Long-haul Whi e Rabbi T ansmission
Jose Voj ech, Michal Spacek, Ja omi Sima,Tomas No ak,
Vladimi Smo lacha, Ond ej Ha lis, Elisabe h And ian sa azo,
Rudol Vohnou , Ma in Slapak, Lada Al manno a, Radek Velc,
Pe Pospisil, Jan Kund a
dep . Op ical ne wo ks
CESNET
P ague, Czechia
[email p o ec ed]
Michal Spacek, Tomas No ak, Elisabe h And ian sa azo,
Ja osla Roz ocil
Czech Technical Uni e zi y
P ague, Czechia
Abs ac — This pape p esen s a compa ison o he bene i s
o op ically ampli ied ime ans e using he Whi e Rabbi
(WR) p o ocol compa ed o egene a ion-based me hods
u ilizing Whi e Rabbi Swi ches (WRS). We highligh he
ad an ages in e ms o simple way o calib a ion, lowe ji e ,
and cos e iciency compa ed o con en ional egene a ion
me hods.
Keywo ds—p ecise ime, s able equency, ibe ans e ,
Whi e Rabbi
I. INTRODUCTION
The dis ibu ion o p ecise ime and equency is c ucial in
many ields and indus ies. Speci ically, in he case o
compa ing accu a e ime scales ha a e implemen ed, o
example, using caesium a omic clocks, ensu ing he ans e
o p ecise ime is absolu ely essen ial. Cu en ly, his is mainly
accomplished using Global Na iga ion Sa elli e Sys ems
(GNSS). The common- iew me hod is one o he me hods ha
u ilize GNSS and allows o compa ing dis an ime scales
when di ec local compa ison is no easible. This me hod
achie es unce ain ies on he o de o a ew nanoseconds. The
esul ing unce ain y is in luenced by se e al ac o s, such as
unce ain ies caused by mul ipa h p opaga ion and ecei e
noise, unce ain ies in he calib a ion o ecei e delays,
an ennas, and an enna cables, unce ain ies in an enna
posi ioning, and ionosphe ic and oposphe ic delays.
Recen ly, GNSS echniques ha e aced inc easing h ea s
om spoo ing and jamming, e ealing ulne abili ies o he
injec ion o alse iming in o ma ion o dis up ion o signals.
These h ea s can ha e se e e consequences in na iga ion,
comp omise he in eg i y o da a in as onomy and physics
esea ch, and in e e e wi h ime-s amping se ices essen ial
o inancial ansac ions. In pa icula , hey pose secu i y
isks o c i ical in as uc u e, such as powe g ids and
communica ion ne wo ks, which depend on p ecise iming.
Addi ionally, hey can ha e economic epe cussions o
indus ies elian on GNSS o logis ics and anspo a ion.
The e o e, he e is a need o esilien ime dissemina ion
echnology ha complemen s sa elli e-based s anda ds while
main aining equi alen le els o s abili y and accu acy.
Highe p ecision in he ans e o p ecise ime and equency
can be achie ed using op ical ib e links. Cu en ly, he Whi e
Rabbi (WR) sys em [1].
II. LONG-HAUL IMPLEMENTATIONS
Despi e he eme ging in e es in WR ne wo ks, majo i y o
implemen a ions o long-haul/coun y wide WR ne wo ks,
p e e s u iliza ion o elecom lambdas o Op ical Elec ical—
Op ical (OEO) egene a ion. In i s men ioned case
calib a ion (b ie ly desc ibed in nex chap e ) is e y
complica ed makes e e enceabili y o an o icial ime scale
UTC(k) almos impossible. In second case i seems a ac i e
o u ilize simple p o ocol agnos ic and e y a o dable
egene a o s. Un o una ely, as shown eg. [2], due o absence
o e iming unc ion ime and equency ans e is becoming
uns able a e ew hund eds o second.
