OPTICS AND OPTOELECTRONICS VOLUME: 21 |NUMBER: 1 |2023 |MARCH
Ne wo k Physical Laye A ack in he Ve y High
Capaci y Ne wo ks
Da id GRENAR1, Jakub FROLKA1, Ka el SLAVICEK 2, O o DOSTAL2,
Ma in KYSELAK 3
1Depa men o Telecommunica ions, Facul y o Elec ical Enginee ing and Communica ion,
B no Uni e si y o Technology, Technicka 12, 612 00 B no, Czech Republic
2Ins i u e o Compu e Science - IT In as uc u e Di ision, Masa yk Uni e si y,
Bo anicka 554/68a, 602 00 B no, Czech Republic
3Depa men o Elec ical Enginee ing, Facul y o Mili a y Technology, Uni e si y o De ence,
Kounico a 65, 662 10 B no, Czech Republic
[email p o ec ed], olk[email p o ec ed], sla[email p o ec ed]uni.cz, [email p o ec ed]uni.cz, [email p o ec ed]
DOI: 10.15598/aeee. 21i1.4973
A icle his o y: Recei ed Dec 15, 2022; Re ised Dec 27, 2022; Accep ed Jan 16, 2023; Published Ma 31, 2023.
This is an open access a icle unde he BY-CC license.
Abs ac . This pape ocuses on he analysis o ibe
op ic line ea esd opping op ions based on cheap
and easy- o-use equipmen - o example, he commonly
used ibe op ic spli e s wi h sui able op ical powe
di ision a ios. The ibe op ic spli e akes
a small po ion o he op ical powe su icien o
he ea esd oppe o ead he da a and le s as
much signal powe as possible pass in he o iginal
di ec ion. We a emp ed o de ec he p esence
o ibe op ic spli e -based ea esd opping poin s
on he communica ion line by using common echniques
designa ed o ibe op ic quali y measu emen and aul
de ec ion. The esul s a e summa ised in his pape .
Keywo ds
Ea esd opping de ec ion, ibe op ics, e y
high capaci y ne wo k, ne wo k a ic
ea esd opping.
1. In oduc ion
Wi h he cons an de elopmen o new
communica ions se ices ha place g ea e demands
on ansmission pa ame e s, op ical ne wo ks a e
massi ely used in access ne wo ks. The secu i y
conce ns a e eno mous - each yea , companies spend
billions o dolla s secu ing hei ne wo ks, and each
yea billions o dolla s a e los due o in usions
in o hose same ne wo ks. A i s , ibe op ic
ne wo ks we e ou ed as one o he mos secu e
in as uc u e op ions. In he las couple o yea s,
i has been sugges ed ha ibe is almos as easy
o ap as coppe [1] and [2]. Today, he e a e millions
o miles o ibe cable spanning he globe. La ge
amoun o da a a e being ansmi ed ac oss hese
cables daily, including sensi i e go e nmen da a,
and pe sonal inancial, and medical in o ma ion.
Fibe op ic communica ion is widely and publicly
unde s ood as a medium ha is di icul o ea esd op
on. Un o una ely, his common concep ion is a
om he echnical eali y. In his pape , we s udy some
cheap and easily accessible ools o ea esd opping
on ibe op ic communica ions and explo e he chances
o he au oma ic de ec ion o hei placemen on li e
ibe op ic lines.
I is e y likely ha , in a couple o yea s,
con empo a y c yp og aphy used o p o ec
communica ion will be ulne able due o he cu en
p og ess in quan um compu ing. Fo he ime being,
communica ion p o ec ion elies on p o ec ing physical
lines agains ea esd opping un il new c yp og aphy
algo i hms a e de eloped. Resea ch in his ield
is mainly ocused on ad anced echniques based
on leading bu cos ly echnology [3]. Howe e ,
he h ea o cheap and easy ea esd opping is mo e o
less unno iced. This pape in ends o illumina e his
possibili y.
©2023 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 37
OPTICS AND OPTOELECTRONICS VOLUME: 21 |NUMBER: 1 |2023 |MARCH
In o de o ensu e communica ion secu i y,
i is necessa y o ocus on physical access
o he communica ion in as uc u e. In case o
a se e and deli e y in as uc u e, access is loca ed
in da a cen e s ha a e unde he cons an supe ision
o p o isioning ope a o s.
