CA1101531A - Continuously expandable switching network - Google Patents

Abstract

Abstract of the Disclosure A telephone central office switching network and a basic switching element utilized therein is disclosed herein. The basic switch element has the capability of reflecting traffic entering any of the inlets thereto back to any other traffic inlet and the capability of connecting any of the inlets thereto to any of the outlets therefrom. The basic switch is implemented in the network in a quasi-folded configuration in which the outlet from a switching stage is never connected to the same or a lower tier stage but rather is always connected to a higher order switching stage such that the outlets of the switching stages are progressively connected in a multistage configuration from the terminal stage into the folding point in increasing order, thereby enabling the outlets of the highest order stages to be used as reflection ports while simultaneously remaining available for connection to higher order switching stages without the necessity of recabling. A
continuously expandable switching network is thus provided wherein incoming traffic penetrates the network only to the decree necessary to complete the required signal connection and is implementable either in space division configuration, time division configuration or any combination thereof, and utilizing either analog or digital encoding techniques.

Description

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K. F. Giesken-J. Cotton 1~1 Backqround o~ the lnvention 1. Field of the Invention Th~ present invention relates to the switching of space and time division multiplexed transmissions and more particularly, to a novel switching element S and networ3c configuration for implementing a substantially continuously expandable switching networ~c in a t~lephone exchange, telephone central office, PABX, remote concentrator, data circuit switch or other device wherein a plurality of terminal interconnections are required.

2. Description of the Prior Art Presently available time division switching networks utilize time-slot-'~ interchan~e modules or space switching modules utilizing time shared space interconnections, usually two of the former modules and one of the latter or two of the latter modules and one of the former. U. S. Patent Mo.

3, 770, 895 is illustrative of a time slot interchange of the prlor art. U . S .Patent No. 3,963,872 is illustrative of a Eolded multiple stage switching network oE the prior art. These prior art switching networks are generally incapable of modification without extensive recabling to accommodate maior system size expansion.
Switching networks of the prior art are designed to cover particular size ranges, i.e., ihe number oE lines that can be switched, whereas the present invention is adaptable to switch over a wide and expandable size range.
In accordance with the present invention, a smaIl switching network, i.e., Eor a few hundred lines, may be economically constructed since there is no specific number o~ sta~es required for implementing such a small ne~work.
There is no upper limit from a network configuration standpoint to the ' iLS3 L
K. F. Giesken-J. Cotton 1-1 expandability o~ such a small network, i.e., the network is readily expandable from a few llundred lines requirillg a small number of stages to a large number of lines, i.e., S0,000 lines requiring a plurality of stages. Also, a worlcing small networ!c can be readily expanded to a large working network without S recabling as would be required in systems of the prior art.
A continuously e~pandable switching network configuration is described wherein the outlets of the stages comprising the network are connected only to the switches in higher level stages, thereby eliminating the need for recabling in the event of system expansion. The connections between terminals are accomplished by use of the reflection and the connection ( ` characteristics of the individual switchin~ elements~ By reflection characteristics j the capability of interconnecting two lnlets within the switchls defined. This network is implementable with either analog or digital transmission schemes over either two or four wire traffic paths and with space and time switchin~ and combinations thereof. In a preferred embodiment of this invention, a combined multistage space switch and time slo~ interchange switching network is described utilizing as individual switching elements ( ` thereof an intesrated signal swi~ch and control circuit by which traffic can be interconnected to another inlet or connected to an outlet The described network configuration is applicable to either analog or digital traffic switching and is particularl~ advantageous when employed in a four wire network as either a group s~,vitch, a concentrator, a deconcentrator or any other type of PCM
switching unit requiring the capability of space and time switching to connect any time slot on any incoming multiple~ed line to any other time slot on any other outgoing multiple~ecl line. The described switch may be incorporated in the networ3c for switching both the forward and return paths of four wire interconnections by means of a controllable reflection point technnique ancl a .

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K. F. Giesken- J. Cotton 1-1 path selectlon control accessible for distributed control command with digitallyencoded speech and control commands with dlrect control of the speech path, thereby eliminating extra control lines. It is therefore a primary obiect of thepresent invention to provide a substantially continuously expandable switching network.
A further object of the present invention is to provide an expandable switching networ3c in which modification of internal or e~ternal connecting links is not rec~uired for such expansion.
A further object of the present invention is to provide a multistage switching network~in which the switching element outlets of any stage are connec~ed -~-- only to switching element inlets of higher order stages~
.~ . . . .
Yet another object of the present invention is to provide a multistage switching netwol-k in which incoming traffic penetrates the networ~ only to the extent necessary to complete required connections.
lS Yet another object of the present invention is to provide a switching element having a plurality o~ inlets connectable to a plurality of outlets, having a reflection capability of reflecting traffic entering on any inlet back to any other inlet, and a connection capability o~ connect~ng any inlet to any outlet .
- Yet another object of the present invention is to provide a PCM switch modu7e contin~lously expandable without recabling over a size range, i.e., the total number of terminals to be interconnected, of lO0:1 or more and which is implementable as a group switch, a concentrator or a deconcentrator.
Yet another object of the present inv~ntion is to provide a PCM switch for connecting any time slot on any multiplexed line to any other tlme slot on any other multiplexe~ line.
Yet another object of the present invention is to provide a combined space cmd timc switchlng module Eor switching both the forward and return paths of a four wire connection.
Yet another object o the present invention is to provide a combined time and syace switch module having a path selection control accessible for control commands by means of the voice path with the conse-quent elimination of extraneous control paths.
According to a broad aspect of the present invention, there is provided a plurality of switches arranged in a plurality of stages of said ~-switches to comprise an expandable switching network with each of said switches comprising: means for providing a plurality of inlets for receiving digital signals and a plurality of outlets; means for adapting each of said outlets to selectively reflect said digital signals back to any of said inlets; means for selectively coupling any of said inlets to any of said outlets to provide an output for said digital signals out of said switch from said outlets; means for coupling said signals from the outlets of the switches of any of said stages of switches to the inlets of switches of higher order switching stages; and means for reserving said outlets of any of said switches Eor coupling said digital signals from said outlets to the inlets of switches of said higher order switching stages.
According to another broad aspect of the invention, there is provided a method for providing an expandable switching network from a plurality of switches comprising for each of said switches the steps of:
receiving a plurality of digital signals at a plurality of inlets of said switch; providing a plurality of outlets from said switch to which said signals are selectively coupled from said inlets; adapting each of said out-lets to selectively reflect said digital signals coupled thereto back to any of said inlets; selectively coupling signals from any of said inlets to any of said outlets to provide an output for said digital signals out of said switch from said outlets; arranging a plurality of said switches into a network of a plurality of stages of said switches; coupling signals from the outlets of the switches of any oE said stages of switches to the inlets of switches of higher order switching stages; and reserving the outlets of 11~1 lL53~L ~

