Note: Descriptions are shown in the official language in which they were submitted.
-/, . . 2 1 78~52
~GR 93 P 1855 P
~'LE, P~' Tr ~ ~. J~-
Foreign version T~:3 T~ r,:_
DQscription
Monitoring optical bLua~ d service cahles up to a
passive interfacs
In accordance with CCITT, an optical B-ISDN
subscriber line is u6ually realized such that at the end
of that part of the optic~l subscriber line for which the
n~twork provider i8 r~p~n~hle, that i~ to say at the
80-Ca11ed IJB interface, the optical li~e i8 ter~inated by
13 means of a so-called network termination (N~l) (CCITT
~c. I.432).
This NTl network ter ination oompriaes optoelec-
tric and alectrooptic transducsrs, correctly t~inAt^~
th~ subscriber lin~ with r~gard to operation, administra-
tion and .^-~nt-~n,n. e (OAM) and ~akea available in the
direction towards the subscriber a standardized
bidirectional broadband interface, the so-aalled TB
interfacQ, also termed the user-network interface (~NI).
The ~ignals in the two transmiasion directions have a
gross baud rate of 155.52 Nbit/s in each case both at the
~xchange end of the line t~;nAt ~ ~n NTl (at the ~rB
interfac-) and on the 3ubscriber sidQ (at the TB inter-
fac~), and comprise either a seguence of bytswise fra~es
in accordance with the ~irst stage STMl (STM T Synchron-
OU8 Transport Module) o~ the so-called synchronous
digital hierarchy (SD~:), in whose in~ormation-carrying
part so-call~d ATM cslls (~x. 149.76 ~bit/s) are trans-
mitted with a 53 byte length each (ATM Asynchronous
Transfer ~ode), or colq?rise a pure se5~uence o_ ATM cells,
~0 the cell data rats useful for information transmi3sion
likewise b~ins 149 . 76 ~bit/s .
Since the NTl line tsrmination is relatively
complex and reguire~ space, electric power and relatively
expensivQ ~lc~ ytic and optoelectric tr~n~ D~s~
pos~ibly Qven battery
_ _
2 ~ 7 8 9~2
GR 93 P 1855 P - 2 -
back-up, in order to bridge failures in th- utility grid,
proposals have b-en made in thQ CCITT and ETSI to realize
optical B-ISDN subscriber lines by means of a so-called
"pas~ive NTl", that i8 to say in essence to provide
5 simply an optical connector at the t~l e~ tions
interfac~ between th~ network provider and user, up to
which the network provider has the r^~F~In~h; 1 ~ ty for
acceptable functioning (CCITT COM XVIII No. D.928, D.lll9
and D.1144; ETSI NA5 No. TD90/96; ETSI TM3 No.
1 0 ( I ' _ "_d) ) .
A similar sltuation exists in the TJSA, wher~ by
contra~t with the conditions ih 3urope and Japar~ and to
the relevant ETSI rs~ Atiora and CCITT re~
tiohs the interfac- between the network provider and user
15 is not the T~ interface but the ~3 interface; the NTl
line ter~ination i8 thus - ,let~ly in the po9~ a~r~n of
the cohnected subscriber. There are proposals similar to
those for the npassiYe NTl~ in the USA, it being assumed
that ah optical bus structur~ having taps (a so-called
20 "daisy chainn) is cornected on the subscrib~r side, which
per_its the simpl~ realization of LANs (I,ocal Area
~T~
In each case, the subscriber ter~nination must now
b~A p~-nDntly _onitored auto_atically with regard to its
25 acceptAble functioning; in modern ~ ~ ~tion retworks,
comprehensive, as far a~ possihle Cully automatic perma-
n~ent _onitoring is a mandatorY requirenent of the network
proYiders. In the case of cos~nection con~igurations which
contaih ~ true NTl l~ne termi~ation in the area of
30 respohsibility of the network proYider, this is pcssihle
in a comprehensive fashion which is r~latively without
problems, since it is poss;hle ih the so-called ~ v~ '
o~E the B-ISDN signal (in bytes, provided for the purpose,
in the STM-l frame or, in the casu of cell tr~n~ aion~
35 in O~M c~lls provided for the purpose) to transmit
c~nt;n~o~ly a plenitude of relevant ite_s of OAM inform-
ation in both directions betweeh the NTl line ter ination
and the ~h~ or an appropriate bL~-lL.qnd subscriber
li3e u:lit at the 3~twork end~
ANENDED S~EET
21 78952
¢R 93 P 1~55 P - 3 -
and since lt 1B p~pa~hle to for~ suit b~e electric,
cptical or aS least logic loops betwoen the outsoin~ and
return dlrections ln the N'rl lin~ t~ n-tlnn .
