WIDE AREA NETWORK TRANSMISSION EQUIPMENT
`
`
`SD indicator. If the ‘SD indicator Hashes. this indicat
`terminal is reaching the modem and it also \'eril'ie.s th:
`of the cable connecting the terminal and modem.
`
`that data from the attached
`it there is L.‘t'JI‘tTiI‘tL1i.t_\' on pin 2
`
`
`
`TR indicator
`
`icator on the Courier 2401) modem refleets the state of
`The terminal ready (TR) ind
`(DTR) control signal. The TH indicator
`the. terminal de\'ice’s data terminal read)"
`aheled DTR on the "l"|U(l0 modem as well as on many other modems.
`is thus 1
`\\'hen the TR indicator is illuminated this denotes that the terminal or eoinputer
`Similarly, a lack of illtirnination incli-
`port is ready‘ to establish comrntinications.
`port is not ready to establish com-
`cates that the. attached terminal or comptmtr
`rve the latter state by power1n,<_v on _\'our modern
`rnunications. You can easily obse
`Only after the computer is
`prior to powering on an attached personal computer.
`po\\‘e1‘t‘.d on and _\-'ot1 have loaded eonmttinications software and prepared _\'('>tn‘
`program to go on-line will the 'l"R indicator illuminate.
`
`MR indicator
`
`tor illuminates when the Courier 2-l-00 modem is
`The modem ready (MR) indica
`on your modem the MR indicator should
`powered on. \\'hen you l'i1‘st power
`illuminate to inform you that the device is operational.
`
`
`
`AL indicator
`
`(AL) indicator is illuminated when your modem is in an
`The analog loophaclt
`aced in this mode of
`an
`alogz lt')Opl)alCl{ mode of operation. \\-'hen your modem is pl
`itted from the attached terrninal device is sent to the modem’s
`operation data transm
`d and looped back to the modern's receiver. The
`transmitter where it is modulate
`to the attaelied terminal device
`reeei\'e.r clemocltilates the data and sends it back
`\‘erit‘_\-' the ope-ratitm of the modem.
`where you can \'isuall_\'
`is not connected to the
`\\-'hen the AL indicator" is
`illuminated the modem
`telephone line and cannot transmit data.
`'l"ht:s_.
`_\'f)Ll must enter the appropriate
`comm-ancl to place the modem back into its data mode to comrnunieate with another
`mo dem.
`
`Other indicators
`Three other common modem indicators that warrant discussion are C95 or C'l"C‘i.
`ARQ, and SYN.
`The C55 or UPS indicator denotes the state of the RS-232 clear to send contwl
`is illuminated, this fact tells you that the modem has
`signal. \\''hen the indicator
`The Al"-{Q (automatic
`received -.1 \'&ll(l carrier tone and is ready to modulate data.
`l.\iI’ error detection
`repeat request) indicator ilhimin-ates when the modem is in its ;\'
`st1eeess‘full_\' made an .\I.\iI’ connection with a remote
`and correction mode, having.r,
`The SYN (synehronotis) indicator is applicable to modems that Lzafi
`modem.
`
`
`
`

`
`.
`I
`
`I.
`
`4.2 MODEMS
`
`427
`
`operate s_\‘nChronousl}'. This indicator illuminates when the. modem is placed into
`its synchronous mode of operation.
`
`Modem testing
`
`'|"o assist users in isolating problems, most modems include a built—in dia;.;{nostie
`testing capability. This tlia,qnostie testing" cap-ahilit_\'
`t'a1np‘e.s in scope from a simple
`seliltest of the moclem'.s circuitry to several more sophistieatecl types oi‘ loopb-acl<
`tests.
`
`Self-test
`
`i.\-"lost modems include a self-test capability that is either initiated as a stand-alone
`test or is used in ctmjunction with a Ioopbaelc test. The basic modem sell"-test is
`desi_s_1netl
`to \'erif_\' the operation of the modem's internal eireuitr_v and uses a
`pattern ;:e.neI'ator to produce a known t-iL’(1LlI._‘.I'1(ZL‘ of data whieli will be used I)_\' the
`transmitter
`
`Figure —l.—l2 illustrates the operation of a basic modem selii—test. Once initiated,
`the mod::m's transmitter is tied to its reeeixcr liireaking an_\' prior connection to a
`ctammtmieations line. Data modulated by the transmitter is demodulated by the
`ret:ei\'er and passed to a pattern comparator \\'liicl1 consists of cireuitr_\' as well as a
`sectitm of l{(.'.).\'l that eontains the same clata sequenee xvhieh is generated by the
`pattern generator. The pattern comparator thus allows the dernodulatecl data to be
`eompared to the seqtienee generated when the. sell’-test is initiated. If the. received
`data does not match the contents of the pattern comparator the modem's Ci1‘cL1iLr_\-‘
`\\'ill eallse a status indicator. normally l:'ll')L‘lI:Ll ER for error. to illuminate. This
`action informs you that the modem is clefeetive and should be returned to the
`manulacturer.
`
`'l"ne hasie seliltest previously described \\'21s origzinally limited to inclusion in
`leased line modems. This was because most S\\‘lIL?l1(.‘(l
`l‘l(3T\-\'()t‘l( modems can be
`
`easily attached to terminals or personal computers which can be used as a pattern
`;:ene1'ator. The operato1"s vision can then be used as a pattern comparator. Today. a
`grtnviiigz percentage of switched network modems include a self—testing capability
`that ean be used with one or more ltJ()}’!i]all_‘l( modes of operation to test a local or
`remote modem or the communications path betwet.-n modems.