any of said switches for coupling said digital signals from said outlets to the inlets of said higher order switching stages.
The invention will now be described in greater detail with refer- -ence to the accompanying drawings: ;
Figure la is a simplified junctor switch of the prior art utilizing the reflection point technique.
Figure lb is a prior art use of reflection and connection verticals in a switching network oE the prior art.
Figures 2a, 2b, 2c and 2d are simplified switching network configurations illustrative of the network expandability of the reflection technique of the present invention wherein exemplary single block, two block, three block and eight block switching network configurations are illustrated, respectively.
Figure 3 is illustrative of a space switch on the inlet side of a time slot interchange also using the reflection technique.
Figure ~ is a graph of blocking versus the number of stages of switching Eor different levels oE traEEic intensity.
Figures 5a and 5b illustrate the switching matrix expansion by use of reflection/connection outlets wherein Figure 5a is a single switching module and Figure 5b is an expanded switching module.

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K. F. Giesken-J. Cotton 1-1 I;'igures 6d through 6e are illustrative of a multistage switching network expansion configuration in accordance with the present invention.
Figure 7a is a representation of a four wire path complementary `
delay.
Figure 7b is illustrative of the control logic for a single entry or exit point.
Figure 7c is an equivalent logical representation of the control logic described with reference to Figure 7b.
Figure 8 is a time switch control circuit for a four wire delay line time switch utilizing the switching logic described with reference to Figure 7b.
Figure 9 is a logic and block diagram of a network crosspoint.
Figure 10 is a block diagram of the network crosspoint of Figure 10 incorporated within a network matrix.
Description of the Preferred Embodiments The raflection point technique has been employed in prior art Al crossbar networks, such as in a space division switch by the closing of two hori~ontals on one vertical. This i9 illustrated by Figure la, wherein traffic on line units 10 and 12 are coupled to a junctor switch 14 via horizontal matrix lines 16 and 18 to a vertical line 20.
Each line unit 10 and 12 may comprise a small network of crossbar switches as are well known in the prior art, having coupled thereto a plurality of input/output lines 15. The reflection concept is imple-mented by the coupling of traffic on line 16 to the junctor switch 14 wherein it is reflected off vertical line 20 and exits from the junctor switch via horizontal line 18.
An improvement of the prior art over the technique of Figure la is shown in simplified form by Figure lb which is illustrative of the reflection point concept utilized by the ESR-l PABX switching network of Standard Elektrik Loren~ A.G. In this system, the vertical lines are connected between switching modules ~r ii3~1~
K. F. Giesken - J. Cotton 1-1 at the same level ln the network hierarchy, thereby limiting the maximum size to which the network can be expanded. Thus, a plurality of line units 22, 2~, 26 and 30 are connected on respective horizontal lines 32, 34, 36 and 38 to switching modules ao and 42. Module 40 serves to interconnect line unîts 22 and 2~ by reflection, module 42 serves to interconnect line units 26 and 30 by reflection and modules 40 and 42 together with link 44 serve to interconnect line units 22 arld 24 with line units 26 and 30.
The numberical designations (1) on lines 32 and 34 is equivalent to the intermodule connection of traffic on lines 32 and 34. For this conditlon, crosspoints 46 and 48 are closed. The numberical designations (2) on lines -!""`` 34, 38 and 44 are equivalent to the intermodule connection oi traffic on lines ~............ . .
34 and 38. For this condition, crosspoints 48 and 50 are closed while crosspoint 52 is open.
The prior art system of Figure lb, while utili2ing the basic reilection techniqua, provides a system whereby the vertical of one switch is connected to another switch at the same level in the network hierarchy, i.e., to the - same level switching stage, thereby limiting the maximum siæe to which the networ}c can be expanded. In contradistinction to the aforedescribed prior art systems and in accordance with the present invention, it has been discovered that by connecting .he reflection~connection verticals only to horizontals oi higher level switches, which higher level switches also have reilection/
connection verticals, a continuously expandable switching networ~c is obtainable .
As used herein, the terms input, output, inlet and outlet are defined as i`ollows. An input is a port to a switch or combination o~ switches, which port carries slgnals irom outside the switch into the switch, while an output is a .S3~L
K. F, Giesken-J. Gotton 1-1 port on a s-witch carr~ing si~nals from the switch. An inlet is a connection to a switch, having both an input port and an output port, which carry the signals relating to the two directlons of transmission forming a full duplex communication path, and whic}l connect to one side o a switch. An outlet S is a connection to a switch havin~ both an input port and an output port which carry the signals relating to the two directions of transmission forming 2 full duplex communication path and which connect to the slde of the switch opposite to the inlet.
Referring now to Figures 2a through 2d, a folded network is described which is illustrative of the reflection/connection technique of the present 1~ inventlon in which the outlet from any switch of a partlcular stage is never connected either to the same or to a lower tier sta~e, and wherein the sequence V~ i331 K. F. Giesl~en-J. Cotton 1-1 of numbering of the stacJes is from the terminal stage into l:he foldin~ point in increasing order. It is to be unclers-tood that this network configuration is ~reatly simplified to illustrate the network expandability. By way of àefinition, every switching matrix conslsts of a number of depths, ranks, or S stages of switches through which the path connecting two terminals must pass.
In a non~folded networ~, the connecting path crosses each stage once only and the path from the originating terminal to the terminating terminal always crosses any or~ stage in one direction only. In a folded net~vork, the connecting path be-tween an originating terminal and a terminating terminal may cross any stage in either direction and will cross at least one stage at least twice, once in each direction.
In accorclance with the present invention, the outletsrof l:he highest numbered switching stage are used as reflection points; however, these ou~lets are always available for connection to yet a hiyher numbered stage without circuit modification. Thus, the outlets ar~ utilized to connect to another switch or may be considered as folding points. A folding point may be deined as that point in a folded network at w}lich a signal switched through the networ}c reverses direction through the network, i.e., stops its progression toward a higher level stage. Additionally, the reflection and connection capability of the switch rna~,r be utilized on alternate connections.
Figure 2a is illustrative of a 2 x 2 line switch having two inlets, -100 and 102, and two reflection points, 104 and 106. Reflection ports 104 and 106 are also connection verticals as will be described. In the event that each of the inlets 100 and 102 were a twenty-fc~ur channel time division multiplex (TOM) line, then switch 108 could provide a switching capability of 150 lines _ '~