9y contr~st, given r^np^n~Thillty of th- network
5 providcr only for th~ optlcal subscriber line auto2~atlc
p~-n~nt ~onitorl~g of thlg optlcal 8~ 'h^ llne i3
no longer directly poE3;hle, even if the subscrlber
pos6esses an NTl line ter~in~tlon wlth which the network
provider could in princlple ~ t~ in th~ way
10 described above. Sp~n;f;~ ly, the line t~n~t~nn can,
for exa~nple, have been swltc~ed off by the subscriber,
acd it is then no longer directly po~o;hle for the
networ~c provider to ~stabli3h whether there is a ~alfunc-
tion ln hls own ar~a of renpnnRih; l; ty, for example
15 becau3e an e~ccavator has damaged the optlcal ~ubscriber
llne, or whether the fault is ln the area o~ r~Rpnno;h;l-
lty of the subscr~ber. Sinc~, on the other hand, the
~bscriber i8 generally by no means t~hnir~lly capable
of judging wheth~r it is the sectlcn of the broadband
20 line in his po~se~o;nn that has falled, or the sectlon at
t_e srid end, a plenltude of possibly uTl~ustified co~-
plaints c n ari3e, ~d the neSwork provider ust then
establi_h by ~eans of relatively expensive neasures
whether he is hiTn3elf re3ponsible for the trouble and has
25 to renove the latter, or whether the reTno~ral of the
troubl~ is the r~RpnnR;h;~ity of the sub_criber.
It ~aa therefor~ proved to be desirable to be
able to nTonltor automatically whether trouble or inter-
ruptions occur on optical 3ubscriber line3 in the area of
30 responR;hll; ty of the network provider.
There is already known for this purpose a method
for ~onitoring the 3ectlon, situated between an OWG line
unit, in particular the subscriber line unit at the
exchange end, and a defined passive optic~l interfac-,
A.~3ND3D S~EET
2 ~ 78952
GR 93 P 1855 P - 4 ~
of an optical broad'oant service cable, in p~lrticular a
broadbaTld gubscriber lin~, to th~ effect t~at a siru-
soidal pilot audio signal of le88er amplitude and having
a r.~u~i~ which i8 situated outside t_e spectral regio~
5 oc~ ri^~T by the infor3ation oignal to be transmittsd Ls
added in thg OWG line u~it to th~ ~lectric drive signal
of the optical trsnsmitter ~rovided th^r^, at the passive
interfac~ ~ small ~ t of th~ optical aigr~al traTls-
mitted ~ro~s t_~ lTn- unit to the subgcriber l8 h~ ar~.h^~7
10 cfC, poasibly ~y refl-^-ction c~used ~ o-~ T~y by mesrs
of an optical ~^ t~hl-~ conn-ction provided ~t the
passive int~rfac~, ~d led bac~c in the ravers~ directior~
to th~^ line u~it whero it is convertDd, in the optical
rGceiver provided t~ers, ~ose~ h~r with the optical sig al
15 received from the subscriber i to an ~l~ctric aignal, and
the pilot audio ~ig~al ~o~t~ ^d t~erein ia branched off
wit~ the ~id of a fre~ency-~iGlGctive filt3r and ~as it~
a~litud~ aubjGctsd to a ~irgl~ tage. or multistage
t_reshold valuG ~ whos^ r~sult for~ ~ measur~ of
20 the quality of the optical aGrvic^ cabl~ between the line
unit ard passive int~rfac..; in this case, th~ ~nfo~-ti~
~ignal of or~e t-?~ ti~ direction which is to be
transs~itted car. be carrier-bor e ~lectrically before the
modulatio:~ of the optical transmitt-^r in JUch ~ way that
25 it i8 convGrtet irto a sp~ctral r_gion not occ~ri^; by
the b~n^T~ i irfor~ation . ig al of t_e opposite direc-
tion, and a pilot audio signal having a r . ~l.G~-.;y situ-
ated outside t~e two spectral regions of thc irfor~atiou
~;g~als can be tran~Tmitted (EP 93113290 6)
Furl h. Gt ~or the purpose of ~onitorirg an
optical ~road~ard aervice cable it is 3~nown to proceed in
such ~ way t~at
- an optical downstr~aTs sig~al formed from an inforsation
signal to ~e transmitted in the downstraam dirGction over
the optical broadba~d ~er~ice cable and a nitoring
tiignal in the for~s of a p~eudo-noise binary ~ignal ~ 8
transmitted ~ro~s an OWG lin~ unit,
A~DED 5~2
21 78952
GR 93 P 1855 P 5/1
- , ~nto, reflected at F-F-;hle reflection pointa of
the optical bL~ '' ' servic~ cable, of the optical
downstream signal are transmitted baclc in the upstrean
direction to the OWG line unlt and converted i~to an
e~lectrlc signal ln the optic^l receiver, provided there,
together with a~ optical ~sLLGeu~l signal received oYer
the optical broadband servicG cable,
- and the reflected monitoring signal, contai~ed therein,
is evaluated by virtue of the fact that the said Qlectric
signal and the pseudo-noise binary signal, which is
dGlayed by a delay time period which co~ ~ c~.,LLds to the
signal propagation tine on the ~. ~ a~d service cable
between the OWG line unit and reflection point out to and
back again, are f ed to a signal correlator, having a
~ultiplier with a downstrea~ integrator, whose output
signal anplitude demonstrat~s correctly in terms of
signal propagation time the oc.-L G ce of a reflected
pseudo-noise bin~ry sicnal f _ ' t (WO92/11710; further
~in Optical Time Domain Reflectometers (OTDR)
WO87/07014; l;!r~ CS L3TT~RS 16(1980)16, 629).
