Hindawi Publishing Co po a ion
In e na ional Jou nal o Dis ibu ed Senso Ne wo ks
Volume 2012, A icle ID 467124, 12 pages
doi:10.1155/2012/467124
Resea ch A icle
Ne wo ked Elec onic Equipmen s Using he IEEE 1451
S anda d—VisioWay: A Case S udy in he ITS A ea
F. Ba e o, S. L. To al, M. Va gas, and J. Bece a
Escuela T´
ecnica Supe io de Ingenie ´
ıa, Uni e sidad de Se illa, A enida Camino de los Descub imien os s/n, 41092 Se illa, Spain
Co espondence should be add essed o F. Ba e o, [email p o ec ed]
Recei ed 16 Sep embe 2011; Accep ed 6 Feb ua y 2012
Academic Edi o : Tai Hoon Kim
Copy igh © 2012 F. Ba e o e al. This is an open access a icle dis ibu ed unde he C ea i e Commons A ibu ion License,
which pe mi s un es ic ed use, dis ibu ion, and ep oduc ion in any medium, p o ided he o iginal wo k is p ope ly ci ed.
The concep o In elligen T anspo a ion Sys ems (ITSs) has been ecen ly in oduced o de ine mode n embedded sys ems wi h
enhanced digi al connec i i y, combining people, ehicles, and public in as uc u e. The sma ansduce concep , on he o he
hand, has been es ablished by he IEEE 1451 s anda d o simpli y he scalabili y o ne wo ked elec onic equipmen s. The syne gy
o bo h concep s will es ablish a new pa adigm in he nea u u e o he ITS a ea. The pu pose o his pape is o analyze he
in eg a ion o elec onic equipmen s in o in elligen oad- affic managemen sys ems by using he sma ansduce concep . An
au oma ed ideo p ocessing senso o oad- affic moni o ing applica ions is in eg a ed in o an ITS ne wo k as a case s udy. The
impac o he IEEE 1451 s anda d in he de elopmen and pe o mance o ITS equipmen s is analyzed h ough i s applica ion o
his ideo-based sys em, comme cialized unde he name VisioWay.
1. In oduc ion
Recen p og ess in semiconduc o echnology and mic op o-
cesso a chi ec u es, on he one hand, and he ubiqui y o
elecommunica ion ne wo ks, on he o he , a ou he
g ow h o a no el ma ke con ex o senso s and ac ua o s
[1,2]. Senso s in eg a ed in o s uc u es—coupled wi h he
efficien deli e y o sensed in o ma ion—p o ide new se -
ices and bene i s o socie y [3–5]. The ac ual implemen a-
ion o such sys ems occu s on local a ea ne wo ks (LANs)
ha look like hie a chical ne wo ks wi h dis ibu ed compu -
ing capabili ies. Using his echnology, senso s and ac ua o s
p o ide a signi ican imp o emen in pe o mance and effec-
i eness h ough he dis ibu ion o hei esou ces.
I is in e es ing o link he de elopmen o such dis i-
bu ed da a acquisi ion sys ems o he s a e o he a and
u u e pe spec i es in he ITS ield, which has a ac ed much
a en ionin ecen yea s[6]. ITS equipmen s a e nowadays
e ol ing in o complex sys ems, allowing ehicle- o- ehicle
(V2V) communica ion and coope a ion [7,8], o ehicle- o-
in as uc u e (V2I) in e ac ion [9]. The public in as uc-
u e ( affic ligh s, s ee lamps o affic signs) is adap ing o
hese echnological ad ances. Some examples a e p omp ing
o ad iso y message sys ems, in o ming he d i e s on
pa icula affic condi ions—including ale s on imminen
dange ous si ua ions—o au oma ed affic-da a acquisi ion
sys ems ansmi ing ele an da a o afficcon olcen e s—
affic low, pe -lane ehicle coun ing, queue-leng h es ima-
ion, conges ion le el, es ima ion o jou ney imes, ed ligh
unne de ec ion, and so o h [7,10,11].
Howe e , he e a e s ill some handicaps o his wide-
sp ead use o elec onic equipmen s in he ITS ield: isk o
b eakage o connec o ailu es in oday wi ed sys ems, limi -
ed scalabili y in cu en ne wo ked sys ems bound o endo -
speci ic p o ocols, and so o h.
Wi eless echnologies a e he bes means o o e come
hese limi a ions, con ibu ing o ins ance o a subs an ial
ease o ins alla ion, o an inc ease o scalabili y [12]o oalle-
ia e main enance o physical links. Nowadays, an ideal wi e-
less ne wo k should ha e some “sma ” ea u es, such as be-
ing highly scalable, so wa e p og ammable, ene gy efficien ,
inexpensi e, and hope ully plug-and-play complian ; on op
o ha , i has o be eliable and accu a e, equi ing a e y low
main enance effo o e he long e m.
Recen ly, one o he mos ele an miles ones in his con-
ex is he in oduc ion o he concep “sma ansduce ,” ac
co ding o he IEEE 1451 s anda d [13,14]. IEEE 1451
p o ides an open pla o m o he de elopmen o scalable
2 In e na ional Jou nal o Dis ibu ed Senso Ne wo ks
Ne wo k
Ne wo k
in e ace
P ocesso
Signal
p ocessing ADC Condi ioning
ci cui
Memo y
T ansduce
Figu e 1: Sma ansduce a chi ec u e.
ne wo ked elec onic modules, using diffe en physical links.