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K. F. Giesken-J. Cotton 1-1 with suitable concentration, as is well known, on one inlet and up to t~venty-four trun~; lines on the other inlet ~vith full interconnectability therebetween as will hereinafter be described. Another example of the reflec-tion/connection technique is the case in which inlet 100 has coupled S thereto a circuit having six lines concentrated thereon, while inlet 102 comprises a two-way trunk line to another switching location in an analog or non-multiplexed configuration. By usin~ only one of the reflection ports 104 or 106, both line-to-line (revertive) or line-to-h-unk, calls may be implemented one at a time. This network is continuously expandable, for 10 - example, to twelve lines and two trunks as illustrated by Figure 2b, wherein ( ~ additional switches 110, 112 and 113 are added on of identical configuration to switch 108 and which results in expans;ion to two stages, For purposes of description, the switch added to expand to a second terminal switch is identified by the numeral 2. When interconnection among channels within switch 108 are required, the outlets 104 and 106 of switch lOB are used ~s reflection points, i.e., for telephone calls among the original lines and trunks. The reflection properties of switch 108 are utilized while calls are also switched among the new terminals in similar manner. Hcwe~er, for calls between a terminal served by switch 108 and a terminal served by switch 110 having coupled thereto the same number of lines and trunks as are connected to switch 108, then the outlets of switches 108 and 110, i.e., both first stages, are switched throush to a common second stage switch, either switch 112 or li3. The reflection points of the second stage at 11~, 116, 118 and 120 are used to complete the connection~ T~lus, it can be seen that for connections between channels or primary svritches 108 and 110, an outlet 3Lt-3~
~..F. (~ies~;en-J. Cotton 1-1 on each of S~`liCI s~JitChes iS used as connection ports to a common higher tierstage switch -where at one of the outlets of such lligher tier stage is utilized as a reflective port.
Figures 2c and 2d are illustrative of the continuous expansion oE the switching S network to three and eiyht primary switches, respectively. This expansion technique without rearrangement either of intemal or external connec~:ing links,can be achieved Wit]l respect to space and time division switching and to any desired size basic switclling elemen-L; however, the space division implementation is illustrated by Figure 2. With reference to Figure 2c, the three primary switching block configuration illustrated provides a capability of six additional lines and another two-way trunk by virtue of the third swi-~ching block 126. Two-thirds of the incominy traffic from switch 126 would statistically be destined Eor the first two switches, 128 and 130/ since two-thirds of the incoming lines and trunks to the switching network are lS coupled to switches 128 and 130. Howe~ver, since each inlet provides one unit of trafEic, then two-thirds oi the two switching units 128 and 130 is ~our-thirds of a traflic unit which exceeds the tra~fic capability of one switch outlet;
hence, two secondary stac3e switches 132 and 134 are provided for the third primary switching unit 126. As will become apparent with respect to Figure 2d, the addition of a fourtll switching unit will not result in the rearran~ement of any existing links. The switching blocks 136 and 138 of the second stage and switching blocks 140 and 1~12 of the third stage are oE the same configuration as are the primary stage switching blocks. The network expandability w~thout rearrangement of èxisting conllecting !in};s is illustrated as extended to eight primary switching blocks, each of which may, Ior example, have couplecl thereto Si~Y lines and a two-way trunk line as illustrated iil Figure 2d. The eight primary switclling bloc};s 150 l:hrough 164 o' the firsi:

