US2275459A - Telephone system - Google Patents

Description

March 10, 1942. H. NYQUIST TELEPHONE SYSTEM I Filed May 31, 1940 l3 Sheets-Sheet 1 S 9 u k t 3 Q k5 K5 6 u g I P. I

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TELEPHONE SYSTEM Filed May 51, 1940 13 Sheets-Sheet 2 /NVENTOR H. N YQ U/ST Y A TJ'ORNE Y March 10, 1942. H. NYQUIST TELEPHONE SYSTEM 13 Sheets-Sheet 3 Filed May 31, 1940 INVENTOR H. N YQ 0/5 T Cw-q A 7'TORNE Y Ma rh 10, 1942.

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Fild May 51, 1940 13 Sheets-Sheet 5 EHIU INVENTOR By H. N YOU/ST wwwqfw ATTORNEY March 10, 1942. I H. NYQUIST 2,275,459

TELEPHONE SYSTEM Filed 'May 31, 1940 13 Sheets-Sheet 6 INVENT'OR B y H. N YQU/S T ATTORNEY March 10, 19.42. H. NYQUIST 2,275,459

TELEPHONE SYSTEM Filed May 31, 1940 13 Sheets-Sheet 7 INVENTOR H.NVQU/$T BKWWWWW A TTORNE Y Marh 10, 1942. H, NY ULST 2,275,459.

TELEPHONE SYSTEM Filed May 31, 1940 13 Sheets-Sheet 8 TRA N: L A TING MECHANISM //v VENTOR H NVQU/ST WWW U .ATTORNE Y March 10, 1942. NYQUlST 7 2,275,459

TELEPHONE SYSTEM File d May 31, 1940 13 Sheets-Sheet mm LLL g L m wggsu m V 1 HNYQU/ST B V wmvgmw @H a A TTORNE V March 10, 1942.

H. NYQUIST TELEPHONE SYSTEM Filed May 31, 1940 13 Sheets-Sheet l0 M/vE/vToR By H N Y6? U/ST ATTORNEY 253mm .89 Q9 39 bQQ March 10, 1942. H. NYQUIST TELEPHONE SYSTEM 13 Sheets-Sheet ll Filed May 31, 1940 INVENTOR By mvrpu/sr mwqonmm v5 .rH I. v9

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FIG /2 TERM/NAT/NG TOLL OFFICE Filed May 51, 1940 H. NYQUIST TELEPHONE SYSTEM 13 Sheets-Sheet 12 MARKER lNl/ENTOR H. NVQU/ST A T TORNEV Filed May 31, 1940 13 Sheets-Sheet l3 SEA/DER B V H NYQU/ST ATTORNEY IN l/ENTOR Patented Mar. 10, 1942 TELEPHONE SYSTEM Harry Nyquist, Millburn, N. J., assignor to Bell Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application May 31, 1940, Serial No. 338,001

22 Claims.

This invention relates to telephone systems and particularly to systems in which long-distance connections are established automatically.

The objects of the invention are to enablea more efficient use of the direct and alternate routes available in the automatic establishment of connections between remote oiiices in large toll areas; to increase the flexibility of switching systems in the extension of such connections; to make provision for automatically varying the routes available in accordance with traffic conditions existing in the area involved; to increase the speed and reliability with which call designations are transmitted over long distances to control switching operations; to utilize the call designation signals for controlling the establishment of long-distance connections and also for determining the transmission characteristics of said connections; and in other respects to obtain improvements in systems of this character.

Systems have been proposed heretofore for the establishment of toll connections by automatic switches controlled by subscribers or operators dials. Also systems have been devised in which calls are extended from any given point over:

direct trunks as a preferred choice and over alternate-route trunks as a secondary choice in case the direct trunks are not available. However, none of these prior plans makes it possible to obtain the most efficient use of the many toll trunks that interconnect the numerous toll offices in a country-wide system.

According to a feature of the present invention, advantages are realized over these prior arrangements by means of a system in which longdistance connections are extended automatically over trunk lines interconnecting successive offices; in which each office makes a registration,

as the call progresses, of the busy and idle condition of all routes tested; and in which the registration thus established in a given omce, which has already extended the call to an office beyond, causes the switching mechanism in said given oflice to reroute the call over an untried alternate path in the event the office beyond fails because all routes available to it are found busy or out of second trial over a new route after its first and initially successful trial over the preferred route has met with failure at some point beyond.