The s anda d offe s he abili y o simpli y he connec i i y o
elec onic equipmen s, allowing he “plug and play” capabil-
i y by means o he physical-link abs ac ion. These, among
o he s, a e some expec ed, in e es ing ea u es in any
IEEE1451-complian equipmen , leading o inc eased scala-
bili y and less expensi e main enance.
This pape analyzes he u ili y o IEEE 1451 o he de-
elopmen o ITS equipmen s. An IEEE 1451-complian p o-
o ype o u ban oad- affic moni o ing is desc ibed and
analyzed as a case s udy. The new p o o ype is buil upon an
exis ing in elligen ideo senso , called VisioWay, which was
de eloped o oad- affic moni o ing applica ions (h p://
www. isioway.com/). VisioWay has been en isaged as pa
o he oad- affic in as uc u e, o affic moni o ing and
da a collec ion. The ele an in o ma ion is ansmi ed o
he afficcon olcen e s, obeused o affic-con ol as-
sessmen o oad- affic managemen .
The pape is o ganized as ollows. Fi s , a b ie o e iew
o he IEEE 1451 s anda d and he sma ansduce concep
is gi en in Sec ion 2.Nex ,Sec ion 3 desc ibes he p eexis ing
VisioWay sys em and i s use in oad- affic moni o ing
applica ions. Then, he in eg a ion o he IEEE 1451 s anda d
in o he VisioWay equipmen is analyzed in Sec ion 4,along
wi h he desc ip ion o he expe imen al se up. Finally, he
conclusions a e depic ed in Sec ion 5.
2. The Sma T ansduce Concep : IEEE 1451
S anda d O e iew
The pu pose o he IEEE 1451 s anda d is o de ine a se o
common in e aces, unc ionali ies, and commands o con-
nec ing senso s and ac ua o s o mic op ocesso -based
sys ems, ins umen s, and ield ne wo ks in a ne wo k-
independen ashion [13]. The main goal o his amily o
s anda ds is de eloping ne wo k- and endo -independen
ansduce in e aces, allowing elec onic ansduce s o be
eplaced and/o mo ed wi h he minimum effo . O he
desi able ea u es include supp essing manual con igu a ion
s eps. The T ansduce Elec onic Da a Shee (TEDS) concep
is de eloped as an elec onic da ashee ha emains wi h he
ansduce du ing no mal ope a ion, allowing he eal- ime
access o da a and calib a ion de ails. Consequen ly, he IEEE
1451 amily o s anda ds p o ides an open pla o m o he
de elopmen o ne wo ked elec onic equipmen s.
T ansduce s ha a e 1451-complian a e also called sma
ansduce s. Conside ing he pu pose o he IEEE 1451 s an-
da d, a sma ansduce should include ce ain elemen s like
a physical ansduce , a p ocesso /memo y co e, and a local
ne wo k in e ace h ough a mic op ocesso de ice. The
ansduce senses a gi en physical magni ude, gene a ing he
co esponding elec ical signal. This signal is con e ed in o
digi al alues o be p ocessed by he mic ocon olle , which
deli e s he esul ing da a o a local ne wo k. Only he selec -
ed o p econ igu ed da a a e accessible h ough he local ne -
wo k. Figu e 1 depic s he a chi ec u e o a con en ional
sma ansduce .
Two majo componen s a e de ined, he Ne wo k Capa-
ble Applica ion P ocesso (NCAP) and he T ansduce In e -
ace Module (TIM). The NCAP ep esen s a ne wo k node
ha pe o ms applica ion p ocessing and ne wo k commu-
nica ion unc ions, while he TIM consis s o a ansduce
sys em, used o signal condi ioning and da a con e sion,
including up o 255 senso s and ac ua o s. Figu e 2 shows he
o e all s uc u e o he s anda d IEEE 1451.
Eigh sepa a e s anda ds a e included in he IEEE 1451
amily, om he IEEE 1451.0 o he IEEE 1451.5, he IEEE
P1451.6, and he IEEE 1451.7.
The IEEE 1451.0 is one o he newes membe s o his
amily o s anda ds. I de ines a common se o commands,
unc ionali ies, and he o ma o he exchanged messages
be ween he TIM and NCAP. The s anda d also p o ides he
s uc u e o he T ansduce Elec onic Da a Shee s (TEDSs).
The se o commands—independen o he physical com-
munica ions media—includes he basic unc ions o eading
and w i ing he ansduce s da a, eading and w i ing TEDS,
and sending con igu a ion, con ol, and ope a ion com-
mands o he TIM. The aim o IEEE 1451.0 s anda d is o
gua an ee compa ibili y ac oss he IEEE 1451 amily.
The IEEE 1451.1 s anda d de ines an in o ma ion model
o he communica ion be ween diffe en NCAPs o be ween
NCAPs and o he sys ems [14]. I de ines he NCAP as he
main in e ace elemen be ween ansduce s and he ne -
wo k. The IEEE 1451 amily o s anda ds p esen s h ee
possible p o ocols ha can be indis inc ly used o access elec-
onic de ices om he In e ne : he Hype Tex T ans e
P o ocol (HTTP) ou lined in he IEEE 1451.0 s anda d,
In e na ional Jou nal o Dis ibu ed Senso Ne wo ks 3
Ne wo k
NCAP TIM
IEEE
1451.1
IEEE
HTTP
1451.0 IEEE
1451.0 IEEE
1451
1451
Web
se ices
IEEE
1451.x
IEEE
1451.x
1451.x
IEEE 1451.x
Physical laye
PHY
TEDS
TEDS
Signal condi ioning and con e sion
ADC/CAD
T ansduce T ansduce
Figu e 2: IEEE 1451 a chi ec u e o e iew.