`
`Line
`
`Communications
`
`Figure 4.42 Modem self-test
`
`
`
`

`
`
`WIDE AREA NETWORK TRANSMISSION EQUIPMENT
`
`Loopback tests
`liaieh of
`'l'ht-re are to-.11" t_\'pe:-1 of l.0(}|')l‘12'I(.‘l\' tests 1Tlt'!(_ll.,‘I‘t’|t-‘~ inn)" he able to pe1'fm'm.
`tltesr tests is illu.~:tr;|tetl
`in Fl}-_"LII‘L‘
`-lr.-l3. Re;iLlt-rs should note that the lm)pl);1el<
`tt:E-5tll’l}_' cap-.1hilit_\' oi‘ mo-;lem.~; \'uries hoth h_\'
`in'.:t1Lll';1u.:tLit‘l-.-I‘ as well as l)_\'
`:1 menu-
`ll1ct1:1'ei".x‘ procluet
`line.
`.-\lthm1_s,:h most lea.~3t-Ll
`line muu.lem.~: will he ezipulale of
`initi:itin;,r all Fotlt louphnel; test.~: illusatmtul in l“i,qure —l.-l-3. many .~:\\'itcl‘u.-Ll I’|f;‘t\\‘()l‘l(
`mmlems are limited to pet'forn'1in;_v :1
`les.~‘.et
`l‘lL1|T1l)(.‘l' of looplnaclt teats.
`
`
`
`Figure 4.43 Modem loopbacks: 1 local digital loop. 2 local analog loop, 3 remote analog
`loop, 4 remote digital loop
`
`Local digital loopback
`The initiation of L1 tligit-t-tl louphaele test (‘.‘tIi.IE-l(i’t-‘- the local modem to tie its transmitter
`and receiver sections together. in elleet, l)_\'pass:ii1;_r its modulator and demo¢.lL.il:1tor.
`The input tlata l'(;'L‘.L'.l\'(_‘Ll from L1 ennnectetl l)'l'l*I on pin 2 of an RS-232 eoncluctor
`are th us 1'iI!.ll.'L‘(l to pin 3 \\'l1lL‘l} is the reeeix-"e (lat-a comlLIu:to1'. In e|‘feet, 2| local cliogiml
`loop l'{;'5-1LllT.'E-‘- in the CStt1l)ll5l1l11l-.'I‘ll' oi’ two loops are illL1.~:t1'-tttetl in l7i_tgure 4.44.
`
`
`
`Communications
`
`Hul1i-
`Conductor
`Calm
`
`
`
`
`
`
`
`llL1$1'I'HtI:‘L'l
`the
`to test
`in l"i5_{ure -I-.43 is emplo}'etl
`loop test i
`tliegitzil
`The lm‘-.-ll
`lucle determining if dam is
`opemtitm of the tltita t::tmit1-.-1l equiment {l)'l‘Ii} to inn:
`le;1\'in_:_r the terminal or etnnputer port. In eompanisrzm, the lmrul an-¢1lo;_: loop tests
`the digital amtl
`:m-.tlu;_r ¢_-ii-._~ui;_u. of the mutlem to determine.
`if they are in um-l{in,t,_r
`em1Lliti:m. The remote umilog loop is LI!-§t‘I.l For testing: the line to the remote modem,
`while the remote I.llg'll'E1l loop is used In L‘.l]t.’L.'li the operating condition of the line and
`the local and remote motlems. Now that we have am o\'er\‘ie\\' of the use of each
`lrmplmek test, let us examine them in more LlI_‘l'dll.
`
`Lines
`
`0: mod altlor
`
`Figure 4.44 Local digital loop test
`
`

`
`4.2 MODEMS
`
`429
`
`A loeal digital loop can he used to test the operation of the UTE as well as visrify
`the multieonduetor ea-ihle eonneetiiig the DTIE to the modem. To aeeomplisli those
`functions you woultl l-irst initiate :1 local digital loop.
`Once this is aecomplislieti.
`_\-'UL1 can type on the |;e_\'hoartl of _\-‘our terminal or
`personal eomputer and \'lSLlk1ll_\'t)l35(;‘l‘\-‘t3 the characters eehoecl hack to _\'our terminal
`or PC. After )'()Ll are satisfied that your DTIC and eahle are performing eorreetly
`you can terminate the ioophaek.
`
`Local‘ analog ioopback
`
`The local amilog looplmek test is designed to \'erif'_\' the operation of the analog
`ei1‘euits of a modem. including its I'I‘tt}Lll1liIi'()}‘ and demodulator. During this test two
`loops are established, resulting in the n1odem’s modulator l‘Jei11g looped to its
`receiver, while the semi and receive paths of the eomtntinieatirms line are tied
`together. The local analo;__r loop test is illtistmted in Iiigtwe -L45.
`
`-
`
`'
`
`‘
`
`_
`
`ll
`
`
`
`Communications
`Lines
`
`Dunodulatnr
`
`
`
`Figure 4.45 Local analog loop test
`
`Flemore analog ioopback
`
`The remote analog looplmek results in the remote modem l)i'id_t_:in§_: the tr:msn'iit
`and I‘et‘.(.‘i\'e wire pairs of a leased line together. This allows you to use test equip-
`ment at the local site to L'l(i‘l.L"I'l"I'1in(_‘ the qtiality of the line. Since modems designed
`for use on the l’.‘5'l.‘N operate on a two-\\'iI‘e s_\'stem this lf.)0[’,)l)£lL‘l{
`test
`is not
`ineludetl in switched net\\'orl< modems.