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K. F. Gies~cen-J. Coi:to~
stage of the s~vitchin(~ netwo-k may be iden~ical in conli~uraiio-.l to the switching units of Figures 2a through 2c. In contradistinction to a single stage folded ne-twork, the switching network configura-tion of the present invention is more economically expandable since the cost of a sinyle stage folded network in terms of crosspoints per line increases linearly with the number of terminals, i.e., inlet ports or lines, while the present network, in terms of crosspoints per line, gro~vs approximately as the logarithm to the base 2 of the number of terminals. This relationship is illustrated by the following table for the eightblock network of Figure 2d.
No. Switches Primary No. Switches Total Switches In Networlc N where N =
Bloclcs (2N) Added In Network Per PrimarY Block (Sta~e No. - l~
.
. ' 1 ~ 1 . . .1 0 - 2 3 4 . 2 3 S 9` 3

4 3 12 3 2 15 5 7 19 3;8 .
6 . s ~d~ 4 . 7 5 29 4;1 16 80 5 ; 4 2032 192 6 s '.
- The s~,vitching blocks added to the networ3~ in stages 2, 3 and 4 are iclentified by numerals corresponding to\the addition of the primary switching block, the addition of which requires the addition of the corresponding hi~her tier stage switching. Thus, for ~xample, the addition of primary switch 158, the fifth primary switch, results in the addition of second stage switches 166 --12 -- .

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3~L K. ~. Giesken-J. Cotto~
and 168, third stage switches 170 and 172, and fourth stage switches 174 and 176 .
Referring now to Figure 3, the characteristics of the elemental switch, a plurality of wnich constitutes the overall switching network, is illustrated for a preferred embodiment~ Each elemental switch must function as a space switch capable of switching m inlet connections to n outlet connections.
Additionally, each elemental switch must comprise at leas-t one time slot interchange (TSI) unit ior each inlet or outlet in which m corresponds to the number of inlet connections and n to the number of outlet connections. It is to be understood that the designation of inlets and outlets is exemplary onl~r and that the number of TSI's would correspond to the smaller number o m or n. In the event that a number of TSI's equal to the larger of m or n or in any event, greater than the smaller oE m or n were used, the networX would still be functionall however at reduced efficiency. Finally, each elemental switch must include enabling gates for signal reflection whlch is critical for a four wire network. The connection/reElection gates are illustrated in Figure 3 in simplified form; ho~vever, it is to be understood that each OI said gates corresponds to the logical implementations described with reference in part ~o Figure 7a. A space switch capable of switching m x n is also required. A
concentration capability may be implemented when m is greater than n and an -expansion capability implemented when n is greater than m. Additionally, for the concentration case, when a symmetrical (n x n) switch is desired, only n of the m inlets need be used, since the non-utilization of the remaining inlets would result in only a srnall number ohinexpensive gates being non-utiLized.
Furthermore, an m x 2n switch may be achieved by connectin~ the inlets of the necessary additional switches to the inlets 234 and 236. Of course, the value of m can vary widely with m being any number of inlet connections and n being ~ L53~l K. F. Giesken-J. Cotton 1-1 any number of outlet connections.
Referriny now to Figure 4, a graph of blocking ~ versus number of switching stages N for four levels of link occupancy is illustrated. The term blocking as used herein may be defined as the inability to interconnect the idle lines or trunks connected to a network because of the imposslbility for whatever reason to achieve such interconnection. The term nonblocking network as used herein may be defined as a network in which there is at all times at least one available path or link between any pair of idle lines or trunks connected thereto, regardless of the number of paths already occupied.
Two Important aspects of network operation are the ability of the network ~.
- to respond to varying traffic levels and the effect of an increased number of (. s' . . . .
stages on the network operating characteristics. In accordance with the present invention, as the number of network stages increases, with each sta~e comprehending a plurality of switches in a switching network, each of which has an identlcal parallel function to another switch in the switchin~ stage of equalrank, the bloc}cing does not continuously increase but approac~es an asymptotic value be-tween zero and one depending upon switch size and traffic intensity.
The term traffic intensity as used herein may be defin2d as the traffic quantity -in one or more traffic paths per unit pf time and Is generally measured in ~rlangs where one Erlang is the intensity in the traffic path continuously occupied or in one or more paths carrying an aggregate traffic of one call hour per hour, one call minute per minute, etc. In accordance with the present invention, the network blocking characteristic B for a particular number of switching stages N
for low, medium and high traffic levels \is such that a relationship exists between the blocking characteristic and N, where N is the number of stages such that .

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IC. F . Giesken-J. Cotton 1- 1 once a ma,~imum J~loc~inc3 level is reached, the network blocking will not further increase/ i.e., the network blocking versus N curve becomes asymptotic at a ma.~imum blocking level. This is illustrated by Figure 4 for four levels of traffic intensity with curve j1 representative of low traffic

- 5 intens;ty, curve 2 representative of low to medium traffic intenslty, curve 3 representative of medium to hi~h traffic intensity and curve 4 representative of higll traffic intensity. As the switch size in each stage in increased, the blocking probability becomes lower for a given traf~ic intensi~ E.
Referring now to Figures 5a and 5b, the network expansion by means of the reflection/connection output terminal is illustrated. Speech connections in f switchin~ bloc~ 300 are provided by the TDM space matri,c 302 and the exemplary channel interchange units 304, 306 and 308. Each inlet tof which 310, 312, 314 are three examples) and eaoh outlet (of which 322, 324, 326 are three examples) have input and output connections which carry the input ancl output paths of the four wire connection. As used herein, the terms cllannel interchange units an~ time slot interchange units are interchangeable.
Each switching matrix module 300 will provide for thirty-two channels on each of eight mlt~ts of which three are illustrated at 310, 312, and 314 (lnlets 0, 2 and 7, respectively) for simplicity of description.
Data on Inlets 3i0, 312 and 314 at the inputs 311, 313 and 315 thereof, respectively, shown as inlets 0, 2 and 7 of eight inlets may be switcbed to the inlets of the channel interchange units 304, 306 and 308 via the time division space switching matrix 302 at 316, 318 and 320, respectively. Thus, data at any of the switchin~ module inp~ts may be selectively coupled to any of the inputs of the cllannel interchange units for each of the channel times. Three .

