered, from Table\ 4/M.580, to be equivalent
to\ 2500\ km.
.nr PS 9
.RT
.ad r
\fBTable 5/M.580 [T1.29], p.\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 14P
.ad r
Blanc
.ad b
.RT
.LP
.bp
.ce
\fBH.T. [T2.29]\fR 
.ce
TABLE\ 6/M.580
.ce
\fBSignal\(hyto\(hytotal distortion ratio for public telephone circuit\fR 
.ce
\fBmaintenance\fR 
.ce
\fBusing a test frequency level of \(em25 dBm0\fR 
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(36p) | cw(36p) | cw(30p) | cw(18p) sw(18p) sw(18p) sw(18p) sw(18p) sw(18p) sw(18p) , ^  | ^  | ^  | c | c | c | c | c | c | c.
Type of circuit	Number of QDUs (Note 1)	Unit	 {
Distance in analogue transmission (Note 3)
(km)
 }
			< 320   \ \   \ \ \ 	321  to  640	641  to  1600	1601  to  2500	2501  to  5000	5001  to  10000 	10 | 01  to  20 | 00
_
.T&
lw(36p) | cw(36p) | cw(30p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) .
Analogue	0 |    (Note 2)	dB	30	28	26	24	21	18	15
_
.T&
lw(36p) | cw(36p) | cw(30p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) , ^  | c | c | c | c | c | c | c | c | c 
^  | c | c | c | c | c | c | c | c | c 
^  | c | c | c | c | c | c | c | c | c 
^  | c | c | c | c | c | c | c | c | c 
^  | c | c | c | c | c | c | c | c | c.
Composite circuit	0.5	dB	29	27	26	24	21	18	15
	1 |  	dB	28	27	25	23	21	18	15	2 |  	dB	27	26	25	23	20	18	15	3 |  	dB	26	25	24	23	20	18	15	3.5	dB	26	25	24	22	20	18	15	4 |  	dB	25	24	23	22	20	17	15
.TE
.LP
\fINote\ 1\fR
\ \(em\ The number of QDUs contributed by various processes are given in
Table 1/G.113 [8].
.LP
\fINote\ 2\fR
\ \(em\ The values are idle noise terminated with a nominal impedance
of 600 ?73.
.LP
\fINote\ 3\fR
\ \(em\ The section of the circuit provided by satellite (between
earth stations), employing FDM\ techniques, contributes approximately
10 | 00\ pWp (\(em50\ dBm0p) of noise. Therefore, for the purpose of
determining the total distortion limits for international public
telephony circuits, the length of this section may be
considered, from Table\ 4/M.580, to be equivalent
to\ 2500\ km.
.nr PS 9
.RT
.ad r
\fBTable 6/M.580 [T2.29], p.\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.sp 2
.ce 1000
ANNEX\ B
.ce 0
.ce 1000
(to draft Recommendation G.136)
.sp 9p
.RT
.ce 0
.sp 2P
.LP
SOURCE:
	THE URSS TELECOMMUNICATION ADMINISTRATION
	TITLE:
	 INTERRELATION BETWEEN ERRORS IN A DIGITAL CIRCUIT AND IMPULSE NOISE IN 
VOICE\(hyFREQUENCY CHANNELS OF THE PCM SYSTEM 
.sp 1P
.RT
.sp 1P
.ce 1000
.sp 1P
.RT
.ce 0
.sp 1P
.LP
B.1
	\fIIntroduction\fR 
.sp 1P
.RT
.PP
Voice\(hyfrequency channels of PCM as well as FDM systems should be
fit for transmitting various types of signals. It is well known that the
transmission quality of discrete signals in voice\(hyfrequency channels is
affected by impulse noise. At present, Recommendation\ G.712 has no requirements 
to voice\(hyfrequency PCM\(hychannels regarding impulse noise. However, 
under 
real\(hylife conditions in a voice\(hyfrequency PCM channel impulse noise
contributes to the error\(hyrate of digital links. The present contribution 
gives the investigation results of impulse noise in voice\(hyfrequency 
PCM\(hychannels.
.bp
.RT
.sp 1P
.LP
B.2
	\fIInfluence of digital circuit errors on impulse noise in an idle\fR 
\fIvoice\(hyfrequency PCM channel\fR 
.sp 9p
.RT
.PP
Evaluation of error influence on digital links on the value of
impulse noise in voice\(hyfrequency channels was conducted experimentally on a
channel equipment (satisfying Recommendation\ G.712) of a PCM transmission
system (2048\ kbit/s). With the help of an error simulator errors had been
introduced into one or several bits corresponding to a chosen idle
voice\(hyfrequency channel of a digital link (Figure\ 1). In the voice\(hyfrequency 
channel impulse noise could be observed with the help of an oscillograph. 
The shape of the pulse response in the voice\(hyfrequency channel is presented 
in 
Figure\ B\(hy2.
.RT
.LP
.rs
.sp 16P
.ad r
\fBFigure B\(hy1, p.\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 24P
.ad r
\fBFigure B\(hy2, p.\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
The parameters of pulse response are given in Table 1 (the values are chosen 
for the point of the relative zero level at a resistance of 
600\ ohms). These data allow us to formulate the following conclusions:
.LP
	\(em
	The pulse amplitude of the response depends on the bit number
which contains the error; the errors in the more significant
bits cause a greater amplitude of the response.