In this case, the test code pulse sequence
re~auired at the transmitting end can be generated by a
first pseudo-noise binary signal generator, and the same
code pulsc secuence can be generated, but shi~ted in
ti7re, by a second pseudo-noise bi~ary aignal generator
operating syTlchronously, the tine shift being effected by
a control device to which there are applied the cloc3c
signal of the first pseudo-noise binary signal generator
and a franing signal irdicating to it the he5;nn;T~ of
each test code pul~e secuence, and which, for its part,
synchronizes the second pseudo-noise binary signal
generator in accordance with the desired tine shift input
into it from a PC (WO-92-11710), the time shift being
effect~d by a ti~e-delay unit which is situated betweer,
the second pseudo-nois~ binary signal generator and the
first psGudo-noise binary signal generator (W087/07014),
AMENDE D SiIEET
2l 7~952
GR 93 P 1855 P 5~2
or the time shift being effected by a time-delay unit vJa
which a synchronous 08cillator directly driving the first
pseudo-noiae binary ~ign~l generator drives the second
pseudo-noise binary signal generator in a cG-~a~- ~;n~ly
delayed fashion (Rr.r--- LElTERS 16 (1980) 16, 629).
~owever, it is rel~tively ~xpensive to producc
thc required time shif t by a PC-controlled synchronous
control device or by a controllable ti3e-delay unit, and
the invention de20nstrates, by contrast, a way of reduc-
ing thia cost.
The invention rslatea to a :lethod for 30nitoring
the section of an optical broadband service cablQ, in
particular ~ broadband sub8criber line, situ~ted betwecn
a~ OWG line unit, in particular a sUb3criber line unit at
the exchange end and a defined passivc optical interface,
to the effect that
- an optical down3tream signal for2ed from an infor~ation
signal, to be transmitted in the ~'- L~c~ direction
over the optical broadband service cablc, and a pseudo-
noise binary signal i8 transmitted from the OWG line
U~Lit,
- a small ~ -nt of the optical downstre~m signal is
trans2itted from the passiv~ optlcal intcrface in the
upstre~ direction back to the OWG line unit, where it is
converted into an electric signal in the optical receiver
provided ther~ together with ~ _~nn~nts, possibly
reflected at other reflection points of the optical
broadba~d service cable, of the optical downstrea3 signal
and with ~n optical upstrea2 aignal received via the
3 0 optical broadband service cable,
- and the r~flected 20nitoring 8ignal cnnt~ne<? therein
is evaluated with regard to it~ reflection at the ~assive
optical i~terfacc by providing that the s~id electric
.aM3NDED S}~EET
2 1 789~2
GR 93 P 1855 P 5/3
signal ~d the pseudo-noi8e binary signal, which i~
delayed by a delay time period which cv ..~.~v~d~ to the
sig~al propagation tim~ on the broadband service cable
from the OWG line unit to the p~ssive optical int~rface
5 a~ld back again, ~r~ fed to a ~ignal correlator which as
a multiplier with ~ downatream integrator and whose
output signal amplitud~ is monitored correctly in ter~ns
of signal propagation time for the oC.~,L~,. ce of th~
p~eudo-noi~e binary signal _ _ - t reflected from th~
10 pas8ive optical interface; this method is characterized
according to the invention in that the pseudo-noise
binary signal r~quired at th- transriitting end and the
time-delayed pseudo-nois~ binary signal to b~ fed to th~
correlator are generated by two separata pseudo-nois~
15 generators having CO~L~ 1ln~1Y differing starting
values .