Another feature is a system in which the routing registration established in any particular office causes the switches in that ofiice to release the connection, originally extended therefrom, when the registration indicates that all available routes are busy, and to reroute the connection over an alternate route from said particular office to another office beyond,and in which the routing registration is then transferred from said particular office to said office beyond. Since this registration shows the condition of the routes tested following the first attempt to complete the connection from said particular office, and since some of these routes are normally available for completing the connection from said office be yond, the transferred registration serves the useful purpose of indicating to the control mechanism in said ofiicebeyond which routes are busy, thus obviating a futile attempt to extend the connection over these routes and directing the trials to other routes.

Another feature of the invention is a system in which the toll oflices are equipped with senders and markers for controlling the selective switches therein to extend the connection from one oifice to another, in which the code designation of the called toll omce is transferred from one sender to the next as the call progresses, in which the trunk network available to one office may differ from that available to the use of other offices, and in which the marker in any particular ofilce analyzes the code received and determines the trunk pattern available to it for the extension of the call.

Another feature of the invention is a system in which the code designation of the called toll of fice is utilized in the originating toll ofiice to determine whether certain transmission equipment, such as echo suppressors, shall be included in the connection and to determine the intermediate office at which this equipment is to be connected. When the connection has been extended from the originating office through the intermediate offices to the terminating ofiice, a signal is transmitted over the connection to identify the particular intermediate ofiice at which the echo suppressor is required. Signals are also transmitted giving the identification of the calling ofhce and the route over which the connection was extended therefrom to the intermediate echo suppressor ofllce. This information, together with similar information concern ing the called office and the route thereto already recorded in the echo suppressor office makes .it possible to adjust the delay values of the suppressor to give the best transmission characteristics. y i

Another feature of the invention is a system of the kind above described in which the designation of the called office and the supervisory and other signals are transmitted over the extended connection by means of carrier frequency channels.

Another feature of the invention is a system in which the signal receiving mechanism in the originating office is tuned to a narrow band for receiving specific signals during the time the connection is established and is automatically tuned to a wide band for receiving the speech signals of the operator or the called subscriber at the distant end. These speech signals serve apparatus of a toll exchange system embodying the features of this invention;

Fig. 2 shows acalling local oifice located inthe area served-by one of the toll offices;

. Fig. 3'shows the controlling equipment in the local o ffice, including senders and markers for controlling the operation of the automatic switches illustrated in Fig. 2;

Fig. 4 illustrates the originating toll omce serving the local ofiice of Fig. 2 and shows automatic switches over which calls from the local office are extended to distant toll offices. This figure also illustrates two of these distant intermediate toll oflices; I

Figs. 5, 6 and 7 disclose one of the common register senders in the originating toll oflice; of Fig. 4;

Fig. 8 shows one of the markers in the origi" nati'ng toll office which cooperates with the register sender to control the operation of the automatic switches;

Fig. 9 illustrates a third distant or intermediate toll office and shows the automatic switches therein for extending incoming calls to still more distant toll offices;

Fig. 10 illustrates one of the common register senders in the third intermediate toll oflice;

Fig. 11 illustrates one of the switch controlling markers and also a timing mechanism located in said third toll office;

Fig. 12 illustrates a fourth intermediate toll office and also shows a fifth toll office, which is here illustrated as a terminating ofiice; and

Fig. 13 illustrates a called local office in the area served by the terminating toll office.

Since each office in the system is interconnected with other offices over a plurality of different trunk routes, it is possible, by providing the necessary switching and controlling facilities, to make the most effective and efficient use of the trunking network in the extension of a toll call originating in any one of the toll offices and destined for completion through any other toll office. To this end each toll office will have a particular route over which it prefers to extend its calls to another office in the system, and this preferred routing may be changed from time to time by simple Wiring alterations made in the The present invention is particularly applicable controlling equipment. Likewise, each ofiice in the system will have a number of alternate routes to any other particular office, and these will be tried successively in a certain fixed order until an available one is found or until it is determined that all routes are unavailable.

For example, the toll office 400 may prefer to use trunks dill, 499, 4H, 9H, and 9M for extending its calls to the office IZM. If trunk M11 is busy, the office Mill may then prefer to extend these calls by way of trunks M6, 432, 4H, 9H and 914. But if trunk 432 is busy, it may then prefer to extend the call by way of trunks MB, $31, 425, 9H and 9M. And in similar manner other patterns may be used as subsequent choices in the extension of the call from office 4M] to office i280. Similarly, each office in the system has a preferred route over these interconnecting trunks to each other office and a plurality of alternate choices.