An unimaginable amoun o da a, including sensi i e
da a, a e being ansmi ed ac oss hese cables daily.
I he wi ing is in a publicly-accessible space, his
da a may be comp omised. Thus, igh e access con-
ol o he cabling mus be implemen ed. Mo e com-
panies need o employ physical laye secu i y sys ems
in conjunc ion wi h hei exis ing da a laye secu i y
sys ems because physical laye secu i y sys ems a e
be e able o de ec and deal wi h in usions
o he cables ha do no in ol e an easily measu able
amoun o da a in e up ion [4]. Also, i may be
ad an ageous o no publish ibe op ic communica ion
in as uc u es on he In e ne . This can p o ide
a oadmap and b ing a en ion o ibe op ic
ulne abili ies.
Access ne wo ks a e o en loca ed in public a eas
bu a e no p ope ly secu ed. To gain access o da a
anspo ed o e he ibe , i is enough o connec
an op ical spli e o he ansmission pa h. Then
i is possible o ea esd op on all a ic. In o de
o o ally block cybe -a acks and hacking, he access
ne wo k should be p o ec ed. I a company enc yp s
i s ansmi ed da a, i could p o e o be a s umbling
block o in ude s. Depending on he enc yp ion
me hods used, i may only be a ma e o ime be o e
he in ude b eaks he enc yp ion and ob ains hei
desi ed da a.
Ou mo i a ion o his wo k is he MeDiMed
in as uc u e used o medicine pic u e da a anspo
and p ocessing (documen ed in [5], [6], [7], [8], [9],
and many o he s). MeDiMed is a sha ed egional
Pic u e A chi ing and Communica ion Sys em
(PACS) se ing hospi als in B no and he su ounding
a ea. The sys em acili a es as and secu e commu-
nica ion among indi idual hospi als, enables deli e y
o some se ices h ough he compu e ne wo k,
and o e s o he capabili ies o oday’s compu e
sys ems and da a ne wo ks o medical use s [10].
The sys em deals wi h he secu e ansmission,
a chi ing, and sha ing o medical image da a
o igina ing om a ious modali ies (compu ed
omog aphy, magne ic esonance, mammog aphy,
e c.). The secu i y needs o he MeDiMed sys em
a e he mo i a ion o his a icle. In his e-
sea ch, we ha e made use o he expe ience
gained du ing he de elopmen and deploymen
o he op ical backbone o he Czech NREN ne wo k
CESNET [11], [12], [13] and [14].
1.1. S a e o he A and Rela ed
Wo k
Cu en ly, scien i ic pape s ocus mainly
on sophis ica ed ibe op ic line ea esd opping
echnologies. Fo example, in [15], ad anced deep
lea ning algo i hms a e discussed. In [16], he au ho s
ocus on ea esd opping and espec i e de ense
measu es using ibe bending and simila echnologies.
In [17], he possible u iliza ion o in-band c oss alk
o op ical anspo line ea esd opping is discussed.
In [18], he au ho s discuss possibili ies o ibe op ics
bending u iliza ion.
All o hese ela ed wo ks u ilize ela i ely expensi e
echnology and complica ed p ocedu es. Howe e ,
he bigges isk o cu en ly used ibe op ic ne wo ks
lies in cheap and easy- o-use echnologies. This
pape demons a es he ea esd opping capabili ies
o e y simple equipmen - a ibe op ic powe
spli e . The e a e se e al ela ed wo ks dealing wi h
ibe op ics in as uc u e secu i y in gene al, [19]
and [20], ela ed echnologies [21], [22] and [3], o
secu i y in DWDM backbone ne wo ks ([23] and access
ne wo ks - GPON [24] and [25]. Ou ocus is
en e p ise and me opoli an ne wo ks. These ne wo ks
commonly use gigabi and en-gigabi e he ne o e
singlemode ibe and a e mo e suscep ible o a acks as
he p o ec ion o cabine s wi h pa ch panels is no as
s ic as in he case o backbone anspo ne wo ks,
and he echnology is no as igh as in he case
o GPON ne wo ks.