The i~vention is attended by t~e advantag~ of
being able to set the desired delay time dir~ctly by
means of al!~Lv~Llately differing prs~etting of t~e two
20 ps~udo-noise generators [generally to bR formed a~ llhift
register chains closed to produce a ring in each case~
with the aid o~ ~ microproc~ssor, which is to be provided
in any case for the purpose of further processing the
corr~lator output signal (integration r~sult), w~thout
25 ther~ being a need ~or a ~upplementary control unit or
time-delay unit; it thus renders it pos~ible in the case
of the monitoring of an optical broadbard service cable
up to a passive interface, the reflection of which i8
utilized, to combat ln a cost-saving way ~
30 caused by additional reflections at other points on the
optical service cahle to be ~onitored, or co~Lplications
in the evaluation of the desired reflection, and thus
r~nders possible in an advantageous way simple ~nd
reli~ble nitoring of the optical broadband service
35 cabl~ between the OWG line unit at the excha~gQ e~d and
th~ defined passive optlcal interfac~, which may delimit
th~ area of resp~n~hility of the networlc provider. The
A25ENDED S~T
_ _ _ . _
-
2 1 789~2
GR 93 P 1855 P - 6 -
line unit at th~ exchange end can in thi~ c/Lse ~180 be
remote from th~ ~ctual exchang~, and lil~w~5~ ther~ iJ no
n~ed for tho pa~JiV~ optical interf~c~ to be provlded
directly uJ~_L~ ~ of a subscriber~ statlon.
In order to tran~mit the blnary pseudo-noise
r~ndo~ signal, it is po~ih~ ~ in a further ~ t of
the invention for the biasing current of a laser dlod~
provided a8 optical transr~itter in the OWG ll~e unit to
be ~pliLud~ ted with th~ binary pseudo-noiso
r~ndom ~lgnal. AJ ~n alternative to this, it ia ~L180
posslble for the binary p8eudo-noise rando~ signal to be
superimposed additively ~n the OWG line unit to the
clactric control signal of th~ optical tranamitter
provid~d ther~.
In order to avoid i llp9~ hl~ noi8e level3
within the useful bandwidth of the optical 8ignal, it is,
f$~ally, also possible ln ~ further ~ ' t of the
invention that in the OWG line unit ther~ i8 added to th~
el~ctric drlv~ signal of th~ optic~l tr namitter provlded
ther~ ~ pilot audlo signal which i8 Jituated outside th~
frequency range occupied by the information ~ignal to b~
tran~itted and has beerL modulated with the blnary
pseudo-nolse random signal; at the recelving end the
carrier-borne pseudo-noise hinary slgnal sequencs will
then have to he ~ -' lated befor~ the correlatlon.
Further particularitie~ of th~ invention ay be
gathered frorL the following description with the aid of
the drawlngs, ln which:
AM~21DED S~ T
21 78952
GR 93 P 1855 P - 7 -
Eigure 1 shows th~ monitoring of an optical l,~oadbc~d
~ervice csbl~ having only one optical fiber,
~nd
Figure 2 shows the monitoring of an optical broadb~d
servic- cablo having two separat~ optical
fibers for thn two tr~n~r~i^n directions; and
Figure 3 shows an exa~ple of a correlation curv~.
Repr~sented diagrammatically in Figure 1 to an
extent re~uir~d to underatand the invention i8 a
bidirectional OWG (optical waveguide) tel~- ;c?tions
system having a ~preferably - '-) OWG s-rvice cable
OA~ with only one optical fiber for tran3mitting the
optical signals of both tr~nP~; ~Einn directions: this
optical fiervic~ cable, which in the exemplary ' ~ t
accorting to Figur~ 1 extend3 between a subscriber line
u it ~T at the a~ch~ end and a 3ubscriber~ 8 sta-
tion TSt, may be r~iuired to be monitored from the
^T~ n~e up to a pas3ive optical interface PNTl.
~n general, various ~odes of operation are
F~E;hl~ at a pnEsive optical interface, aa will also b~
~urther illustrated in the following ~ n~ti^n~ such
as, for exa~ple,
l-fiber wavelength divi3ion multiplex with 1.3~+ and
1. 3 ~L-, and
l-fiber wavelength division multiplex with 1.5~L and
1.3~, and
2 - ~iber operation;
~'130 possible is a data 8ignal tr~n~ lnn in one
dl rection in the basebar,d ar,d in the other direction in
modulated form.
The principle of the invention can be applied
independently of the optical con~iguration used and of
the type of data tran3mission. Only the attenuation and
reflection parametsrs diffar from one another. For this
reason, the optical cirouit in Figure l is also to be
urderstood only as a diagram of the principle.
