(12) United States Patent
`(10) Patent N0.:
`US 6,169,735 B1
`
`Allen, Jr. et al.
`(45) Date of Patent:
`Jan. 2, 2001
`
`USOO6169735B1
`
`(54) ATM-BASED DISTRIBUTED VIRTUAL
`TANDEM SWITCHING SYSTEM
`
`(75)
`
`Inventors: George c_ Allen, Jr_; Haifeng Bi;
`Steven R. Partridge; Samuel Sigarto;
`Richard W. Stephenson, all of Austin,
`TX (Us)
`
`(73) Assigneei SBC TEChHOIOgy Resumes: 1119-,
`Austin, TX (US)
`
`(*) Notice:
`
`Under 35 U.S.C. 154(b), the term of this
`patent shall be extended for 0 days.
`
`(21) Appl. No.2 09/287,092
`(22)
`Filed:
`Apr. 7, 1999
`
`Related US. Application Data
`Provisional application No. 60/083,640, filed on Apr. 30,
`1998.
`Int. Cl?
`
`(60)
`
`(51)
`
`H04M 7/00. H04L 12/66.
`H04L 12/28; H04L 12/56
`........................ .. 370/352; 370/410; 370/395;
`379/220; 379/230
`(58) Field of Search ..................................... 370/352 353
`370389 396 409 524 354 385’ 384’
`’
`39’s 41;). 37’9/236 219’ 220’
`’
`’
`’
`’
`References Cited
`
`(52) US. Cl.
`
`(56)
`
`.
`
`US. PATENT DOCUMENTS
`11/1993 Fleischer et a1
`11/1994 H6mmdy 6t a'L'
`2/1995 Robmck, 11.
`7/1995 Hemmady et a1.
`7/1995 Focarile et a1.
`.
`8/1995 Hemmady et a1.
`10/1995 Sherif .
`“1996 D0591 6t a1~ -
`4/1996 Pun] ;
`Flejgrllgdzi’"""""""" 370/397
`4/1997 Hiekali.
`4/1997 Skoog .
`
`.
`
`.
`
`5 260 978
`5’363’369
`5:392:402
`5,434,853
`5,434,854
`5,438,565
`5,459,722
`574837527
`595139174
`
`5,619,500
`5,623,491
`
`5,638,365
`5,703,876
`5,710,769
`
`.
`6/1997 Duault et a1.
`12/1997 Christie .............................. .. 370/395
`1/1998 Anderson et a1.
`.
`
`5,719,863
`
`2/1998 Hummel ............................. .. 370/392
`Eng it a.l'
`’
`3/1999 R0“ “mg'
`598839893
`.
`umer et a1.
`,
`,
`6/1999 Williams ............................ .. 370/395
`5,914,956
`8/1999 St—Hilaire et a1.
`370/259
`5,943,321
`
`..... ..
`9/1999 Lazar et a1.
`370/230
`5,953,316
`
`..
`9/1999 Chu et a1.
`370/352
`5,956,334
`11/1999 Christie .............................. .. 370/395
`5,991,301
`6,009,100 * 12/1999 Gausmann et a1.
`................ .. 370/397
`OTHER PUBLICATIONS
`
`Mailik, 0., “It’s the Voice, Stupid”, Forbes, Digital T001,
`sep‘ 8’ 1999‘
`* cited by examiner
`.
`.
`vu
`Prlmary Exammer—Huy
`Assistant Examiner—Kevm C. Harper
`(74) Attorney, Agent, or Firm—Greenblum & Bernstein,
`PLC’
`(57)
`
`ABSTRACT
`
`48 Claims, 7 Drawing Sheets
`
`
`
`
`
`
`
`
`
`
`@
`
`2354111
`
`
`
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`a
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`35
`
`
`
`END
`
`
`
`.
`.