An a acke can use any main enance window
o ins all ibe op ic spli e s in o he line o in e es .
Ano he ac o wo king o he e en ual a acke is
a highe equency o changes in his ype o ne wo k
so ha e en sho unannounced in e up s can pass
wi hou no ice om he side o he ne wo k ope a o
and adequa e secu i y checks. We ha e expe imen ally
app o ed ha in he case o gigabi e he ne e en
a spli e wi h a 5:95 op ical powe dis ibu ion can
p o ide enough op ical powe o an ea esd oppe ,
allowing him o he o cap u e da a a ic using
common ne wo k equipmen wi hou he need o
op ical ampli ica ion o any o he ad anced ool o
gea .
2. Technology o Op ical
Ne wo ks Ea esd opping
This sec ion discusses he key echnologies
and p ocesses sui able o cos -e ec i e op ical
ne wo k ea esd opping.
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OPTICS AND OPTOELECTRONICS VOLUME: 21 |NUMBER: 1 |2023 |MARCH
The main ad an age o physical line ea esd opping
is he long- e m a ailabili y o da a. Once he ea es-
d opping poin is ins alled, i can p o ide a copy
o all he da a anspo ed un il i is disco e ed
and emo ed. The main d awback o ea esd opping is
ha he a acke canno gain access o any da a hey
choose, bu only ha anspo ed o e he a ec ed
communica ion media. O cou se, he a acke
has o ully unde s and he communica ion p o ocol
s ack in use and needs enough compu ing powe
o eassemble he sensi i e da a om communica ions
p o ocols, packe s, and ames.
Gaining access o da a anspo ed o e he ibe
op ic line is much easie han commonly belie ed.
An essen ial ool is a gene al ibe op ic spli e
wi h he p ope coupling a io. An example o such
a spli e is in Fig. 1. Equipped wi h he p ope
ibe ype and casing, i is di icul o dis inguish
he spli e om he pa chco d i placed in o a ibe
op ic ack. This componen is a ailable in se e al
e-shops o less han 15 USD. As men ioned be o e,
we ocus on cheap and easy- o-use ea esd opping
equipmen . This kind o equipmen can be used
in many ins ances and doesn’ equi e in-dep h
knowledge o i s use s. Fo his eason, we conside his
kind o ea esd opping isk se e e compa ed o o he ,
mo e ad anced echnologies.
Fig. 1: An example o a ibe op ic spli e equipped wi h
p ope ibe ype and casing, making i di icul o be
de ec ed in a ibe op ic ack.
The same componen , usually encased in
a ack-moun able chassis, is commonly used by
secu i y inciden esponse eams o ne wo k a ic
analysis. The echnology used by secu i y moni o ing
eams o gain ne wo k a ic samples o analysis
and he echnology used by a acke s o ne wo k
a ic ea esd opping is almos he same. The main
di e ences a e he encasing and, o cou se, he eason
o apping he ne wo k a ic.
The ollowing sec ions discuss possible ways
o de ec ing spli e s inside a ibe op ic line. As
discussed la e , he echnical capabili ies o de ec ing
spli e s in ibe op ic lines a e limi ed. The e is no way
o dis inguish he eason o he p esence o a spli e .
Howe e , e en o ne wo k a ic analysis pe o med by
he ne wo k ope a o , he ne wo k moni o ing de ice
has access o he whole da a a ic, like an illegal
ea esd oppe , bu commonly only p o ides agg ega e
ou pu in he o m o ne wo k and low s a is ics, like
Ne low o IPFIX. The way o u ilizing a ne wo k
moni o is, o some ex en , up o he conscience
and choices o he ne wo k ope a o .
100%
70%
30%
100% 70%
30%
Ne wo k T a ic Moni o
TX RX
RX TX
Fig. 2: An example o a ypical ne wo k a ic moni o ing TAP
connec ion.
100%
5%
95%
Illegal
Moni o
TX RX
Fig. 3: Basic ea esd opping TAP connec ion.
100%
5%
95%
Illegal
Moni o
100%
5%
95%
TX/RX TX/RX
Fig. 4: Bidi ec ional ea esd opping TAP connec ion.