In the l ~ t considered, as also
i3dicated in Figur~ 1, the passive interface PNTl i3
r~ali~ed by me~n3 of an optical demountable connection ir.
which the optical
GR 93 P 1855 P - 8 - 21 7 8 9 52
endfaee of the part of the ~ ' hle eon~ecticn whic}l
is ~LL~ ~,1 at thH eYchange Qnd m~y be provided with a
ref lecting eoating r
At the passive interfae- P~ll, a small fraetio ~
5 of th~ optieal ~ignal transmittet from th~ li3e unit } T
to thY 8 ~hlvQ~--ih~ '~ statio~ TSt is l-- _- - l-or3 off and fed
~c3c in the r~verse direetion to thQ l~nl~ unit LT In th~
1 9 y , t aecording to PlgurQ 1, this is
p_L' `1 in sueh a way as to rQfleet at t~e passive
10 ~ntarf~e~ PNTl a portion of the light transm~ tted from
the li 8 unit LT T~- optieal signal fed }~aek to t~e line
Lnit LT is eorverted there in the optieal reeeiver e\o
(a~ th~ e~s~ may ~e, together ~it~ the optieal sig3al
r~eaived from t e ~ubscri~er' 8 tatio3 TSt~ into an
15 eleetrie l~ig~al
In the ~Y~ a~y ~ ' ' t aeeordi g to
Figure 1, aecording to whieh tbe optic~l serv~ co
~able oal has o ~ly one opt~ eal ~ber via which t e
optical ~ gnals of ~oth ~ an~; nr ~n dir~etions ~re
20 transmi~ted, tbis t; a~ r~^n c~n proc-Qd i3 ~oth
directions in tho ~ame optical ~rindow: Tho wavelength cf
t'~e laser transmitter Q/O at t Q ~ y~ end is in t is
case, at 1 3 IL, for eYample, ~pproxi2at~ly ~gual to the
wavelensth of t~e (not represented in d~tail in Fisur~ 1)
25 #lc_L-~ tical t I nQ~llr~ of the ~lhs~-~h~' s ~tation
~st; in order to prevent mutual intsrf~rence between the
two ele_L,~ tieal ~ nQ~ 8 ~ven in eost-optimized
syat~s C~t~ 5 no isolator3, a~d to prevent p~Q~hl~
heterodyning (form Ition of ~xed product~ from tl~e
30 d~ffarent signals because of th~ 'nl ~n~ response of
the opt ~ cal receiver) - whieh het~r~dynir~g may lead to
undesired int~rf erenee ~ot_ with t e useful signal and
with ~e pilot audio 9ignal, the wavelengths used ~or t e
two tr~n~m; Qsi^n direetions ar~, however, not per~itted
35 to be exactly egual or ne~rly exactly ~cual For this
reason, in Pigure 1 the wavelengths are denoted as 1 3 ~-
~nd 1 3 ~+ ~owever, inste~d of an opt~ eal l,rindow situ-
~ted at 1 3 f~, it is also por~hlL~ to usel a3 optical
wi~Ldow 8ituat8d, fo~ oxampl~, ~t 1 55 f~
2 1 78~52
GR 93 P la55 P - g -
~ f, in a departure ~ro~ the conditions indicated
in Figure 1, the optical signalg or the two tr~ n
directicns ar~ trans_itted in dif rereIlt optical windows,
for exa_ple at 1.3 ~ in on~ tr~nD--;ssion direction and at
5 l . 55 ~ in the other tr~n~$ ~s~n direction, tb.c reflec-
tion point ~t the passive optical interfaco PNT1 can also
b~ constructed in a wavelength-selective fashion, with
t~e result that it is ~ !''nt~ y only the optical signal
w:~ich is trans3litted in th~ direction towards the sub-
10 s~riber's 6tation TSt and c~n~ l~n~ the pseudo-noise (PN)
binary 3ignal which is parti~lly r2flected.
Represe3t~d diagram~atically in Figure 2 to the
extent required to understand the invention is an ~xemp-
lary ~ J~ t of a bidir~ction~l OWG tel~. ~c2tions
15 syst2m having a (preferably ~ ) OWG service cable
OAI which has a separate optical fiber for each trans-
mission direction, it being possible for the optical
~ignals of the two tr~n~m~ ~s1~n directions to be trans-
m tted at the game wav~length or at di r rerent wave-
20 lengths. This optical service cable OAI" which in the
_ l ~ry ~ t according to Figure 2 again extendsb~tween a subscriber line unit ~T ~t the exchange end and
a ~ubscriber' 8 station TSt, may, ~gain, need to be
monitored ~rom the exchange end up to a passive optical
25 interf~ce PNT1. For this purpose, again a PN binary
~i.gnal is added to tl~e infor~ation signal to be trans-
m~ tted o~er the OWG service cable 0~.
