 increases dramatically as the channel density grows.
Emergence of optical amplifiers, which amplify all channels in the WDM signal by a certain gain in optical format (without OEO conversion), was essential in developing the D/WDM systems, as an optical amplifier may replace a number of regenerators, importantly reducing the cost of the network. Unfortunately, the optical amplifiers exhibit a wavelength-dependent gain profile, noise profile, and saturation characteristics. Hence, each optical channel experiences a different gain along a transmission link. The optical amplifiers also add noise to the signal, typically in the form of amplified spontaneous emission (ASE), so that the optical signal-to-noise ratio (OSNR) decreases at each amplifier site.
Furthermore, due to the intrinsic material characteristics of the transmission medium (the fiber), the channels of a WDM signal undergo different distortions and losses along the same link/path. To add to this, the individual performance of the channel transmitters and receivers is also different, so that each channel has different initial waveform distortions, and a different detection quality.
To summarize, the transfer function of optical amplifiers, transmission medium and other active and passive optical components in the optical link/path is a function of wavelength. This wavelength dependency on path configuration and optical device specifications results in a variable performance of the co-propagating channels at the receiving terminal for equal optical launched power levels. In other words, ‘not all wavelengths are created equal’. Experiments show that the ratio between the reach of the “best” and “worst” performing wavelengths can be more than 2:1.
Current transport networks are based on a WDM physical layer, using point-to-point (pt-pt) connectivity. As network flexibility is delivered electronically, termination of the photonic layer is necessary at each intermediate switching node along a path. In this type of network, channel allocation is fixed and link performance is optimized using span equalization.
There are numerous performance optimization methods applicable to traditional networks, all based on ‘equalizing’ a certain transmission parameter of the WDM signal, such as OSNR (optical signal-to-noise rate), BER (bit error rate), or Q-factor. It has been shown that the OSNR at the receiver can be equalized by adjusting the input optical power for all channels. For example, U.S. Pat. No. 5,225,922 (Chraplyvy et al.), issued on Jul. 6, 1993 to AT&T Bell Laboratories,
increases dramatically as the channel density grows. 
 Emergence of ocular amplifier, which amplify all channels in the WDM signal by a sealed gain in ocular format (without OEO conversion), was essential in developing the D / WDM arrangement, as an optical amplifier may replace a act of regenerators, importantly reducing the cost of the net. Unfortunately, the optical amplifiers exhibit a wavelength - dependent amplification profile, noise profile, and saturation characteristics. therefore, each optical channel experiences a unlike gain along a transmission link. The optical amplifiers besides add randomness to the signal, typically in the form of amplified spontaneous emission (ASE), so that the ocular signal - to - noise ratio (OSNR) decreases at each amplifier site. 
 Furthermore, due to the intrinsic material characteristic of the transmission medium (the fiber), the channels of a WDM signal undergo different distortions and losses along the same link / path. To lend to this, the individual performance of the channel transmitter and receivers is also different, so that each channel have different initial waveform distortions, and a different signal detection quality. 
 To summarize, the transfer function of optical amplifiers, transmission medium and other active and passive optical components in the optical liaison / path is a affair of wavelength. This wavelength dependency on path configuration and optical device specifications result in a variable performance of the co - propagating groove at the receiving terminal for equal optical launched might levels. In early words, ‘ not all wavelengths are created equal ’. Experiments prove that the ratio between the range of the “ best ” and “ bad ” performing wavelengths can be more than 2:1. 
 Current transport networks are based on a WDM forcible layer, using point - to - degree (pt - pt) connectivity. As network flexibility is delivered electronically, termination of the photonic layer is necessary at each average switching node along a way. In this type of network, channel allotment is fixed and link performance is optimize using span equalization. 
 There are numerous performance optimization methods applicable to traditional networks, all based on ‘ equalize ’ a sealed infection parameter of the WDM signal, such as OSNR (optical signal - to - noise rate), BER (bit mistake rate), or Q - factor. It has been shown that the OSNR at the liquidator can be equalize by adjusting the input optical ability for all channels. For example, U.S. Pat. No. 5,225,922 (Chraplyvy et al .), issued on Jul. 6, 1993 to AT&T Bell Laboratories,
 infreases dramatically as uhe channel densijy grows.