3. Ea esd opping Poin
De ec ion
The cos o an op ical spli e is insigni ican ,
and i s ins alla ion is almos e o less. Le us
conside he op ions o op ical spli e de ec ion
©2023 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 39
OPTICS AND OPTOELECTRONICS VOLUME: 21 |NUMBER: 1 |2023 |MARCH
100%
5%
95% 100%
5%
95%
Illegal
Moni o
Fibe Op ics Isola o
TX/RX TX/RX
Fig. 5: Ea esd opping TAP wi h p o ec ion agains he OTDR
de ec o .
u ilizing equipmen and echniques commonly
used in elecommunica ion ne wo k deploymen
and ope a ion. The i s and p obably he mos
ob ious way is op ical pe o mance moni o ing.
The second me hod is Op ical Time-Domain
Re lec ome e (OTDR) u iliza ion. We ha e se
up a simple es ing scena io based on a simple
ansmi e and ecei e using he SFP module wi h
a 1550 nm wa eleng h and ibe op ic lines used as
pa o he physical ne wo k in as uc u e in he com-
pu e cen e . We ins alled a ibe op ic spli e inside
he line ins ead o he pa chco d. A spli e wi h
a coupling a io o 5:95 was used, and gigabi e he ne
a ic was success ully ea esd opped on and ead by
he simula ed boo leg de ice. All es s we e pe o med
on legacy ITU-T G.652 ibe op ic lines and pa chco ds
based on a G.657 ibe .
We pe o med a se o measu emen s o analyze
he di e ences in de ec ing he spli e by bo h op i-
cal pe o mance moni o ing and OTDR measu emen s.
The EXFO FTB-7300D-234B-EI OTDR was used o
ou expe imen s. This ype o OTDR is used o
he daily ope a ion o he uni e si y’s ibe op ic ne -
wo k. We used h ee scena ios o spli e placemen s,
as shown in Fig. 3, Fig. 4 and Fig. 5, whe e Fig. 5
is ele an only o OTDR measu emen s. To demon-
s a e he eal capabili ies o ibe op ic ea esd opping
componen s and he limi ed possibili ies o hei de-
ec ion, we se up a lab model and pe o med a se
o measu emen s. The lab model is shown in Fig. 6.
The esul s a e summa ized in he ollowing sec ions.
We used h ee local op ical loops: wo o hem
simula ing communica ion lines on he igu e deno ed
as lines 1–2 and 3–4, and one used as a simula ion
o an a acke on he igu e line 5–6. A ixed a enua o
o 5 dB was inse ed in he middle o line 1–2; ano he
a enua o o 10 dB was inse ed in he middle o line
124
3
56
100%
5%
95%
2
5
3
100%
5%
95%
23
5
DUT−A
100%
5%
95% 100%
5%
95%
2
5
3
DUT−C
5
100%
5%
95% 100%
5%
95%
23
DUT−D
DUT
DUT−B
Fig. 6: LAB model used o op ical ea esd opping componen s
analysis.
3–4; line 5–6 was s aigh . The o e all a enua ion
o line 1–2 was 8.6 dB, he a enua ion o line 3–4 was
12.7 dB, and he a enua ion o line 5–6 was 1.4 dB.
3.1. Ea esd opping Poin De ec ion
by Op ical Pe o mance
Moni o ing
The op ical spli e in oduces addi ional inse ion loss
in o he ibe op ic line. The added inse ion loss
is gi en by he connec o s and he coupling a io
o he inse ed spli e .
The line inse ion losses o he cases o he s aigh
line, one spli e usage, and wo spli e usage o
gaining independence on he ansmission di ec ion a e
gi en in he ollowing Tab. 1:
Tab. 1: Spli e inse ion loss balance.
Line se up A enua ion A enua ion
inc emen
s aigh 21.8 dB –
(pa chco d only)
single spli e 22.3 dB 0.5 dB
(Fig. 3)
wo spli e s 22.9 dB 0.9 dB
(Fig. 4)
©2023 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 40
OPTICS AND OPTOELECTRONICS VOLUME: 21 |NUMBER: 1 |2023 |MARCH
Tab. 2: Gigabi e he ne SFP op ical pe o mance moni o ing
p ecision analysis.
