129
ELECTRONIC
AND PHOTONIC
SWITCHING
IN
THE
ATM
ERA‘
J.
Masip- To &,
J.
Sole-Pa e a
and
G.
Junyen -Gi al
Uni e si a Poli scnica
de
Ca alunya, Spain
ABSTRACT
B oadband ne wo ks equi e high-capaci y swi ches in o de o p ope ly manage la ge amoun s o a ic luxes.
Elec onic and pho onic echnologies a e being used o achie e his objec i e bo h allowing di e en mul iplexing
and swi ching echniques. Focusing on he Asynch onous T ans e Mode (ATM), he inhe en di e en
cha ac e is ics o elec onics and pho onics makes di e en a chi ec u es easible. In his pape , di e en
swi ching s uc u es a e desc ibed, se e al ATM swi ching a chi ec u es which ha e been ecen ly implemen ed
a e p esen ed and he implemen a ion cha ac e is ics discussed. Th ee di e se poin s o iew a e gi en om he
elec onic esea ch, he pho onic esea ch and he comme cial swi ches. Al hough all he a chi ec u es whe e
success ully es ed, hey should also ollow di e en ma ke equi emen s in o de o be comme cialised. This
cha ac e is ics a e p esen ed and he a chi ec u es p ojec ed o e hem o e alua e hei comme cial
capabili ies.
INTRODUCTION
Mul imedia communica ions a e expec ed o eplace
elephony as he p edominan communica ions
se ice. The cu en needs o
6.4
Gb/s o elephony
o se e one million people may g ow o
600
Gb/s
when high de ini ion MPEG ideo se ices
(6
Mb/s)
a e deployed. Thus, e y high-capaci y (Tb/s)
swi ching will be equi ed in he u u e. ATM is he
as packe swi ch echnique eme ged wi h he aim
o se ice in eg a ion and bandwid h gain.
The e is no doub abou he leade ship o pho onics
o he anspo unc ions o Tb/s bandwid hs. This
is possible due o he unique p ope ies o pho onics:
25
THz bandwid h, low c oss alk be ween he
pho onic channels and s ong in e ac ion be ween
ligh and semiconduc o s. Ins ead, swi ching
unc ions a e solidly based on elec onics -high-
speed elec onic ATM swi ches a e al eady
comme cially ma u e hanks o an ex ensi e e o in
unc ion implemen a ion (ha dwa e-so wa e
codesign and
VHDL
au oma ic syn hesis) and high
densi y ga e and in e connec ion capabili ies (mul i-
chip modules). Ne e heless, a signi ican esea ch
e o in pho onic swi ching implemen a ion has been
done in spi e o he cu en poo p ocessing capaci y
o he pho onic echnology. The scope is
o
su pass
he speed limi o elec onics (abou
10
Gb/s) a a
easonable cos and o a oid he elec o-op ic
1
This wo k has been possible hanks o a ellowship o he
“Comisiona pe a la Uni e si a
i
Rece ca de la Gene ali a de
Ca alunya” (1997Fl 00725) inside he CICYT p ojec “Field T ial
o
CMC and ATM” (TlC96-1127).
con e sion bo le-neck owa ds an all op ical
ne wo k. An ATM op ical swi ch wi h elec onic
con ol is a i s s ep. The eme ging consensus
is
ha swi ching a o abo e ATM should be done
elec onically,
so
pho onics may s ill ha e a ole in
ATM swi ching.
In
(1
),
complexi y ac o s o elec onic swi ching,
a ic demands and op ical unk swi ching a e
discussed o b oadband ne wo ks. Ou pu pose is
o ex end
(1)
p o iding a e iew o he ATM
pano ama, gi ing compa isons o u u e esea ch
de elopmen s ocusing on a chi ec u al and
comme cial issues.
This pape is o ganised as ollows: Sec ion
2
iden i ies he gene ic swi ching unc ions. Sec ion
3
p ojec s hem o e bo h he elec onic and pho onic
echnologies. Sec ion
4
desc ibes he gene ic swi ch
a chi ec u es. Sec ion
5
p esen s he mos ecen
implemen a ions om he esea ch and he
comme cial communi ies. Sec ion
6
e alua es hese
implemen a ions om di e en poin s o iew.
Finally, Sec ion
7
concludes his pape .
GENERIC SWITCHING FUNCTIONS
Mul iplexing.