A call may progress successfully over several interconnecting trunks and then find itself blocked because all routes ahead are busy or otherwise unavailable. This does not mean, however, that the call must fail, because there still may be several available routes between the originating oilice and the called office. For instance, a call fromoffice liili to office [280 may have progressed successfully over trunks Ml, W9 and MI to the office 980. Office 908, however, finds both trunks 9H and 52! busy, but some or all of the trunks 423, 42L 9M, 428 and Q29 may be idle at this time; therefore, the call should not be permitted .to fail notwithstanding the fact that office 9% is powerless to reach these idle trunks with its own switching equipment. To make use of these idle trunks rather than allowing the call to fail, it is only necessary to provide some means for releasing the partial- 1y completed connection back to the preceding ofilce 28 and to provide means in office 420 for rerouting the call over its alternate route 423 to the ofiice Add. Thereupon the ofiice 440 is free to further extend the call over trunks 421 and 9M if both are idle or, alternately, over trunks $28 and 429 to the called ofiice I200. Should the ofiice Mil on its second attempt find the alternate route trunk 4323 busy the connection is released back to the next preceding office M0. In like manner the office m reroutes the call over its alternate route trunk 424 to the office 43%, assuming this trunk to be idle, and office 2-33 proceeds to further extend the call over available routes between it and the called office I200.

This comprehensive method of routing and rerouting a call to obtain the fullest advantage from the trunking system is made possible by providing each toll oifice with a route registering mechanism. The function of the route registering mechanism in each toll ofiice is to establish and maintain a complete registration of all trunk routes beyond that office that are tested in the process of projecting a connection toward a terminating oflice in the area. Since, therefore, each office through which the connection is extended keeps a registration of every trunk route tested beyond, it is possible for any particular oflice to release the connection forward as soon as it determines that the call has failed to find an idle route and to reroute the call over an alternate trunk route to an untried office beyond. The routing pattern available to a particular office will, of course, vary in accordance with the called office in the system. The route recording mechanism, however, is universal in this respect and is capable of selecting the proper route pattern as soon as the designation of the called office is received. Hence any ofiice in the system, when called upon to extend a connection toward any distant terminating office, is capable of automatically determining a pattern of preferred and alternate routes available for that particular call and to keep a registration of the condition of each trunk tested in the selected pattern. With this information, the controlling mechanism in the ofiice is able to determine what routes are available, to cause second trials as long as there is hope of extending the connection. over the chosen route, to recognize the existence of a complete failure over the chosen route, and to release an office from the connection in favor of a preceding office which may ultimately succeed in completing the desired connection.

A general understanding of the equipment used in the system disclosed herein may be had by referring to Figs. 2 to 13, inclusive, of the drawings. These drawings'illustrate a calling local oflice, an originating toll ofi'ice, several intermediate toll offices, a terminating toll office and a called local ofiice. It will be obvious, however, from the foregoing description of Fig. 1 that any number of intermediate toll offices may be involved.

The calling local office 209, shown in Figs. 2 and 3, may be of any type. ever, it is an office of the automatic type and is provided with the usual operators position equipment 220 and with operators cord circuits 2!! for extending calling lines to the toll office. For this purpose the operator has access to trunks, such as the trunk 21', terminating in the district selector switch 202. The trunk 20! also has access through a sender link connector 203 to idle register senders, one of which is disclosed partly in detail in Fig. 3. The register sender when associated with the trunk 29! seized by the operator responds to the operators keyboard and registers the code designation of the terminating toll office and also the code designation of the called local oifice and the number of the wanted line in the called local ofiice. Thus the complete information concerning the call is first stored in the sender of the calling local ofiice. Without limiting the invention in any way it may be assumed that the toll area is of such magnitude that five code digits are required to designate any particular called toll office and to include such other information as may be required in the extension of the connection. These five toll code digits are registered in any conventional manner on registers 3&2, 303, 324, 305 and 305 in the sender. The called office code, which may comprise three digits, is registered on registers 331, 386 and 369, and the number of the called line called is registered on the As illustrated, how

numerical registers 3H 3! I, 312 and M3. After the designations have been registered, the sender seizes an idle marker 3! through a marker connector 3l5. The toll code digits are then transferred to the marker, and the marker utilizes this information to selectively operate the district and ofiice switches 202 and 204 to seize an idle trunk 205 extending to the originating toll office 400. The marker controls the district and office switches in the usual manner by connecting itself thereto through the frame connectors 206 and 201. The marker also translates the toll code and sends the translated registration back to the sender where it is registered on a set of transmitting registers 3l6.

