ta munlcatlons• • A USER'S Arr----l HANDBOOK • I _I • 11 ..1 .. 1111 .. 11 .. 11 li Racal-Vadic RACAL-VADIC - World leader in low- and medium­ serious problems sue h as line turnaround delay speed modems for lhe OEM and lhe end user. associated with Bell 202-type hall duplex trans­ Founded in 1969, Racal-Vadic today is lhe largest missions. Racal-Vadic has already delivered over independenl manufaclurer 01 low- and medi um­ 200,000 VA3400s to a customer base 01 more than speed modems that handle 300 through 2400 bps 5,000 companies. transmission. Racal-Vadic also supplies CCITI modems lor Racal-Vadic's broad product line serves both OEMs international use and a series 01 automatic dialing and end users 01 voice-grade line lacilities, whether systems. switched or private line. The VA300 and VA1200 Racal-Vadic again scooped the industry in 1977 by series, both introduced in 1969, are used widely by becoming the li rst manufacturer to have a modem the communications industry in place of Bell 103/113 (VA317S) approved under Rule 68 01 the FCC 's long­ and 202 datasets. To date, Racal-Vadic has delivered term reg istration programoThe VA317S, Be1l113- more than 450,000 modems to a world-wide compatible, is available as a PC card, in a stand­ customer base. alone cabinet, or in Racal-Vadic's 16-channel Multiple Racal-Vadic stunned the data communications Data Set System. industry in 1973 by announcing a modem capable 01 In April, 1978, the VADIC Corporation was acquired lull duplex operation at 1200 bps in both directions by RACAL Electronics Limited 01 Reading, England. simultaneously over dial-up or 2-wire leased lines. Vadie operates as a subsidiary under the new na me Using the same protocol, the VA3400 improves the Racal-Vadic, Inc. data transmission rate lour times over the BeIl103/113. With sales at an ali-time high, Racal-Vadic now This technical development is viewed as one 01 the occupies 165,000 square feet of facilities in the Moflett most signilicant accomplishments in the modem Industrial Park, Sunnyvale, and Fairfield, Calilornia. marketplace in the past decade since it eliminates 1able of Contents SECTION 1 Telephone Systems ..... , . • . • . • . .. 1-1 SECTION 2 Telecom Services . ... 2-1 SECTION 3 Why Modems ....... ... ... .. .. ... .. ... ..... .... •.. ..•....... .. .... 3-1 SECTION 4 Network Interface 4-1 SECTION 5 Modes and Protocols ..... .. .. ..... .. ..... .. ... ... ..............•..... 5-1 SECTION 6 Modems .......•.......................... .. ........... 6-1 SECTION 7 Automatic Calling Units/Accessories ........ ...... .. .. ... .•. ... ..... 7-1 SECTI ON 8 Diagnostics . .... .•. ... ....... 8-1 Racal-Vadie VA103 Modemphone - 8e11103/11 3 compatible modem ci rcuitry built inside a standard rolary ar tone telephone. ChapterOne 1able of Contents The Telephone System Page Title 1.1 Basic Switched Network Elements 1.2 The Metropolitan Area Switched Telecommunications Network 1.3 Connecting Metropolitan Areas 1.4 Switehing Centers 1.5 Satellite vs. Terrestrial Conneetion 1.6 Signaling 1.7 Typical Long Distance Telephone Conneetion 1.8 2/4 Wire Terminating Set 1.9 Echo Suppressors 1 .10 Echo Canceler 1.11 Public (Switched Network) Lines 1.12 3002 Unconditioned Voiee Grade Line 1.13 The Private Line Telecommunications Network 1.14 Private Line Transmission Facilities 1.15 Leased Line Networks 1.16 Unloaded Lines 1.17 Digital Data Service 1.18 Multipoint Systems 1.19 Two Wire Bridge 1.20 Four Wire Bridge Notes i, I!!L%* Raeal-Vadie VA315 Computer Site Modem - Di reet eonneet, originate/answer 8elll03/113 compatible modem /j designed for singleline ar multiline automatic dialing. LI Basic Switched Network t:lements • 1. Tran smission System • 2. Switching • 3. Signaling • 4. Terminal Equipment Users of data communications services should have some • Signaling involves supplying and interpreting the understanding 01 lh e switched network design, structure, supervisary and addre ss signals needed to perlorm the and operation. The network is a complex arrangement switching operalion. 01 tra nsmission, switchi ng , signaling, and terminal • The termina l equipment provides an interface lo lhe equipment. network. This intert ace may be acoustic, digital (as • The transmission syslem provides lhe electrical path for provided by a modem), ar analog (as provided byan data lrom one location to another. access arrangement). • Switching includes identilying and connecling independent transmission li nks to form a continuous path Irom one location to lhe olher. 1.2 The Metropolitan Area Switched Telecommunications Network Subscriber Localion F G A Local Terminal Site 00-2Loop:'--{ r r o on ue>. Local E Loop C H B Terminal Site The elements 01the network in a metropolitan area beginning ai lhe subscriber location or terminal site are: 1. Terminal equipment Telephone Voice Jack Data Jack 2. Local (Station) Loop 3. Central (End) Office 4. Interoffice Trunk Racal-Vadic VA317 Compute r Site Modem - Direct connect version 01 Bell's 113B/O auto answer 300 bps lull duplex modem. L3 Connecting M.etropolitan Areas Tol!