In o de o p ope ly manage la ge
in o ma ion lows, a ic concen a ion in di e en
mul iplexing laye s is equi ed a p esen , al hough
he numbe o laye s may be educed. The
in e change
o
in o ma ion be ween di e en
channels o he same laye is ca ied ou by di e en
swi ching unc ions acco ding o he mul iplexing
In e na ional B oadcas ing Con en ion,
12-16
Sep embe 1997
Con e ence Publica ion
No.
447,
D
IEE,
1997
s a egy. The e is a di e en echnology and p o ocol
o e e y laye which gi es di e en cha ac e is ics
o
each one. A possible mul iplexing hie a chy is shown
in Figu e 1. In his example, he mul iplexing
s a egies a e WDM (Wa eleng h Di ision
Mul iplexing), TDM (Time Di ision Mul iplexing) and
ATDM (Asynch onous TDM). WDM, uses he op ical
bandwid h spli in o ixed, non-o e lapping spec al
bands ha a e anspa en
o
he bi - a e and code
o ma . Con e sely TDM di ides he ansmission
ime in o ames, which in u n a e spli in o
slo s
and
hen one o mo e
slo s
a e assigned o a channel.
TDM o e mul i-channel WDM will be based on he
ITU (In e na ional Telecommunica ions Union)
wa eleng hs s anda ds. Speci ica ions s a ed in
ea ly 1997 and a e no s ill inished, bu a clea
pic u e o he wa eleng h g id has eme ged wi h a
channel spacing ixed
o
mul iples o 100 GHz wi hin
he 1.5 ym wa eleng h window. As can be seen,
TDM o e WDM has a ixed capaci y pe channel
and he alloca ed esou ces canno be exceeded
when necessa y and a e was ed when no used.
ATDM sol es his p oblem by using a s a is ical
alloca ion o he ansmission capaci y
o
a channel
whe e in o ma ion packe s a e mul iplexed.
Vi ual Ci cui
S .
Ci cui
G3-
Se ice
Op ic
WDM
Figu e 1. Mul iplexing hie a chy.
Swi ching.
The undamen al pu pose o swi ching is
he econ igu a ion o ou es and hei capaci ies as
he a ic demands ac oss a ne wo k change o e
ime. Any swi ch has
o
pe o m wo basic unc ions
i espec i e o ans e mode: demul iplexing
incoming channels acco ding o a gi en ou ing
pa e n and mul iplexing he channels on o he
ou going link. The swi ch is hus buil o a pa icula
mul iplexing and ou ing s a egy. The ne wo ks can
be ca ego ised acco ding
o
he combina ion o
hese unc ions in ci cui -swi ching ( ixed capaci y
and ou e), i ual ci cui -swi ching (s a is ical
capaci y and ixed ou e) and da ag am-swi ching
ne wo ks (s a is ical capaci y and ou e). This pape
is ocused on ATM i ual ci cui -swi ching.
Two di e en swi ching s uc u es a e possible,
namely space-di ision and sha ed medium. Space-
di ision in e connec ion s uc u e whe e an inpu has
dedica ed links o all ou pu s and hus equi es
demul iplexing be o e mul iplexing. Sha ed medium
s uc u e whe e all inpu s sha e a common link
o
all
130
ou pu s and hus mul iplexing comes be o e
demul iplexing. Basic swi ching elemen s a e based
on hese s uc u es and can be in e connec ed in o a
la ge swi ching ab ic. Besides muddemux, bo h
s uc u es equi e ou ing unc ions. The ou ing
unc ions a e s a ic o WDM and TDM once he
connec ion is made, bu i is no s a ic o ATDM
since packe s do no ollow any o de . Muddemux
o WDM channels equi e combina o s and
selec o s o he di e en wa eleng hs, while TDM
equi es synch onisa ion
o
a oid channel
o e lapping and ATDM equi es bu e ing o sol e
packe con en ion.
Elec onic and Pho onic Technologies S a e
O
The
A
F om abo e, o a gene al swi ching sys em, h ee
main unc ions can be iden i ied:
1.
Tempo al muddemux wi h bu e ing and
2.
Wa eleng h muddemux wi h wa eleng h
3. Space-di ision swi ching.
synch onisa ion.
con e sion ( o imp o e ou ing).
The ATM swi ch a chi ec u es use hese unc ions
when hey a e a ailable o as packe swi ching
(2).