At the paEIsive interface PNT1, again, a s_all
fracti on of the optical signal transm tted from the line
30 unit 21T to the subscriber TSt is ~ranched off and fed
bsck in the reverse d~ rection to the line unit ~T . ~t is
indicated in Figure 2 in this regard that couplers V in
the fo= of passive optical couplers between which an
optical feedbac3c path R extr-nds are provided on the side
35 of the passive optical intarface PNTl facing the lire
u~i t LT .
1 78952
G}~ 93 P 1855 P - 10 _ 2
The optiaal signalg can be ln~n~ and coupled
out in this case by means of a ,y -tLlcal passive optical
couplers
Via the~ feedback path R, a small fraction of the
5 optioal signal tranamitted ~rom the subscriber lin-
u~it LT to th~ subscrib~r~ 8 stat~ on TSt passes back in
th~ direction towards the subscriber line unit LT where
it is convert-d in the optical receiver ~\o provided
there into an electric signal togethQr with the optical
10 signal received fro~ the ~ubsoriber TSt
It is indicated i3 Figure 1 that a ~odulation
circuit M for the information signal to be transmitted
and an operati g point control circuit A belong to the
laser diode provided as optical tran~mitter Such cir-
15 cuita ar~ knowQ i principle (for exa~ple fro~D~-A1-4125075) and do not requirQ further explanation
here
In th{~ exe2plary -'; t in acco ~c~ with
Figur~ 1, the method according to the invention is baaed
20 on the corr-lation betwee~ d paeudo-nois~ (PN) bit
8ecue"ce generated by a generator G and the reflected
-~t of an optical signal whose ~ean value was
dulated ~y meana of the la~er biasing current ib~ with
t~e aame PN bit aec,uence TQe PN bit aequence i8 a pseudo
25 raQdom sequenc~ of binary signal ~le2ents O, 1 (or -1,
I 1~ such as can be generated with a period p 2n-1 by
means of an n-stage shi~t regiater haviT~g linear feed-
bac3c ~he biasing CurreQt i~ " of tQe laser diode at the
LT end (LT beiQg the line termination at the subacriber
-30 line networX end) ia a2plitude-nodulated u~ins the raQdom
sequence of the PN geQerator G WitQ a 8mall raQge of, for
example, 10%
The optical dowQatream aigQal, which is modulated
by the information sigQal which is to be traQsmitted from
35 the OWG line UQit LT over the optical broadbaQd service
cable 0~ L in tQe down~tream direotion, on the one haQd,
aQd whose meaQ value is 1 ~te~l using the PN bit
sequenc~, on th~ other haQd, is more or less strongly
re_lected at all Fo~P;hle reflection points
21 78952
GR 93 P 1855 P
of the optical broadband service cable OA~, and thus al80
at the passive optical interfac~, which effects a deflned
(deaired) reflection (for example, with ~ reflection
factor of 10%).
The optic~l signal receivced by th~ line unit LT
in the upstrea~ direction cnnt~n~ the TSt ;nforT^-tinn
signal ori~;n ~t~ng in the subacriber~8 station TSt,
reflected ~ of the LT infor;l~ation signal trans-
mitted in the down8trea~ direction, reflected ~
of the PN bi~ary signal and interference (for cxample,
noiae) in the receiver input atageg, the levelg ~p-~n~?;n5
on the optical configuration and the type of data trans-
fer. Thia aignal is now correlated - as the case ~ay be,
amplified but not yet regenerated (in tis~e) - with the
PN aeguence, delayed in time by a delay time period r
which corresponds to the signal propagation ti~e from the
line unit ~T to the passive interface PNT1 and bac3c
again, that is to say this signal is 31ultiplied and
sub8equently integrated over a plurality of PN s~, r~r~;
the output sig~al resulting fro~ the correlation corres-
ponds in amplitude to the reflected aign~ ^nts
having an optical aignal propagation ti~e in the region
of ~he ti~e delay ~. ~his correlation aignal is finally
monitor~d correctly in ter~s of signal propagation ti~e
for the DC~u~ ~ c ~ce of the pseudo-noiae binary signal
reflect2d from the passive interfacs PNTl, something
which can procced in th~ manner of an amplitude threshold
value decision. Threshold value ~ ; nn~ are generally
~cnown, and 80 there is no need for any further explan-
ations on thia. It may be pointed out in particular in
this connection that the correlation signal can alao, as
the case nay be, be subjected to not o~ly a single-stage,
but alao a ~ultistage threshold value ~c;~n the result
of which additionally for 8 a ;lleasure of the guality of
3 5 the optical service cable OAI, between the OWG line
unit LT and the pas8ive interface PNTl.