Table 1: Gene ic o ma o TEDS.
Field Desc ip ion Type No. oc e s
0 TEDS leng h UIn 32 4
1 oNDa ablock Va iable Va iable
N+ 1 Checksum UIn 16 2
an objec and da a model in oduced in he IEEE 1451.1-
1999 s anda d, and he p oposed Sma T ansduce Web
Se ices o STWS de i ed om he Web Se ices Desc ip ion
Language o WSDL [15,16]. The simples web access is he
HTTP p o ocol p o ided by he IEEE 1451.0 s anda d. The
IEEE 1451.0 s anda d in oduces an HTTP API ha can be
used o access he NCAP o e TCP/IP ne wo ks. This HTTP
p o ocol ocuses on accessing ansduce da a and TEDS
h ough he HTTP 1.1 p o ocol. Use s send an HTTP eques
o a HTTP se e unning on he NCAP, ecei ing esponse
om he se e in Hype Tex Ma kup Language (HTML),
eX ended Ma kup Language (XML), o Tex o ma . HTTP
and IEEE 1451.0 by hemsel es do no p o ide any means
o disco e he nodes in he ne wo k; ne e heless, he e a e
se e al off- he-shel ne wo k disco e y ools ha make use o
diffe en p o ocols ha can be used o ha ma e .
Diffe en physical in e aces a e allowed be ween NCAP
and TIMs, being one o he mos in e es ing cha ac e is ics
o he s anda d. Fo ins ance, he IEEE 1451.2 s anda d, i s
app o ed in 1997, speci ied a en-wi e poin - o-poin in e -
ace called T ansduce Independen In e ace o TII and he
ela ed p o ocol [17]. I de ines a unique TIM named STIM
o Sma T ansduce In e ace Module. Howe e , a e ision
o his s anda d is expec ed due o he lack o manu ac u e ’s
in e es and i s incompa ibili y wi h he IEEE 1451.0 s an-
da d. This u u e e ision will allow he suppo o mo e
popula in e aces like USB and RS-232 [18].
The IEEE 1451.3 s anda d es ablishes a dis ibu ed mul i-
d op in e ace ne wo k sha ing a common pai o wi es. This
s anda d speci ies mul iple TIMs named TBIM o T ansduc-
e Bus In e ace Modules, and i is in ended o allow syn-
ch onized eading o la ge senso a ays on a pa allel ans-
duce bus. Mul id op connec i i y is used by de ining
channel iden i ica ion p o ocols, ho -swap p o ocols, ime
synch oniza ion p o ocols, and he ead and w i e logic un-
c ions used o access he TEDS and ansduce da a. The
s anda d is now being e ised o be adap ed o he equi e-
men s o he IEEE 1451.0 s anda d.
The IEEE 1451.4 s anda d p esen s a mixed-mode in e -
ace (MMI) o analog ansduce s. TEDS o be used wi h his
s anda d a e also de ined due o hei speci ici y as hey do
no comply wi h TEDS de ined in he IEEE 1451.0 s anda d
[19]. The IEEE 1451.4 s anda d de ines a mechanism o add-
ing sel -iden i ica ion echnology o adi ional analog sen-
so s and ac ua o s.
The IEEE 1451.5 s anda d de ines wi eless communica-
ion me hods be ween TIM and NCAP. S anda ds such as
802.11 (WiFi), 802.15.1 (Blue oo h), 802.15.4 (ZigBee), and
6LowPAN a e adop ed as iable wi eless in e ace. Finally,
o he well-known in e aces, he CANopen in e ace and he
Radio F equency Iden i ica ion (RFID) in e ace, mee , o
will mee soon, he s anda d.
The p oposed IEEE P1451.6 s anda d es ablishes a ans-
duce - o-NCAP in e ace using he CANopen ne wo k. I
also de ines a mapping o he IEEE 1451 TEDS o he
CANopen dic iona y en ies.
The ecen ly app o ed IEEE 1451.7 s anda d desc ibes
communica ion me hods and da a o ma s, p o iding a
TEDS o RFID senso s.
The TEDS is a key concep o he IEEE 1451 s anda d
[20]. I s anda dizes ansduce s in o TIMs, so any applica-
ion can dynamically disco e equipmen s, accessing hei
da a and cha ac e is ics. TEDSs a e classi ied in o manda o y
and op ional TEDSs, ollowing he IEEE 1451.0 speci ica-
ions. The manda o y TEDSs include he Me a TEDSs, he
T ansduce Channel TEDSs, he PHY TEDSs, and he Use
T ansduce Name TEDSs. In addi ion o hese essen ial
TEDSs, he IEEE 1451.0 s anda d suppo s o he TEDSs: Cal-
ib a ion TEDS, F equency Response TEDS, T ans e Func-
ion TEDS, Manu ac u e -De ined TEDS, End Use Appli-
ca ion-speci ic TEDS, and Tex -Based TEDS (including Me a
ID TEDS, T ansduce Channel ID TEDS, Calib a ion ID
TEDS, Command TEDS, Loca ion and Ti le TEDS, and Geo-
loca ion TEDS).
