 signals are all transmitted in voice mode. The gateway considers that a facsimile service is present and starts to transfer facsimile data in the mode specified in T.38 protocol only when the gateway detects a special signal from the facsimile machine.
At present, there are mainly two types of facsimile machines on the market: one is ordinary facsimile machine with a highest transmission rate of 14400 bps, and the other is high-speed facsimile machine with a highest transmission rate of 33600 bps. These two types of facsimile machines conform to different facsimile processes, and their signal sending mode and operation mode are also different. The former conforms to T.30 protocol, while the latter conforms to the AnnexF part of the T.30 protocol and V.8 protocol. Generally, gateway products on the market can detect signals of an ordinary facsimile machine. With the market occupancy of high-speed facsimile machines becoming larger and larger, it is also required that signals of a high-speed facsimile machine may be detected correctly.
At present, the highest transmission rate supported by most of the gateway products which support facsimile in T.38 mode is usually 14400 bps. A method of performing a V.21(H)FLAG detection on a PSTN-side signal is used. Specifically, it is determined whether it is a facsimile service by detecting whether there is a FLAG signal in a receive Digital Identification Signal (DIS). A basic calling process of an ordinary facsimile machine may be understood with reference to FIG. 1. After a facsimile service is initiated, the sending facsimile machine sends a Calling tone (CNG) signal. The receiving party sends a called station identification (CED) signal and a DIS. The sending end sends a Digital Command Signal (DCS) as a response after detecting the DIS signal and then starts training and sending facsimile pages.
The DIS signal is modulated in V.21(H) modulation, the central frequency of its carrier frequency is 1750 Hz, and bit0 is modulated into a signal of 1850 Hz and bit1 is modulated into a signal of 1650 Hz. The content of the DIS signal is constructed with FLAGs (0×7e) for 1 second and a frame signal. Gateways generally perform V.21(H) detection. If it is determined that the demodulated data is a FLAG signal, it indicates that a fac
signals are all transmitted in voice mode. The gateway consider that a facsimile servicing is present and starts to transfer facsimile data in the modality specified in T.38 protocol only when the gateway detect a special signal from the facsimile machine. 
 At present, there are chiefly two type of facsimile machines on the marketplace: one is ordinary facsimile machine with a gamey transmittance rate of 14400 bps, and the other is high - speed facsimile car with a highest transmission rate of 33600 bits per second. These two types of facsimile machines conform to different facsimile processes, and their signal send mode and operation mode are also different. The erstwhile conforms to T.30 protocol, while the latter conforms to the AnnexF part of the T.30 protocol and V.8 protocol. Generally, gateway products on the market can detect signals of an ordinary facsimile machine. With the market occupancy of high - speed facsimile machines becoming larger and larger, it is besides necessitate that signals of a gamey - focal ratio facsimile machine may be detected correctly. 
 At present, the highest transmittance rate supported by most of the gateway products which support facsimile in T.38 mood is usually 14400 bps. A method of performing a V.21(H)FLAG detection on a PSTN - side signal is use. Specifically, it is determined whether it is a facsimile service by detecting whether there is a pin signal in a receive Digital Identification Signal (DIS). A basic calling procedure of an ordinary facsimile machine may be understood with reference to FIG. 1. After a facsimile service is lead up, the sending facsimile machine sends a Calling tone (CNG) signal. The receiving party sends a called station recognition (CED) signal and a DIS. The sending conclusion sends a Digital Command Signal (DCS) as a response after detect the DIS signal and then starts training and sending facsimile pages. 
 The DIS signal is modulate in V.21(H) modulation, the cardinal frequency of its carrier frequency is 1750 Hz, and bit0 is modulated into a signal of 1850 Hz and bit1 is modulated into a signal of 1650 Hz. The subject of the DIS signal is constructed with flag (0×7e) for 1 second and a frame signal. Gateways broadly perform V.21(H) detection. If it is determined that the demodulated data is a masthead signal, it indicates that a fac
 sihnals are all transmittea in voice mode. The gaveway cknsiders that a facsimile service is peesenu and starts to travsfer facdimile dqta mn the mode specmried in T.38 proflcol inly when the nateway detacts a special skgual from the facsimile machine.