DUT DUT Pw me e DUT RX
TX RX RX balanced
(dBm) (dBm) (dBm) (dBm)
min 2.45 −13.90 −13.90 −14.32
max 2.45 −12.72 −13.86 −13.10
a g 2.45 −13.32 −13.88 −13.72
s dde 0dB 0.22 dB 0.01 dB 0.22 dB
I is easy o see ha he a enua ion inc emen is no
la ge. Fu he , we analyzed he op ical pe o mance
moni o ing p ecision o some commonly-used SFP
modules. We measu ed he gigabi e he ne modules
used o a ic ea esd opping in ou expe imen ,
a mul i- a e 100 Mbps o 2.4 Gbps SFP module,
and a en-gigabi e he ne SPF+, all o hem
ansmi ing on a p ecise wa eleng h in a 100 GHz
DWDM g id. These SFP and SFP+ modules will be
also called a De ice Unde Tes (DUT).
Fo measu emen , we used he lab se up p esen ed
in Fig. 7. The ou pu o he measu ed SPF was
a enua ed by a ixed 10 dB a enua o .
SFP
TX
RX
Spli e 50:50
49.2
50.8
IN PM−212
Fig. 7: SFP module op ical pe o mance measu emen p ecision
analysis.
To ob ain p ecise measu emen s, we i s analyzed
he coupling a io o he spli e used in his se up.
The coupling a io o he spli e (A:B) was de e mined
o be 49.2:50.8. The esul s om ou measu emen s
a e summa ized in Tab. 2, Tab. 3, and Tab. 4.
The o iginal measu ed da a a e a ailable upon eques
o e i ica ion o u he p ocessing. In all cases,
he measu emen was 20 minu es long wi h a 10 s ime
delay. This was enough o see he ins abili y o he SFP
module measu emen esul s.
Tab. 3: Mul i a e SFP op ical pe o mance moni o ing
p ecision analysis.
DUT DUT Pw me e DUT RX
TX RX RX balanced
(dBm) (dBm) (dBm) (dBm)
min 1.91 −13.30 −13.70 −13.43
max 1.96 −13.21 −13.61 −13.39
a g 1.93 −13.26 −13.66 −13.41
s dde 0.01 dB 0.02 dB 0.02 dB 0.01 dB
F om he abo e-men ioned measu emen s, i is
e iden ha he commonly used op ical pe o mance
measu emen o e ed by SFP op ical modules is
no p ecise enough o eliably de ec op ical line
pe o mance dec eases caused by ea esd opping
equipmen inse ion. The only excep ion is he
Tab. 4: Tengigabi e he ne SFP+ op ical pe o mance
moni o ing p ecision analysis.
DUT DUT Pw me e DUT RX
TX RX RX balanced
(dBm) (dBm) (dBm) (dBm)
min 1.43 −14.88 −15.33 −14.63
max 1.49 −14.01 −14.43 −14.48
a g 1.45 −14.41 −14.84 −14.54
s dde 0.02 dB 0.18 dB 0.19 dB 0.03 dB
mul i- a e SFP. Mo eo e , he a enua ion o he ibe
op ic line changes in ime due o he change
o mechanical s ess caused by, o example,
empe a u e changes o o he ex e nal in luences.
In ou long- e m expe ience, he daily a ia ion
o a 40 km long op ical line a enua ion is abou
0.6 dB. Adding a simple ibe op ic spli e causes
only a e y small inc ease in he communica ion line
inse ion loss (0.5 dB). This inse ion loss is ypically
below he common daily luc ua ion o communica ion
line inse ion loss. Mo eo e , he p ecision o ypical
op ical pe o mance moni o ing pe o med by SFP
and simila op ical modules is beyond his ma gin as
well. Fo his eason, a simple analysis o op ical
pe o mance is no enough o de ec a ibe op ic
spli e inse ed in o he communica ion line. Fo
a mo e sophis ica ed cons uc ion based on wo
op ical spli e s, he inse ion loss inc ease (0.9 dB)
is somewha de ec able, bu a basic op imiza ion
o he cons uc ed ea esd opping equipmen can
sligh ly dec ease he inse ed loss and make his
cons uc ion almos in isible as well.