The IEEE 1451.0 s anda d speci ies he o ma o hese
TEDSs, as i is shown in Table 1.This o ma is lexibleand
4 In e na ional Jou nal o Dis ibu ed Senso Ne wo ks
Figu e 3: VisioWay p o o ype.
ex ensible o handle a wide a ie y o senso s, and i is com-
pac o sa e memo y space in he sys em. Each TEDS has a 4-
oc e leng h ield, a da a block wi h a a iable size depending
on he TEDS, and a 2-oc e checksum ield o e i y he in eg-
i y o he TEDS. The da a block includes diffe en en ies,
and i uses a Type/Leng h/Value (TLV) s uc u e o s o e each
en y. The “Type” ield is a 1-oc e ag ha iden i ies he da a,
he “Leng h” ield speci ies he numbe o oc e s o he da a,
he “Value” ield includes he ac ual da a.
The in o ma ion in he da a block depends on he TEDS,
excep in he case o he “TEDSID” ield o TEDS iden i ie
heade . This ield is s anda d in all TEDSs, including p o-
pe ies such as amily (always 0), class (TEDS access code),
e sion (IEEE 1451.0 s anda d e sion), and he numbe o
oc e s in he leng h ield o all TLV uples in he TEDS excep
his one (no mally 1).
The TEDS is no mally s o ed in non ola ile memo ies in
he TIM, while he NCAP has a ans e ed copy. I he TEDS
is no s o ed in he TIM, i is called i ual TEDS and he
manu ac u es a e expec ed o p o ide hem. The s anda d
allows he use s o p og am some o hese TEDSs once he
sma senso is ins alled, anyway. Hand assembly o TEDS is
a e y edious ask, e en o he mos simple TIMs. Hence, a
TEDS compile is highly ecommended o his pu pose.
Many sma senso applica ions using IEEE 1451 a e
being de eloped [21,22], including web-based senso sys-
ems [23–26]. In his pape , he u ili y o he IEEE 1451
s and-a d o he de elopmen o ubiqui ous elec onic
equipmen ne wo ks in oad- affic applica ions is analyzed.
In pa icula , an exis ing ideo-based affic senso , VisioWay
[27], is aken as a s a ing poin o build an IEEE-1451 com-
plian sma affic senso , capable o p o iding new web se -
ices o he afficcon olcen e s.
3. VisioWay in he Road-T a ic
Managemen Field
VisioWay is a p o o ype o a no el elec onic equipmen
o applica ion in he ITS ield using a i icial ision [27].
Figu e 3 shows he equipmen . I has been designed o com-
me cial pu poses in affic in as uc u es, p o iding web
se ices o he use s o he in as uc u e and p ese ing i s
Figu e 4: De ec ion a eas in an ins alled p o o ype: de ails o he
di ec ional egions beha io (R3, R4, and R5) and queue de ec ion
a eas (R1 and R2).
obus ness as sma senso in IP-based ne wo ks. VisioWay
was designed as a oad- affic pa ame e es ima ion sys em,
p o iding use ul affic in o ma ion such as affic low,
lane a e age speed and occupancy, o conges ion le els. The
da a collec ion is s uc u ed acco ding o a numbe o use -
con igu able polygons wi h a bi a y shape o size, called
de ec ion a eas (Figu e 4). Each one o hese de ec ion a eas
has in e es ing unc ionali ies like p esence and di ec ional
de ec ion unc ionali ies. The au oma ic ehicle de ec ion
me hod implemen ed in VisioWay is based on ad anced
backg ound sub ac ion me hods [28,29].
VisioWay has he ollowing ea u es.
(i) The F eescale i.MX21 mul imedia p ocesso is he
co e o he ha dwa e sys em.
(ii) Wi e (E he ne ) and wi eless (Blue oo h) connec i -
i y is included.
(iii) In e ace o ypical da a s o age media like USB o
SD/MMC is p o ided.
(i ) The ha dwa e is d i en by embedded Linux OS (ke -
nel 2.4.20).
( ) A i icial ision algo i hms ha e been implemen ed
o ga he ing in o ma ion abou ele an o eg ound
objec s ( ypically ehicles) in a afficscene.
The i.MX21 p ocesso is based on he ad anced and
powe -efficien RISC p ocesso ARM926EJ-S co e, ope a ing
a speeds up o 266 MHz. On-chip modules a e p o ided, in-
cluding LCD and MMC/SD con olle s, USB con olle s,
CMOS senso in e ace, and an enhanced Mul iMedia Accel-
e a o (eMMA). The CMOS senso in e ace p o ides he
capabili y o acqui e digi al images, ypically BT656 o aw
da a s eams in he RGB o YUV componen s, deli e ing
hem o he media p ocesso . The eMMA module consis s
o ideo p ocesso uni s and encode /decode modules ha
suppo MPEG-4 and H.263 eal- ime encoding/decoding
o images om 32 ×32 pixels up o CIF o ma a 30 ps.
The p ocessing uni is based on a p ep ocesso module ha
esizes inpu ames om memo y o om he CMOS senso
In e na ional Jou nal o Dis ibu ed Senso Ne wo ks 5
Figu e 5: VisioWay embedded sys em.
Figu e 6: Ke nel p omp o he p o o ype.
in e ace, pe o ming colo space con e sion, and a pos p o-
cesso module ha akes aw images om memo y pe o m-
ing addi ional p ocessing o a MPEG-4 ideo s eaming o
deblock, de ing, esize, o colo space con e sion on decoded
ames.
The p o o ype boa d (Figu e 5)isalsop o idedwi h
a mini USB-OTG connec o , a SD ca d connec o , a RJ45
E he ne connec o , a Blue oo h expansion connec o , and
an analog ideo connec o owed by a ideo decode chip o
allow analog ideo (PAL and NTSC o ma s) p ocessing. On-
boa d memo y allows ideo p ocessing and OS s o age. A
32 M ×16 Flash memo y is used o s o e he OS ke nel image
while wo 16 M ×16 SDRAM modules a e used o ideo
p ocessing and o decomp essing he ke nel image. An ARM
Linux (ke nel 2.4.20) ope a es he i.MX21 ideo p ocesso ,
allowing access o a wide a ie y o open sou ce so wa e
modules (Figu e 6).