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K . ~ . Gieskcn-J. Cotton 1- 1 channel interchanse units 304, 306 and 308, one Ior each of ~:he illustrated switching module outputs illustrated at 322, 324 and 326, introduce a predel:ermined delay, effectively switching data from a time channel on the input thereto to a different time channel on the output such that no two S channels occupy the same position in time on each channel interchange output.
For example, data on ~put 313 of inlet 312 is switched'~7la crosspoint 354 ' input 24~ of channel interchange 306 inlet 318. Channel 15 data on input 313 is effectively converted to channel 21 data on output 32~.
The channel interchange units may comprise well known units such as are 10 . described in U. S. Patent No. 3,740,483, and which patent references a number . of well knowll time slot interchange references. In accordance with the present invention, the output 328'of channel interchange 3~6 outlet 324, for example, may b:e controllably forced into a changed impedance state to connect to the input 330 of channel inter~hange 306 outl~t 324 as illustrated. The channel interchange can cause, for example, the data on input330 for channel' 21 to be converted to the data in time channel 9 on the output'33'4Of inlet 318.Switch 302 by means of crosspoint 340 switches the data from output334 to . output'338 of module i'nlet 314, This describes the data path corresponding to two wires of the four wire path. The other half of the data'path is describecl a s follows. Data on input315 of irilet 314 at channel time 9 is switched - via crosspoint 342 to the input244 of inlet 318 of channel interchange unit 306.
- The channel interchange unit 306 transposes in time the data on channel 9 to channel lS on output'334Of inlet 318 and couples same to crosspoint 350 which couples the data in channel lS to output352 of inlet 312.

~16-K . F . Giesken-J . Cotton 1- 1 The control is such that independent access is provided from each of the switch matrix module inlets 310, 312, 31~1, etc. to the channel interchange inlets, all in a predetermined format .
S Referring now to Figure Sb, the expanded switch o~ 5a is illustrated with an exemplary na~,v traffic path and connections therefor when a plurality of lil~e switching modules are interconnected in a multistage switching network.
Thus, it may be seen that a traffic path is established from input channel lS
of inlet 2 of module 300 to output channel 21 of outlet 6 of module 300. Outlet

6 of module 300 is connected to inlet æero of module 3GOA. Input channel 21 of inlet zero of module 300A is connectecl to output channel 30 of outlet 7 of module 300A. Thus, channel 30 of outlel: 7 of modùle 300A becomes the reflectionpoint for the described connection as lllustrated. The connec-tion is completed via input channel 30 of outlet 7 of module 300A which is coupled to output IS channel 17 at inlet 7 of module 300A. Inlet 7 of module 300A is connected to outlet 6 of module 300 B, which connects input channel 17 of outlet 6 to output channel ~ of inlet 7 of module 300B. This illustrates the connection of input channel 15 of inlet 2 of module 300 to output channel 9 of inlet 7 o~ module 300B by reflection at channel 30 of outlet 7 of module 300A. The return half of the four ~,vire connection is the complement of this sequence. The path selected through switch 300 as described in relation to Figure 5a before expansion of the net~vort,~ is equally possible Eor switch 300 after the expansion shown in Figure Sb. The choice of reflection or through transmission at outlet 6 of module 300 will depend upon the pàth required. Thus, it has been shown that the switching module of Fisure Sa is expanded modularly in a multistage ~1~- ' , 1.53~1L

K. F. Giesken-J. Cotton l-l configuration by the reflection technique to permit any requisite input interconnection while simultaneously leaving the reflection output availa~le for further expansion by connection to a higher order stage.
Other switching modules 300C, 300D are of like configuration as the aforedescribed modules.
Referring now to Figures 6a through 6e, distribution networks wherein each switching block is comprised of a 2 x 2 switch illustrates quantitative examples of the present invention. Of course, in actual practice, larger switches in the order of 8 x 8, 16 x 16, 32 x 32, etc.
could be utilized depending upon packaging, cabling and other economic considerations. For 192 lines on a thirty-two channel carrier at a traffic density of .l Erlang/line, a traffic density of .6 Erlang for each of the thirty-two channels results. Assuming that fifty percent of the traffic is intraoffice, then trunk traffic is 19.2 Erlang divided by two, or 9.6 Erlangs per 192 line carrier. If trunk traffic is one-way over one group in each direction, each trunk group would require the capability to carry 4.8 Erlangs per 192 lines. The following table refers to Figures 6a through 6e of the combined time and space network of the present invention.