`
`Remote di'gi‘t‘aI loopback
`
`results in the remote modem tlemocltilating
`loopboek test
`The remote tligital
`i'eeei\'etl data and then pal.‘-§SiI‘t}_’,‘ it to its transmitter for remoclulation back onto the
`line. This test is simihtr to the local cli;_{ital
`l(}t3]‘)l‘J‘¢1I_‘l( test p1'e\'ious|_\‘ illustrated in
`Figtlre -L-H-_ Omte the remote modem is placed into its tlierital loopbaek mode of
`operation data transmittetl from the local site is looped at the remote modem back
`to the data origin2ltor_.
`in e|‘I"eet, p|‘o\'idit1[.I :1 meel1:1I‘iism for clietrking both the
`L'|LI£1lit_\-‘ ol‘ the ciretiit as \\'ell as the operation of the loeal and remote modems.
`\\'l‘iile zmalog and digital looplmtrlcs are the main tests huilt into rnotlems. .'se\-'eral
`\'ent'lors offer '.1t'lt'lition:':l Liiagnostit‘ e21p:1l)iliTit'Stl12It may \\":11'l'l'H1l. attention. A lieu-' 0|:
`
`
`
`

`
`
`
`
`
`NCS
`
`Primary dcltcl
`
`—-—---- Control channel
`
`Figure 4.46 Modem wraparound unit utilization. The modem wraparound unit permits the
`use of a network control station produced by one vendor with modems manufactured DY
`other vendors
`
`
`
`430 .
`
`. WIDE AFIEA NETWORK TRANSMISSION EQUIPMENT
`
`these cliagnostit: tests that deserve mention include bit error rate testing and alarm
`threshold ITI()[1lTt)1'lI’I§_I.
`.\'ormall_\' these two diagnostic functions are implemented
`h_\' the user obtaining a netw:':rl< control system (f\7C.‘t"a} designecl to operate with
`modems mant:f:1ett.iretl by the company that prodtieed the .\'C.‘a'.
`'l'ypit:ally,
`the
`NCH is a miemeornputer—hasecl systern that monitors the status of the modems in
`an trig-anizatit':i1's networlt. generates alarms when eertzrin predetinecl eontlitions
`occur, and in some eases it E1\Tlf1.lflll_\‘ performs t:or1'eeti\'e action prior to a disruption
`in network’ opertltitm ot‘CLII't‘ing.
`The NCS is normally installed at the central eornptiter site and on a periodic
`has-is queries the status of the remote modems on both point-to—point and
`mtiltitlrop lines. 'l'hi't'itI;_,1'l1t|1e 1980s most .\‘('.'.S systems worl<etl in eonjunetion with
`motlems that pt=.r’foi'n1 testing and status queries via the use of 21 secondary eharinel.
`This permits data tran.smission to continue on the prin1ar}‘ channel, with testing
`and t't_=:,;pr':i1h‘.e1-.‘-
`to the testin;__r flowing eonet1r:'entl_\' at a lower data rate on the
`seeondar_\' channel. Since then N(_f.S s_\'stems were developed to worlt in conjunc-
`tion with intelligent modems t'lesi;.»;ned to recognize certain datapatterns as a reqtiest
`to perform testin;_,r antlfor issue status responses. \\"hen used with this t_\'pe of
`modem. one’s actual inI’ormation flow of data is interrupted by the testing.
`To allow users to implement network eontrol functions in :1 data communications
`netwoi'k without having to replace existing_: inoderns, some vendors offer what is
`eommonl_\' ealletl :2 ‘modem wraparound unit’ or modem network adapter. Such
`dmiees are cabled to lmth ends of the. modem and in schematic tli-agmms appear to
`wraparotind the modem, hence the term 'wraparotind unit‘.
`l’i;_,rttt'e —l,~l-6 illustrates
`the titili'/,-ation of an _\_Ct_-3 maiitifacttired h_\' one \'I:11Cl0I' with local and remotely
`located n1ot'leins n1-anufaettired by a second vendor by the employment of two
`moden1 \\'l"¢lI)':1I'E_)l1l'](_l units. 'l"hrou;_z_h the use of the wrap-a round units, the NCTS can
`eondtltit rnotlem and line tests. even when the modems are In-ai1L.ifaett1re(l by
`L"! i fie ren r \'en do rs.
`
`

`
`-
`
`.
`
`ii.
`
`‘I
`
`'
`
`I’,
`
`4.3 INTELLIGENT MODEMS
`
`431
`
`4.3 INTELLIGENT MODEMS
`
`tmly memor_\_'
`In this section We will exzimine hr.)\\' Iniemproeessnrs and I't’di‘..l
`(ROM),
`I‘11Tltl(Jn1 access memm'_\‘
`(R.-—\.\l), and erasable pi'ngi‘aintneIl.ile 1‘t"t‘It'l only
`memm‘_\' (lil’I{();\'[) are used to :-icltl intelli,qenee to modems. Althuu,gl1 the ability to
`zitltl iiitt-lligeiiee to modems e-tin ]‘n't)\-'iL'le an iilmnsat infinite numher 0|‘ features aincl
`i"L.lI‘IL.‘tl(]l'1S. we will
`ftJt‘.Lis niit zitterititm upon three l<e_\'
`.'cll't.'_":1S that :11'L’ 1i0I'm:ill_\‘
`E15-E-§()t.‘.l£1U..‘Ll with the term ‘intelligttnt nmtlem’—-t:m'nmiintl sets, e.i‘i‘0r detection and
`eurreetitm, antl tlztta e0i11pI'essirin.