Se e al p ocesses and se ices a e in concu en ope a-
ion wi h he main p ocess ( oad- affic moni o ing applica-
ion). These p ocesses a e a wa chdog p ocess o eboo ing
he sys em when a pe iodic signal is no ecei ed om he
main p ocess, a MPEG se e ha ope a es as an in e ace o
he i.MX21 MPEG ha dwa e module o ame eeding om
he applica ion, and a HTTP se e o con igu a ion and
supe ision pu poses, including an SSH se e o emo e
logging in o he sys em, and an FTP se e o upload and
download ope a ions.
4. VisioWay Sma Senso and
Expe imen al Resul s
The VisioWay sys em mus be adap ed o comply wi h he
IEEE 1451 s anda d. The o iginal HTTP and FTP se ices,
adop ed o eading da a and con igu ing he VisioWay
equipmen , canno p o ide by hemsel es a simple way o
access all he sys em in o ma ion, especially when plug-and-
play capabili ies a e expec ed. This p oblem affec s he de-
elopmen o applica ions ha makes use o his da a in
wo diffe en ways. Fi s , he applica ion is dependen on he
da a s uc u es and p esen a ion o ms and hus needs o be
modi ied acco ding o u u e changes. Second, i makes he
de elopmen o new applica ions mo e difficul since a deep-
e knowledge o he de ice is equi ed. As he de ices a e
in ended o es ima e and s o e affic measu emen s, i seems
easonable o conside hem as mul ichannel senso s, in e -
connec ed in o a senso ne wo k. VisioWay was also in ended
o ha e diffe en unc ionali ies and o be ins alled in di -
e en loca ions o e he u ban a ea. Consequen ly, i is es-
sen ial o ha e a common da a s uc u e and in e ace in
o de o gua an ee ull compa ibili y be ween diffe en
VisioWay equipmen s, making necessa y a unique da abase
wi h all he in o ma ion ha should be p o ided o uppe -
le el sys ems and applica ions.
A ne wo k-compa ible sma senso node is implemen -
ed in VisioWay using he IEEE 1451 amily o s anda ds. The
objec i e is o g oup VisioWay equipmen s in o a single clus-
e ed ne wo k, some o hem beha ing as clus e heads—
NCAPs in he IEEE 1451 no a ion. A common da abase
(TEDS) mus be designed, allowing connec ion ega dless
o he in e ace ype. The in elligence o he de ice ob ia es
unnecessa y asks when making he connec ion be ween
sys ems, p o iding he in e ace in o ma ion a connexion
ime, as a plug- and play- unc ion. O he implemen a ion
de ails a e as ollows.
(1) The sys em has been designed acco ding o he IEEE
1451.0 s anda d speci ica ions since his s anda d
inco po a es all he speci ica ions excep o IEEE
1451.4.
(2) VisioWay can implemen diffe en unc ionali ies,
desc ibed in each T ansduce Channel TEDS.
(3) The ole pe spec i e: since VisioWay is in ended o be
ins alled ac oss he ci y and connec ed hough TCP/
IP ne wo ks, each de ice can be conside ed as he
NCAP o a pa icula senso ne wo k using he HTTP
API de ined in he IEEE 1451.0 s anda d. A he same
ime, i is possible o connec o he VisioWay de ices
in o he ne wo k as TIMs, using he IEEE 1451.x s an-
da ds and p o iding he NCAP a ga eway unc ion
be ween TIMs and he In e ne . The ollowing al e -
na i es a e possible acco ding o he de eloped im-
plemen a ion.

6 In e na ional Jou nal o Dis ibu ed Senso Ne wo ks
HTTP
NCAP/TIM TIM HTTP
NCAP/TIM
TCP/IP ne wo k
TIM
IEEE 1451.5
Figu e 7: VisioWay equipmen s in o he same TCP/IP ne wo k,
playing diffe en oles (NCAP and/o TIM oles).
(a) A VisioWay sys em in eg a es a NCAP and a
TIM in o a single de ice. The In e -P ocess
Communica ion mechanisms a ailable in he
embedded Linux ope a ing sys em link he
NCAP and he TIM. As explained be o e, he
VisioWay sys em is unning unde an ARM
Linux ke nel [27].
(b) A VisioWay sys em se es as NCAP o o he
de ices (TIMs using IEEE 1451.x in e aces).
The cu en implemen a ion suppo s he Blue-
oo h s anda d, as speci ied in he IEEE 1451.5
s anda d.
(c) TCP/IP-based TIMs can be connec ed in o he
TCP/IP ne wo k. This app oach has he limi-
a ion o being only s anda dized o he IEEE
802.11 in e aces ia he IEEE 1451.5 s anda d.
Ne e heless, his op ion makes sense since he
communica ions a e based on he IEEE 1451.0
message o ma , and he aim o he IEEE
1451.0 s anda d is o encou age compa ibili y
ac oss he IEEE 1451 amily, making easie he
addi ion o new in e aces, especially when
TCP/IP is used.