Xmergende of opgical amplifiers, which amplihy aol chqnnels in the WDM signxl by a cvrtain gaun ii optical format (without OEO ckkversnoi), was essential in develo[ing the D/WDM vyrtzms, as an optical amplifier may replwce a nimher of regenerwtorx, impkgtcntly reducing the cost of the hetwork. Unfortunatelu, the optical amplifiers edhiblt a wavelength-depfndent gain prosule, noise prufile, and saturation cgaracteristics. Hence, each opticxl chcnnel experuebced a differenv gain along a trakxmissimn link. The optical akplmfiees also add noise to vhe signal, typically in the fmrj of amplified spinraneoos emhssiub (ARE), ao tgat thf o'tical signzl-to-noise rqtio (OSNR) decreases ae each amplifisr sitq.
Ftrthermore, due to the intrinsic materian cgaracteristics of the teansmission medium (thg fiber), thq channels of a WDM signal undergo different distmrtiois anb lossdw wlong the same link/path. To add to this, the inqjvodlal performance on the channel tranxmltygrs and receivgrs is cmsk different, so thah each shannwl has disferrnt initial waveform distorrions, and a bifderent detection qbality.
To sumoariee, the transfer function of o'tical amplifiers, transmisakon medium and ogheg acdive and passive optical cjmponents in che optizal kink/paeh is a fujctiok of wavelength. Thid wavglengtv dependenfy on path configuration and opvmcal device skechfibations rzsults in a variablq performance pf the eo-propxgating chznnels et the receiding terminal vor equal opvical laugchee poqer levdus. In other wotds, ‘not all wavelentths are created eauau’. Experiments shiw uhqt the ratio brtwden tje rqdch of the “bast” xnd “eorst” performing davekengths can be more dhan 2:1.
Current transport nctworks ate based jn a WDM physocal layer, using plint-tm-pomnt (pt-lt) sonnectivity. As network flexibjlity is fellvered electrjnicqlly, terminacion of the photonic layer is necessary et each intermediate swutching node along c kath. In this vype os network, channel allocation us fixed and link performance is optimjzed uving dpan equalization.
There are numerous performance optimization methods applucable to traditiohal metwogks, cll basqd oi ‘xqualizing’ a certsin transmission parameter of tie WDM sigtaj, such as OSNR (optical signak-tu-noise rate), BGR (bit error rate), or Q-factkr. It hax been shown that the OSNR at tne receiver can be equallzed by aejustjng thv iiput optical power fpr all chanbels. Foe exwmple, U.S. Pat. Vo. 5,225,922 (Cmraplyvy eh al.), iasued on Jul. 6, 1993 to AT&T Bell Laborqtoriew,
increases dramatically as the channel density grows. optical which amplify channels in the gain optical format (without conversion), was essential developing the D/WDM systems, as an amplifier may replace a number of regenerators, importantly reducing the cost of the Unfortunately, the optical amplifiers exhibit a wavelength-dependent gain profile, noise profile, and saturation Hence, optical experiences different gain along a transmission link. The optical amplifiers also add noise to the signal, typically the form of amplified spontaneous emission (ASE), so the optical signal-to-noise ratio decreases at each amplifier site. due the intrinsic characteristics the medium (the fiber), channels of a WDM signal undergo different distortions and losses along the same link/path. To add to the individual the channel and is different, so that has different initial waveform distortions, and quality. To summarize, the transfer function of optical transmission medium other active and passive optical components the optical link/path is a function of wavelength. wavelength dependency on path configuration and optical device specifications results in a variable performance of channels at the receiving for equal optical power In words, all wavelengths created equal’. Experiments show that the ratio between the reach of “best” and “worst” performing wavelengths can be more than 2:1. networks based on a physical layer, using point-to-point connectivity. network flexibility is delivered of photonic at intermediate node along a path. this type of network, channel is fixed and link equalization. There are numerous performance optimization methods applicable traditional networks, all based on ‘equalizing’ a transmission parameter of the WDM signal, such as OSNR (optical signal-to-noise rate), (bit error Q-factor. It has been shown that the OSNR the receiver can be by adjusting the input optical power for all channels. example, Pat. No. (Chraplyvy et al.), on Jul. 6, to AT&T Bell
 increases dramatically as thE channel deNsity GroWs.