`The em‘m‘n21J1£l set 1i.~;eLl l)}'
`21 niotlem _s_{m'ei'1‘L.'a its tipettitimtzil LT£l[_Tdl)lil[_\'. t:n:1l‘1lir1;g
`'r1lltt_)l‘I1'r1I'l£'
`tli-tiling untl
`rec|i;ilingg of telephone I‘|l11‘I‘ti')L.'!'!-‘s, s~:eleetiun cut‘ an ope:-atin_L_r,
`1”.l'1lI‘IHl‘l'ii5-it-§i(_‘JI‘I
`rate. and E.!Tl1(.‘l'
`i‘lll'I(‘1'i01‘l!-I
`to he ]')(.’.I‘i‘(Jl‘t‘I‘l(.‘t..l
`\'i:I et>mmL1Iiic.'Ititms
`:-2()i"f\\"d!'L.' 01' by 2| pet‘::sm1 t_\'ping__I
`(.‘f.)ITIITI':1I‘I(lS from his or her te1'tni11-.il
`tit‘ pet's0ntIl
`t‘m'nputei‘ tn the nmtlem.
`_-\n ei'rm' tleteetirm zmtl t:ni':'eL‘tit)n Ctipziliility restllts in the ti':tI'ism1ittirig ITI{)(_lt.'l‘I'I
`iitlditig 1| E-i}"J(?LIl}ll
`‘tt';tilei" to eattrli
`l)l0(Ti( of (_l‘rll'.Ei
`\-\'|1ieh is Fm'I'tieLl 2ieet)i'Lliri}_{ to it
`precleliiied 2ilgm'ithm_ 'l-‘l'lL’ reeeix-'in_LI, 1‘I‘I()Ll(.‘ITI
`[)Cl'l‘()I"ITIF5 the same ttl;_{tJi'ithm on eatch
`received tiara l‘)lt)elt and et>inp;'ii'es its t;(}r‘r'l[)LlIIl«ltilJI1 to the tran.-mtittetl ‘trailei’. If the
`'[I‘JI’1.\‘.1"I‘Iittt'Ll
`:=mt| enmputed "trailers" mzuteli,
`the. claita block is e.mis;iclei‘ecl
`to he
`t‘eCei\'etl et'ii'1'eetl_\'. ll they eh‘: not n'12Itel'i, the ret:ei\'ii“1g 1’1'Il'JLl(‘:1"l"I will transrnit this fact
`tn the ti‘emsmittiti;_I mutlem, \\'hielt will then i'etrz1i'i.-emit the block. The L‘(JTl‘L“‘C[l(‘Jl1 of
`Llaln thus ('Jt_‘.(_‘t_1rF‘-
`l‘)_\‘ I'(.'i|'dI1t-il"I1l!-it-Eltlfi.
`it exttrniiies (l:'iT.':1 for
`“"hei‘| an intelligent |'1'1()(lL’I1’I pe1'I‘t)ri'i'is Clzltil et}1ripi'essit)i‘|
`i'et'lunclaiie_\'. i'eplueirig, as am exzimple, striiigs til‘ ehzirzieters h_\'
`51 special code aiicl
`count \\.'l‘1iCl‘t the |‘eCei\'ir‘|g modem reeugtiises and uses to 1'C}_!_C1'1El'&lIU the data hack
`into its original ftn‘n“i.
`'l"Iii'tiLigIi the use 0|‘ clam C()lT1]‘)]'{':SSil')I'I
`21 m0clem's el"fecti\'e
`iiifnrmatiuii ti‘:insl'er t3£l}"Jdl)ili[_\-' is ittt_‘:'e:t5eL'l F‘.ll‘1CL" each elmraeter tran:miil'tecl may
`teprestent imure than one clam L‘h2ll'::lt.‘t('_'l'.
`
`Command sets
`
`tI1lllL’(.l Bizeom cle\'elopecl the
`ti em)-till C()I‘I‘II‘I‘H1i'1l(Z'rIlfil)T‘1S Li()n'1]')llI‘|_\'
`DLt1‘i1‘ig the l‘.J70.~;,
`eoneept of adding intelligence to t“I‘!()LlL'l"r15-i tlimugli the Lise 0|‘ codes that the modem
`\\'eiultl reet);,rni7.e and tie‘: upon. The .~:erie.~; of eticles that at muclem is tlesi5._{i1et'l tn
`interpret and act upon is ix-l‘eri'ed to us its enmmzmd set.
`In aclclition tr.)
`the pioneering wnrk of Bi’/.e.t')n‘1, other modem lTttlI‘ILlf':1L‘tLll‘t'l‘S
`tleveltipetl similar perfoi'iiiin;_z r‘t1()Lle1‘I"IS.
`l7rifm'tL:ii;1tel_\'. tltiring the eti1'l_\' clays of
`intelligzeiit mocleni tle\'elnpment.< the emrmmritl sets built into ITl(.‘I(lL:l‘I"IS im1ti1tfat'—
`tui't:el h_\' clifferent
`\'I.':n(l0I‘S \\'ere ninre than likely to he inermipzttihle with one
`:mr_:tliei'. _\Itm_\' eommunieations s:0t‘tw:'ire |‘J1't'Jl_ll1(_‘.I:€ were thus tJI‘i}_1'_intlll_\' 1'est1'ieted
`to operating with 1] speeilie mc.itlem m‘ :1 few modems lmwtl upon the t‘0I‘I‘II‘I‘|EIl’t(l set.-<
`the :st.>ft\\'aI't-
`.~3uppm'tetl. Due to the ]‘J0pLIl:-’lI'if§' of the lltiyesq '.\-liwneompiiter
`l’i'utluets series of 511121l'tlT1U(lt.’T‘I‘I'c1T'\I
`\\'l'1ieh at one time captured m'et' 51)".-1. of the
`persmnnl enmputer modem mzirltet, that fii‘rn's; eemmancl set Cl‘I1(.‘.I'§_>,'€'.(‘l as -:1 r)'e~frm'ri
`intlimtry .~.;t'2Ii1tl:1rt'l.