Acco ding o he p e ious pa ag aphs, diffe en VisioWay
sys ems, playing diffe en oles, can be connec ed in o he
same TCP/IP ne wo k, as i is shown in Figu e 7.Uppe -le el
applica ions need only o dis inguish be ween NCAP and
TIM access. Consequen ly, i a inal use applica ion is com-
munica ing wi h a TIM o an NCAP, IEEE 1451.0 o HTTP
messages a e, espec i ely, exchanged. No ice ha e e y
NCAP can be connec ed o mul iple TIMs.
4.1. NCAP Implemen a ion. An IEEE 1451.0 HTTP se e
has been de eloped in C language o implemen NCAP un-
c ions o e he VisioWay Linux ke nel. Figu e 8 depic s he
block diag am o he designed NCAP applica ion, while
Table 2 shows all he implemen ed commands.
Al hough VisioWay, in i s o iginal o m, uns a gene al
pu pose HTTP se e , i is p e e ed o de elop a new IEEE
1451.0 complian HTTP se e , aking in o accoun he com-
munica ion wi h mul iple TIMs o e diffe en physical
in e aces and main aining a minimum CPU and memo y
usage. The in o ma ion ans e (HTTP and IEEE 1451.0) is
managed using he Linux selec sys em call, a oiding he need
o mul iple h eads. No ice ha mo e complex con igu a-
ions a e allowed unning se e al HTTP se e s wi hin he
same p ocess. When he implemen ed HTTP se e ecei es
a eques , i is analyzed o check i i is an implemen ed
command. IEEE 1451.0 commands a e dispa ched o TIMs i
equi ed and TIMs a e con olled o pe o m measu emen s
o accessed om he clien o ead he esul s in he IEEE
1451.0 o ma . No ice ha each egis e ed TIM has a queue
o eques s in he NCAP implemen a ion, and ha each TIM
eques can be eplied o no . I a eply is no expec ed, he
NCAP uses he iming pa ame e s included in he Me a-
TEDS o he TIM o de e mine whe he he TIM is eady
o ecei e new commands. In he case o being eady, he
eply is e ie ed om he queue o eques s. On he con a y,
i a eply is expec ed, he nex command is sen only a e
i s ecep ion, akingin oaccoun imeou e o s oconside
ailed ope a ions ha a e epo ed o he HTTP clien . I is
also possible o p io i ize commands, o example, eading
a senso agains w i ing a TEDS, which equi es mo e p o-
cessing ime.
4.2. TIM Design. The TIM implemen a ion is based in he
IEEE 1451.0 s anda d, allowing diffe en physical in e aces.
Eigh s anda d command classes (0–7), some ese ed classes
(8–127), and open classes o manu ac u e s (128–255) a e
included, and he TIM is implemen ed as an independen
p ocess wi h he abili y o manage and s o e he basic
in o ma ion and unc ionali y o he senso de ice using
TEDS o ms. A e ini ializa ion, he TIM uns like a da a
sou ce se e . I checks he physical in e ace o diffe en
eques s om he NCAP and decodes he command, which
indica es he ype o unc ion eques ed and he channel
add ess. The mos common unc ions include eading o he
channel ansduce da a, eading da a ypes, o eading he
channel s a us. I an e o is de ec ed on any o he T ans-
duce Channels du ing he se ice, he TIM se s an app o-
p ia e lag in he channel s a us egis e .
All messages be ween TIM and NCAP can be classi ied
in o command messages, TIM ini ia ed messages and eply
messages, ollowing he IEEE 1451.0 s anda d ecommenda-
ions. All ansmi ed in o ma ion is bundled oge he in o a
payload, which is hen encoded in o an oc e a ay.
The IEEE 1451.0 and 1451.5 s anda ds allow he imple-
men a ion o a poin - o-poin (P2P) o gene al ne wo ked
connec ion o he TIM. A P2P connec ion is chosen because
each TIM does no no mally alk wi h mo e han one NCAP,
allowing o a simple TIM implemen a ion, as nei he
add essing no disco e y p o ocols a e equi ed.
4.3. TEDS Realiza ion. A simple TEDS compile and a TEDS
eade ha e been de eloped o gene a e and es he TEDS
iles o he VisioWay equipmen . The TEDS compile ap-
pli-ca ion is a WEB-based in e ace ha allows use s o
in oduce he equi ed pa ame e ields and gene a es he
TEDS acco dingly. The gene a ed TEDS is displayed as
In e na ional Jou nal o Dis ibu ed Senso Ne wo ks 7
HTTP
se e IEEE 1451.0
TIM1
1
HTTP
eques
HTTP
esponse
2i
1 2 j
1 2 k
TIM2
TIMn
IEEE 1451.x
NCAP
TCP/IP ne wo k
···
···
···
Figu e 8: Block diag am o he implemen ed NCAP applica ion (IEEE 1451.0-compa ible HTTP se e ).
Table 2: Implemen ed commands.
Module Ope a ion Task
Disco e y API TimDisco e y Lis a ailable TIMs
T ansduce Disco e y Lis channels in one TIM
T ansduce Access API ReadDa a Read access o measu ed da a in a speci ic channel
W i eDa a W i e access o a speci ic channel
TEDS Manage API
ReadTeds Read a speci ic TEDS (Access Code)
ReadRawTeds Read TEDS om TIM bypassing NCAP cache
W i eTeds W i e a speci ic TEDS
W i eRawTeds W i e TEDS in TIM bypassing NCAP cache
Upda eTedsCache Upda e TEDS Cache
T ansduce Manage API T igge Pe o m a igge on he speci ic channel
Figu e 9: TEDS eade applica ion.
a comma-sepa a ed lis o by es, which can be used o ini ia-
lize memo y buffe s in he TIM p og am sou ce code. The
TEDS eade applica ion is ano he WEB-based in e ace, as
i is shown in Figu e 9.