The ti e delay T can be realized ~dvantageously
by generating the PN se~ for the biasing current
1 ~t~r A ~in
2 1 78952
GR 93 P 1855 P - 12 -
Fisure 1) and for t_e corr~lator S, J (in Figure 1 and
Fisur~ 2) by two separatQ PN gen-rators (G, G in Fig-
ure 2) formed by means of shift register chains, in which
diferent start~ng v~lues ar~ prescribed, from a ~icro-
processor I~P, in the form of an ~Lyyl~p lately dlffering
pLc~c~ 2 of their shif t resistQr chAins . The ~elec-
tion of these starting values det~;n~ th~ tima delay 7
of the PN se~iu~n~ e, fed to th~ correlator X, J (in
Figure 1 and Figure 2), with respect to the PN 8-, ~a
f~d to the ~ ' lator (A in Fisur~ 1; e/o in Fisure 2).
Interf erence terms ar~ filtered out hy the
i tegration downstr~am of the multiplication of the
re1ectsd signal and time-delayed sis al. The achievable
signal-to-noise ratio of the integrated sisnal, and thus
o~ the correlator output sisnal, depends on the param~-
tars of the optical signal c ~nta, ~ut al~o essen-
tially on the integration time. The correlator output
signal (integration result) can ~e subject~d to A/D
converaio3 and further processed in the downstream
mi~ ,y OCe~60L ~LP. The distance of the reflection loca-
tio~ can be calculated given a known group velocity of
the optical signal.
The microprocessor ~P can ~irstly also tak~ over
the setting of different time delays 7 in a --1 ;hrat ;~
operation, in order to dete~;~ all the reflection
e~n1-~ on the individual route sections. The spati~1
resolution ~1 increases linearly in this case with the
clock rate at which the laser biasing current is a=pli-
tude-modulated; it is ~1 ~ c/2f, in which c is the ~roup
velocity of the optical signal and f the clock fraquency
of the pseudo-noise bit sequence. The maxinum ~oritorable
route length 13a,~ is also det~;n~d by the temporal
length of the PN period; it is 13~ cp/2f, in which p
is the period of th~ PN bit sequenca.
Figure 3 shows diagrammatically the characteris-
tic of th~ correlator output signal as a function of the
time delay r. The measurement points h;~hl ;~hee~' on the
correlation curvq have a spacing
21 78952
,, .
GR 93 P 1855 P - 13 -
which cu~ u,.ds to the length of ~ individual bit of
the PN 8~, r nl~o. The correlatlon curve 2ay be baaed in
the exa~nple on a clock rate of 100 k!~z and a paeudo-~oise
~it se~uence having a length of 25-l bits (and thus a
period o 310 ~8); the group velocity of the 3ig al 03
the optical rout~ 2ay be 0 . 2 k2/,us . CG~ ". r~; n5 to a
forward and return tirle or ti2e delay r of 200 ~8 in the
~xa2ple, is a diatance ~ro2 tha r-flection location of
20 k2; the passiv~- inturfac~ PNTl (in Fisure 1 ~nd
Figur~ 2) 2ay bo located at this distzmc~ in the exa2ple.
raki2s account o~ the two-fold ~-~ nn ti2e of the
~ignal to the r~flection locatlon ~nd back aga n, ther~
is a spatial re~olu~ ;nn A1 C 11 k2 and a 20nitorable
route lengt~ ", of at 20st 31 km.
~or th~ normal op~-at~ fol~ A'n~J tke calibra-
tion operation, a fixed ti2e delay r of 200 ~8 i~ the
Qxa2ple is then selected i~ order to
~onitor the part of the optical b ~ nrl ~ervice
cable OAI~ (in Pigure 1 and Figur~ 2) ~tuated betweQn the
- 20 OWG line unit ~T (in Figur~ 1 and Fisur~ 2) ~d the
defined passive optical interface PNTl (in Fisure 1 a~d
Figuro 2), in order to 20nitor the o~ ~ca, correctly
in t~r~s of ti2e, of the pseudo-roiae ~inary siglal
reflectad fro2 the passive int~rfac~ PNTl (in Figure 1
and Figure 2) with the aid of the oc _-C8 of a corr~s-
pnrlr~; nrJly high correlator output sig~al a--plitude A, as
it is given in accor-l~c~ with Flsure 3 precisely in the
case of ~ forward and retur~ t~ ma or delay ti2e r o~
200 IL8 in the exa2ple in accorda~ce with a distane~ of
the reflective passive interface PNTl (in P~gur~ 1 a~d
Figura 2) of 20 k2. Sinc~ t_e reflQction condit~o~s
change in the case of ~m int2rruptios: of t_e optical
trans2issioII path, all that is now roquir~d i~ to det2r-
2ine ~nd ~valuato deviations of t_Q correlatio~ ~ig~al
a~plitude fro2 the valu~ es~hl i ~h~d during the cali-
bration operaticn.