The local office sender is provided with carrier frequency signaling equipment having a substantial number of frequency channels by means of which information is transmitted from the sender to senders in the distant toll offices and by means of which supervisory and other information is received from the distant offices. The various designation characters and supervisory signals may each be represented by a single frequency or by a code of frequencies simultaneously sent over the signaling circuit. To this end the transmitting signaling equipment in the local ofiice sender includes a source of alternating current 3", a harmonic generator 3|8, channel filters 319, 32!], 32!, etc., detector amplifiers 322, 323, 324, etc. For example, these transmitting signal channels are used to transmit the translated toll code from the calling office to the toll office, to transmit supervisory information when the connection has finally been extended to the terminating toll office, and to transmit the called ofiice code and line number to said terminating oflice. The signal receiving mechanism in the sender comprises a plurality of frequency selecting filters and detector amplifiers, including filters 325, 326, 321, 328, 341, and detector amplifiers 329, 330, 33L 35$ and associated circuit controlling relays.

The trunk 265 extending from the local office enters the toll oflice 400 and appears in the automatic switch M2. Since the trunk 205 may be a two-way circuit, the function of the switch M2 is to extend this trunk to an idle junctor 4M on an inward call and to seize the trunk 205 on an outward call for the purpose of extending the desired connection from the toll oflice to the local ofiice. The junctor or trunk 40! appears in the district selector switch 492 and also has access, through a sender link connector 433, to register senders, one of which is shown in Figs. 5, 6 and '7.

The register sender in the toll office 400 includes toll designation registers 53L 532, 503, 504 and 535 for registering the designation of a terminating toll omce. These registers are set in response to carrier current signals incoming to the signal receiving mechanism in the sender from a distant local or toll ofiice. depending upon the origin of the call. The signal receiving mechanism 5% includes a plurality of channel filters and detector amplifiers. The sender also includes signal transmitting mechanism comprising generators 59'! and 598, harmonic generators M2 and 559 and associated channel filters and amplifier detectors and switching relays for transmitting designation routing and supervisory signals over the extended connection, both in the direction of the originating ofiice and in the direction of the terminating office.

The toll office sender also includes the routing terminating ofiice.

';mechanismshown in Figs. 6 .and 7. Thismechanism comprises :a plurality .of relays which :are operated, when thecall is first received, in accordance with the designation 'of the terminating toll office to determine the pattern of the trunk network beyond that will be used "in extending the call to the terminating office. This pattern :determinaticnis effected by the switch :controlling marker 86!;which is seized by the register sender through a marker connector 382 andwhich receives on its registers 803, 3%, '885, 836 and 81 the'toll designation of the terminating ofiice. This code designation is translated and analyzed by the marker and utilized to operate the necessary relays in the routing mechanism to determine the available route :network for the extension of the call.

The marker 89!, having received the toll code and'having translated it, proceeds to control the operation or" the selector switches M32 and Mi l, through the frame connectors M35 and 486, to

extend the connection over the preferred or direct route trunk AM outgoing to the next toll office MU beyond. If the trunk M1! is idle and the call is successfully extended over this route, a signal is transmitted to the routing mechanism to register the fact that the first tested link in the network pattern is idle. V

Thereafter the toll offices beyond, which will be described presently, further extend the connection over the preferred routes, if idle, toward the If the preferred routes are found idle, success signals are transmitted back 'to the originating ofiice sender, causing the 0peration of the relays in the routing mechanism. These-operated relays register the fact that the preferred links beyond are idle. On the other hand, if any one of the preferred links beyond is busy, an alternate route is attempted, and a failure signal is sent back to the originating toll office where it causes the operation of a relay in the routing mechanism to register the busy condition of the tested link. In this same manner success and failure signals are transmitted back over the connection each time a route is tested .3

during the progress of the connection toward the terminating oflice, and the routing mechanism registers these signals and thus establishes a complete registration of the condition of the tested links or routes in the routing pattern chosen for the particular call being extended.

To explain more specifically how the marker 'SGI determines the initial setting of the routing mechanism for the selection of the appropriate patern, it may be noted that the marker is provided with the usual route relays, such as the relays 898, 899, 8H], EH9, 820. Generally speaking, there is one of these relays in the marker for each toll code designation that may be received on the registers of the marker. However, in some cases remote olfices which are not regional centers may be represented by a single route relay. The route relay, therefore, represents the terminating toll ofiice, and its contacts may be wired in such a manner that relays in the routing mechanism are operated to determine the particular trunk routes available for the completion of a call to that terminating ofiice. By extending the circuits from the contacts of the route relays through a wiring rack or terminal strip I type for extending calls in both directions.

route relays may the .made common to .a number of :markers which seize them for use when required.

'The marker IiIlI, having received and analyzed the toll code, transmits this registration, either in its original form or in translated :form according to the location of the terminating office, back into the sender where it is registered on the transmitting registers 5m in the sender. When the proper time arrives, this registration in the sender will'be transferred therefrom .over theiextended connection to the .sender in the succeeding toll ofiice. Where translation of the toll code is not required, the sender may bearranged to send this code to the oflice beyond under :con-

'trol of the registers von'whichiit is received "from the preceding ofiice and without the assistance of the marker.