`l.)t1I'it‘I_L‘ the l‘}8{.ls 111-mi)’ modem manul1ietiire1‘s inem'pm'ut'ed a
`E-tiI“I'lilF.11' enmmimtl set into their pmtlticts. restiltine in it
`l‘1i}_fl’I level of e<_imp:itihilit_\'
`
`
`
`

`
`
`
`The Hayes
`
`432
`
`WIDE AFIEA NETWORK TRANSMISSION EQUIPMENT
`
`laetween ctammtmications snft\\‘:u‘c tltttt supports the cmmnatntl set used l)_\‘ Il:i_\'es
`.5-'an1;t1'tn1mlems Eflltl modems I1’IdllLlll1IL't[|I'{.'v’.'l h_\_' other vendors.
`‘lltiycs
`as
`Tr>tl:t_\', m-tiny nmtlem mant.il7ncttt:'crs
`atl\'e1‘tise
`their prntlticts
`eump2Itih|e'; lit')wc\'t.-1'. this term can he misle.-t1tlin_tz as it ITI21_\' not intlictlte whether
`or not ‘l"l21§'es comp;itil)le' st)ft\\-'2tI‘t- will support all of the fettttires of 2: p;1I‘l'lt.‘.l1l1:ll‘
`mutlem. ln :1(lLll[llJl'I, cnnimttniczttions :;<'>ft\\'2ti'e :|tl\'ci'tisetl as Sl.1ppt')I'tlT’t}_{ the ll:l_\'es
`(‘()I'l'H"I}tEI’tLl set rn-.1)’ not estipptirt all of the features of 21 specific ll-.1_\'es Hiemconiptiter
`Pmducts E'5tn:ii'tnmtlt-m. To ttnt'lersta1nt'l why these incmnpntihilities can nccttt and
`him" they can he E1lli.;’\'i'dYL?(.l.
`let us lirst c.xe'tmir1e the I-l:':_\'cs conimtintl set and then
`focus ()L1I' attention tiptm :-}(_'\'t’1".'ll
`I'I}('1:Llt‘.l'D pmtlttcts anti
`the eui“ninamt.l sets the)‘
`:~'tl[‘)1'}{'Jl‘T.
`
`command set
`
`The II-ayes enmmatntl set :1L.‘tLl:1ll}' consists of :1 lmsie set cat‘ cmnmantls and comm-.-ind
`extensions.
`'|'hc basic c.nimmIm,ls, stteh as placing: the mntlem tnflllttmlt, cliatlintg ti
`ntimhcr and pt-.1‘t‘0i'1*nii1g similar r npcratinns are cnmmtm to all Ila_\'cs mntlems. 'l'he
`CU1‘["t!1’Idl'II‘..l extensions, such as placing a rrmclem into at specific OI1(‘.'["rlTli'1g speed are
`only appliettble to modems huilt tr.) trtmsmit and receive Lliltkl at their speed.
`The cmmnantls in the l‘i£I_\'C‘.S crmimttitcl set are initiated hy tramsinitting an
`attention code to the motlern.
`t'0llm\'t-cl by the upprtJpi'i:1te comm-tmtl or set til‘
`commands one desires the modem to implement. The atttentitm code is
`the
`(‘l'I'<1T'd(:tl.’1‘ seqttcncc .-\'l', which must he specitieti us all ttppei-case or all lt_m't.-tease
`letters. The reqtiircment tn preiix all emmnantl lines with the cotle AT has resultccl
`in mtm_\'
`I’l‘ItJt‘l(,'I'I1 :'nai1tif:tcttii'ci's clcnr_itin_s._v their muclems as llE1_\'t’.S .~\'I' cnmputihle.
`'|‘hc L‘.t"J1’1’t1’1’t2il‘ILl httffer in -(.1 llztyes .‘Smtti'ttn<.:(len'i lmlds —Hl ch;-tracters, perniittintz :1
`sequence (ll: coi'ni'na1nt'ls to he trttnsmittccl to the mtnclcm on one cnmrn2int'l line. Tliis
`-l-ll—(.‘l12'tI‘1lCtL‘I‘ limit tines not include the etttentiun codc., nor does it include sp:'tc.es
`int'luclet'l in 2| eummantl line to n’t'tll\'{' the line nmre. i'eutl:il)|e.
`'l‘;1hlc -l.2l
`lists the
`|mi_iu1' ct'Jmtna1i1t.ls incltttletl in the basic Ii-ayes cuitirnantl set. Other i1mt'lems, such
`as 'l'elehit's 'l'r:iilhlt1zei' employ 2] emnmaintl set tlmt can he crmsitleretl
`to he at
`superset of thc lht}-‘es commtmtl set. While commtmicatitms st:ft\\'21i't- that uses the
`H 21_\'es cr>n1m-.1nc| set will operate with this inotlem, such sn|‘t\\'arc e:innt)t utilize the.
`full putentietl of the mtidern. This is because the I121)-‘cs cmnmantl set (Ines nut
`strpport S{".\'I;‘l‘:ll Telehit "l‘r-.1ilhl;1zei' t'eatt:1‘es, such as its pmprietairy method inf t'.l'l'Ui‘
`tlctcctitm.
`
`reqtiired to transmit eomrnands to 21 H:i_ves C0iTl]‘)dl.'llllL.'