TABLE 1 summa ises he s a e o he a o bo h
elec onic and pho onic echnologies when
implemen ing he p e ious unc ions. Ma u e
elec onic echnologies a e cu en ly a ailable a e
decades o e olu ion. Elec onic swi ching has
mos ly adop ed CMOS echnology, which allows o
high ha dwa e complexi y, al hough wi h a line speed
limi ed
o
155 Mb/s (STM-1) in p ac ice. Highe line
speeds a e achie ed by ei he using pa allel buses
o mo e powe consuming elec onics han CMOS
like
GAS.
These echnologies can implemen all
p e ious unc ions excep o he wa eleng h
domain. High-le el in eg a ion is possible o space-
di ision swi ching, which is only limi ed by cu en ly
a ailable chip packages. Time di ision swi ching is
limi ed by he elec onic bandwid h, which is abou
10
Gb/s.
One o he easons o he slow p og ess o pho onic
pene a ion in swi ching is he imma u i y o he
pho onic de ice echnology, compa able
o
he s a e
o
elec onics in he
‘60s.
Howe e , apid p og ess in
his ield is being made specially in he de elopmen
o in eg a ed pho onics. Op ical TDM has con ibu ed
he las ad ances in empo al mul iplexing and
demul iplexing unc ions while bu e ing is sol ed
using simple ibe delay lines. Synch onisa ion is no
a comple ely sol ed p oblem ye . WDM and spa ial
swi ching echnologies ha e e ol ed quickly and
seem o be eady
o
be in oduced in comme cial
de ices. Thei componen s can al eady ope a e a
131
ATM cell le elbas demons a ed in Sec ion
4.
Fo
u he in o ma ion abou he subjec s o his sec ion
e e o
(1)
and
(2).
II
II
I
A-
Rea&
o
sys em
6-
Good
pe "?
C-
Rudimen a y
D-
Femible
E-
Nd
eadble.
TABLE
1
-
Elec onic and pho onic s a e o he
a o swi ching unc ions.
RECENT SWITCHING IMPLEMENTATIONS
Nex , a e e iewing he main high capaci y
swi ching a chi ec u es, di e en ATM swi ching
implemen a ion a chi ec u es a e desc ibed om
h ee poin s o iew: elec onic esea ch, pho onic
esea ch and comme cial swi ches. Implemen a ion
de ails a e gi en in TABLE
2.
High Capaci y Swi ching A chi ec u es Re iew
Bu e ing in any packe swi ch is una oidable. The
need o con en ion esolu ion has gene a ed di e en
bu e ing s a egies. Inpu bu e s hold incoming
packe s (cells) while he e is no possible pa h
h ough he swi ch. In con as , ou pu bu e s hold
con ending cells when he e a e mul iple cell a i als
a he ou pu po s. Ou pu bu e is supe io since
inpu bu e su e s om
head
o
line
blocking, ha
is, cells wi h a ailable pa hs can no be swi ched
because o he
FIFO
discipline ha holds one
unswi chable cell on he head. Howe e , inpu bu e
is easie
o
implemen because i does no equi e
he speed necessa y o suppo ou pu bu e s.
Di e en high capaci y swi ching a chi ec u es
(Figu e
2)
a e now p esen ed acco ding o hei
basic swi ching s uc u e as p esen ed in he
p e ious sec ion. Fu he in o ma ion can be ound in
(3).
a) ~~~ Sha ed
Medium
b) C ossba
c)
Banyan Based
Figu e
2.
Swi ch ab ics.
mul iplexed among se e al inpu ou pu connec ions,
based on disc e e ime slo s. A bus is an example o
a physical conduc ing medium ha can
accommoda e ime-di ision mul iplexing.
A
memo y
module can also implemen connec ions based on
ime di ision since i holds cells supplied by inpu
po s ha a e emo ed by ou pu po s. This
kind
o
swi ches a e limi ed by bandwid h and he e in scale.
Mul icas ing and b oadcas ing a e easy
o
accommoda e since all ou pu s ha e access
o
all
inpu da a.
C ossba Swi ches.
This single s age, single pa h
nonblocking swi ches we e i s de eloped o ci cui
swi ching and la e used
o
connec mul ip ocesso s.