The toll trunks 481, 489, All interconnecting the successive toll oflices may be of the two-Way At the intermediate oflice 9%, for example, the automatic switch 9M serves to extend .the trunk MI in either of two directions, depending upon the direction of the particular ca'll'involved. On an inward call from ofiice 420, the trunk MI 'is extended by the switch Bill to the junctor 962 which appears in the contacts of the district selector switch '9ll3. The junctor 9512 has access through the sender link "connector 934 to're'g'ister senders in the oiiice 900, one ofwhich is illustrated in Fig. 10.

It will be understood that the register senders in the several toll offices may be substantially the same, although the sender illustrated in the drawing for the originating toll ofiice 400 shows some parts that are omitted from the sender in the ofiice 9G0, and the latter sender illustrates some parts that are omitted from the sender of the originating oflice. Like the sender in the originating toll office, the sender of the intermediate ofiice 9'00 is provided with registers mm, I002, I903, I064 and I885 for registering the code designation of the terminating toll office. This designation is transferred, as above mentioned, from the sender in the originating toll office and is received by the carrier signal receiving mechanism H386 and registered on the registers IIIBI to I885. The sender in the intermediate oflice is also equipped with a routing mechanism I6 I1,

similar to the one shown in Figs. 6 and 7.

The intermediate 'toll oflice is also provided with a marker IIBI which cooperates with the sender through the marker connector H02 and serves to control the operation of the automatic switches 933 and 905 to extend the connection over a toll trunk "9H to the next succeeding toll In view of the long distances that may be involved in some toll connections where several trunks are connected in tandem, it is desirable to provide certain of the toll oflices in the area with devices, such as echo suppressors, for improving the transmission characteristics of these long connections. "It may be assumed that the intermediate toll o'flice 960 is equipped with a number of echo suppressors, such as the "suppressor 996. The function of the suppressor is to respond automatically to speech transmission in either direction and after an interval of delay to open or disable the transmission circuit in the opposite direction. The purpose of opening the circuit is to prevent an echo reflected from the called end of the line from passing the suppressor and returning to the talking party. The,

amount of delay should be just long enough to intercept the returning echo. In the present system disclosed herein the inclusion of a suppressor in any particular connection or its omission therefrom is determined automatically from the code of the called office, and the inclusion of the suppressor, when required, is effected automatically. Moreover, the delay intervals for transmission in both directions are adjustable automatically in accordance with the transmission distances between the suppressor office and the terminals of the connection. The selection of a suppressor is effected by transmitting a distinctive signal from the originating toll office to the'suppressor ofiice. This signal is received like the other signals and causes the operation of a suppressor connector switch 908, which merely serves to connect the suppressor 906 in the talking conductors of the junctor 902. The amount of delay for the transmission circuit extending from the originating toll office to the suppressor ofiice is determined by the code designation of the originating office and by the particular route that was used in extending the connection from the originating office to the sup pressor office. The code designation of the originating office is transmitted therefrom at the proper time to the suppressor office and is registered on the registers I001, I008, I009, IMO and IBM in the sender. The exact route used in extending the connection from the originating office to the suppressor oiiice is known by the routing mechanism in the originating office. Accordingly, this information is transmitted in the form of carrier signals over the extended connection and registered on the calling route registers IOI2, IOI3, I014, H and IOI6in the sender. The setting of these registers is transferred through a connector I I03 to a decoder I I04. The decoder I104 analyzes the calling oince code and the route information and utilizes this information to set the variably operable delay switch 909 in the suppressor 906. Concerning the delay required for the transmission line between the suppressor office and the terminating office, it will be noted that the sender in the suppressor ofiice already has recorded therein the designation of the called office. Furthermore, when the connection has been fully completed to the called oflice the routing mechanism IOI'I has a full registration of the particular route chosen in extending the call from the suppressor ofiice to the terminating oflice. Hence the called toll office code and the routing information are similarly transferred to the decoder H04, which analyzes this information and proceeds to operate the variably adjustable delay switch 9I0 in the echo suppressor to determine the amount of delay appropriate for the transmission line between the suppressor ofiice and the terminating toll office.

The toll trunk 9| I extends to the next toll office 9I0, from whence the connection may be further extended over trunk GM to the office I200, which is assumed to be the terminating toll office. At office I200 the trunk 9M, which also may be of the two-way type, appears in an automatic switch I20I. The switch I20I extends the connection to a junctor I202 terminating in the district selector switch I203. The junctor I202 also has access through the sender connector I204 to the sender I205, which is similar to the senders in the other toll ofiices. The sender I205 has access to the marker I205 through the marker connector I20! and the marker, in cooperation with the sender, controls the switches I203 and I208 to extend the connection over a trunk I200 to the called local office I300, illustratedin Fig. 13.