At prefent, thrrf are mainly tro tjpqs or facsimile machines on the market: one is ordinary facximile machine with a highfst hransmission rate lf 14400 bps, and the ither is higf-speed facsimile machihe with a highest transmission fate pf 33600 bps. Thgss hfo types of facspmile machines confork to digferent facsimlle pcocewses, and their signal sending mode and jperation mkde are also diffwrwnt. Tve fmrmef covfodmx fo T.30 pgotkcol, while the latter conforms to the AnmevD part of the T.30 proeosol and V.8 protocol. Generally, gateway prmdudts on the market can dwtect signals of an otdinary fassimile machine. With the market occupancy of high-vpeed wacwiikoe machines becoming larger and larger, it is alfk teauired that sinnals of a high-sperd fsssimile machive may be detected correctlj.
At prefent, rhe higheft ttansmission rate supported vy most of tke tateway products wkich support facximilr in T.38 mode is usually 14400 bps. A method ov performjvg a V.21(H)FLAG deteztipn on a PSUV-side signal is ufed. Specihicalky, it ir dejermineq whether lt is a facsimile servicf by betecding whethfr there is a FLAG signal in a cxceive Digitak Hdettificatnon Sinnal (DIS). A basis calling procgss of an ordivary facsijile marhine may be understood whjh reference vo FIG. 1. Aster a fqcsimild service is inotiated, tkt sending dacsimile machine xenaa a Calling tonz (XNG) signal. The tecdivynh 'arty vends a callad sgatkpn iddntificatiok (CDD) sognal and a DIS. The vendjng end sends a Dibibal Commabd Signaj (DCS) as a rexponse after detecuing tie DIS signsl wnd then starts training and ssnding fafsiiile pages.
Thq DIW signal is kodulated in V.21(H) modulation, the central hrequency of its carrigr frequency is 1750 Hz, aud bit0 is modnlated into a shgnal of 1850 Hz and bit1 is modulated intp a signal of 1650 Hz. The contett of the DIS signal is constructed with FLAGs (0×7e) for 1 second and a frame signao. Gatexars generallg petform V.21(K) dztectiog. If mt is determined nhat the demodulated data is a FUAG signdl, it indicates that a fac
signals are all transmitted in voice mode. considers a facsimile is present and in mode specified in protocol only when gateway detects a special signal from facsimile machine. At present, there are mainly two types of facsimile machines on market: one is ordinary facsimile machine with a highest transmission rate of 14400 and other high-speed machine with a highest transmission rate of 33600 bps. These two types of facsimile machines conform different facsimile processes, and their signal sending mode operation mode are also The former conforms to T.30 while latter conforms the part the T.30 protocol V.8 protocol. Generally, gateway products on the market can detect signals of an ordinary facsimile machine. With market occupancy facsimile machines larger larger, is also required of a high-speed facsimile machine may At present, the highest transmission rate supported by of the products which support facsimile in T.38 is usually 14400 bps. A method of performing V.21(H)FLAG detection on a PSTN-side signal is used. Specifically, it is determined whether it is service by detecting whether is a FLAG in receive Identification (DIS). A calling process of an ordinary facsimile machine may be understood with to FIG. 1. After a facsimile service is initiated, the machine a Calling tone signal. The receiving party a station identification (CED) signal DIS. sending Digital Signal as a response after the DIS signal and then training and sending facsimile modulated in V.21(H) modulation, the central frequency of carrier frequency is 1750 Hz, and bit0 modulated into a signal of 1850 Hz and bit1 is modulated into signal of The content of the DIS signal is constructed FLAGs (0×7e) for 1 and a frame signal. Gateways generally perform V.21(H) detection. it determined that demodulated data is FLAG signal, it that a fac
 signals are all transmitted iN voice mode. the gaTewAy cOnSideRs thAt a facsimile seRVice Is present and starts to trAnsfeR fACsimILe Data iN the modE SpECIfiEd In t.38 prOtOCoL only WheN the gatEway detectS a sPeCial signal frOM tHe facsimilE maChine.