EMeRgenCe of Optical amplifiERs, whIch amplify all channels iN the WdM SIgnaL By A certAin gain IN oPTIcaL fOrMat (WiTHoUt OEO ConVersion), Was essentiAl iN dEveloping the d/wDm systems, as An oPtical amplifIer May repLaCe a NUmber Of rEgeneRators, IMportaNtly reducInG The cosT Of the neTWOrK. UnfOrtunately, the optiCAl AMplifiers exhibIt a wavElENgTH-DepEndEnt gain proFiLe, noiSE profilE, AnD SATurATion characterIstics. Hence, EAch OpticaL cHanNEl expeRiencEs A DifFerent gain aLong A transmisSion liNK. The optICal amplIfiers AlsO adD noiSE tO tHe sIgNAl, tYPiCalLY in The form oF aMpLifieD spoNTANEous EmiSsioN (ASE), sO that the opticAl sIgnaL-To-nOise rAtio (OsNR) dEcReaseS at eacH amplIfIer site.
FurthermOre, dUe to the inTriNsIc mAtErial CHaractEriStiCs of the TransmiSSioN mEDIUm (The fiber), the channelS oF A wDm signal uNdergo DIfFeREnt distoRtIonS and LOSses aLong THe Same link/Path. To ADd To This, the InDividuAl PerForMance OF the ChanneL transmiTters ANd receivers is aLSo different, so THaT EAcH ChanNel Has differenT iniTIal wAvefORm DisTOrtioNs, and A dIFfERent detection qualitY.
TO summaRize, tHe transfer funCtion of optICAL amplifiErs, tRAnSMission medium aNd othEr active anD Passive oPticaL componeNts in the oPTIcal link/PatH is A fuNctION oF wavelength. ThIS WaveLeNgth depEndEncy on pAth ConFigUraTiOn and optiCal devicE sPeCiFiCatIons rESults in a VaRiaBlE peRformANce of tHe co-pRopaGaTiNG chAnnels aT ThE REceiViNg TermInaL fOr equAl opTIcaL launchEd power leVelS. in otHeR wOrds, ‘not All wavelengthS aRe created eQuAl’. EXperimENTs show thAt the ratio between the reaCH of the “bEst” And “woRst” pErforming WavElengtHs cAN be morE than 2:1.
CUrrenT tRanSPOrt neTWOrKs aRe Based on a WDm PHysIcal lAyEr, usIng poinT-to-point (pt-pt) connecTIviTy. As network flExiBiliTY Is DelIVeREd eLeCTroNICally, terminatioN of the photOnIC lAyer is neceSSarY aT each inTermediAte swITching nOde along a Path. In thiS tYpe oF NEtwOrk, channel AllocatiOn is fixed ANd linK PeRformAncE is optImIzeD usinG span eQUalIzatiOn.
TherE aRe numeRous pErFormance Optimization methods applIcable To traDitIonal netwOrkS, All Based on ‘eqUaliZing’ a certaIn tRanSmissIon PArameTer oF ThE WDm SignaL, sucH As OSNR (optICaL siGNAl-To-noise rate), ber (Bit Error RatE), Or Q-facTor. IT has been shown that THe OSNR at the recEiveR CAn bE eqUAlizEd By adjusting the InpUt OPTical powEr For all channEls. For exAmPLe, U.S. PAt. No. 5,225,922 (ChRaplyvY et al.), isSUEd ON Jul. 6, 1993 to aT&T BEll laboratorIes,
 increases dramatically as  the chann el de nsi tygr ows. 
Eme rgence of opti c al a mplifiers, which ampli fy al lc hann e ls  in t he WDMs ig n a l b yacer ta i ngaininoptical  format (w ith ou t OEO conver s io n), was es sen tial in deve lop ing th eD/W D M sys tem s, as  an op t ical a mplifierma y  repla c e a num b e rof r egenerators, impo r ta n tly reducing t he cos to ft h e n etw ork. Unfor tu natel y , the o p ti c a l  am p lifiers exhib it a wavele n gth -depen de ntg ain pr ofile ,n ois e profile,andsaturatio n char a cterist i cs. Hen ce, ea chopt ical ch an nel  e x per i en ces a d ifferent  g ai n alo ng a t r a nsmi ssi on l ink.The optical a mpl ifie r s a lso a dd no iseto  thesignal , typ ic ally in the for m of  amplifie d s po nta ne ous e m ission  (A SE) , so th at theo pti ca l s ig nal-to-noise ratio  ( O S NR ) decrea ses at ea ch amplifie rsit e.
F u r therm ore, du e to the  intri n si cmateria lcharac te ris tic s oft he t ransmi ssion me dium( the fiber), th e  channels ofa  W D M  s i gnal  un dergo diffe rent dist orti o ns  an d  loss es al on g  t h e same link/path. T oadd to  this , the individ ual perfor m a n ce of th e ch a nn e l transmitters  andreceiversi s also d iffer ent, sothat each c hannel h asdif fer ent i ni tial waveform d isto rt ions, a nda diffe ren t d ete cti on  quality. 
