 permit a limited number of errors in the data bits to be corrected by the receiver performing similar operations and subsequently examining the FEC overhead bits.
Good FEC algorithms will typically provide correction for up to 9 bytes out of 200 with an associated bandwidth overhead on the order of 5 percent. However, impulsive noise may be of a significant duration and thus may corrupt frames beyond correctability by the FEC algorithm in use. To mitigate the effect of lengthy bursts of impulsive noise on a transmitted data signal, prior art modems employ a technique known as interleaving. Using this approach, data frames are segmented and the individual segments from a number of consecutive frames are interleaved.
It is conventional to interleave data spanning a period of 20 or more times the duration of the maximum impulse to be survived. Thus, when affected by a burst having the duration of one-half frame, the effect of the burst is to in fact corrupt each of at least 10 consecutive frames by at most 5% of the bits contained therein. The corrupted frames then easily lend themselves to correction by a standard FEC algorithm.
Unfortunately, a practical system employing sufficient interleaving to reduce error rates for multimedia traffic will introduce a delay on the order of nine milliseconds before the first bit in the first frame is actually transmitted. For real-time applications such as telephony, such long delays caused by a transmitting modem are unacceptable, especially since a de-interleaving procedure, which introduces an additional delay of similar magnitude, must be performed at the receiver. In addition, there are considerable memory requirements at both transmitter and receiver when storing dozens of frames, each of which may have a length of 250 bytes or more.
Therefore, there is a need for a modem with error correction which improves the protection afforded to data under conditions of impulsive noise, while continuing to minimize both the amount of overhead bandwidth introduced by the corrective measures applied by the modem and the delay through the modem.
It is an object of the present invention to mitigate or obviate one or more disadvantages of the prior art.
Therefore, the invention may be summarized according to a first broad aspect as a method of communicating frames of digital data across a communications medium extending between a first modem and a second modem, each frame comprising a data field and an error field, the first modem having a first startable timer, comprising the steps of: the first modem receiving a first set of frames sent by the second modem; the first modem determining, for each frame in the first set, whether the data field
permit a limited number of errors in the datum bit to be corrected by the receiver performing exchangeable operation and subsequently examining the FEC overhead bits. 
 Good FEC algorithm will typically provide correction for up to 9 bytes out of 200 with an associated bandwidth overhead on the ordering of 5 percent. However, impulsive randomness may be of a significant duration and thus may corrupt frames beyond correctability by the FEC algorithm in habit. To mitigate the effect of lengthy bursts of impulsive randomness on a transmitted data signal, prior artwork modems employ a technique known as interleaving. Using this access, data frames are segmented and the individual segments from a number of back-to-back frames are interleaved. 
 It is conventional to interleave data spanning a period of 20 or more times the duration of the maximum impulse to be survived. Thus, when affected by a burst having the duration of one - half frame, the effect of the explosion is to in fact corrupt each of at least 10 consecutive skeletal system by at about 5% of the snatch contained therein. The corrupted frame of reference then easily lend themselves to correction by a standard FEC algorithm. 
 Unfortunately, a practical system use sufficient interleaving to reduce error rates for multimedia traffic will introduce a delay on the decree of nine milliseconds before the first bit in the first frame is actually transmitted. For actual - time applications such as telephony, such long delays caused by a air modem are unacceptable, especially since a de - interleaving procedure, which insert an extra delay of similar magnitude, must be performed at the receiver. In addition, there be considerable memory requirements at both sender and receiver when store dozens of skeleton, each of which may have a duration of 250 bytes or more. 
 Therefore, there be a need for a modem with erroneousness correction which improves the protection afforded to data under conditions of impulsive noise, while continuing to understate both the amount of overhead bandwidth introduce by the corrective measures applied by the modem and the delay through the modem. 
 It is an object of the present invention to mitigate or obviate one or more disadvantages of the prior artwork. 
 Therefore, the invention may be summarized according to a first broad aspect as a method of communicating frame of digital datum across a communication medium extending between a first modem and a second modem, each frame comprising a datum field and an error field, the first modem having a first startable timer, comprising the steps of: the first modem meet a first set of frames sent by the second modem; the first modem determining, for each frame in the inaugural set, whether the data field
 pegmit a limited number of errors in the bqta bivs to bs correcged by the receiver performiig sumilae operations and subseduently eqamining rhe HEC overhead bits.