­ Connecting Tol! Trunk OHice Metropolitan areas are connected through Local Inter­ expanded networks with the fottowing Loop Office elements: Trunk • TolI Connecting Trunks • tntertott Trunks • Hlgh Usage tntertol! Trunks High-Usage Intertoll Interto!! Trunk CityB Local Loop Tol!­ Central Connecling Tol! Office Trunk Qffiee 1.4 Switching Centers Regional 1'1 ITT Genter Class 1 " UT ...,-- / / The trunks terminate in tive classes of switching Seclional ,.- / centers, These centers operale in sequential and Center HUT /" hierarchical nades. Class 2 / ./ Switching Center Type Total Number (3 ~/ ~ Class, 5 Central Oflice over 60,000 /' (2) ..... -­ Pnmary Class 4 Tal! Center over 1,500 Cenler --I" Class 3 Primary Center Class 3 Class 2 Sectional Center "UT -- ....... - Class 1 Regional Center 10 TOII "UT Center -- ----~------ Class 4 Centlal TolI Connectlng IQT TOII Connectmg 1. Number in ( ) indicates order of choice of roule aI each cenler (End) 1I~~~"~o~"k~~----~-----C~~TruC="k~~1I c~~~s for calls originating at EO 1. Oflice EO' 2. Oashed lines indicate high-usage groups. Class 5 51allon Stat,on 3. ITT - Inlertolllrunk. Loop Loop 4. HUT - High-usage intertoll trunk. 5. IOT - Interoffice trunk. 6. First three digits of lhe phone number indicale central office. Subscllber SubSClloor Location A Locatlon B Racal-Vadic VA355 Remate Terminal Modem - Series of low cosI. standalone, direct connect 8e1l103/113 compatible modems specifically designed for the remate terminal user. L5 Satellite vs. TerrestriaI Connection Sal .Q /2ooL~ Earth Station ! Earth $Ialion H ~ H -6- -6- H ~ H - 22,000 Mires to 26,000 Miles - H ~ H -6- a ----=::::::===:::::::::::- o. -Ls H ~ H _ ___ 30 Mites---_ Prior to lhe use 01 satellites, lhe transmission paths were of a salellile is ils altilude above lhe earlh. The salellile is terrestrial. These transmission paths consisted of: launched in a geosynchronous orbit; lha! is, il rotates aI lhe • 2 and 4 wir8 voice grade lines same velocity as lhe earth does and il appears to be stationary. In arder to achieve this stationary orbit, lhe • High-speed coaxiallines salellile musl be launehed ai an altilude of approximalely • Microwave 22,000 miles. • Fiber oplies (reeentty inlrodueed) From a líansmission standpoint , a salellile connection In comparing a long-haul connection Qver salellite to is better. In particular, beca use its beams lend to traverse our traditional microwave Iink, Ihere are several obvious lhe earth's atmosphere in a vertical direction, it is nol as differences. In lhe microwave link, there are many repeater affeeled by lhe phenomena of layering of lhe earl h's sections; whereas with lhe satellile link, Ihere is a single almosphere, which results in microwave fading for repealer - lhe salellile. The mosl nOlable eharaelerislie radio links. L6 Signaling NETWORK SIGNALlNG IS USED TO: 1. Identify called and calling stations. 2 Set up connections in the network. 3. Identily the status 01 lines. 4 Provide billing information. 5. Release eonnections. The signals are generally calegorized as: 1. Supervisory a. Une status b. Offhook/Onhook 2. Address a. Call destination b. Dial pulse/Toueh lone 3. Audlble Tone Signals a. Dial tones b. Busy lones c. Ring ing lones Raeal-Vadie VS300P OEM Modem Card - Direel eonneel Be1l103/113 eompallble modem built on a eompael PC board Ihal occupies less than 42 square inches of space. L7 'JYpical Long Distance Telephone Connection A typicallong distance connection always Ed>o Soppressor ut ilizes specific elements Df lhe nelwork. These elements consist Df: ----l ,---­ a. 2 wire connection, localloop, to lhe central I office. BaJancing 11 Fou r Wilc I Balancing Network Une I NctWOl'k b. 2/4 wire termina lion sei I _____ J L ____ _ c. Uni-directional Ampliliers d. Echo Suppressors (depending on E,,,. distance) StlppresSOt Amp tifier e. Echo Cancelers (VLSI)" ' VL$I - Very Large Scale Inleg raled ClrCUlts L8 2/4 Wire Terminating Set r-----------------i , Amplifier I ! ~_-------11 "'" ' ~" ,,' -TW-Ow-ire--+!,+l±J l ~ .~ # iJ II FOr~n~ire Une , Hybrid Coil 8 aI a nclng Networ k I I I1 I Receive Pai r I . @] I L_______ Amplifier ______ J The 2/4 wire lerminalion sei takes lhe 2 wi re localloop, converts lhe tran smission path to a transmit pair, and receive pair. Racal-Vadic VA1244/45 Computer Site Modem - Direcl connecl 8ell202 compalible modem capable 01 singleline and multiline aulomalic dialing. L9 t:cho Suppressors l mpedance Irregularilies ~ r-____li.,r anS m~ ig nal Receiving Tr~~~~ng ~__ ~ ... _\.3-_ "-+ .~"""~~~-_~.-...J-f3....... -- ......-- ......-i ...... --- ...t----i----.~ Modem (Talker) • .-. ......... ~. • .. ........ "-------I .. r' L-_(L_is_t_en_e_r)---" Talker Echo Li stener Echo Echo Palhs on a Transmission Une Because af impedance irregularities in lhe terminating CharacteriSl ics of lhe echo suppressors are: networks, a smal1 amoun! of lhe energy transmitted in one 1. There is normally only one echo suppressor in each direclion over lhe swilched nelwork is olten rellecled ai lhe transmission paI h and il is between reg ional centers.