III. NECESSITY OF CALIBRATION
The synch oniza ion be ween indi idual WR nodes can be
signi ican ly a ec ed by asymme y in he op ical
ansmission pa h. Asymme y e e s o he di e ence in
signal p opaga ion ime in he o wa d and e e se di ec ions,
bo h in elec onics and he op ics. Asymme y in he op ical
pa h despi e i bidi ec ional use, is among o he ac o s, in
majo i y caused by ch oma ic dispe sion. Since he WR
sys em uses bidi ec ional communica ion and ypically
di e en wa eleng hs o he o wa d and backwa d channels,
calib a ing he op ical pa h’s asymme y is c ucial o co ec
Fig. 1. WR ime ans e o e 400km o ib e - op ically ampli ied se up
and accu a e synch oniza ion o he nodes. When wo
synch onized nodes a e a apa , he calib a ion becomes a
ela i ely complica ed ma e . Calib a ion consis s o local
asymme y calib a ion and ib e delay asymme y. P inciples
o Whi e Rabbi calib a ion a e discussed in [3] and p ac ically
e alua ed in [4]. Me hod o he au oma ic e alua ion o
asymme y in he op ical ansmission pa h is shown in [5].
IV. LONG HAUL FRIENDLY SOLUTION
Chap e II indica ed also possibili y o egene a ed and
e imed solu ion, i has been es ed e.g. he e [6] and also
deployed he e [7]. Howe e his solu ion equi es o pe o m
calib a ion o each segmen and i s ecalib a ion in case o any
se ice wo ks ha ing signi ican in luence on ib e leng h o
o he sou ce o asymme y. This can be a oided by
deploymen op ically ampli ied solu ion. Such solu ion has
been shown by [8] o [9].
To compa e wo p e iously men ioned scena ios we se in
labo a o y se up consis ing o 4 imes 100 km o G.652D ib e
on spools, each spool 50km. Labo a o y se up consis s o wo
WR swi ch de ices, con igu ed as g and mas e and sla e, as
shown in Fig. 1. The WR sys em u ilizes comme cial Small
Fo m Pluggable (SFP) anscei e s. The e o e, we ha e used
he pai o 1.25 Gbps SFPs designed o channels 8 and 9 o
Dense Wa eleng h Di ision Mul iplex (DWDM)
(wa eleng hs 1571.24 and 1570.42 nm) ea u ing ex ended
inpu sensi i i y o -32 dBm and +1 dBm o highe ou pu
powe . A i s , he a enua ion o he whole line was
compensa ed by h ee ully bidi ec ional EDFA ampli ie s
CzechLigh wi h single pa h o signal in bo h di ec ions
placed in be ween spans. De e mined Maximal ime in e al
e o (MTIE) is shown in Fig 2 wi h o ange line. La e we
eplace hese ampli ie s wi h WRSes. Measu ed MTIE is
shown in Fig 2. by blue line.
To achie e eliable ope a ions, we will conside dual
powe supply solu ions bo h o WRs and also o
bidi ec ional EDFA ampli ie s wi h emo e managemen .
Se ing cos o such ampli ie o abou 0.2 o cos ully
ea u ed WRs we a e ge ing cos compa ison o egene a ed
(blue) and ampli ied solu ion (o ange). Numbe o inline hu s
is on X axis.
CONCLUSION
We con inue wi h e i ica ion o p op ia e se ups od long
haul WR lines wi h excessi e a enua ions (o e op ical
budge o SFP anscei e s). On labo a o y 400 km ib e se up
we measu ed ha bo h egene a ed and ampli ies scena ios
will keep a ge sub ns MTIE. Howe e ampli ied se up
o e pe o ms egene a ed se up in e ms o MTIE and
CAPEX and OPEX cos s. As ou measu emen s ill
con inuous we a e planning o e i y beha iou o e eal
ib es bu ied in g ound.
ACKNOWLEDGMENT
This wo ks was suppo ed by Minis y o educa ion, You h
and Spo o he Czech Republic as a pa o he QUEENTEC
p ojec , eg. n . CZ.02.01.01/00/22 008/0004649 Quan um
Enginee ing and Nano echnology. Au ho s would like o
hank membe s o WR communi y a GEANT SIG-TFN
communi y o e y aluable, open and iendly discussions.
We also would like o hank ou colleagues o e y use ul
suppo in WR ans e deploymen s wi hin ope a ional
ne wo k.
Fig. 2. MTIE[s] o egene a ed solu ion in Blue and ampli ied solu ion in
O ange.
Fig. 3. A bi a y cos compa ison egene a ed in Blue and ampli ied
solu ion in O ange. Numbe o inline hu s on X axis.
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