Good FEG algkvithmv will typicalli provide cosrection for u[ go 9 bytes out of 200 with an associated fandwidyh overhead on tre ogdqr or 5 percent. However, impulsive noise may be of a signifivant duration and thus may corgupt frames beyond correctabioity vy the FEC augorithm in use. To mitjgate the effect of lengthy burrts oy impulsive niisf on a transnitteq data signal, prior drt modrms employ a tcchnixue known as interleavinj. Using this approacr, data frdmzs are segmented and rhw indhvidgal rwgmdnta hroj a nulbec of consechtive framew are interleaved.
It if conventional to ineewleave data spanning a period of 20 or moge tjmes the duration of thw maximum impulse to he survivqd. Thus, when affected by a burst having the durathon oh une-kqlf ffqmf, the effect of the burst is to in fact corru[f tacm of at least 10 cjnsecutive grwmrf by at most 5% of thz bjts contained therfin. The corrypted fraies yhen easily lend themselves to correctijb by a standard FEE algorithm.
Uufortumatelu, a practical system em'loyinf sufficienh interlezxing to reduce efrog rades for multimedia traffic will intcoducz a delah on the owder of nije milliseconds before tje fitst bid in the flrst frame is actually transmitvxd. For real-tike apilicationf sucm as telephony, fuch long delais caused by a transmittpng modem are unacce[table, especidply since a ve-interlewvint pricedure, dhich introducrs an addptnonal delqy of similar magnltude, just be performzb qt the receiver. In adqinioi, thewa are considarabue ormory requirtiekts at noth transmitter and recsiver when storing djzens of frames, qach of which may have a length of 250 uytes ur mote.
Trerefore, there is a need for a modem wihh crror correctyon qhich improvzs the protection afforded to data under conditions of imkulsive noise, while cpktinuing to kinimyze both dhe amount of overheqd bandwidth intrpduced by the correctjve medsured applied by the modem and the delay through the modem.
It is an object of rhe prxsqnt inventikn tp mitpgace pr obvyate une or more disacvantages of the prior art.
Therehore, the itvzntion may be summarized accotdkng to a firsj broad aspect as a method of comminicating frames of digital dats across a communicationx medium extehding betwxen a first modem anc a seeond midem, eaxh fvame comprisine a dwta field and au error field, the first modem havung a digst startable tiker, comprislnn the ateps jf: the first modsm rsfeivivg a first sey of frames semt by the second modvm; ehe first moden determining, for gcbh frame in tie first set, whether the data field
permit a limited number of errors in bits be corrected the receiver performing the overhead bits. Good algorithms will typically correction for up to 9 bytes of 200 with an associated bandwidth overhead on the order of 5 percent. impulsive noise may be of a significant duration and thus may corrupt frames correctability the algorithm use. To mitigate the effect of lengthy bursts of impulsive noise on a transmitted data signal, art modems employ a technique known as interleaving. this approach, data frames segmented and the individual segments a of consecutive are It conventional to interleave spanning a period of 20 or more times the duration of the maximum impulse to be survived. when affected burst having duration one-half the effect of is to in fact corrupt each 10 consecutive frames by at most 5% of bits contained The corrupted frames then easily lend to correction by a standard FEC algorithm. Unfortunately, practical system employing sufficient interleaving to reduce error rates for multimedia traffic will introduce a the order of nine before the first in first is transmitted. For applications such as telephony, such long delays caused by a transmitting are unacceptable, especially since a de-interleaving procedure, which introduces an of magnitude, must be at the receiver. In there considerable memory requirements at and when frames, of may have a length 250 bytes or more. Therefore, is a need for which improves the protection afforded to data under of impulsive noise, while continuing to minimize the amount of overhead bandwidth introduced by the corrective measures applied by modem and through the modem. It is an object of present invention to mitigate obviate one or more disadvantages of the prior art. the may be according to a broad aspect as method of communicating digital data a medium first modem and a second modem, frame a data field and an field, modem having a first startable timer, comprising the steps of: the first modem receiving a of frames sent by second the first modem determining, for each frame in the first set, whether field
 permit a limited number of errOrs in the daTa bitS to Be cOrRectEd by The receiver perFOrmiNg similar operations and SubseQuENtly EXaMininG the FEC OVeRHEad BiTs.
gooD Fec aLgoriThmS will tyPically proVidE cOrrection for UP tO 9 bytes out oF 200 wiTh an associatEd bAndwidTh OveRHead oN thE ordeR of 5 perCEnt. HowEver, impulSiVE noise MAy be of a SIGnIficAnt duration and thuS MaY Corrupt frames bEyond cOrREcTABilIty By the FEC alGoRithm IN use. To mITiGATE thE Effect of lengtHy bursts of iMPulSive noIsE on A TransmItted DaTA siGnal, prior arT modEms employ A technIQue knowN As interLeavinG. UsIng This APpRoAch, DaTA frAMeS arE SegMented anD tHe IndivIduaL SEGMentS frOm a nUmber Of consecutive FraMes aRE inTerleAved.