The incoming trunk I209 appears in the incoming selector switch I30l in the local office, and the selector I30I, in conjunction with the final switch I302, serves to complete the connection to the called subscribers line I303. The switches I30I and I302 are controlled by the sender I304 and marker I305. Since the invention is not particularly concerned with the types of automatic switches that are used in extending the connections, nor with manyof the details of the controlling mechanisms which determine the selective operation of the switches, the disclosure has been simplifled to a large extent to faciiltate a clearer understanding of the invention by omitting many of the unessential circuit details.

It is assumed, however, that the local and toll oflices in the system herein disclosed are equipped with automatic switches of the well-known crossbar type, although these offices might be provided with other kinds of switches, such as step- .by-step switches, panel switches, or relay switches. The register senders and markers provided in each office for controlling the cross-bar switches therein are, in general, similar to those disclosed in numerous prior art patents. Also the several connecting devices, such as the sender connectors, the marker connectors and the frame connectors, may be essentially the same as those already disclosed in the prior art patents. For a more complete disclosure of the cross-bar system, of the manner in which the register senders receive and register the designations, of the manner in which these senders cooperate with the markers, of the manner in which the markers test the trunk groups, select idle trunks, control the selective operation of the switches to extend the desired connections, of the manner in which the marker supplies the sender with information concerning the further extension of the connections, of the manner in which the senders transfer information to distant offices and receive supervisory information therefrom, and of the manner in which the established connections are held during conversation and released thereafter, reference may be had to the following: Carpenter Patent 2,093,117 of September 14, 1937; Carpenter Patent 2,089,921 of August 10, 1937; Williams et al. Patent 1,543,967, June 30, 1925; Moody et al Patent 2,161,376 of June 6, 1939; Carpenter Patent 2,235,803 of March 18, 1941;

-and King et a1. Patent 2,236,246 of March 25,

For the manner in which the senders and markers cooperate to effect repeated trials and to choose alternate routes when the direct route trunks are busy, reference may be had to the Williams et al. Patent 1,543,967 of June 30, 1925; Kerr Patent 1,577,033 of March 16, 1926; and to the Carpenter Patent 2,093,117, September 14, 11937 and the Carpenter Patent No. 2,235,803, above noted.

Although the signal sending and receiving equipment is illustrated herein as comprising an individual part of each sender, it will be understood that this equipment may be common to the senders in an oflice and may be seized by any sender whenever it is needed to transmit or receive signals.

The operators position equipment in the calling local office may be of any suitable type,

equipped with a keyboard or with a dial for. setting the register sender.

The trunks interconnecting the several oifices:

sumed first that the subscriber of line 299. wishes.

to converse with the subscriber on line E3533. in a distant office. Referring to Fig. 1, it may also be assumed that the calling line 229 belongs to the local ofiice 2M: served by the toll ofiice 480. Also, it may be further assumed. that the called line I 383 belongs to a local ofiice 83526 which is served by the terminating toll office. iiiifl. It will be noted, further that theoriginating and terminating toll ofiices ilifi and i238, respectively, and the four intermediate toll ofiices M0,, 426, BOO-and 9m, disclosed in, the detailed drawings, correspond to the toll omces illustrated in the routing diagram of Fig. 1.

The calling subscriber manipulates his dial 2 I0.

and-extendshis line over automatic switches.(not

7 shown), to theservice operators position in the local ofiice. The operator responds with. her cord circuit 2H, obtains the information con cerning the desired subscribers office name and line number and proceeds to forward. the call by connecting her cord circuit 2H to an idle trunk 28! extending to the district selector switch 202. Seizure of the trunk 2% causes the trunk control mechanism 2P2 to function and: initiate the operation of the sender connector The connector 2% connects the trunk 2&5 to an idle register sender, and a visualsignal oradial tone is sentto the operator. The operator verifies the calling subscribers number, if necessary, and then manipulates her dial or keyboard associated with the position equipment 228' to. transmit designation signals over the trunk Ziii through thesender connector to the selected idle register sender. The signal or, impulse circuit over which these; designation signals are transmitted includes the tip and ring conductors-oi the trunk 20!, conductors H3 and 2M, conductors. Ziiand 216; and a signal receiving relay 33.3, The first fivedigits represent the code of the terminating.

toll ofmce, and the impulsesrepresenting these digits are transmitted, by the relay, 333,111 the well-known manner to the fivesuccessive toll code registers 3532 to 396, inclusive. The next seven digits represent the code of the local called ofiice and the number of the ,called line, and these digits are successively registered on the registers 30! to M3, inclusive.