Number Trunks Total No. Line Trunk One-Way (1% blocking Number Number 20Fig. Lines Erlangs Traffic Traffic probability) Trunks Switches 6A 192 19.2 9.6 4.8 11 22 6B 384 38.419.2 9.6 18 36 4 6C 576 57.628.8 14.4 25 50 7 6D 768 76.838.4 19.2 31 62 9 6E 960 96.048.0 24.0 37 74 12 \
A switch in accordance with a preferred embodiment of the present inven-tion may be implemented on a single LSI chip, combining both space and time switching and may be cascaded and interconnected to form a continuously ,,~
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i31 K~ F . Giesken-J . Cotton 1 - 1 expandahle l~et~,vork of, for e~an-ple, two thousand to one hundrecl thousand lines. Functionally, the channel interchange portion of this switch can be operative as a delay line which, whether in~plemented by charge coupled devices (CCD) or as an MOS dynamic shift register performs -the complementary delay required to produce a four wire path as shown by Figure ?a in which two slgnal inpu-ts are illustrated by Sl and S2 on lines 700 and 702, respectively, wherebySl ancl S2 have variable delays illustrated for S2 at 706 and 708 typically from 5 to 125 microseconds, while the delay of signal Sl is illustrated at 709.
The total delay 706 plus 708 plus 709 is typically 125 microseconds.
Logic ior implementing this delay is illustrated by Figure 7b. Each signal entry and exit point has the capability of entry, e~ctraction or coupling a presently existing signal through the switch. ~ time slot interchange control signal C
on line 710 is çoupled to AND gates 712 and 714 and to AND gate 716 via an inverter 718. A digitized voice signal Sl is AND'ed with the control signal at AND gal:e 712, while S2 is AND'ed with the control signal at AND gate 714. The digitized voice signal S2 is coupled from a shift register 720 to AND gates 714 and 716, and is AND'ed at gate 716 with the inverted control signal. The output of AND ga-te 716 ~signal S2) is OR' ed with the output of AND gate 7i 2 signal (Sl) at OR gate 722. Thus, either Sl or S2 is coupled through to shift register 724. Thesimplified logic of Figure 7c is illustrative of shift registers 720 and 724 and- the aforedescribed logic 726, and will be utilized hereinafter. When the descriJ:ed control logic is for an inlet, the control signal in line 710 is a selected stored control signal; however, when the described control logic is for an outlet, the control signal is a ref\lection control.
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K. F. Giesken-~. Cotton 1-1 Figure 8 is illustrative of a time switch and its associated control gating -logic as described with reference to Figure 7b for a multiple channel four wire con~iguration. The input signal Sl is coupled to the switch inlet 800 input line802 while the S2 output~ the return path of the four wire connection, is extracted from the switch ihl~t output 1ine 804. Outlet 806 includes an outlet input line 816 and an outlet output line 818~ The signal delay for signal Sl between inlet 800 input 802 and outlet 806 output 818 is selectably variable by selectirlg thedesired signal input point 802, 808, 810, 812, etc . or other input polnts ~not shown) in the delay line Ume switch, under the programmed control of control store 81~, which contains the addresses of the signal input points in a predetermlned and variable order. By accesslng the address o the desired s~gnal input polnt from the control store 814, signal Sl is entered into and S2 is extracted rom the selected access point in the delay line. The control store 814 is timed by a timing circuit 82û to be synchronous with the speech delay line such that the address to be selected for each Sl input point is coupled from the control store 814 via line 822 to a serial-to-parallel shift register 824.
The ou~pu~ of register 8Z4 is used to select and operate one of ~e logic sa~ing circuits which are provided for each of the thirty-two channels controlling the .
selected Input gates 802, 810. 812, etc. These control signal loglc gating clrcuits are illus rated for channels one, two, three, thirt~ and thirty-one at 826, 828, 830, 832 and 834, respecti~ely. The parallel output irom register 824 is coupled to gates 826 through 834 ~ia lines 836 thraugh 844. Line 846 serves as the delay line return line ~rom reflection gate 848. A synchronizationsignal supplied to timing circuit 820 ser~es to match the speech sample rate and the control code rate o~ the control store 824 in time. The two rates need ot be bit synchronous since the two codes may di~er, i.e., the speech sample 1~La)~a53~
K, F. Giesken-J. Cotton 1-1 may comprlse eLght bits, while the control code may comprise five bits. Each signal insertion, extraction and bypassing switch 850, 852, 854, 856, and 858 between the input and output delays 860 through 870 associated therewith provides the mechanism to allow the selection of the insertion/extraction point S of the S1 and S2 signals, respectively, to provide the required amount o~ delay between inlet and outlet or Sl and the complementary delay of the return path for signal S2. The insertion, extraction and bypassing switch 848 enables signalreflection at the switch output when the path chosen between calling and called subscriber requires the folding of the path at this point in the networl~.
The reflection of a particular connection, when desired, is accomplished b~r ( ~ the activation of control lead 872 of the reflection gate 848 at the appropriate time. By way of example, a sample o the signal Sl is entered on input 802 of inlet 800 and is to be reflected and retu~ned from output 8oa of inlet 800 at a predetermined later time, such as two ahannel times later as the signal Sl* at the same channel time when the complementary signal S2* (whlch is a sample of the sgnal in the other direction o conversation) is entered at input 802 oninlet 800 and output at 804 on inlet 800 as sisnal S2 at 30 channel times later,which is representative of thirty-two n~inus two channel times, at the same channel time when the next sample of Sl is being entered at 802. To accomplish the foregoing, the seleGtion gate 826 activates the input/output logic 858 to insert Sl into the delay line and reflection control 872 on reflection gate 848 - is activated one channel time later to reflect Sl into path 846. Selection gates 834 are then activated to control input/output logic 85 0 one channel time :later to extract signal Sl and place it as Sl*`on the output 804, while simultaneouslyinserting the signal S2* on input 802 into the shift register delay line 862. Upon ' K. F. Giesken-J~ CottoR 1-1 the expiration of thirty additional channel times, selection gates 826 will again activate inpu-t/output logic 858 to extract the signal S2* and output S2* on output line 804 as signal S2~ Simultaneously with the oregoing, the next sample of Sl from input line 802 is inserted into shiEt register delay 870. The 5 described switch thus transmits and reflects signals Sl and S2 in accordance with the requirements of the particular switchin path as determined by the control storage 82A.
