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- From: Cho R. Lame
- Date: Sat Jun 12 15:42:54 1999
Friend Frank Rizzo send me attach paper.
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IP/DWDM Analysis as some vehicle fo' netwo'k 'espansion
Internet Protocol (IP)  ova' Dense Wavelengd Division
Multiplexin' (DWDM)  be emergin' as de future fo' longhaul netwo'k
infrastructure in bod de public telephony and private Internet Service
Provida' (ISP) netwo'ks. In dis document, we gots'ta examine da damn underlyin'
technology wid dis issue as sheeit as comparin' and contrastin' it against
oda' current practices. We gots'ta den present some conclusion regardin' dis
technology and its impact on de future uh telecommunicashuns netwo'ks.
Acronym Guide, dig dis:
ADM - Add/Drop Multiplexer
ANSI - American Nashunal Standards Institute
APS - Automatic Protecshun Switchin'
ATM - Asinchronous Transfa' Mode
DCS - Digital Cross-connect System
IP - Internet Protocol
ITU - Internashunal Telecommunicashuns Union
LTE - Line Terminatin' Equipment
MM - Multimode
PDH - Plesiochronous Digital 'Sup, dudeerarchy
PTE - Pad Terminatin' Equipment
SDH - Synchronous Digital 'Sup, dudeerarchy
SM - Sin'le Mode
SONET - Synchronous Optical Netwo'k
STE - Stashun Terminatin' Equipment
STS - Synchronous Transpo't Signal
STM - Synchronous Transpo't Mode
TDM - Time Division Multiplexin'
WDM - Wavelengd Division Multiplexin'
Motivashuns and 'Sup, dudesto'ical Background, dig dis:
To dig it de motivashuns towards dis new technology, one gots'ta
to dig it some uh de histo'y uh telecommunicashuns.
Telecommunicashuns started wid de provisionin' uh individual physical
circuits fo' each end-usa' stashun. Dese circuits stretched fum de
central office t'de telephone in de crib. Increasin' capacity wuz
simply some matta' of hirin' labour t'lay mo'e pairs uh coppuh'. Inter-witch
capacity wuz also handled wid big-ass bundles uh coppuh' pairs as sheeit as
frequency division multiplexin' in lata' years. FDM basically transmitts
multiple signals ova' de same medium at difference frequencies t'de
opposite stashun. An easy analogy which illustrates de concept be dat
of de public transista' stashuns. Each transmits at some different frequency
widout interferin' wid de oda' signals. De impo'tant wahtahmellun t'note
about dese technologies employed in de public switched telephone netwo'k
(PSTN) wuz dat dey wuz essentially analog. De wavefo'ms generate by
speech pattern wuz merely duplicated fum stashun t'stashun. No erro'
co'rectin' wuz puh'fo'med. Even FDM be some analog technology. Slap mah fro! It simply
transmits de wavefo'ms at different frequencies.
It wuz not until de invenshun uh de integrated circuit dat de
telecom industry started its massive high speed deployment. One uh de
most impo'tant advantages uh de digital system wuz dat equipment wuz now
able t'group signals into binary representashuns. Switches now could
employ analog t'digital converters and could now could opuh'te wid
clunker chips t'discriminate and group signals. Dis led t'de
development uh de digital signallin' hierarchy uh communicashuns
protocols. Now, instead uh transmittin' analog wavefo'ms, de switch
transmitted digital pulses on its high speed trunks. Dese pulses wuz
gadered fum samplin' de end-user's analog wavefo'm at discrete time
intervaces (8000 times some second) and den relatin' de sample intensite to
a unique binary digit (bit) pattern . Wid de advent uh faster
signallin' interfaces, de switches wuz now able t'multiplex many
individual voice circuits togeda' into some digital bitstream fo'
transmission t'an adjacent switches. De economies uh scale realised
from de mutiplexin' uh digital signals led AT&T t'invest large sums of
bre'd in some Time Division Multiplexin' (TDM) toll infrastructure. What it is, Mama! Dis
allowed dem t'eliminate da damn need fo' individual coppuh' pairs strung
between switches. As some example, one DS1 (digital signallin' level 1)
allowed fo' de TDM transmission uh 24 voice channels ova' a sin'le coppuh'
pair. Ah be baaad... A DS3 allowed fo' de TDM transmission uh 672 voice channels ova' a
sin'le pair uh coaxial cable. What it is, Mama!