`The lmsie lltlI‘1’i'I':1lI
`ll}l.L"lllgL‘fit modem is shown l)elm\'.
`
`XI‘ Lhinimintl[[’a1i'z1:'1'icter[s}iCmninanti|l’ati';1meter(s}]
`
`Return
`
`the atpproprizttc
`followed in"
`line includes the prefix AT,
`iizteli cmnmamcl
`cuminand and the er:mmt1ncl‘s p:ir2trnetci's.
`'l"he cr.>n1n'mncl pm'si‘riett:rs are usually’
`the digits l} or I
`. which serve to deline 21 spec-ilie cmnnttmtl state. As an extimple. H0
`is the (‘.()I‘nI‘I1EI!"t(l that tells the mntlem to hang: up EH" tliscnnnect a call. while I'll i9
`the t;<.m1rmu1c.l that results in the modem guing titit‘-litmlt, which is the term USl..‘Ll
`tn define the :-tctitm that occurs when the tttlt-phone l'|E1l'1(.lSf3I
`is
`lifted. Sines
`
`
`
`

`
`4.3 INTELLIGENT MODEMS
`
`433
`
`Table 4.21 Basic Hayes command set (major commands)
`
`Command
`
`Description
`
`N<x<+mpovo§r—:fimUQmgb3
`
`Attention
`Answer call
`Repeat last command
`Select the method of modem modulation
`Turn modem’s carrier on or otf
`Dial a telephone number
`Enable or inhibit echo of characters to the screen
`Switch between half- and fu||—duplex modem operation
`Hang up telephone (on hook) or pick up telephone (off hook)
`Request identification code or request check sum
`Setect the speaker volume
`Turn speaker off or on
`Place modem on-line
`Pulse dial
`Flequest modem to send or inhibit sending of result code
`Change modem mode to "originate-only‘
`Set modem register values
`Touch-tone dial
`
`Send result codes as digits or words
`Use basic or extended result code set
`Enable or inhibit long space disconnect
`Fleset the modem
`
`+ + +
`
`Escape command
`
`Commands followed by an asterisk {' } are not applicable to the Hayes \.r'—series Smartmodem
`2400 but are recognized by earlier Hayes modems and modems manufactured by many other
`vendors.
`
`those terms are cm'losed in ln':u:kets
`l1:1\'e par-anteters,
`many eommantls do not
`to illustrate tlmt they are optional. A number of commands can be ineludctl in
`one c:'m1manL| line as l:m;:; as the number of eltaraeters does not exceetl -H), which is
`the size oi" the moclem's command btiffer. Finall_y, each command line must he
`l(.’l‘lT1‘iI1Ell.'I.’(.'l
`l3_\‘
`:1 C21i'1‘in,L_{e re1'.Liri'1 cltzlmctei‘.
`
`Conwnand use
`
`To illtistrate the utilization of the II:i_\'es command set let us asstime we desii'c to
`autorriatieailly clinl Ne-\\= York Cit)‘ informatirm. First, we must tell the modern to go
`oft"-lmolc, which is similar to one m-.1nuall_\‘ picking up the telephone handset. Then
`we must tell the. modem the type of telephone S_\‘$‘-I{‘.I‘t"t we are using, pulse or touel1—
`tone. and the telephone number to dial. Thus. if we have at terminal or personal
`computer connected to :1 I-Inyes eon'1|.1:Itil.1l:: modem, we \\'oultl send the Following
`comm-ancls to the modem:
`
`A'l' HI
`
`AT l'J"l‘| ,212-555-12 I 2
`
`the l parameter used with the H (‘.{)l'nl‘I'!11T‘l(_l places the
`In the first command.
`modcm oft‘—l1<_:ol<.
`In the second (‘.U|Tll]1::IT'tLl, UT tells the modem to dial (D) at
`
`
`
`

`
`
`
`434
`
`The Iirst comm-.ind, .-\'l‘ Q0, would etiuse the modem to respond to eon'n"n-.1nds by
`ti'2insrnittiri_::
`result eodes zilter eaeh command line is executed.
`"|‘he seeoncl
`(Tf}l']'1l'l'1&'lI1Ll.
`.—\'l‘ V1. would e'tuse the modem to transmit E‘¢lL‘.l‘I result code as :1 word
`eodc. Returnirrg to Table -l-.22 this would ettuse the. modem to generzite the wortl
`
`
`
`WIDE AREA NETWORK TRANSMISSION EQUIPMENT
`
`l was included in the
`'l'he cliggit
`telephone number using: toueh-tone (T) dialing.
`telephone number since it wzis ttssumed we l1E1\'t‘. to dial long-distance, while the
`eomma between the long—disttinee aieeess ntimher (
`l ) :-lI“ILl the area code (El 2} L"r1llS€‘S
`the modem to patise for 2 s prior to dialing the tiren eode. This 2 s pause is usually" of
`sLtt'l:It:.ient duration to permit the lnn_t{--;'listeIt‘|t.‘e dial
`tone to be reeei\‘ed prior to
`dialing the area code number.
`I’IuI"r1hL"I‘. this
`\\"l'|L‘!‘l Cliztling it
`tfiince kt Smairtinodem '.ttiton12itieull_\' goes oft‘-lit.-oli
`first eoinmzintl line is not actually required and is normally used for receiving ealls.
`In the second command line_. the type oli dialing does not h-.i\-'e to he specified il‘ ‘cl
`p|'e\'ious call was made, since the modem will
`then use the last type specified.