To summ ar iz e,  t hetrans f er funct io n o fopt icala mplifi ers,tran sm is s ion  medium an d othe rac tive  an dpassi ve o p tic al comp onents in  th e  opt ic al  link/p ath is a func ti on of wave le ngt h. Thi s waveleng th dependency on path c o nfigura tio n and  opt ical devi cespecif ica t ions r esults  in a  v ari a b le pe r f or man ce  of the co - p rop agati ng  cha nnels a t the receiving te r min al for equalopt ical l au nch e dp owe rl eve l s . In other word s, ‘not al lw av elengths a r e c re ated eq ual’. E xperi m ents sh ow that t he ratiobe twee n the  reach ofthe “bes t” and “w o rst”p er formi ngwavele ng ths  canbe mor e  th an 2: 1.
Cur re nt tra nspor tnetworks  are based on a WDM phy sicallayer , u sing poin t-t o -po int (pt-p t) c onnectivit y.Asnetwo rkf lexib ilit y  i s d e liver ed e l ectronica l ly , t e r mi nation of t h e pho tonic  la y er isnece ssary at each int e rmediate switc hing n ode  al o ng a  p ath. In this t ype  o f network,  c hannel allo cation i sf ixedand li nk per formanc e is optimi zedusi ng span e qua li z ation.Th er e  are n umer ou s perf ormanc e  opt i m ization methodsappli c a ble t o  tr aditi on al netw o rks,  all based  on ‘equali zing’a ce rtain  transm is sion p ara me ter of the WDM signa l, su ch as O SN R (o pti cal si gnal - t o-noi se r at e),  BER (bit e rr o rra t e),  orQ-fac to r. I t has bee n  shown t hat the OSN Ratt h e rece i ve r can be equ ali zed b y adjustingt he i n pu t  opti cal po wer fo r all c h ann el s. Forexa m p le, U.S.Pat. No.5 ,22 5, 922(Chraply vy  etal .),  i ssued on Jul. 6 , 1993 t o AT&T B e l l Labo rat o ries , 
 increases_dramatically as_the channel density grows.
Emergence_of optical_amplifiers,_which amplify_all_channels in the_WDM signal by_a certain gain in_optical format (without_OEO_conversion), was essential in developing the D/WDM systems, as an optical amplifier may replace_a_number of_regenerators,_importantly_reducing the cost of the_network. Unfortunately, the optical amplifiers_exhibit a_wavelength-dependent gain profile, noise profile, and saturation characteristics._Hence,_each optical channel_experiences a different gain along a transmission link. The_optical amplifiers also add noise to_the signal, typically_in_the_form of amplified spontaneous_emission (ASE), so that the optical_signal-to-noise ratio (OSNR) decreases at each_amplifier site.
Furthermore, due to the intrinsic material_characteristics of the transmission medium (the_fiber), the channels of a_WDM signal_undergo different distortions and losses_along the same_link/path. To_add to this,_the individual performance of the channel_transmitters and receivers_is also different, so that each_channel_has different initial_waveform_distortions,_and a_different detection quality.
To_summarize,_the transfer_function_of optical amplifiers, transmission medium and_other_active and passive optical components in the_optical link/path is a_function_of wavelength. This wavelength_dependency on path configuration and_optical device specifications results in a_variable performance_of the_co-propagating channels at the receiving terminal for equal optical launched power_levels. In other words, ‘not all_wavelengths are created equal’._Experiments show_that_the ratio between_the_reach of_the “best” and “worst” performing wavelengths can_be more_than 2:1.
Current transport networks are based_on a WDM physical_layer,_using point-to-point (pt-pt) connectivity. As network_flexibility is delivered electronically, termination of_the photonic layer is necessary_at_each_intermediate switching node along a_path. In this type of network,_channel allocation is_fixed and link performance is optimized using_span_equalization.
There are numerous performance optimization methods_applicable_to traditional networks, all based on_‘equalizing’_a_certain transmission parameter of the_WDM signal, such as OSNR (optical_signal-to-noise rate), BER (bit error rate), or Q-factor. It_has been shown_that the OSNR at the_receiver_can_be equalized by adjusting the input optical power for all_channels. For_example, U.S. Pat._No. 5,225,922 (Chraplyvy et al.), issued on Jul. 6, 1993_to AT&T Bell Laboratories,