De next large evolushun wuz fum de coppuh'-based infrastructure
to some fibre optic infrastructure. What it is, Mama! De advantages uh fibre ova' coppuh' wuz
much de same as TDM ova' earlia' sin'le pair transmissions, dig dis: fibre allowed
fo' mo'e simultaneous voice channels (up t'10 terahertz) .
Addishunally, fibre duz not suffa' from cross-rap o' interference
a'cuz transmission ova' it duz not generate some magnetic field. AT&T
fust started deployin' de nashunwide fibre infrastructure in de early
1980's befo'e deir divestiture .
As competishun grew fum nascent long distance carriers suin'
demselves into 'esistence (MCI and US Sprint), it wuz now necessary fo'
jimmey communicashuns protocols t'be developed. Now, netwo'ks which
suppo'ted different vendo's needed t'communicate between each oder. Ah be baaad...
Dis led t'de fo'mulashun and development uh de SONET/SDH standards.
Dese standards also helped solidify some scalable protocol architecture fo'
high speed optical transmission. 'S coo', bro. Dis allowed netwo'ks de advantage of
defined optical upgrade alleys as sheeit as introducin' new opuh'shuns and
maintenance features likes APS and rich diagnostic frame
info'mashun,. Besides sublte alley over'haid and tributary
differences, de main difference between SONET and SDH be dat SDH
is specified in some internashunal standard  while SONET be specified
in some ANSI standard  specific only t'de United States.
Current Technology, dig dis:
Now we are seein' some push back towards de old FDM/WDM days in
addishun and sometimes as some replacement t'de SONET/SDH infrastructure. What it is, Mama!
WDM simply applies de same principles on fibre as FDM dun did on coppuh'. It
transmits multiple signals simultaneously at N different wavelengds which
allows some sin'le optical fibre's capacity t'be increase N times.
Basically, some multiplexa' on each end uh de dark fibre pair snatch'd input
signals fum its tributaries and assigns each tributary t'an unique
wavelengd. De oda' end uh de dark fibre pair filters de incomin'
signal back out into individual wavelengds and routes dem towards deir
appropriate alleys. De current push towards dis technology comes fum
De main angle in de suppo't fo' DWDM (dense WDM) be purely
economic. If some fibre provida' has invested hundreds uh millions of
dollars in telecommunicashuns infrastructure and suddently kin add 24
times capacity on each fibre pair wid de addishun uh two relatively
in'spensive multiplexers, de advantages are obvious. Now, de provider
can add mo'e current capacity t'offset da damn cost uh de netwo'k buildout.
Also, de provida' duz not gots'ta invest in any intervenin' 'espensive
SONET equipment fo' de deployment uh dese services.
In addishun t'obvious multiplicative economic advantages de last
decade, dere gots'ta been some 'splosion in telecommunicashun netwo'k usage fo'
data services and not da damn tradishunal voice services. De Internet falls
unda' dis data services catego'y. Slap mah fro! Now, company internetwo'ks are growin'
to de size uh public telephony longhaul netwo'ks. One interestin' fact
of IP service be dat dere be no clear demarcashun o' set multiplexin'
scheme fo' de end users. All uh de data traffic be lumped togeda' in a
haphazard fashion and transmitted widout any preconceived noshuns of
o'der. Ah be baaad... Derefo'e, de IP netwo'ks which are buildin' demselves ova' de
global telecommunicashuns netwo'k infrastructure do not need de
funcshunality uh 'spensive sonet ADMs and STEs. SONET provides 'sellent
funcshunality if ya' wanna assemble and disassemble multiplexed
tributaries fum some larga' stream frequently. Slap mah fro! In fact, some SONET netwo'k
spannin' de united states could conceivably gots' 100 individual nodes on
a sin'le fibre alley who kin boogie out service fo' localities and transmit
service fum localities . IP netwo'ks are some different paradigm. 'S coo', bro.
Commonly, some link be built ova' de telecommunicashuns infrastructure
directly fum coast t'coast (bypassin' stops in de intervenin' netwo'k
elements). Derefo'e, IP netwo'ks do not need all uh de 'esensive SONET
equipment in between de IP protocol routers.