`Although users with only pulse ditilirit; avail-nl)ilit}' must specify P in the dialing
`eornm-.inel when using 21 I-'li1_\'es Smairtmotlem, several \'L'I1(_l()l‘S now offer nioclems
`that can :1utom:1ti‘:ill_\‘ determine the type of dit1ling_ l";1eilit_\‘
`the modem is
`connected to and then Lise the d})l')]‘l'.)p|‘lklTL‘ Llialing method without requiring the
`user to specify the type of dialing. For other non-I-It-1_\'es modems, when the method
`of dialing: is unspecified, such modems will tiutrmttttiettlly attempt to perforrn ll
`touch—tone dial and, if tttistiecessftil, then redial using: pulse di:ilin;__r.
`the lloycs
`To ohtain an tippreciution of the \‘t"I'S':1tllit§‘ of operations that
`Cl)ITI!‘f’I21l1Ll set provides, El!-‘-SLl!1’1(_‘ two personal computer users are comrnunienting
`with one another.
`ll’ the users wish to switch froni modem to voice operations
`without hanging up or
`rediztling. one user would send :-i message via
`the
`eommunie.:1tions }'H't')gI'kHTt he or she is Lising to the other user inelieming that voice
`C()I’t‘lI't‘IL1T1lCi-1T.'lU1‘l.'< is desired. Then, hoth users would lift their telephone handsets
`and type —l— + -+-
`(Return) All-l (Return) to switch from on-line operations to
`command mode {han,=__r—t1p). This will cause. the modems to lmiig-L11), turning off the
`modem carrier sigmils and permitting the users to con\‘erse.
`
`Result codes
`
`The response of the 1'5mzirtinodem to eornrritinds is known as result codes. The Q
`eomimmd with at pL1‘E1l‘nt."L't_’1‘ of l
`is used to enable result codes to be sent from the
`modem in response to the execution of command lines while :1 p2u'atnete1' of U
`inhibits the modem from respoi'iding to the e..\'ecution of each comm-ctnel line.
`[I’ the result codes klI'(;‘ enabled, the \' eomrnand ean he used to determine the
`formtit of the result codes. \\-'hen the Y eoi'nm:ind is used with a |}E1I‘ElI'1'1t"IE‘1' of ll. the
`result codes will he t1'dllS!Ttll'l't.’Ll as cligits. while the Lise of ‘<1 pt1i-'.1inetei- of 1 will eause
`the modem to trtinsmit the result codes 215 words. Ttible 4.22 lists the Basie Results
`Codes set of the llE1_\'t.’5 Stntartmodern Zilllll. As an exuinple ol‘ the. use of these result
`codes, let us assume the t'ollowin;1' commands were sent to the modem:
`
`A'l‘ Qt:
`:'\'I‘ \'l
`
`

`
`
`
`4.3 INTELLIGENT MODEMS
`
`435
`
`Table 4.22 Smartmodem 2400 result codes
`
`
`Digit code
`
`Word code
`
`CEOm"~.lG'JU"|-I5-K.-JF\J—lD
`
`OK
`CONNECT
`RING
`NO CARRIER
`ERROR
`CONNECT 1200
`NO DIALTONE
`BUSY
`
`NO ANSWER {replaces NO CARRIER if the @ is included in the dial
`string)
`Reserved for future use
`CONNECT 2400
`
`
`
`I.I2II'I'l{.'I' signal is detected. If the command .'—\'I' W.) was
`code ‘C(JN-t\'E(.‘T’ when zi
`sent to the modem. Ll result code of 1 would he transmitted by the modem, since the
`U parameter would cause the modem to transmit result codes as digits.
`B}-' combining an exzimimttion of the result codes issued by a Hinartrnodem with
`the genei‘.'-ttitm of appropriate ttommzamls. software can be developed to perform
`such operations as l‘(.'Lll21lll‘1,L{ H previously dialed telephone number to resume
`transmission in the event
`it eornmunittations session is
`iriterrupted and auto-
`mattieally ai“1s\\'ering_{ irtetarning calls when ‘cl ring signal is detected.
`
`Extended AT commands
`
`l"la)'es
`b_\'
`A large numher of extended AT commands were (_l(.‘\'I.fl()]')t.'(l
`KIieroeomputer l’rotlt1ets to control the operation and Lltilizzition ofspeeial modem
`features. Tzthle 3.21 lists the extended .—\T eomimmds supported by the I-[ayes \'—
`series Sm-Ltrtmodent 2400. Note that each of these commands uses the ztmpersanel
`(ft) elmrittrter to indicate it is an extension to the hitsie eommztnd set.
`
`ll2I_\'es Sm-artrnoden1s (.)pL‘.I"a1.'lI’L,‘_! above 2400 hps support most, if not all. of the
`extended commands listed in Table 4.23 while adding certain extended commands
`that reflect the addition ofee1't-uin features he_\'ond those included in the \-'—series
`Srmtrtmodem 2-I-(ll). For e,\':tmple, a I-Iayes Smetrtrnodem 9601) that supports the
`\'.32 sttmdurd includes the extended C.I:')r1"tl‘1"tdl’lL'lS &LTJ and &U1. The &L'0
`
`e_xte-nded eomm'.mL| emuhles trellis coding when the modem operates at 9600 bps,
`while the &l'l extended command disables trellis tztnditig.
`All extended AT eomrmmds are initiated in the same 1mmrn=.1' as basic commands
`
`and have the E-i‘.lI‘I‘Ii: rules and constraints with t'espe¢:t to their use. For example, the
`81C con“1mamd mus-:t he prefixed h_\'
`‘_'—\T' 01' ‘at’ to be recognized by the modem.