The implemen ed Me a TEDS desc ibes he ela ions
among he diffe en T ansduce Channels o he TIM and
s o es he iming pa ame e s in he wo s -case scena io. I
indica es he numbe o implemen ed T ansduce Channels,
being possible o g oup hem in o con ol, ec o , geog aphic
loca ion, and ansduce channel p oxies g oups. The iming
pa ame e s a e used by he NCAP o es ablish ime-ou
alues in he communica ion so wa e and de e mine a
non esponse e en om he TIM. This TEDS also includes
an “UUID” ield, o globally unique iden i ie , which is an
iden i ica ion da a associa ed wi h he TIM whose alue is
unique and i can include some manu ac u ing de ails.
Some ields a e a ailable o he manu ac u e s. Two o
hese ields ha e been used o sa e he geos a iona y posi ion
o he de ice: la i ude ( ype 150) and longi ude ( ype 151).
Each ield includes 5 oc e s, he i s one being used o
indica e he sign (i.e., no h/sou h o eas /wes ), while he
es speci ies he deg ees, minu es, seconds, and hund ed hs
o second o he posi ion. This o ma has been adop ed o
simplici y easons.
Figu e 10 shows he TEDS compile applica ion de ining
he Me a TEDS. The ob ained ile in HEX o ma is shown in
Figu e 11, including he o al leng h in oc e s, he checksum,
and he TLV uples o he da a block. A his s age, he Me a
TEDS mus be s o ed in he memo y sys em o he TIM.
The T ansduce Channel TEDS shows all he cha ac e -
is ics o he a ailable senso s (each senso has an associa ed
T ansduce Channel TEDS). VisioWay has been adap ed in
such a way ha each unc ionali y ( ehicle-p esence de ec-
ion, di ec ional ehicle de ec ion, ehicle-queue de ec ion,
ehicle coun ing, occupancy, and afficinciden de ec ion)
is conside ed as an independen senso , ha ing hei own
8 In e na ional Jou nal o Dis ibu ed Senso Ne wo ks
Figu e 10: TEDS compile applica ion gene a ing he Me a TEDS.
Figu e 11: Me a TEDS “ ile” in HEX o ma .
T ansduce Channel TEDS. The ollowing in o ma ion is
s o ed in he da a block o he TEDS.
(i) The na u e o he measu ed da a (e.g., physical uni s
and lowe and uppe ange limi s).
(ii) The o ma o he da a o be ead om he TIM.
This includes he da a ype (e.g., UIn 8 o Floa 32) o
he numbe o indi idual da a samples in each da a
se , speci ied in ields like da a model, da a model
leng h, model signi ican bi s, and maximum da a
epe i ions.
(iii) The iming pa ame e s desc ibing he maximum
equi ed ime o pe o m diffe en p ocedu es (e.g.,
ansduce channel ead se up ime o sel - es ime),
as well as he senso sampling pe iod.
(i ) The a ailable sampling modes o he senso . Diffe en
sampling modes a e suppo ed in he s anda d
(con inuous, ee- unning, immedia e, and igge -
ini ia ed), as well as mul iple buffe s. Rele an
ypes (i.e., ields) o hese p ope ies a e sampling
a ibu e, sampling mode capabili y, de aul sampling
mode, buffe ed a ibu e, and da a ansmission
a ibu e.
Figu e 12 shows he TEDS compile applica ion c ea ing
he T ansduce Channel TEDS. This TEDS is lexible enough
Figu e 12: TEDS compile applica ion gene a ing he T ansduce
Channel TEDS.
o accommoda e o diffe en ansduce s. The s anda d de-
ines a small se o basic uni s ha can be combined o p o-
ide mos o he exis ing physical uni s. This se includes he
adian and s e adian and he se en in e na ional sys em base
uni s. Any pa icula uni used in a sma senso can be de-
ined as a ma hema ical combina ion o hese se o uni s. In
pa icula , occupancy es ima ion, pe cen age o ull queue,
and o he dimensionless quan i ies a e ob ained using
VisioWay; he eby, he base uni s ield is se o 0. O he mea-
su emen s can be ob ained om he a io o wo quan i ies,
and hei uni s can be speci ied using he Physical Uni s
In e p e a ion ield o his TEDS. Floa 32 da a ypes ha e
been chosen o be used in VisioWay channels.
O he cha ac e is ics and speci ica ions de ined wi h his
TEDS o he sma senso based on VisioWay a e he
ollowing
(i) F ee unning wi h p e igge as sampling mode,
al hough he immedia e mode is also possible.
(ii) One buffe is used.
(iii) The sys em e u ns da a when ins uc ed. The sma
senso does no con ain any s eaming capabili y, and
he da a ansmission a ibu e in his TEDS, which
es ablishes he a ailable ansmission modes (s eam-
ing mode o eques - igge ed mode), is omi ed.
Ne e heless, s eaming suppo could be included in
u u e de elopmen s.
(i ) The equipmen boo ime was used as he wa m-up
ime. No ice ha iming pa ame e s a e highly de-
penden on he ha dwa e and op imiza ions o he
VisioWay so wa e. Fo example, ields like T ans-
duce Channel upda e ime, which indica es he
maximum ime be ween a igge o a ead command
ecep ion and he da a a ailable e en in he da a se ,
a e de e mined by he ideo p ocessing algo i hms.