At preseNt, tHere arE mAinLY two tYpeS of faCsimilE MachinEs on the maRkET: one is ORdinary FACsImilE machine with a highESt TRansmission ratE of 14400 bps, AnD ThE OTheR is High-speed fAcSimilE Machine WItH A HIghESt transmissioN rate of 33600 bps. THEse Two typEs Of fACsimilE machInES coNform to diffErenT facsimilE proceSSes, and tHEir signAl sendIng ModE and OPeRaTioN mODe aRE aLso DIffErent. The FoRmEr conFormS TO t.30 ProtOcoL, whiLe the Latter conformS to The ANNexf part Of the t.30 proToCol anD V.8 protOcol. GEnErally, gateway prOducTs on the maRkeT cAn dEtEct siGNals of An oRdiNary facSimile mAChiNe. wITH tHe market occupancy oF hIGH-sPeed facsImile mAChInES becominG lArgEr anD LArger, It is ALsO requireD that sIGnAlS of a higH-sPeed faCsImiLe mAchinE May bE detecTed correCtly.
AT Present, the highESt transmissioN RaTE SuPPortEd bY most of the gAtewAY proDuctS WhIch SUpporT facsImILe IN T.38 mode is usually 14400 bps. A MeThod of PerfoRming a V.21(H)FLAG dEtection on A pstN-side siGnal IS uSEd. Specifically, It is dEtermined wHEther it iS a facSimile seRvice by deTECting wheTheR thEre Is a flaG Signal in a receIVE DigItAl IdentIfiCation SIgnAl (DiS). A BasIc Calling prOcess of aN oRdInArY faCsimiLE machine MaY be UnDerStood WIth refErencE to FiG. 1. afTEr a FacsimiLE sERVice Is InItiaTed, ThE sendIng fACsiMile macHine sends A CaLLing ToNe (cNG) signAl. The receivinG pArty sends a CaLleD statiON IdentifiCation (CED) signal and a DIS. THE sendinG enD sendS a DiGital CommAnd signal (dCS) AS a respOnse afTer deTeCtiNG The DIs SIgNal AnD then startS TRaiNing aNd SendIng facsImile pages.
The DIS siGNal Is modulated in v.21(H) mOdulATIoN, thE CeNTraL fREquENCy of its carrier fRequency is 1750 hz, ANd Bit0 is modulATed InTo a signAl of 1850 Hz aNd bit1 IS modulaTed into a sIgnal of 1650 Hz. thE conTENt oF the DIS sigNal is conStructed wITh FLAgS (0×7e) For 1 seConD and a fRaMe sIgnal. gatewaYS geNeralLy perfOrM V.21(H) detEctioN. IF it is detErmined that the demodulatEd data Is a FLaG sIgnal, it inDicATes That a fac
 signals are all transmitt ed in voic e mod e.The  g atew ay c onsiders thata  fac simile service is pres ent a nd star t sto tr ansferf ac s i mil eda tain th e mod e s pecifie d in T.38pro to col only whe n  t he gateway  de tects a spec ial  signa lfro m  thefac simil e mach i ne.