A8 may ~o seen fro-- Figurs 3, the ti2e delay r is
exps~ ntly sQlectod for nor~al operation ~uch that it is
at lQast
_ _ . _ , _ _ _ _ .. .. , . ... _ _ _ _ _ _ _ _
21 78952
GR 93 P 1855 P - 14 -
approximately equal to the signal propagation time from
the OWG line unit LT up to th- passive optical interface
PNT1 ~in Figur~ 1 ~nd Figure 2) and b~ck, because then
the ~plitude spacing a from the dc - ~ ~nt ucs
(~ndesired correlation signal) of th~ corselator output
aignal is particul~rly large. This dc _ _ ort is to be
5~"rlhe~, on the one hand, to the fact that in a
P~ ~ o ~e the nu~ber of -1 signal ^7~ t~ is not equal
to th- nur~ber of tl signal elelsents and, on the other
hand, that ;n addition to the r~flection signal origi~at-
ing in the passive interfacs PNTl (in Figure 1 and
Figure 2) yQt other signals reach the correlator input.
I~: may he noted in this regard that in Figurs 3 increased
correlation signal amplitudes are also indicat~d in the
le~t-ha d and right-hand edges of the correlatio2 curve,
~d these ~ay be ascribed to reflections at a pA~s;hl~
connector at the LT end. ~owever, this can be neglected
for nitoring the oc~ ~LL~ce of the pseudo-noise binary
signal reflected by the p~asive intQrface PNT1, becau8e
these increased correlation sign~l a~plitudes would occur
o~ly in the cas~ of the associated time delays, to be
seen in Figur~ 3, of, for exa~ple, O or 310 fi8, _ut not
in the case of the o~Te~7~o~ly selected tisle delay of,
~or example, 200 ~8.
If an a~plitude modul~tion of the laser biasing
current should not be te~-h~c~ y rDD~ hle, it is also
poasible for a COL ~ N a nplitude signal to be
superi3lposed additively on t~e electric i3formation
signal, as is indicated in Figurs 2. The total signal
3 0 then dulateQ the optical output power of the la~er .
Ii' an amplitude ~odulation of the laser biasing
current, or if an additive aignal superimposition should
lead to ~rpe~; QQ;hl~ noise levels within the useful
b~ndwidth of the optical signal, it is also posaible in
the OWG line unit LT to add to the drive signal of the
optical trans nitter provided ther~ a pilot audio signal
which has been ~ tod with the pseudo-noise binary
~ignal and whose frequency is outsido the
2 1 78952
GR 93 ~ 1855 P - 15 -
freguency ranse occ~ riecl by the infor~ation aignal to be
transmitted in the upstream directlon; it i~s then necesa-
ary for the carrier-bor~e PN bin~ry aignal 89, ~ -e to be
tfi~d again in th~ receiver section before the
5 correlation
It i8 r,ot a rsstrictio n of the invention that
i~ldividual ~ , OWG line unita (1T ir~ Figure 1 ;~d
Figur~ 2) are respectively provided i~ an exchange in
each case with a~ individual subscriber optical service
10 cablH (OA~ in Figur- 1 and Ficura a); rather, the ir,ven-
tion can al90 bo appli-d i- a passive optical networX ir
w~ich a plurality of subscribers or, in general terr~s, of
df~central t ~l e~ tiona devices are r~spf ctively
cornect~d via a dedicatad optical aervics cable to an
lS optical coupler which is connected directly or via at
leaat one further optical coupler to a commor, OWG line
u~it ~t th- ~cchange end via an optical waveguide bus
S~le~ fro3n the exchange f~nd u~8~. ~ of the
ju~ctions, thf ra is provided in this cas~ a paasive
20 opt~ cal interfac~ PNT1 witk the aid of which it ia
posaible to ~or,itor the optical tr~"f~m; f~f~i~n route fr
the exchange end at least up to this interface; the
st7<tf tf~ ~nade in relatio~ to Figurs 1 (or in the case
of thf~ two- f iber design of Figure 2 ) apply in this ca~;e
in a co.~ "g way