At the proper time the registersender causes.

the operation of the marker connector 3E5, to connect the numerous control conductors from the, sender to the marker. Thereuponthe toll code digits are transferred from registers 332, to 306 over a plurality of conductors, represented by the line 334, to the marker 3M. The marker transmits the toll code (translatedif necessary) to set the transmitting registers 3 i 6'. The signals for setting the transmitting registers are sent;

from the marker back to the sender-over con-- ductors.335. The marker also tests the group of trunks extending to the originating'tolloffice Mill; selects an idle trunk 2&5 inthe group, and

operates the switches 2G2oand 2534- throughthe-- connectors 286. and 20:7 to. extend the connection from; trunk Ziill and. over the trunk 285. to the: toll office. The connection. havingthusbeenew tended to the toll. office, a; signaling relay 33.55 is; operated to transmit, a seizure. signal to the toll oifice. Relay 336 connects: the channel filter 3,315 and amplifier 338 to the winding of transformer: 3.39. A signal current. of the selected frequency is thus transmitted from the harmonicgenerat-on 3H3 through the primary Winding of the transformer 339. Current of thisv frequency is in.- duced in the secondary winding of the transformer and flows over the signal circuit. 3M1; through the connector 2665, over signal circuit 2!], and thence over the extended connection. to the controlling equipment al sassociated with the incoming end of the trunk 2S5 in the toll oflice. signal causes the automatic switch idzto extend the trunk 205 to the junctor Mid; and the junc tor 4611 initiates the operation of: the sender connector 403 toextend the junctor: through to an idle register sender in the toll. office.

Assoon as the toll offi'ce' sender is seized, it

transmits a signal-back to the sender in the calling local office to notify thelatter sender that.

the toll code may be transferred to the tolloifi'oe. Thissignal' may be transmitted by operating the relay 5. Relay 5! I oonnectsthe harmonic gen-- erator M2 through the channel filter and amplifier 5i3 and 5M to the primary-'windingof the transformer 5H5. The signal. current generated in the secondary winding of the trans-- channel filter and detector 326 andB'B'bto operate thesignal relay 34!. The operation of relay 3%! is a signal to thesender that the sender in the-originating toll office-is ready to receive the-tollcode, Thereupon the signal transmitting channels 322 are rendered-effective b'y'the transmitting registers and controlling circuit-s 3-16 toenergize the primary winding-of transformer 353 with currents of frequencies representing the translated digits of the called tol-l' ofiicecode.

Signal currents of correspondingfrequencies: are induced inthe transmitting circuittfi and sent" overthe extended connection, to the, originating toll ofiice Wherethey are conducted? over'the circuit fill-through the normal contacts ofrelay 51-6 to the signal receiv-ing mechanism- 566. After.

passing the amplifier and after: being selected:

by thecorresponding channel filters 549, 520',

52!, they are detected and utilized to setthe toll" office registers l, 562, 583,596 anditfi iniaccordance with the code; of the called tolloffi'ce. At,

the same time, a signal is sent by the channel transmitting mechanism 3M in, the callinglocal' oificeto' notify the toll ofice 4G3 that. itis to be the originatingtolloflice for this. particular call. This signal may betransmitted by the. operationof relay 345', which. serves tov complete.

the signal channel including the filter 3%: At

the toll oifice the signal isireceivedjand;selected.

bythe channel filter 522'and. causes. the. opera? tion of relay 523.1 The operation of relay 5233s, the signal to the tollpoflice sender. that the callis one that originated-inithis toll ofiice.

Following-the receipt of the toll code from the In any. Wfillr-kIIOWl'I manner: the seizure local office, the marker connector 602 is operated to connect the sender to the marker I. Thereupon the toll code is transferred from the registers 50! to 505, inclusive, over a group of conductors 523 through the connector 002 and over conductors M3 to set the corresponding registers 803 to 801 in the marker. The code is analyzed by the marker and is sent back over conductors 814 and registered on the transmitting registers 5I0 in the sender. The marker also utilizes the toll code registration for selecting and operating a route relay 810 representing the preferred route 401 outgoing from the originating toll office 400 in the direction of the terminating office I200. In the well-known manner the route relay 0i0 causes the testing of the trunks in the preferred route, the selection of an idle trunk therein and the automatic operation of the switches 402 and 404 to extend the connection from the junctor 401 over the trunk 401 to the first intermediate toll office 410.