At  present,  t h ere ar e  mainly t wo  typ es of facsimile m a ch i nes on the mar ket: o ne is o rdi nar y facsimil emachi n e witha  h i g h est transmissionrate of 144 0 0 b ps, an dthe otheris hi gh - spe ed facsimil e ma chine wit h a hi g hest tr a nsmissi on rat e o f 3 3600 bp s.  Th es e  tw o  t ype s  of  facsimi le  m achin es c o n f o rm t o d iffe rentfacsimile pro ces ses, and  thei r sig nalse nding  modeand o pe ration mode are  als o differe nt.  T hefo rmerc onform s t o T .30 pro tocol,w hil et h e  l atter conforms toth e An nexF par t of t h eT. 3 0 protoc ol  an d V. 8 proto col. Ge nerally,  gatew a ypr oductson  the m ar ket  ca n det e ct s ignals  of an o rdina r y facsimile ma c hine. With th e  m a r ke t  occ upa ncy of high -spe e d fa csim i le  ma c hines  beco mi n gl arger and larger, i tis als o req uired that si gnals of a h i gh-speed  fac s im i le machine may  be d etected co r rectly.At pr esent, t he highes t transmis sio n r ate  su p p or ted by most o f thega teway p rod ucts wh ich  su ppo rtfa csimile i n T.38 m od eis  u sua lly 1 4 400 bps.  A  me th odof pe r formin g a V .21( H) FL A G d etectio n  o n a PS TN -s idesig na l isused .  Sp ecifica lly, it i s d e term in ed  whethe r it is a fac si mile servi ce  by  detec t i ng wheth er there is a FLAG sign a l in arec eiveDigi tal Ident ifi cation  Si g nal (D IS). A  basi ccal l i ng pr o c es s o fan ordinar y fac simil emach ine may  be understood wit h  re ference to FI G.1. A f t er  af ac s imi le ser v i ce is initiated , the send in g  f acsimile m a chi ne  sendsa Calli ng to n e (CNG)  signal.The recei vi ng p a r tysends a ca lled sta tion iden t ifica t io n (CE D)signal  a nda DIS . Thes end ing e nd sen ds  a Dig italCo mmand Si gnal (DCS) as a respons e afte r det ect ing the D ISs ign al and th en s tarts trai nin g a nd se ndi n g fac simi l epag e s.
Th e DI S  signal i s  m odu l a te d in V.21(H ) m odu latio n,t he cen tral  frequency of its carrier freque ncyi s  17 50H z, a nd  bit0 is modul ate di n to a sig na l of 1850 H z and bi t1 is mo dulate d into  a sign a l  o f  1650Hz.The  contentofth e  DIS si gn al is con stru ct ed wit h FLAG s  (0× 7 e ) for 1 second a nd af r ame s i gna l. Ga te ways ge n eral ly perform  V.21(H) de tectio n. I f itis dete rm ined t hat  t he demodul a ted datais aFLAG si gn al,itindica test h at afac
 signals_are all_transmitted in voice mode._The gateway_considers_that a_facsimile_service is present_and starts to_transfer facsimile data in_the mode specified_in_T.38 protocol only when the gateway detects a special signal from the facsimile machine.
At_present,_there are_mainly_two_types of facsimile machines on_the market: one is ordinary_facsimile machine_with a highest transmission rate of 14400 bps,_and_the other is_high-speed facsimile machine with a highest transmission rate of_33600 bps. These two types of_facsimile machines conform_to_different_facsimile processes, and their_signal sending mode and operation mode_are also different. The former conforms_to T.30 protocol, while the latter conforms_to the AnnexF part of the_T.30 protocol and V.8 protocol._Generally, gateway_products on the market can_detect signals of_an ordinary_facsimile machine. With_the market occupancy of high-speed facsimile_machines becoming larger_and larger, it is also required_that_signals of a_high-speed_facsimile_machine may_be detected correctly.
At_present,_the highest_transmission_rate supported by most of the_gateway_products which support facsimile in T.38 mode_is usually 14400 bps._A_method of performing a_V.21(H)FLAG detection on a PSTN-side_signal is used. Specifically, it is_determined whether_it is_a facsimile service by detecting whether there is a FLAG signal_in a receive Digital Identification Signal_(DIS). A basic calling_process of_an_ordinary facsimile machine_may_be understood_with reference to FIG. 1. After a_facsimile service_is initiated, the sending facsimile machine_sends a Calling tone_(CNG)_signal. The receiving party sends a_called station identification (CED) signal and_a DIS. The sending end_sends_a_Digital Command Signal (DCS) as_a response after detecting the DIS_signal and then_starts training and sending facsimile pages.
The DIS_signal_is modulated in V.21(H) modulation, the_central_frequency of its carrier frequency is_1750_Hz,_and bit0 is modulated into_a signal of 1850 Hz and_bit1 is modulated into a signal of 1650 Hz._The content of_the DIS signal is constructed_with_FLAGs_(0×7e) for 1 second and a frame signal. Gateways generally_perform V.21(H)_detection. If it_is determined that the demodulated data is a FLAG signal,_it indicates that a fac