`A.“ Asynchronous .Tra9sfer MOde (ATM)'f’aSed.dlsmt.’med
`v1rtua1 tandem sw1tch1ng systemas provided 1n wh1ch a
`network of ATM-based dev1ces IS combined to create a
`distributed virtual tandem switch. The system includes an
`ATM switching network that dynamically sets up individual
`switched virtual connections. The system also includes a
`trunk interworking function (T-IWF) device and a central-
`ized control and signaling interworking function (CS-IWF)
`device. The trunk interworking function device converts end
`office voice trunks from TDM channels to ATM cells by
`employing a structured circuit emulation service. The cen-
`tralized control and signaling interworking function device
`performs call control functions and interfaces narrowband
`signaling and broadband signaling for call processing and
`control within the ATM switching network. Consequently,
`the ATM based distributed virtual tandem switching system
`replaces a standard tandem switch in the PSTN.
`
`
`
`
`
`
`
`
`
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`28
`
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`END
`OFFICE \10
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`YMAX EXHIBIT 1031
`YMAX CORP. V. FOCAL IP
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`Jan. 2, 2001
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`
`
`US 6,169,735 B1
`
`1
`ATM-BASED DISTRIBUTED VIRTUAL
`TANDEM SWITCHING SYSTEM
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`
`This application claims the benefit of US. Provisional
`Patent Application No. 60/083,640 filed on Apr. 30, 1998,
`entitled “ATM-Based Distributed Virtual Tandem Switching
`System” to ALLEN et al.,
`the disclosure of which is
`expressly incorporated herein by reference in its entirety.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention relates to a telecommunications
`architecture. More particularly, the present invention relates
`to tandem switching systems for use within a public
`switched telephone network (PSTN). The present invention
`enables voice trunking over an asynchronous transfer mode
`(ATM) network by replacing tandem switches with a dis-
`tributed virtual tandem switching system that includes a high
`speed ATM network. The replacement is virtual because as
`far as the end offices are concerned, the ATM-based distrib-
`uted virtual tandem switching system is functionally equiva-
`lent
`to the traditional
`time division multiplexed (TDM)
`tandem switching system.
`2. Background Information
`Within the public switched telephone network (PSTN), an
`originating caller communicates with a destination by estab-
`lishing a connection between an end office serving the
`originating caller and an end office serving the destination.
`FIG. 1 shows the architecture of the current PSTN. In
`
`today’s PSTN, end office switches 10 are connected to each
`other via tandem trunk groups 12, direct trunk groups 14, or
`both tandem trunk groups 12 and direct trunk groups 14.
`Each trunk within a trunk group is typically a digital service
`level 0 (DSO) (i.e., 64 kilobits per second) communication
`line that transmits between the end offices 10 in a time
`
`division multiplexed (TDM) manner. When an end office
`utilizes a direct trunk group 14, the connection between the
`end offices 10 is without any intermediaries. When an
`end/central office 10 utilizes a tandem trunk group 12, the
`connection between end offices 10 is via a tandem switch 16.
`The tandem switch or office 16 is an intermediate switch
`
`or connection, between an originating telephone call loca-
`tion and the final destination of the call, which passes the call
`along. Tandem switches are often utilized to handle overflow
`calls. That is, when all paths are busy on a primary route,
`e.g.,
`the direct
`interoffice trunk group 14 between the
`originating and destination end offices 10, alternative routes
`through the tandem switch 16 handle the overflow call
`volume. The tandem switch 16 can also function as a
`
`physical path to non-directly-connected offices in addition to
`functioning as an overflow path for directly connected
`offices. If the overflow route through the tandem switch 16
`becomes full, an alternate final route may be provided. The
`alternate final route is via another end office 10,
`thus
`employing two interoffice trunk groups 14.
`Signaling is needed within the PSTN to establish a
`connection (i.e., setup a telephone call) between a calling
`party and a destination. The signaling enables line acquisi-
`tion and sets up call routing, in addition to performing other
`functions. The signaling can be transmitted through a chan-
`nel common with the voice data (in-band signaling) or can
`be transmitted through a dedicated channel (out of band
`signaling). The dominant signaling protocol currently in use
`
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`today is transmitted via the dedicated channel and is called
`Signaling System 7 (SS7).