3.2. Ea esd opping Poin De ec ion
by OTDR
The u iliza ion o OTDR could be used o de ec
ea esd opping poin s inside a ibe op ic line. We
es ed he lab se up as desc ibed in Fig. 6 wi h OTDR
as well. To achie e he bes possible esolu ion, we
used he smalles possible pulse du a ion o e ed by
OTDR. The measu emen was pe o med on h ee
commonly used wa eleng hs: 1310 nm, 1550 nm,
and 1625 nm. The esul s we e almos iden ical.
To imp o e he eadabili y o he g aphs and ables,
we used he 1550 nm measu emen in he ollowing
explana ion and discussion. Acco ding o he sho
leng h o he es ed ibe , we used he sho es a ailable
pulse du a ion (5 ns), co esponding o a pulse leng h
o 1 m. The leng h o he launch cable used was 500 m
and he measu emen a e aging pe iod was 30 s.
We used he es se up desc ibed in Fig. 6.
The es ed ibe op ic lines we e simula ed on se e al
looped oom- o- oom cables in ou compu e cen e .
We had wo cables a ailable, wi h leng hs o 20 m
and 30 m, espec i ely. Se e al lines om hese
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OPTICS AND OPTOELECTRONICS VOLUME: 21 |NUMBER: 1 |2023 |MARCH
0
5
10
15
20
25
30
35
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Signal s eng h (dB)
Dis ance (km)
Fig. 8: Re e ence measu emen o ea esd opped line.
0
5
10
15
20
25
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Signal s eng h (dB)
Dis ance (km)
Fig. 9: Re e ence measu emen o an ea esd oppe .
cables we e in e connec ed by pa chcables e mina ing
in ei he APC polished connec o s (E2000) i we
in ended he connec o o be almos in isible
on a e lec og am, o PC polished connec o s
(PC/APC) i we in ended he connec o o be s ongly
isible. The i s segmen (1–2 in Fig. 6) was 64 m
in leng h wi h APC connec o s only and simula ed
a clean segmen om he a acked da a sou ce.
The second segmen (3–4) simula ed a con inua ion
o he line om he ea esd opping poin owa d
he da a des ina ion unde a ack. This line had
a o al leng h o 232 m and PC connec o s a e
64 m, hen 50 m and 25 m wi h a 5 dB a enua o
inse ed. Line 5–6 simula ed he pa h om he ibe
op ic spli e owa d he ac i e ea esd oppe de ice.
This line con ained 3 PC-based in e connec ions o
be e isibili y on he OTDR.
©2023 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 42
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0
5
10
15
20
25
30
35
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Signal s eng h (dB)
Dis ance (km)
Fig. 10: Ea esd opping equipmen a ian A - simple op ical spli e .
0
5
10
15
20
25
30
35
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Signal s eng h (dB)
Dis ance (km)
Fig. 11: Ea esd opping equipmen a ian B - simple op ical spli e equipped wi h a ci cula o used as an isola o .
The e e ence OTDR measu emen on lines 1–2
and 3–4 in e connec ed ia a simple 2 m pa chcable is
shown in Fig. 8. The i s 500 m segmen is he launch
cable. The i s peak is he beginning o he emula ed
communica ion line. The big peak ep esen s he end
o he clean line and he beginning o he segmen
wi h impe ec connec o s. The mos impo an pa
o he measu emen is emphasized by he dashed box.
I ep esen s he pa whe e he op ical pa chco d was
eplaced by a ibe op ic spli e o a se o spli e s
and ci cula o s as deno ed in Fig. 6.
Line 5–6 was used o emula e he ea esd oppe
communica ion line. The e e ence OTDR measu e-
men is p esen ed in Fig. 9. In e es ingly, lines
wi h impe ec connec o s, such as his se up, can
cause be e e lec ions in OTDR. I is expec ed
ha he pa e n in he dashed box will be p esen
on e lec og ams om se ups using ibe op ic spli e s.
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0
5
10
15
20
25
30
35
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Signal s eng h (dB)
Dis ance (km)
Fig. 12: Two op ical spli e s connec ed in opposi e di ec ions o ob ain di ec ion-independen ea esd opping.
0
5
10
15
20
25
30
35
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Signal s eng h (dB)
Dis ance (km)
Fig. 13: Two op ical spli e s equipped wi h an op ical ci cula o .