`Similarly, the modem must he in an oftlline or an on-line eomrmmd mode to be
`able to I-eeognixe and act upon the emmnand. You should not eonhise the I-[ayes V'-
`series Smzirtmodem 2-lllll e_\'t(:1'1(l{.’(l AT commands listed in Table 4.23 with the
`
`term ‘extended ;—\'[' eommzn'1ds' mun}-' modem vendors udxrertise. The latter is
`
`

`
`436
`
`WIDE AREA NETWORK TRANSMISSION EQUIPMENT
`
`Table 4.23 Enhanced AT command set (Hayes V-series Smartmodem 2400)
`Command
`Description
`
`&C0
`&C‘l
`&DU
`&D1
`&D2
`
`Assume data carrier always present
`Track presence of data carrier
`Ignore DTFI signal
`Assume command state when an on-to-off transition of DTFI occurs
`Hang up and assume command state when an on-to-off transition of DTR
`occurs
`
`Fleset when an on-to—oft transition of DTR occurs
`&D3
`Fleset when enter low power mode when DTFt is low
`&D4
`No guard tone
`&C-30
`550 Hz guard tone
`&G1
`1800 Hz guard tone
`&G2
`FI.l—11fFIJ—41Sl'H.J-455 telco jack
`&J0
`FIJ-12fFI.l—13telcojaok
`&Jl
`Disable local flow control
`&KD
`Enable RTSJCTS local flow control
`&K3
`Enable XONJXOFF local flow control
`&K4
`Enable transparent XONIXOFF local flow control
`&K5
`Asynchronous mode
`&l\/ID
`Synchronous mode 1
`&lVI1
`Synchronous mode 2
`&M2
`Synchronous mode 3
`&M3
`Track CTS according to FITS
`&Fl0
`Ignore FITS; always assume presence of CTS
`&Ft1
`Assume presence of DSFI signal
`8:80
`Track presence of DSR signal
`8:81
`Terminate test in progress
`&T0
`Initiate local analog loopback
`&Tl
`Initiate local digital loopback
`&T3
`Grant request from remote modem for RDL
`&'l'4
`Deny request from remote modem for FtDL
`&T5
`Initiate remote digital Ioopback
`&T6
`Initiate remote digital loopback with self test
`&T7
`Initiate local analog loopback with self test
`&T8
`Save storable parameters of active configuration as profile 0
`&W0
`Save storable parameters of active configuration as profile 1
`&W1
`Modem provides transmit clock signal
`&X0
`Data terminal provides transmit clock signal
`&)<'I
`Fieceive carrier provides transmit clock signal
`&X2
`Specify stored user profile 0 as power-up configuration
`&Y0
`Specify stored user profile 1 as power~up configuration
`&Y1
`
`&Z Store telephone number?
`
`
`
`at term used by \'i:l}(lI)l‘S other than I-laycs Xlicroconrptrter Products to
`tIsu:1ll_\'
`deline the cornmancls used by their products to access and control such features as
`_\'I_\'P. V".-I2,
`\-’.42 his, and |‘)i‘{_)[)T'II;’.tIIl'_\' methods of error control and data com-
`pression. .\Iicrocom has defined 21 series of ;—\'I' command extensions to control and
`access error control, data compressimt, and Hl)\\' control. Used by the ;\[icrocom
`AX se1'tesol‘modems, the extensions have been zrdopted by Intel, ()l<idu1'a. I-‘tactical
`I‘cripl1em1s, I’romethcus. and \"en—"[‘e|.
`.\'lodcms I“I1‘¢lI‘lLIf'.t(:tLl1‘t?L‘i by other \-‘curlers
`
`
`
`
`
`

`
`i
`
`‘,
`
`4.3 INTELLIGENT MODEMS
`
`.
`
`437
`
`rior1mt|!_\' use unique comm:-mds and >3 t'e;_1iste1' settings to access and control those
`}'n't:\'i0tISi_\' mentimtett i'eatLtres.
`
`Modem registers
`
`tn the degree of eompattibility between ntm—I Iat_\'es and ["‘Itl_\-'t_‘.‘-1
`third t<e_\'
`.-\
`Strutrtmnderns is the number, use and p1'o;_:i'2ttt1t1121|)iiity of registers emitztitteti
`in
`the modern.
`i[i:1_\'C5'i i‘$mett‘tninclems crmtuin it series of |)t'f.i}__{t'k1l‘I1I11‘¢lbiI:
`t‘egistet‘.~: that
`govern the futiction of the modem and the t')pe‘I":tti()l‘I of some of the ezitmnamls in
`the moderrfs emrinittnd set‘. Tztbie 424 lists the fttnetions of the first 13 I‘t.;‘.}'__{tS[(:‘l'.\‘
`huilt into the ii-ztyes Smztrtmotiem 240i}. to inclttcle the tietuttlt \-‘1-titlt.’ ofeaeh regzister
`and the rztmze rafsettirtgs permitted. Tltese registers are i\'I‘I0\\'t'1 as H register.~s. since
`the-_\' are set with the F5 cmnmand in the ['Ia_\'es command set.
`In tt(i(iifi()l‘I. the
`current value of each regi.~':te1' can he read under pt'<.n_9,rt1m etmtml,
`}':t:1't‘r‘tittiI‘I;_1f
`suftwatre developers to marliet commtmicattitms pi'o;zt'att‘ns that permit the user to
`eusi]_\'
`tnot1it”_v the tiefatilt values of the modem‘s S t'e.g_zistt-rs.
`
`Table 4.24
`
`S register control parameters
`
`Register
`
`Function
`
`Default value
`
`Range
`
`80
`81
`82
`83
`84
`S5
`86
`87
`88
`89
`810
`
`811
`
`812
`
`Ring to answer