Many ATM swi ches a e based on c ossba swi ches
o use i as a basic building block. C ossba swi ches
a e a ac i e because hey a e non-blocking, simple,
modula and wi h minimal delays. La ge ull
c ossba s can be made wi h a ew VLSl chips,
whose in eg a ion is only limi ed by he a ailable chip
packages. Howe e , hey su e om squa e
complexi y and as con ol mechanisms o a
c ossba swi ch a e di icul . Many ou pu s selec ing
one inpu easily pe o m he b oadcas unc ions. In
o de
o
imp o e he c ossba pe o mance any o
he bu e s a egies explained in he i s pa ag aph
can be applied.
Banyan Based Swi ches.
The mul is age concep
i s appea ed in he ci cui swi ching a ea. This kind
o swi ches we e de eloped wi h he objec i e o a
non blocking swi ch wi h lowe complexi y han
c ossba swi ches. Fo ins ance, del a class
ne wo ks ha e been p oposed o mul ip ocesso
sys ems. This ne wo ks ha e a single sel - ou ing
inlou pa h bu su e om in e nal blocking. These
swi ches, which a e usually e e enced as Banyan
based swi ches, a e modula , ha e he same la ency
o all pa hs, suppo synch onous and
asynch onous a ic and a e sui able o VLSl
implemen a ion. The in e nal blocking makes he
h oughpu dec ease wi h a highe ab ic dimension
and inc ease wi h a highe swi ching elemen
dimension. Thei main d awbacks a e he di icul y in
dealing wi h conges ion due
o
he ex ensi e pipeline
and bu e ing h ough he swi ch and also he
di icul y o implemen b oadcas ing and mul icas ing.
Sha ed Medium Swi ches.
The physical connec ion
be ween inpu and ou pu po s is implemen ed using
a single high speed physical esou ce which can be
a conduc ing medium o a memo y. This esou ce is
ou
di e en
w&Ilengh s
each.
'
One
delay
S&
wi h
ou
&m
&elen&@.
Fou
ou &
wi h
ou
di e en wd elengh s
each.
TABLE
2
-
Implemen a ion de ails.
132
Elec onic Swi ching P o o ypes
The e a e many di e en app oaches o he
elec onic swi ching.
As
Banyan based swi ches had
VLSl
implemen a ion acili ies se e al swi ches we e
de eloped. One
o
his muil i-s age swi ches,
oge he wi h a single s age swi lch ope a ing on he
elec onic limi s, a e now p esen ed.
A
Banyan based swi ch.
Figu e
3
p esen s he
UTXC a chi ec u e. I is o ganised in pe iphe al and
cen al planes. The pe iphe al planes include he
exchange e mina ion pe o ming heade ansla ion
and policing. The cen al planes con ain he ATM
swi ching ab ic whe e he
BASE8
swi ching
elemen s o m a del a class ne wo k. The global
h oughpu depends on he numbe o s ages and
planes. The BASE8 also se es as an in e ace
be ween he pe iphe al and cen inl planes.
Figu e
3.
Elec onic Banyan based swi ch
(4).
The elec onic limi swi ch.
A
simple a chi ec u e has
been used o ca y elec onic echnology owa ds
i s
limi s.
As
can be seen in Figu e
4,
cells a i ing on
each se ial link a e demul iplexed o
424
bi s
(cell
wid h), ou ed o dedica ed ou pul -side FIFO s o age
acco ding o he con en s o he i ual channel and
i ual pa h ields in he ATM cell heade , hen
mul iplexed back
o
se ial o m and ansmi ed o
des ina ion. The e is a high,-speed pa h wi h
dedica ed FIFO bu e om each incoming link o
each
o
he o he ou going links.
I
TolF om
O he
Links]
while op ical in e aces a e a longe e m objec i e.
Follows a desc ip ion o each concep and a mixed
elec o-pho onic a chi ec u e in he las pa ag aph.
Figu e
5.
Fibe delay line swi ching ma ix
(6).
Fibe delay line swi ch concep .
Signals a e ou ed
on he basis o hei assigned wa eleng h and he
con en ion is sol ed by op ical ibe delay lines
adjus ed o mul iples o he cell du a ion.
As
shown
in Figu e
5,
a as uneable OWC (Op ical
Wa eleng h Con e e ) assigns o each ATM cell he
wa eleng h co esponding o i s a ge ou pu . Then,
he wa e-space ma ix p o ides access o he ibe
delay lines o inc easing leng h. Finally he ou pu
il e s a e uned o a di e en wa eleng h de ining
he ou pu add ess o he cell. The elec onic con ol
d i es he OWCs and manages he wa e-space
ma ix and delay lines as a FIFO.