.LP
	\(em
	With single errors the maximum value of the pulse
peak\ \fIA\fR\d1\u(in case of an error in the second bit) is
\(em22.1\ dBm0.
.LP
	\(em
	With burst\(hybuilding and with an increase in the number of
errored bits in the code word of the prime digital path
(2048\ kbit/s) the response amplitude values\ \fIA\fR\d1\u,
\fIA\fR\d2\u,\ \fIA\fR\d3\u, . |  |  grow, but their duration, as determined
by the response of the channel's low frequency receiving filter,
remains unchanged. This applies to the cases where in a prime
digital path, the error bursts affect the digital stream for not
more than one discretization period, i.e.\ the number of the
errors in a burst does not exceed\ 256. With errors in code words
occurring every 125\ \(*ms the superposition of responses takes
place as a result of the receiving filter reaction on the error
pulses in each following discretization period.
.ce
\fBH.T. [T3.29]\fR 
.ce
TABLE\ B\(hy1
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(66p) | cw(30p) sw(30p) sw(30p) | cw(24p) sw(24p) sw(24p) , ^  | c | c | c | ^ | ^ | ^ , ^  | c | c | c | c | c | c 
^  | ^  | ^  | ^  | c | c | c.
 {
Errored bits in a frame of
primary multiplex
 }	Amplitude of pulse response	Duration of pulse response
	\fIA\fR 1	\fIA\fR 2	\fIA\fR 3
	dBm0	dBm0	dBm0	\fIt\fR 1	\fIt\fR 2	\fIt\fR 3	\(*ms	\(*ms	\(*ms
_
.T&
lw(66p) | cw(30p) | cw(30p) | cw(30p) | cw(24p) | cw(24p) | cw(24p) .
2	\(em22.1	\(em28.2	\(em33.8	\ 320	160	130
.T&
lw(66p) | cw(30p) | cw(30p) | cw(30p) | cw(24p) | cw(24p) | cw(24p) .
3	\(em34.1	\(em40.2	\(em45.8	\ 320	160	130
.T&
lw(66p) | cw(30p) | cw(30p) | cw(30p) | cw(24p) | cw(24p) | cw(24p) .
2 and 3	\(em10.1	\(em16.2	\(em21.8	\ 320	160	130
.T&
lw(66p) | cw(30p) | cw(30p) | cw(30p) | cw(24p) | cw(24p) | cw(24p) .
2 and 3 and 4  from 2 to 8,	\(em4.1	\(em10.2	\(em15.8	\ 320	160	130
.T&
lw(66p) | cw(30p) | cw(30p) | cw(30p) | cw(24p) | cw(24p) | cw(24p) .
 {
2 discretization periods
from 2 to 8,
 }	+4.3	\(em6.7	\(em14.8	\ 440	180	100
.T&
lw(66p) | cw(30p) | cw(30p) | cw(30p) | cw(24p) | cw(24p) | cw(24p) .
 {
3 discretization periods
from 2 to 8,
 }	+4.3	\(em4.9	\(em14.8	\ 600	200	100
.T&
lw(66p) | cw(30p) | cw(30p) | cw(30p) | cw(24p) | cw(24p) | cw(24p) .
 {
4 discretization periods
from 2 to 8,
 }	+4.3	\(em4.7	\(em14.8	\ 680	180	120
.T&
lw(66p) | cw(30p) | cw(30p) | cw(30p) | cw(24p) | cw(24p) | cw(24p) .
 {
5 discretization periods
from 2 to 8,
 }	+4.3	\(em6.7	\(em14.8	\ 840	200	120
.T&
lw(66p) | cw(30p) | cw(30p) | cw(30p) | cw(24p) | cw(24p) | cw(24p) .
 {
6 discretization periods
from 2 to 8,
 }	+3.8	\(em4.3	\(em14.8	\ 930	200	100
.T&
lw(66p) | cw(30p) | cw(30p) | cw(30p) | cw(24p) | cw(24p) | cw(24p) .
7 discretization periods	+5.25	\(em8.7	\(em14.8	1100	180	140
_
.TE
.nr PS 9
.RT
.ad r
\fBTable B\(hy1 [T3.29], p.\fR 
.sp 1P
.RT
.ad b
.RT
.PP
.sp 2
Thus, when errors, on a 2048\ kbit/s digital path grow into burst of 2\ 
errors and more there is a certain probability that the value of the 
impulse noise in a PCM voice\(hyfrequency channel exceeds \(em21\ dBm0 given in
Recommendation\ M.1020, \(sc\ 2.6.
.PP
With error bursts of 256 and more bits the above\(hymentioned impulse
noise will always be present.
.PP
The quantitative relationship between the number of bursts, the number 
of errors in them within a definite time interval and the number of impulse 
noise interferences and the BER in a voice\(hyfrequency channel is under 
study at present. 