Digitally encoded speech and control messages to direct the selection of :
swltching module interconnection paths and channel interchange delays coupled via the switch module interconnectlons are encoded for each channel into sixteen serially transmitted bits. Typically, 8k frames per second are transmll:ted, with thirty-two channels per rame and 16-bits/channel. Timing is provided such that~
channel O, ior example, occupies the same time slot tor period) on both the input and output connections. The channel interchange perm~ts the 16-bits contained by each channel to be controllably transferred to a dierer~ channel by the introduction oF delay into the bit stream Such delay (~or the t~rty-two chann~l case) is a minimum of one channel period and a maximum o~ thirty-one channel periods~ Reflection is accomplished by controllably changing the impedance switch outlets corresponding to either channel interchange to the high impedance state and connecting together the output and input of the selected channel interchange outlet.
Refe~ring now to Figure 9, a typical time division space crosspolnt xy utilized with the time switch hereinbefore described, is illustrated at 900 for the crosspoin of inlet x comprising input line 902 and\output line 904 and outlet y ~omprising input line 9Q6 and output line 908 rom and to the associated crosspoint channel ~nterchange ~hereinbeore described), respectively. Switch 910 has coupled 53~
K.. F. C;ies~en-~. Cotton 1-1 thereto as one input a s~.vitch selec~ signal from the control storage and the output via line 90G from the channel interchange unit associated therewith and has an output coupled to the output line 90~1 of inlet x. Switch 912 has coupled thereto- a switch select signal from the control store and the signal on the input line 902 of inlet x and has an output therefrom on line 908 to i~s associated channel inter-change unit. Output and input switches similar to 910 and 912 from up to seven other inlets may be connected to lines 906 and 908 at commoning points 924 arld 926, The input and output lines 902 and 904 of inlet x are also coupled to a port recognition redundancy chec~ fault detection circuit 91~ and to a channel idle detec-tion circuit 916 via AND gates 918 and 920, respectively, with the other input to said AND cJates 918 and 920 being a monitor for enabling the gates at desired times.
`- The port reco~nition and redundancy check fault detection circuit 91~ which may be of conventional design is provided to detect messa~es on input 902 directed to the control circuits associated with outlet y, to chec~ the coding of messages to determine that such messa~es do not contain errors, to detec~ idle channels on the inlet input 902, and to output signals on inlet output 904 to indicate the busy~free condition of outlet y. Port recognition and ledundancy check ~ault detection circuit 914 receive~ commands such as a send busy command from the control circuits asso-.
ciated with outlet y and consequently couples out a signal indicative of a busy/fault message to line 904. When circuit 914 recognizes a selection request message on input line 902 destined for outlet y, circuit 91~ couples a priorlty select signal to a crosspoint priority control circuit which arbitrates among simultaneous requests on more than one inlet for output to outlet y. The output of channel idle detectcircuit 916 is coupled to a free channel se~ection circuit ~ia line 922.
A matrix of crosspoints xy as described with reference to Figure 9 is illustrated by Figure 10 wherein one representative outlet 960 and its control 3~L
K. F. Gieskç~n-J. Cotton l-l out of a possible eiyht other outlets in a matri:~ of eight inlets by eight outlets is sho~n connected to t~^10 inlets, 962 and 964 out of the possible eight inlets, zero throu~h seven. Crosspoint xy illustrated al: 900 corresponds to the cross-poinl: described with reference to Figure 9. Also as hereinbefore described with 5 reference to Figure 9, eight such crosspoin-ts may be connected to the time switch (channel interchange) 928 via lines 906 and 90&. Time switch 928is described with reference to Figure 8. The port recognition redundancy check fault detection channel idle detection circuits at 930 and 932 operate in like manner as circuit 914 described with reference to Figure 9, and channel idle detection circuitry 934 and 936 operate in like manner as does the channel idle detect circuit 916, also described with reference to Figure 9. The outputs 922, 938 and 940 of port recognition circuits 914, 930 and 932, respectively, are indi~:atlve of the receipt of messages at those respective circuits requesting connection to channel interchange 928 and are individually and separately connected to the .
15 crosspoint selzure priority control circuit 942. Upon receipt of simultaneous requests on two or ~nore lilles, circuit 942 is operative to select one of the requesting inlets and commands the sending o~. busy signals to the other non-selected requesting inlets by means of signals on lines 944, 946 or 948 as the case may be, to the respective circuits 930, 914 and 932 as appropriate, which 20 busy signals are applied to i:he respective output lines on the crosspoint inlets as described with respect to Figure 9. Crosspoint selection circuit 950 accepts and stores in a control delay line therein of like design to control store 81-1 described with reference to Figure 8, the crosspoint selected by crosspoint selection circuit 942 for each of the thirty-two channel periods, and will open 25 and close the selected crosspoint for each channel period by coupling signals K~ F. Gies};en J. Cotton l-l onto the a~proyriate control lines 952, 95'1, etc. Signals on input 956 of outlet 960 may include path selection control signals received from a higher stage switch after reflec-tion and which si~nals are recognlzed by previously described circuit 932. Outlet 960 thereby forms one of the inlets of such hi~her stage switch. Channel idle detect circuits 934 and 936 perform the same function as does channe1 idle detection circuit 916 described with reference to Figure 9.It is to be understood that the matrix illustrated by Fi~ure l0 is exemplary only.
However, and by way of example, an additional seven matrices identical to I:ha-tdescrlbed with reference to Figure 10 may be connected to the inlets 962 and 964at the commoning points 966 and 968. Up to six additional inlets having circultry and connectivity identical to that illustrated by inlets 962 and 964 are implementable .
While the present invention has been described in connection with a prefer~ed embodiment thereof, it is to be understood that additional embodiments ,-modifications and applications which will become obvious to those skilled in the- art are iricluded within the spiri-t and scope of the invention as set forth by the claims appended hereto.
JPM:rb - January 20, 1977 ' ':