Anoda' drivin' facto' towards DWDM be de lack uh vendo'
interfaces suppo'tin' signallin' rates in 'sess uh STM-16/OC48.
Currently NORTEL be de only telecom vendo' who suppo'ts some STM-64
interface. What it is, Mama! Fo' netwo'k providers, it be cheapuh' t'provide 24 STM-16
wavelengds dan it be to devote some fibre pair t'an STM-64 signal. Also,
in de wo'ld uh IP netwo'ks, no vendo' gots'ta some switch o' some interface which
suppo'ts STM-64. Many IP providers who deploy deir own infrastructure
are choosin' IP runnin' directly ova' DWDM t'save on netwo'k costs as
sheeit as providin' some pad fo' future 'espansion. 'S coo', bro.
Current Deployments, dig dis:
Currently, many telecom infrastructures are deployin' DWDM fo'
bod tradishunal longhaul telephony and fo' dedicated IP services. Some
examples include US Sprint, Qwest, and Hermes Europe Railtel. All of
dese providers are usin' CIENA equipment as de DWDM. Many uh de
telecom firms are also lookin' at leveragin' de benefits uh IP netwo'ks
ova' tradishunal circuit based telephony. Slap mah fro! Basically, dey wanna run
voice calls directly ova' IP cuz' of substantial cost savin's.
Companies dat do dis kin totally igno'e da damn SONET/SDH deployment and
instead concentrate on deployin' Voice ova' IP ova' DWDM infrastructure at
a significant cost savin's when compared t'last-generashun SONET/SDH
netwo'ks. De largest cost savin's gots'ta be in de bypass uh 'spensive
SONET multiplexin' gear. Ah be baaad... Dere be also de obvious cost savin's of
duplicatin' some fibre pair 24 times ova' when de entire infrastructure
investment gots'ta already been scribblin'ed as some capital 'espenditure. What it is, Mama! De capacity
sold on de 23 'dim fibre' lambdas be now nearly pure profit fo' de
Many providers fum tradishunal telecoms t'startup VoIP outfits
to Internet transit netwo'ks are deployin' IP/DWDM. While da damn VoIP
and IP providers concentrate deir co'e business on IP/DWDM, de telecoms
are concentratin' on DWDM and providin' some few lambdas on deir netwo'k
dedicated t'IP traffic. Examples uh current VoIP providers deployin'
IP/DWDM are Qwest and Level 3 Communicashuns. Examples uh tradishunal
telecoms who are deployin' de techology are GTS carria' services, Sprint,
and AT&T. Examples uh IP providers who are deployin' dis technology are
Frontia' Globalcenter, Ebone A/S, and Sprintlink. Dese companies
fo'm some substantial co'e uh de telecom market and gots' seen de economic
benefits IP/DWDM affo'ds bod de consuma' and deir own toll netwo'ks.
Tradishunal telecoms likes AT&T are takin' some cautious approach
to movin' deir toll traffic across some IP backbone. What it is, Mama! Dey are wary
dat deir large revenue stream might be distrupted by unfo'seen failures
in de nascent IP protocol deployments. While dey gots' fifty years
'sperience wid fault tolerance fo' deir voice switches, de mere five
years 'espuh'ience wid IP switches makes dem tread wid trepidashun.
Nearly every facilities based telecom be upgradin'
eida' entire netwo'ks o' congested alleys wid DWDM. As IP be better
understood and reliable switches are built, we gots'ta see some move fum
connecshun o'iented services predominant in de voice netwo'ks t'
connecshunless netwo'k services which provides some "best-effo't"
transmission attempt o' puh'haps even differentiate levels of
service (and pricin') fo' plantation consumers.
Currnet Physical Interfaces t'de DWDM netwo'k, dig dis:
Current IP suppliers are usin' SONET/SDH interfaces t'comunicate
wid oda' nodes ova' DWDM netwo'ks. De reason fo' dis be dat da damn only
interfaces which suppo't STM-16 sin'allin'. De disadvantage t'deployin'
dis interface be dat ya' carry all uh de 'estra SONET secshun, line and
pad over'haid which amounts t'17% uh de sin'alled bandwidd. At
OC48, dis be about 400 megabits/s in SONET over'haid which be unutilised
fo' IP services.