IT is cOnVentiOnal to InterLeAve data spanning A perIod of 20 or moRe tImEs tHe DuratIOn of thE maXimUm impulSe to be sURviVeD. tHUs, When affected by a burSt HAViNg the durAtion oF OnE-hALf frame, tHe EffEct oF THe burSt is TO iN fact corRupt eaCH oF aT least 10 cOnSecutiVe FraMes By at mOSt 5% of The bitS containEd theREin. The corrupteD Frames then easILy LENd THemsElvEs to correctIon bY A staNdarD fEc alGOrithM.
UnfoRtUNaTEly, a practical system EmPloyinG suffIcient interleAving to redUCE Error ratEs foR MuLTimedia traffic Will iNtroduce a dELay on the Order Of nine miLlisecondS BEfore the FirSt bIt iN thE FIrSt frame is actuALLy trAnSmitted. for Real-timE apPliCatIonS sUch as telePhony, sucH lOnG dElAys CauseD By a transMiTtiNg ModEm are UNaccepTable, EspeCiAlLY siNce a de-iNTeRLEaviNg PrOcedUre, WhIch inTrodUCes An additIonal delaY of SImilAr MaGnitude, Must be performEd At the receiVeR. In AdditiON, There are Considerable memory requiREments aT boTh traNsmiTter and reCeiVer wheN stORing doZens of FrameS, eAch OF Which MAY hAve A lEngth of 250 bytES Or mOre.
ThErEforE, there iS a need for a modem witH ErrOr correction wHicH impROVeS thE PrOTecTiON afFORded to data under Conditions Of IMpUlsive noisE, WhiLe ContinuIng to miNimizE Both the Amount of oVerhead baNdWidtH INtrOduced by thE correctIve measurES applIEd By the ModEm and tHe DelAy thrOugh thE ModEm.
It iS an objEcT of the PreseNt InventioN to mitigate or obviate one Or more DisadVanTages of thE prIOr aRt.
TherefoRe, thE invention May Be sUmmarIzeD AccorDing TO a FirST broaD aspECt as a methOD oF coMMUnIcating framES OF diGital DatA Across A comMunications medium EXtending betweeN a fiRST moDem ANd a sEcOnd modem, each frAme CoMPRising a dAtA field and an Error fieLd, THe firSt modeM havinG a first STArTAble tiMer, cOmpRising the StePs OF: the firSt MoDEm receIvinG a First sEt of frAMes sENT by the second modeM; the fIRSt modEM deTermiNiNg, for eaCH fraMe in the firSt set, whetheR the daTa fiEld
 permit a limited number o f errors i n the  da tabi ts t o be  corrected byt he r eceiver performing sim ilarop e rati o ns  andsubsequ e nt l y  ex am in ing  t h eFEC o ver head bi ts.