O he pa ame e s like T ansduce Channel ead delay
ime, which indica es he maximum delay be ween
In e na ional Jou nal o Dis ibu ed Senso Ne wo ks 9
Table 3: New ypes o he p og ammed T ansduce Channel TEDS
o VisioWay.
Func ionali y Value
Vehicle-p esence de ec ion 1
Vehicle di ec ional de ec ion 2
T affic inciden de ec ion 3
Vehicle coun ing 4
Occupancy 5
a ead command ecep ion and he co esponding
s a - ansmission e en , a e also difficul o e alua e
in he VisioWay equipmen .
The ypes ha he s anda d de ines o his TEDS do
no allow a comple e desc ip ion o VisioWay. The plug-
and-play mechanism o VisioWay equi es he use o one o
he open- o-manu ac u e ypes in he T ansduce Channel
TEDS (Table 3). No ice ha mo e ITS-based se ices can be
used, inc easing he u ili y o he p oposed sys em. Fo in-
s ance, i he s a e o a affic ligh is a ailable in eal ime o
he VisioWay equipmen , applica ions like ed-ligh unne
de ec ion a e easible.
The PHY TEDS is dependen on he physical communi-
ca ion media ha connec s he TIM and he NCAP al hough
he da a a e ead-only oc e s a e he TED is p og ammed.
I includes de ailed in o ma ion o he IEEE 1451.X physical
laye , es ablishing he minimum ansmi la ency, he maxi-
mum connec ed de ices, and he maximum da a h oughpu
cha ac e is icsin hecaseo awi elesslink.New ypeswe e
de ined o iden i y he IP and he physical add esses o he
VisioWay wi eless module. No ice ha he in o ma ion con-
ained in his TEDS is no essen ial o access he TIM since
mos physical laye s p o ide au o-con igu a ion deg ees
comple ely independen o he IEEE 1451 s anda d.
The Use T ansduce Name TEDS s o es he TIM name
( he name assigned by an end-use o a speci ic TIM),
es ablishing he name o iden i y a speci ic ansduce in
he comple e sys em. The s uc u e o his TEDS is ecom-
mended in he s anda d, and he manu ac u e mus p o ide
a blank space o non ola ile memo y ha can be p og am-
med by he end-use using he s anda d TEDS access
me hods.
4.4. T affic Moni o ing Applica ion Based on VisioWay Sma
Senso Equipmen s. The IEEE 1451 amily o s anda ds
allows using VisioWay o p o iding eal- ime afficda a
access o be used in web-based affic con ol and in o ma-
ion applica ions. Diffe en p o o ypes a e ins alled ac oss
he ci y o Se ille and connec ed o a p i a e Local A ea Ne -
wo k (LAN) using i s 10/100 Mbps E he ne po and a RJ45
connec o . Figu e 13 shows wo equipmen s moni o ing a
c oss oads. The link speed and he de ice h oughpu on he
p i a e LAN ha e been analyzed.
A ho ough s udy o he VisioWay capabili ies and pe -
o mance is equi ed, p io o i s con e sion in o a sma
ansduce . A mul icas con ol mechanism mus be applied
o make an effec i euseo hea ailablebandwid h[30]. An
VisioWay
Figu e 13: VisioWay in wo eal emplacemen s in he ci y o Se ille,
Spain.
expe imen has been pe o med o p o e he obus ness o
he p o o ype in conges ed ne wo ks wi h mul icas ideo
deli e y. One ex e nal PC uns he ne wo k affic moni o -
ing so wa e, called moni o ing p og am, based on libpcap
lib a ies (Tcpdump/libpcap p ojec ). Libpcap u ili y is wide-
ly used o low-le el packe moni o ing and il e ing. The
main idea o his u ili y is o cap u e SOAP incoming and
ou going packe s, while being comple ely independen om
clien coding. Using libpcap u ili y, each bi sen o ecei ed
h ough he physical link can be cap u ed, allowing he
moni o ing o he whole LAN affic. O he se o PCs wo k
as Da a Se e s. Two es s ha e been pe o med.
(i) The conges ed ne wo k is emula ed using he da a
se e s, and he pe o mance o VisioWay is s udied.
Fi s , he h oughpu o he main algo i hm—p o-
cessed ames pe second (FPS) when pe o ming
ypical ehicle de ec ion asks—is e alua ed unde
conges ed ne wo ks (up o 8000000 bps o ne wo k
affic) wi h a mul icas con ol mechanism. The e-
sul s show ha he sys em h oughpu does no de-
g ade in hese condi ions, emaining a s eady alues
a ound 7 FPS. No ice ha his abili y depends on he
ha dwa e design. The E he ne con olle included in
VisioWay analyzes ne wo k affic a he ne wo k
laye , a oiding any o e load o he VisioWay CPU.
The pe o mance o VisioWay has also been es ed
unde mo e ad e se condi ions, such as unicas con-
ol mechanism, wi h a 8000000 bps ne wo k affic
add essed o VisioWay. In his case, he gene a ed
ne wo k affic deg ades he sys em h oughpu ill
5,57 FPS.
(ii) Second, VisioWay pe o mance is analyzed unde
cons an eal- ime ideo deli e y, using UDP p o o-
col. The eal- ime ideo (MPEG-4 elemen a y ideo
using CIF o ma , a 384 Kbps and 25 FPS) is de-
li e ed o he ne wo k moni o ing PC. Table 4 and
Figu e 14 summa ize he ob ained esul s. The ime
be ween packe s is accep able o mos MPEG-
4 playe s in he 85% cases wi hou necessi y o
incoming buffe s. These buffe s, usually included in