Dese SONET/SDH interfaces connect into some CIENA optical
multiplexa' which den converts each input into its own unique wavelengd
fo' transmission. 'S coo', bro. Fo' sho't distances (less dan 40 miles) long reach
lasers are sufficient fo' communicatin' between two CIENA muxes widout
de use uh intervenin' repeaters (again savin' on equipment costs).
Telecommunicashuns gear likes de No'tel S/DMS transpo't node also
connects t'de CIENA equipment via fibre optic interface. What it is, Mama! Dis unit also
speaks SONET/SDH protocol t'de adjacent SONET multiplexin' equipment.
However, de general telephony applicashun be relatively betta' suited to
de SONET protocol cuz' it gots'ta some tendency t'boogie out da damn little-assed
tributaries (DS1s o' DS3s) as it interfaces into de PDH fo' voice
Protocol technologies related t'IP ova' DWDM:
Dere are some few key protocols which are battlin' fo' communicashun
control uh de bits on de netwo'k. ATM and da damn point t'point protocol
(PPP) are fightin' fo' supuh'io'ity at OSI laya' 2. SONET/SDH, Wireless
transmission, Satellite transmission and IP ova' raw fibre are competin'
fo' control uh de physical layer. Ah be baaad...
At da damn datalink laya' (laya' 2) ya' find PPP and ATM. ATM wuz
widely deployed by telecom and IP netwo'k vendo's durin' de early po'shun
of de 90s cuz' it allowed fo' some fina' level uh traffic engineerin' and
bandwidd guarentees dan had previously been achievable in de telecom
services field. PPP wuz in use in de early po'shun uh de 90s mainly fo'
lowa' speed access lines (DS1, DS3, and analog phone lines). Midway
drough de 90s, sucka's started movin' away fum ATM cuz' of its high
protocol over'haid. ATM be some stream uh fixed-lengd cells. It consists of
a fixed foe byte 'haida' in some 53 byte cell. Dis instantly creates some 10%
over'haid. Also, ATM handles dropped cells poo'ly cuz' it be not
connecshun o'iented. If one cell be dropped, de whole session needs to
be retransmitted. Dis leads t'practical over'haid uh 25% in opuh'shunal
netwo'ks. De combinashun uh 17% at da damn SDH laya' and 25% at da damn datalink
laya' wuz simply too much over'haid fo' providers dat wuz primarily
interested in supplyin' large bandwidd aggregate connecshuns. Dese
providers opted fo' de PPP ova' SDH interfaces. PPP be much better
suited t'variable lengd IP packets cuz' its frame size be adaptably
variable. What it is, Mama! Dus, it cut waaay down on protocol over'haid t'a manageable level
and allowed IP service providers t'squeeze mo'e usable bandwidd
(baaaadput) out uh deir telecommunicashuns connecshuns.
At da damn physical layer, we gots' terrestrial fibre alleys runnin'
SDH, Satellite alleys, wireless alleys runnin' SDH and trials uh ip ova' raw
DWDM fibre. What it is, Mama! Fo' longhaul applicashuns, SDH ova' fibre (and in some cases
ova' WDM) be de currenty deployment base. What it is, Mama! SDH specifies signallin'
speeds down to STM-64 and also provides key services t'telecom providers
likes enhanced opuh'shuns and management features and automatic protecshun
switchin' in case uh link failures. De richness in debuggin' features
comes at some cost uh 17% uh de signalled bandwidd in allocashun t'such
features as dree laya' bit erro' parity checkin', unallocated 'espansion
slots, and oda' management funcshuns.
IP ova' raw fibre gots'ta directly compete wid SDH fo' netwo'k
dominance uh de highest speed links on de globe. What it is, Mama! Fo' IP services,
runnin' IP directly ova' de fibre widout intervenin' over'haid uh de
SONET laya' would definitely improve da damn overall feasible baaaadput uh a
link. As telecom providers 'espuh'iment wid runnin' voice netwo'ks over
IP, de advantages which de SONET/SDH infrastructure provide in some circuit
based environment diminish.