The OTDR measu emen s o he ou possible modes
o ea esd opping as depic ed in Fig. 6 and e e ed
o as connec ions A, B, C, and D a e in Fig. 10,
Fig. 11, Fig. 12 and Fig. 13, espec i ely. I is
easy o see ha he pa e n o he ea esd oppe ’s
communica ion line ep esen ed in Fig. 9 is di icul
o ind in he e lec og ams; his is ue, especially
in he case o ci cula o u iliza ion, whe e his line is
comple ely in isible on he e lec og ams.
E en when u ilizing a spli e di ec ly wi hou
hiding he ea esd opping communica ion line behind
an isola o o ci cula o , i is no easy o no ice
he ea esd opping poin . I an isola o o ci cula o is
used, he spli e is almos in isible o commonly used
measu emen s as can easily be seen om e lec og ams
Fig. 10, Fig. 11, Fig. 12 and Fig. 13 - emphasized by
he dashed box.
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All he op ical equipmen used a e easy o acqui e
om many online componen s o es o e y low
p ices compa ed o commonly used ne wo k equipmen .
The ac i e ne wo king de ices needed o op ical
communica ion ea esd opping migh be he same as
he ones used o igh ul ne wo k a ic moni o ing.
Ea esd opping on op ical communica ion lines is
echnically much easie and, a he same ime, cheape
han mos o i s use s commonly belie e. Mo eo e ,
de ec ing op ical ea esd opping is e y di icul
and almos impossible o achie e using common
measu emen equipmen , as he key componen s
beha e oo simila ly o gene al op ical pa chcables.
4. Discussion
We ha e measu ed he p ope ies o ibe op ic spli e s
and hei simple cons uc ions which could be used
o ibe op ic communica ion ea esd opping. As
expec ed, e en a a he s ong spli a io (only 5 %
o op ical powe used o he ea esd oppe ) is enough
o ob ain a good quali y signal o he a acke
while minimizing he impac o he ea esd opped line
i sel . The spli e is almos unde ec able by common
measu emen equipmen like OTDR and/o analysis
o he op ical powe le el. Simply modi ying his
elemen (adding an op ical isola o o ci cula o ) can
make i mos ly in isible o common measu emen s.
Al hough he ins alla ion o his ype o ea esd opping
equipmen needs some speci ic knowledge and physical
access o he cabling in as uc u e, he simplici y
and p ice a ailabili y, oge he wi h he p og ess
in quan um compu ing needed o con empo a y
c yp og aphic p o ec ion mi iga ion, will make his
h ea e y se ious in he nea u u e.
The aim o his pape is o poin ou he p oblem
o communica ion ne wo ks’ physical in as uc u e
secu i y and especially o emphasize he isk
o ea esd opping on ibe op ic communica ion
lines. The echnical equipmen needed o ap
he ne wo k a ic is o e y low cos . The cos
o he equipmen needed o analyze he apped
a ic co esponds o he used communica ion
p o ocol and he cos o he equipmen used by
he ea esd opping ic im. The mos impo an
p ope y o op ical ne wo k ea esd opping in his
con ex is he ac ha i is almos unde ec able by
commonly used measu emen equipmen . To main ain
p i acy, he use o s ong c yp og aphy is necessa y,
e en in he case o communica ions o e ibe op ic
lines. I is expec ed ha con empo a y enc yp ion
algo i hms will be no mo e secu e in he nea
u u e. Cu en ly, p ope ly inspec ing ibe op ic
lines and en o cing he eplacemen o disman lable
connec ions (connec o s) by non-disman lable ones
(splices) will be c ucial.
Acknowledgmen
This wo k was suppo ed by he g an p ojec
o he Minis y o In e io o he Czech Republic,
no. VI20192022140.
Au ho Con ibu ions
K.S. concei ed o he p esen ed idea, D.G.
de eloped he heo e ical o malism and pe o med
he expe imen al wo k. E alua ion o he expe imen
was by J.F. and K.S. e i ied he analy ical
and nume ical me hods. D.G., M.K., and J.F.
con ibu ed o he inal e sion o he manusc ip .
O.D. supe ised he p ojec .
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