Claims (16)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A plurality of switches arranged in a plurality of stages of said switches to comprise an expandable switching network with each of said switches comprising: means for providing a plurality of inlets for receiving digital signals and a plurality of outlets; means for adapting each of said outlets to selectively reflect said digital signals back to any of said inlets; means for selectively coupling any of said inlets to any of said outlets to provide an output for said digital signals out of said switch from said outlets; means for coupling said signals from the outlets of the switches of any of said stages of switches to the inlets of switches of higher order switching stages; and means for reserving said outlets of any of said switches for coupling said digital signals from said outlets to the inlets of switches of said higher order switching stages.

2. A switching network in accordance with claim 1 wherein said switches are space division switches,

3. A switching network in accordance with claim 1 wherein said switches are time division switches.

4. A switching network in accordance with claim 1 wherein said switches are combined space division and time division switches.

5. A switching network in accordance with claim 1 further comprising:
traffic path selection control means for controlling the path of said digital signals through the network; and data storage means for deriving a control signal for accessing said traffic path selection control means such that said control signal is coupled over the same path as said digital signals.

6. A switching network in accordance with claim 5 wherein said digital signals are comprised of a series of samples representing a speech waveform, each of said samples being digitally encoded.

7. A switching network in accordance with claim 6 wherein said encoded digital signals are linear pulse code modulated signals.

8. A switching network in accordance with claim 6 wherein said digital signals are comprised of digitally encoded analog signals.

9. A switching network in accordance with claim 1 wherein each of said inlets and said outlets of said switches includes an input and an out-put and wherein each of said inputs and outputs of each of said inlets and said outlets receives time division multiplexed signals in a plurality of channels.

10. A combination in accordance with claim 1 including control means for reflecting said digital signals after completion of a partial coupling thru said network, such that said digital signals penetrate said network to the stage required to complete a desired connection.

11. In a telephone switching system for intercoupling a plurality of lines and trunks, an expandable switching network comprised of a plurality of switches, arranged in a plurality of stages, each of said switches com-prising: means for providing a plurality of inlets for receiving digital signals and a plurality of outlets; means for adapting each of said outlets to selectively reflect said digital signals back to any of said inlets;
means for selectively coupling any of said inlets to any of said outlets to provide an output for said digital signals out of said switch from said outlets; means for coupling said digital signals from the outlets of the switches of any of said stages of switches to the inlets of switches of higher order switching stages; and means for reserving said outlets of any of said switches for coupling said digital signals from said outlets to the outlets of switches of said higher order switching stages.

12. In a telephone switching exchange in accordance with claim 11, further comprising: traffic path selection control means for controlling the path of said digital signals through the network; and data storage means for deriving a control signal for accessing said traffic path selection control means such that said control signal is coupled over the same path as said digital signals.

13. A method for providing an expandable switching network from a plurality of switches comprising for each of said switches the steps of:
receiving a plurality of digital signals at a plurality of inlets of said switch; providing a plurality of outlets from said switch to which said signals are selectively coupled from said inlets; adapting each of said outlets to selectively reflect said digital signals coupled thereto back to any of said inlets; selectively coupling signals from any of said inlets to any of said outlets to provide an output for said digital signals out of said switch from said outlets; arranging a plurality of said switches into a network of a plurality of stages of said switches; coupling signals from the outlets of the switches of any of said stages of switches to the inlets of switches of higher order switching stages; and reserving the outlets of any of said switches for coupling said digital signals from said outlets to the inlets of said higher order switching stages.

14. A method for expanding the size of a switching network comprising the steps of: establishing a plurality of stages of switches, each of said switches having two or more inlets and two or more outlets and being adapted to selectively reflect digital signals entering any inlet thereto back to any other inlet thereof and to couple said signals from any inlet to any outlet; selectively coupling signals from the outlets of the switches of any of said stages to the inlets of switches of higher order switching stages of said switching network; adding an additional stage of switches, each of said switches of said additional stage having two or more inlets and two or more outlets and being adapted to selectively reflect digital signals entering any inlet thereto back to any inlet thereof and to couple said signals from any inlet to any outlet; and selectively coupling signals from the outlets of the plurality of stages of switches to the inlets of the switches of said additional stage whereby the outlets of said additional stage of switches are adapted for reflection of said signals and are also reserved for coupling said signals from said outlets to higher order switch-ing stages.

15. A method in accordance with claim 14 wherein said selectively coupling step further provides that no previously coupled outlets of switches in any of said plurality of stages of switches are physically uncoupled from inlets of other switches.

16. A switching network in accordance with claim 1 wherein said net-work is a one-sided network.