.bp
.RT
.sp 2P
.LP
\fBSupplement No.\ 30\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fBTRANSMISSION\ PLAN\ ASPECTS\ OF\ LAND\ MOBILE\ TELEPHONY\ NETWORKS\fR 
.EF '%	Fascicle\ III.1\ \(em\ Suppl.\ No.\ 30''
.OF '''Fascicle\ III.1\ \(em\ Suppl.\ No.\ 30	%'
.ce 0
.sp 1P
.ce 1000
Draft Recommendation G.173
.sp 9p
.RT
.ce 0
.sp 1P
.PP
(This Supplement is proposed for study during the present study
period with the aim to convert it into a Recommendation.)
.sp 1P
.RT
.sp 2P
.LP
\fB1\fR 	\fBGeneral\fR 
.sp 1P
.RT
.PP
This Recommendation is primarily concerned with the special
planning aspects which pertain to analogue or digital land mobile systems. 
Such systems, due to technical or economic factors, will prevent a full 
compliance with the general characteristics of international telephone 
connections and 
circuits recommended by CCITT.
.PP
The scope of this Recommendation is thus to give guidelines and advice 
to Administrations as to what kind of precautions, measures and minimum 
requirements which are needed for a successful incorporation of such networks 
in the national PSTN. 
.PP
The performance objectives of such systems may vary between different groups 
of customers. For normal customers the objective should be to reach a 
quality as close as possible to CCITT standards. For other groups of very
disciplines customers other performance objectives might be acceptable.
.RT
.sp 2P
.LP
\fB2\fR 	\fBNetwork configurations\fR 
.sp 1P
.RT
.PP
Under study.
.PP
Under this headline Administrations should be advised to use 4\(hywire
transmission to avoid problems when accessing inherently 4\(hywire mobile
links.
.RT
.sp 2P
.LP
\fB3\fR 	\fBNominal transmission loss of mobile links\fR 
.sp 1P
.RT
.PP
Under study.
.PP
Under this headline the problems with the application of loudness
ratings and the correct loading of the radio channels should be discussed.
.PP
The recommended LR values in CCITT Recommendation G.121 are not
directly applicable due to the fact that the background noise level is 
higher in a car than what is assumed in Recommendation\ G.121. 
.PP
What is the design objective for the speech levels from the radio path 
and what levels should be delivered to the network? 
.RT
.sp 2P
.LP
\fB4\fR 	\fBStability\fR 
.sp 1P
.RT
.PP
Under study.
.RT
.sp 2P
.LP
\fB5\fR 	\fBEcho\fR 
.sp 1P
.RT
.PP
Under study.
.PP
Under this headline the need for echo control devices should be
discussed.
.RT
.sp 2P
.LP
\fB6\fR 	\fBNoise\fR 
.sp 1P
.RT
.PP
Under study.
.PP
(Can the European group give indications of the inherent noise
performance of the codec algorithms being considered?)
.bp
.RT
.sp 2P
.LP
\fB7\fR 	\fBDelay\fR 
.sp 1P
.RT
.PP
Under study.
.RT
.sp 2P
.LP
\fB8\fR 	\fBEffects of errors in digital systems\fR 
.sp 1P
.RT
.PP
Several coding methods, such as SBC, ATC, RELP and APC\(hyAB with
transmission bit rates 16\ kbit/s have been proposed to achieve spectrum
utilization efficiency and quality comparable with conventional analog 
FM
systems. However, the application of such highly efficient speech coding
methods to land mobile radio can lead to a significant degradation in quality 
because of transmission errors. 
.PP
Mobile radio links are not always error\(hyfree. Burst errors occur
frequently due to multipath fading. It has been reported that the average 
bit error rate (BER) performance of diversity reception is\ 10\uD\dlF261\u2\d\(hy10\uD\dlF261\u4\d 
in the 
10 to 20\ dB range of the average carrier to noise power ratio (CNR), and 
burst error length reaches 20\ to 100\ bits in case of 16\ kbit/s digital 
signal transmissions. Therefore, robustness against burst error is an important 
characteristic for speech coding applied to mobile communication. Speech 
CODECs in mobile radio links should involve error control techniques so 
as to provide robustness in multipath fading channels. Thus, the transmission 
bit rate 
includes redundancy bits for error control.
.PP
Concerning quality evaluations, it may be better to use the average
CNR as the receiving level for comparisons among analogue and digital systems. 
This is because it can present the receiving level as a normalized unit 
for 
both analog FM and digital systems. In quality evaluations between digital
systems, the average signal energy per bit to noise power density
ratio (\fIE\fR\d\fIb\fR\u/\fIN\fR\d\fIo\fR\u) is suitable for the presentation 
of the 
receiving level. This is because it can describe the receiving level as a
normalized unit for any transmission bit rate and receiving bandwidth.
.RT
.sp 2P
.LP
\fB9\fR 	\fBQuantizing distortion\fR 
.sp 1P
.RT
.PP
Under study.
.RT
.sp 2P
.LP
\fB10\fR \fBEffect of transmission impairments on voiceband data performance\fR 
.sp 1P
.RT
.PP
Under study.
.RT
.LP
.rs
.sp 21P
.ad r
Blanc
.ad b
.RT
.LP
.bp