Figu e
6.
Fibe loop swi ching ma ix
(6).
Fibe
loop
memo y swi ch concep .
I is based on a
ibe
loop
memo y
o
one cell du a ion. The di e en
wa eleng hs
o
he loop a e used as di e en
memo y posi ions. In case o con en ion he cell
is
con e ed o one a ailable wa eleng h in he
loop
and s o ed by uning on he ela ed op ical ga e in
he loop. When con en ion is sol ed, he cell is
ou ed o he des ina ion link uning he
co esponding ou pu uneable il e and dele ed
om he loop uning o he op ical ga e. The
elec onic con ol, on he basis o he a ached
ag,
manages he memo y posi ions as a sha ed bu e .
Figu e
4.
A as elec onic a chi ec u e
(5).
Pho onic Swi ching
P o o ypes
Based
on
ealis ic analysis o he po en ial
capabili ies and pe o mance achie able by he
pho onic echnology, h ee di e en app oaches o
ATM
bu e ing and hei in eg a ion in ou di e en
sys em concep s o he swi ching ma ix a e
p esen ed
in
(6).
They a e
all
composed
o
an
all-
Mul idimensional swi ch concep .
I
exploi s
he
op ical high-speed ou ing ne wo k elec onically wa eleng h domain o minimise he amoun
o
con olled. Incoming ATM cells a i e in phase, op ical bu e s equi ed in a mul is age swi ch. In
accomplished by elec ical in e aces in a i s s ep case o con en ion he cell
is
con e ed o a di e en
Figu e
7.
Mul idimensional swi ching ma ix
(6).
133
wa eleng h and ansmi ed a he same ime
slo .
The con ending cells a e no delayed in a bu e ,
hen bu e s can be elimina ed excep a he las
s age o he swi ch.
he ASX-200. The cells d ain om he swi ching
ab ic memo y o he second- ie sha ed memo y
swi ching/bu e ing modules, and om he e, a e
ansmi ed o he ne wo k.
155
MWs
ATM
in e
1.25
GWs
Op ical
bus
Figu e
8.
Co po a e op ical ATM ne wo k
(6).
Co po a e op ical
ATM
ne wo k concep . Sui able o
bo h access and p i a e ne wo ks. In his case,
elec onic swi ches a e in e connec ed wi h an
op ical double ibe ing h ough dedica ed op ical
access nodes. Cells a e inse ed and d opped a he
bi le el using mul i- unc ional high speed swi ches
wi h dedica ed hyb id d i e s.
Elec o-op ic
swi ch
An a chi ec u e ha also
in e connec s elec onic swi ches h ough an op ical
co e is p esen ed in
(7).
The ibe ing is subs i u ed
by an op ical c ossba . Then, a complex con ol
managemen p o ocol es ablishes op ical
connec ions acco ding
o
he bu e occupancy, he
p edic ed loads and he connec ion se -up ime.
Comme cial Swi ches
Mos comme cial ATM swi ches use single-s age
echnologies o he sake o simple con ol and a ic
managemen . They ypically ha e a o al swi ch
h oughpu om
1
Gb/s o
10
Gb/s. La ge swi ches
achie ing a capaci y close o 100 Gb/s ei he use
mul is age swi ching ab ics o in e connec smalle
swi ches o se e al gigabi pe second. In
(8)
a ious
comme cial swi ches a e es ed; he one wi h he
bes pe o mance was ASXQOO. This swi ch also
has a good ma ke pene a ion ac o .
So
we ha e
conside ed i as a good comme cial example. I s
a chi ec u e is explained now oge he wi h he nex
gene a ion swi ch ASX-1000.
In he ASX-200 a chi ec u e (Figu e 9.a), cells a e
p ocessed in h ee s eps. A he inpu , cells en e an
ing ess po , a e sen h ough wo s ages
o
VPlNCl
ansla ion and a e checked o compliance wi h hei
a ic con ac . Cells a e hen dis ibu ed, using
TDM, o mul iple sha ed memo y swi ching ou pu s.
In he ASX-1000 a chi ec u e (Figu e 9.b), cells pass
h ough he inpu unc ions in he same h ee-s ep
o de as in he ASX-200. The majo ou pu -side
di e ence
is
he p esence o
a
wo- ie hie a chical
swi ching/bu e ing sys em. T a ic is dis ibu ed om
he inpu s o he app op ia e i s - ie sha ed memo y
ia as many as ou indi idual 2.56
Gb/s
unidi ec ional TDM dis ibu ion ab ics. These
dis ibu ion buses use he same TDM echnology as
a)
Comme cial
a chi ec u e.
b)
A chi ec u e expansion.