Good F ECal gorithms wil l  t ypically p rov ide correcti onfor up  t o 9 bytes  ou t of200 wi t h an a ssociated  b a ndwidt h  overhe a d  o n th e order of 5 perc e nt .  However, impu lsiveno i se m aybeof a signi fi cantd uration an d t hus may corrupt f rames beyon d  co rrecta bi lit y  by th e FEC  a l gor ithm in use . To  mitigate  the e f fect of lengthy  burst s o f i mpul s iv enoi se ona  t ran s mit ted data  s ig nal,prio r a r t mo dem s em ploya technique k now n as int erlea ving.  Usi ng  this  appro ach,da ta frames are s egme nted andthe  i ndi vi duals egment s f rom  a numb er of c o nse cu t i v eframes are interle av e d .It is co nventi o na lt o interl ea vedata s panni ng a pe riod of20 orm or etimes t he  durat io n o f t he ma x imum  impul se to be  surv i ved. Thus, whe n  affected bya  b u r st havi ngthe duratio n of one- half fr ame ,  theeffec to ft he burst is to in f ac t corr upt e ach of at lea st 10 cons e c u tive fra mesb ya t most 5% of t he bi ts contain e d therei n. Th e corrup ted frame s then eas ily  le ndthe m s el ves to correc t i on b ya stand ard  FEC al gor ith m.Unf or tunately,  a pract ic al  s ys tem  empl o ying suf fi cie nt  in terle a ving t o red uceer ro r  ra tes for mu l t imed ia  t raff icwi ll in trod u cea delay  on the o rde r  ofni ne  millis econds before  t he first b it  in  the f i r st frame  is actually transmitte d . For r eal -time  app lications  su ch astel e phony,  suchlongde lay s cause d by  atr ansmitting m ode m are  u nacc eptable , especially since a d e-interleavin g p roce d u re , w h ic h  in tr o duc e s  an additionaldelay of s im i la r magnitud e , m us t be pe rformed  at t h e recei ver. In a ddition,th erea r e c onsiderabl e memory  requirem e nts a t  b oth t ran smitte rand  rece iver w h enstori ng doz en s of f rames ,each ofwhich may have a length  of 25 0 byt esor more.The r efo re, there  isa need for  amod em wi the rrorcorr e ct ion which  imp r oves thep ro tec t i on  afforded t o d ata  unde r c o nditio ns o f impulsive noise ,  while continu ingt o  mi nim i ze b ot h the amount o f o ve r h ead band wi dth introdu ced by t he corre ctivemeasur es appl i e db y themode m a nd the de lay  t h rough t he  m o dem.
I t is  a n obje ct oft he p r e sent invention t o mit i g ate o r  ob viate  o ne or m o re d isadvantag es of the p rior a rt.There fore, t he  inven tio nmay be sum m arized ac cordi ng to a  f irst  br oad as pect a s a m etho dofcommunica t i ng fr am e s o f di gital  d ataacross ac ommunica tio n s mediu mext e n ding b e tw e e n a firstmod em an d a second m o dem, ea c h fra me com prisin g a dat a  fi el d and a n e r r or field,  the firs t  mo de m ha ving a f ir st s ta rta bl e timer, compri sing the  steps o f :  the f irs t  mod e m rece iv ing a firstset o ff rames s e n t b y the s e con d m ode m; t hefirs t  modem determining, foreach  fram e  in  thefirst  s et, whet h er t he dataf ield
 permit_a limited_number of errors in_the data_bits_to be_corrected_by the receiver_performing similar operations_and subsequently examining the_FEC overhead bits.
Good_FEC_algorithms will typically provide correction for up to 9 bytes out of 200 with_an_associated bandwidth_overhead_on_the order of 5 percent._However, impulsive noise may be_of a_significant duration and thus may corrupt frames beyond_correctability_by the FEC_algorithm in use. To mitigate the effect of lengthy_bursts of impulsive noise on a_transmitted data signal,_prior_art_modems employ a technique_known as interleaving. Using this approach,_data frames are segmented and the_individual segments from a number of consecutive_frames are interleaved.
It is conventional to_interleave data spanning a period_of 20_or more times the duration_of the maximum_impulse to_be survived. Thus,_when affected by a burst having_the duration of_one-half frame, the effect of the_burst_is to in_fact_corrupt_each of_at least 10_consecutive_frames by_at_most 5% of the bits contained_therein._The corrupted frames then easily lend themselves_to correction by a_standard_FEC algorithm.
Unfortunately, a practical_system employing sufficient interleaving to_reduce error rates for multimedia traffic_will introduce_a delay_on the order of nine milliseconds before the first bit in_the first frame is actually transmitted._For real-time applications such_as telephony,_such_long delays caused_by_a transmitting_modem are unacceptable, especially since a de-interleaving_procedure, which_introduces an additional delay of similar_magnitude, must be performed_at_the receiver. In addition, there are_considerable memory requirements at both transmitter_and receiver when storing dozens_of_frames,_each of which may have_a length of 250 bytes or_more.
Therefore, there is_a need for a modem with error_correction_which improves the protection afforded to_data_under conditions of impulsive noise, while_continuing_to_minimize both the amount of_overhead bandwidth introduced by the corrective_measures applied by the modem and the delay through_the modem.
It is_an object of the present_invention_to_mitigate or obviate one or more disadvantages of the prior_art.
Therefore, the_invention may be_summarized according to a first broad aspect as a method_of communicating frames of digital data across_a communications medium extending between a first modem and a second_modem, each frame comprising a data field and_an error field, the first modem having_a first startable timer,_comprising_the steps of: the first modem receiving_a_first_set_of frames sent_by the second_modem; the first_modem determining,_for each frame_in the_first set, whether_the_data field