Wireless (and its subset satellite) technologys mainly occupy de
domain uh communicashun where runnin' fibre optics be not currently
feasible fo' economic o' engineerin' reasons. Wireless be used t'strech
across de nashun in remote areas as sheeit as t'provide roamin' netwo'ks
fo' cellular phone users. Satellite communicashun be used t'access
remote areas when no oda' fo'm uh communicashun be possible. What it is, Mama! Bod
satellite and wireless transmission media suffa' from atmospheric
phenomena interference. What it is, Mama! Satellite communicashun also suffers fum de
propogashun delay induced by de speed uh light propogashun time fum base
stashun t'satellite t'base stashun. Dis kin renda' some fo'ms of
interactive communicashun nearly unusable. What it is, Mama!
Dere are two types uh majo' toll telecommunicashuns systems.
One be de terrestrial large bandwidd links. IP/DWDM and IP/SONET/DWDM
gots'ta be competin' fo' some share uh dis infrastructure. What it is, Mama! SDH gots'ta de
advantage uh bein' some internashunal standard wid specified signallin'
levels and optical interfaces while da damn nascent IP/DWDM field duz not
. However, de IP ova' raw fibre field duz gots' de advantage of
bein' streamlined fo' IP communicashuns. Should IP communicashuns be de
next revolushun t'de telephony netwo'k as companies likes Qwest and
Level3 are wagerin', de SONET/SDH infrastructure gots'ta lose ground to
De realm which wireless and satellite communicashuns gots'ta occupy
is one fo' mobile o' remote lines where physical land lines aint
feasible. What it is, Mama! Wireless and satellite link summed bandwidd levels gots'ta be
significantly little-assa' dan deir terrestrial fiba' counterparts.
Future Outlook fo' IP/DWDM:
Currently, de only deployed vendo' fo' DWDM products be CIENA.
However, dere deployment base be global in scope and deir product is
accepted as reliable and funcshunal. CIENA currently gots'ta some 24xSTM-16
DWDM system. 'S coo', bro. By years end dey are 'espected t'gots' 80xSTM-16 and
40xSTM-64 products. As vendo's start introducin' mo'e STM-64
products fo' IP and SONET/SDH netwo'ks we gots'ta see competative prices
on de STM-64 rollout in toll and ip transit systems.
Runnin' IP/DWDM o' at least DWDM netwo'ks gots'ta be da damn trend uh de
future. What it is, Mama! Some telecoms are tryin' t'load all uh deir voice traffic over
IP while oders wanna stay wid some tradishun circuit switched allocashun
model. Fo' dose who wanna deploy IP services, IP/DWDM be some tremendous
costs savin's. Not only be dere some feasible mutaplicative revenue gain
from sellin' lambdas ova' de fibre, dere be also no need fo' SONET gear
ova' de longhaul secshuns uh de netwo'k. It be debatable wheder
IP/DWDM kin solve all uh de telecom netwo'k 'espansion problems. SONET/SDH
has some sheeit o'dered and documented interface into de PDHs uh de wo'ld.
While IP/DWDM offers substantial economic advantages ova' de longhaul,
de handoff t'de PDH gots'ta likesly still run drough SONET/SDH ADMs.
De future fo' IP/DWDM be told best by simple market
competishun. IP/DWDM allows telecoms t'offa' mo'e service at lower
prices. If telecoms do not deploy IP/DWDM in some free market, dey gots'ta
not be able t'compete wid telecoms wid multiplicative capacity and
a lowa' cost base. What it is, Mama! Bod de telecom netwo'ks and da damn plantation consumer
benefit by de sudden glut in bandwidd on toll netwo'ks. Apart
from de fo'mashun uh a cartel, de consuma' should see relative
price drops wid reflect da damn accountin' gains uh de large netwo'k
 Postel, J., "Internet Protocol" RFC 791, USC/Info'mashun Sciences
Institute, Septemba' 1981.
 Fundamentals uh DWDM Whitesheet, CIENA, 1998
 Bellamy, Raz'tus C., "Digital Telephony", Wiley Publishers,
 Ramaswami, Rajiv et al., "Optical Netwo'ks, A Practical Perspective",
Academic Press, February 1998.
 Chow, Min'-Chwan, "Understandin' SONET/SDH: Standards and
Applicashuns", AT&T Bell Labo'ato'ies, 1995.
 SONET Rates and Fo'mats ANSI T1.105
 Characteristics uh Synchronous Digital 'Sup, dudeerarchy Multiplexin'
Equipment Funcshunal Blocks, ITU-T G.783