Figu e 9. Comme cial swi ch (9).
EVALUATION ISSUES
F om he implemen a ion poin o iew, op imum
cos o a la ge swi ch is achie ed by selec ing a
simple opology and using he highes -speed
componen s a ailable a a easonable cos . Figu e
10.a illus a es his idea: o cons uc a swi ch
o
a
gi en capaci y, ewe pa s o a highe -speed
echnology can be used. The exac shapes o he
cu es depend on he a chi ec u e, and hey can
also shi wi h ime.
So
low speed elec onics equi e
a la ge numbe o pa s.
I
op ical pa s a e
in oduced a a easonable cos , he numbe
o
pa s
can be conside ably educed as he elec o-pho onic
a chi ec u es do. Finally,
i
e y high speed op ics
a e used, he o al cos inc eases a he momen bu
as men ioned ea lie , cos s could shi
(7).
F om he comme cial poin o iew, acquisi ion and
main enance cos s a e no he only economics
su ounding ATM due o he as echnological
changes o i s componen s. Many ac o s o he han
complexi y and pe o mance mus be used o
e alua e he p e ious a chi ec u es. They a e
enume a ed and discussed now ollowing he same
s uc u e used in
(10).
Coexis ence. Comme cial ma ke s equi e a high
le el
o
ATM in eg a ion in o de o coexis wi h o he
LANNVAN echnologies. LAN emula ion is he
solu ion o e ed by he ATM Fo um (11). In (12)
di e en comme cial ATM elec onic swi ches whe e
es ed and esul s demons a ed a good
pe o mance in LAN emula ion. Bes pe o mances
whe e ob ained wi h elec onic con e sion o ATM
lows e en o local swi ching. Op ical swi ches wi h
hei highe capaci y could be a desi able backbone
i
he educed p o ocol unc ionali ies did no became
a d awback o LAN emula ion. Coexis ence o
elec onic and pho onic echnologies is also
equi ed. Exis ing elec onic swi ches can bene i
om pho onic swi ching speed while e ol ing
owa ds all-op ical ne wo ks.

134
Eiec o.op lc
a ch.
a)
Technology
cos s
(7).
b)
Hie a chical
clus e ing
(10).
Figu e
10.
A chi ec u e cos s and scalabili y.
Complexi y and scalabili y*
Scalabili y e e s
o
a
sys em capabili y o e ol ing o expanding in
esponse o inc eased demands. This equi emen is
c i ical, since ATM echnology is in i s in ancy s age
and i s comme cial success depends on inc emen al
deploymen and a mig a able s a egy. Two aspec s
o he a chi ec u e mus be scalable: he numbe o
po s and he speed o e mina ing po s. They a e
somehow equi alen . Po scalabili y is closely
ela ed
o
he complexi y measu es o he
a chi ec u es. They a e summa ised in TABLE
3,
whe e he i ial conclusion is ha he linea o de o
he sha ed medium a chi ec u e is p e e ed.
Howe e , he limi ed sha ed medium bandwid h
limi s i s maximum scalabili y. A possible solu ion is
o inc ease he le el o pa allelism wi hin he swi ch
ab ic, ha is,
o
ou e a ic lows h ough mul iple
and pa allel pa hs like mul iple buses wi hin he
swi ch. This was he solu ion adop ed o he
SX-
1000.
Fo hose a chi ec u es wi h swi ching
ne wo ks he solu ion would be
o
accommoda e
pa allel ne wo k planes as he p esen ed Banyan
based a chi ec u e does. Finally, a clus e
a chi ec u e wi h mul iple swi ch ab ics
in e connec ed ia an in e clus e swi ch (Figu e
10.b) seems a good solu ion o elec o-op ical
swi ches like he ones p esen ed ea lie . Upwa d
scalabili y o he a chi ec u e ela i e
o
po da a
a es has a d as ic implica ion o he in e nal
esou ces o he swi ch ab ic. Thus, scalabili y
ela ed
o
po da a a es is mo e di icul
o
assess.
1
Ma ix
TABLE
3
-
Po scalabili y
(10).
I
O de
o
F
E icien use o bandwid h.