It is assumed that the trunk 401 is the preferred route trunk for extending calls from the toll office 400 to the toll office 1200 and that trunks 409, 4H, 9H and 014 are the preferred routes, respectively, for toll offices 0, 420, 900 and 9I0. Therefore, no initial adjustment is needed in the routing circuit (Figs. 6 and '7) of the originating office 400;

Since the preferred route 401 is found idle and chosen as the first link in the desired connection, a success signal is sent to the routing mechanism to register therein the fact that route 401 has been chosen. The success signal is effected by closing a circuit from the marker over conductor 815 through the connector 802, conductor 524, through the winding of relay 525 to battery. Relay 525 operates and closes a circuit from the positive pole of battery through its armature and contact, contact of relay 521, conductor 526, back contact of polarized relay 60!, back contact and winding of polarized relay 602 to ground. This circuit is also extended through a back contact of relay 602 and the back contact and winding of relay 60! to ground. The polarity of the relays is such that only relay 602 responds and attracts its armatures. It may be noted at this point that the success and failure signals are recorded in the route recording mechanism by the operation of polarized relays, the positive relays serving to register success signals and the negative relays the failure signals. The polarity of these relays is indicated in the drawings by the positive and negative signs. When relay 602 operates, it extends the circuit over conductor 526 through the front contact of relay 602, conductor 603, contacts of relay 608, conductor 609, and thence to the next pair of polarized relays 604 and 605.

This circuit 526, however, is held closed long enough to insure the operation of relay 602 but not sumciently long to cause the operation of the relay 605 of the next pair. Relay 602, in operating, looks through its front contact over a control conductor to the positive pole of battery. Thus, the operation of relay 602 extends the incoming circuit 526 through to the circuit 603, this being an indication that the toll connection has been extended successfully over the trunk 401 to the toll ofiice M0. Had the preferred route 401 tested busy, the marker BI2 would have closed a circuit over conductor 816, causing the operation of relay 521. Relay 521 operating would close a circuit from the negative pole of battery over conductor 526 to the polarized relays 6M and 602. In this case, relay Bill contact of relay 608,

would operate, extending the circuit 526 to the polarized relays 606 and 601 which serve to register the busy or idle condition of the alternate route M6 extending from the toll ofiice 400.

In the manner already described, a seizure signal is transmitted by the signal transmitting mechanism 529 in the originating oifice sender over the trunk 401 to the toll office 4 l 0. The toll office 410 responds to this signal and connects an idle sender to the trunk 401. The sender in the office 4l0 transmits an acknowledgment signal, as above described, back over the connection to the sender in the office 400. Thereupon the transmitting register 5!!! sends the toll code by means of signaling frequencies selected by the filters 530, 53! and 532 through the transformer 533 and over the extended connection to the registers of the sender in office 410.

The sender and marker in the ofiice 410 pro- 'ceed in the manner already described to, extend the connection toward a succeeding ofiice. To this end the marker in oflice M0 first tests the preferred route 409 for an idle trunk. If an idle trunk in this preferred route is found, the connection is extended thereover to the toll ofiice 420. At the same time, the sender in the office 410 transmits a success signal over the trunk 401., to the receiving mechanism 506 in the sender at office 400. This success signal is of a frequency corresponding to the channel filter 534, and relay 525 operates. The positive pole of battery is connected to conductor 526, and the circuit may be traced through the back contact of relay 60I, front contact of relay 602, conductor 603, back conductor 600, thence through the back contacts and windings of relays 604 and 605 to ground. Relay 605 alone operates and locks in its holding circuit, thus extending the route registering circuit to conductor 6H1. Thus, the route mechanism in office 4l0 has a registration that the connection has been extended successfully over routes 401 and 409 to the office 420. At the same time that the office 4! transmits the success signal to ofiice 400, it establishes in its own routing mechanism, in the manner previously described, a registration to the effect that the preferred outgoing route 409 has been tested and selected. This is accomplished by operating a relay in the routing mechzaizism at office 4l0, corresponding to the relay Next, the sender in the office 4|0 transmits the toll office code over the trunk 409 to the seized sender in the oflice 420. Thereupon office 420 further extends the connection over the preferred route 411 and transmits a success signal back over the connection to the senders in office M0 and in office 400. It should be noted at this point that the markers in the successive omces release as soon as they have performed their controlling functions, but the senders are held to receive and transmit the necessary signals while the connection is being established. The success signal received in office 400 again operates relay 525 and applies positive potential over conductor 526 to conductor 610. The circuit over conductor 6 I 0 may be further traced through the back contacts of relay 608, back contacts of relay 6, thence through the contacts of polarized relays (H2 and M3 to ground. Relay 6l3 alone operates in response to the success signal, looks through its holding circuit, and extends the route registering circuit over conductor M4 to the next pair of registering relays H5 and M6. The success signal, however, is removed before relay 6H3 has

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