The comme cial ma ke
iews bandwid h in e ms o cos . ATM is a ac i e
hanks o he capabili y o dynamic bandwid h
alloca ion. Swi ching a chi ec u es ha employ a
complex p o ocol o es ablishing connec ion and
ou ing decisions do no use he in e nal bandwid h
e icien ly. Con en ion esolu ion phases and cell
duplica ion o b oadcas ing a e some examples.
a e elec onically con olled. Thus, ha dwa e o
so wa e bandwid h managemen p o ocols seem
o
easible in all cases.
Reliabili y and aul ole ance.
ATM as a LAN wi h a
s a opology equi es a high le el o eliabili y and
aul ole ance om he swi ch. Mul iple edundan
swi ches ha ope a e in p ima y and backup modes
a e a mus since chip ailu es would mos likely
disman le se e al (i no all) pa hs. Elec o-op ical
swi ches can p o ide qui obus pe o mance
depending on he eliabili y o he op ical co e.
CONCLUSION
As o oday, he mos immedia e e olu ion owa ds
he comme cial a ea seems o be domina ed by
pho onics as a highe le el swi ching, while
elec onics keep hei in e ace posi ion dealing wi h
i s limi ed bandwid h. Rega ding he in e ace,
elec onic TDM a chi ec u es can suppo
expandabili y, nonuni o mi y o po da a a es and
bandwid h managemen p o ocols. Inside he swi ch,
pho onic a chi ec u es can p o ide o concu ency
and speed. Thus, he imp o emen s in bo h
elec onic and pho onic a chi ec u es should be
in eg a ed in o de o comme cial implemen a ions
o
inc ease hei cos -e ec i eness.
REFERENCES
1.
Hui, J.
Y.
and Cheung, K. W., 1996. Op ical Ve sus
Elec onic Swi ching o B oadband Ne wo ks.
IEEE
Ne wo k,
No embeVDecembe 1996. pp. 21 o 25.
2.
Thylen,
L.,
Ka lsson, G. and Nilsson,
O.,
1988. Swi ching
Technologies o Fu u e Guided Wa e Op ical Ne wo ks.
Communica ions Maaazine, Feb ua y 1996. pp. 106 o 113.
3.
Awdeh,
R.
Y.
and Mou ah, H.T., 1994. Su ey o ATM
Swi ch A chi ec u es. Comw e Ne wo ks and ISDN -S s ems,
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I,
4.
Cla e o, S., Fassino, M., Liccia di, L. and Tu olla, M., 1994.
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RapDo o
Tecnico CSELT,
Sep embe 1994.
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Bu ne ,
S.
E. and Chi ukula,
R.,
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Elec onic ATM Swi ching. IEEE Ne wo k, No embedDecembe
1996. pp. 26 o 31.
6.
Mase i, F. and o he s, 1996. High Speed, High Capaci y
ATM Op ical Swi ches o Fu u e Telecom. T anspo Ne wo ks.
IEEE
J-SA in Communica ions, June 1996. pp. 979 o 998.
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E.
and o he s, 1995. A High-Capaci y ATM Swi ch
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lEEE
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64
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Mande ille, R., 1995. The ATM S ess Tes .
Da a
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9.
Fo eRunne ATM Swi ch A chi ec u e, Ap il 1996.
10.
Rooholamini and o he s, 1994. Finding he Righ ATM Swi ch
o he Ma ke . IEEE ComDu e , Ap il 1994. pp. 16 o 28.
11. ATM Fo um Technical Commi ee. LAN Emula ion o e ATM.
Ve sion .1.0, Janua y 1995.
12. Mande ille,
R.
and Johnson,
J.
T., 1996. Fo ge he Fo kli .
Da a Communica ions, Sep embe 1996. pp. 121 o 134.
ACKNOWLEDGEMENTS
ATM
po en ials
a e
due
o
i s
ha dwa e
We hank P o esso Guido Albe engo om he Poli ecnico di
implemen a ion capabili ies;
hus,
complex
so wa e
To ino o sugges ing us his opic, as well
as
P o esso Jose A.
p o ocols used
o
p o ide op imal bandwid h
Delgado Penin om he Uni e si a Poli ecnica de Ca alunya o
managemen do no con ibu e o achie e a good
encou aging ou co-ope a ion. We also hank Joan Vila Sallen o
pe o mance on ATM.
All
p esen ed a chi ec u es
his