`A conventional connection setup between two end offices
`20, 22 in a tandem network is now described with reference
`to FIGS. 2 and 3. When a calling party 19 (e.g., 235—1111)
`dials a telephone number (e.g., 676—2222), the originating
`central office 20 interprets the dialed digits and routes the
`call to either a direct interoffice trunk group 14 between end
`offices 20, 22 or a pair of tandem office trunk groups 12 and
`the corresponding tandem switch 16 between end offices 20,
`22. Assuming the pair of tandem office trunk groups 12 and
`the corresponding tandem switch 16 is utilized, a trunk from
`each of the trunk groups 12 needs to be selected and reserved
`by signaling within the SS7 network. Thus, necessary infor-
`mation is transmitted from the originating end office 20 to its
`associated signaling transfer point 18. Although only a
`single signaling transfer point is shown in the figures, a
`network typically includes many signaling transfer points.
`Thus, each signaling transfer point 18 transfers signals from
`one signaling link to another signaling link in the SS7
`network that transports SS7 messages.
`The transmitted information is in the form of an ISUP
`
`(ISDN user part) message. It contains a unique point code,
`which uniquely identifies each end office, corresponding to
`the originating end office (originating point code (OPC)) and
`the destination (destination point code (DPC)). Because the
`message must first go to the tandem office 16, the ISUP
`message contains the destination point code of the tandem
`office. The message also contains a circuit identification
`code (CIC) that corresponds to the physical circuit that will
`be employed to transport the data. Thus, interoffice trunks
`are identified by originating point code (OPC), destination
`point code (DPC), and circuit identification code (CIC).
`As shown in the example illustrated in FIG. 3, initially an
`ISUP message is sent containing a DPC equal to 246 1 2, an
`OPC equal to 246 1 1, and a CIC equal to 22. Consequently,
`a circuit will be setup between the originating end office 20
`and the tandem office 16. The tandem switch 16 receives the
`
`SS7 message and determines from the called number, which
`is embedded in the protocol, where to route the call, i.e., the
`appropriate destination end office 22. Then, via the SS7
`network, the call is setup between the tandem switch 16 and
`the appropriate terminating office 22 in a similar manner.
`Thus, because the tandem office 16 needs to transport the
`data to the destination end office 22, the tandem office 16
`sends an ISUP message to the signaling transfer point 18,
`including the destination end office’s destination point code,
`i.e., 246 1 3, the tandem office’s origination point code, i.e.,
`246 1 2, and the circuit identification code corresponding to
`the circuit between the tandem office 16 and the destination
`
`office 20, e.g., circuit 7. After this ISUP message is sent to
`the signaling transfer point 18, the signaling transfer point
`18 forwards the ISUP message to the destination end office
`22 in order to setup the connection between the tandem
`office 16 and the destination office 22, thus reserving the
`circuit. The terminating central office switch 22 receives the
`SS7 message and determines where to terminate the call by
`interpreting the called number embedded in the protocol.
`A call flow scenario is now described with reference to
`
`FIG. 2. A caller 19 dials the telephone number of a desti-
`nation 23. The first end office 20 (end office A) collects the
`digits of the called number and checks routing tables to
`determine to which end office 22 the dialed telephone
`number belongs. Then the originating end office 20 finds a
`direct trunk group 14 between itself and the end office
`owning the dialed telephone number. Subsequently,
`the
`originating end office finds an idle trunk within the trunk
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`US 6,169,735 B1
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`3
`group 14. The originating end office 20 selects and reserves
`the idle trunk of the trunk group 14 and initiates an SS7 IAM
`(initial address message) message containing the following:
`signaling transfer point routing address of the destination
`end office;
`the calling telephone number; the called tele-
`phone number, and the trunk ID (CIC) for the selected trunk
`of the trunk group.
`The signaling transfer point 18 receives the IAM message
`and forwards it to the destination end office 22. The desti-
`nation end office 22 then receives the IAM message and uses
`the CIC information to reserve the selected trunk within the
`
`trunk group 14. The destination end office 20 (end office B)
`then checks the called telephone number 23 for on-hook and
`feature support and holds the line, assuming the dialed
`telephone number is on hook. The destination end office 22
`then applies a ring to the line and ring tone to the selected
`trunk in the trunk group 14. Next, the destination end office
`22 connects the dialed telephone number line to the selected
`trunk in the trunk group 14, initiates an SS7 ACM (Address
`Complete Message) message and forwards it to the signaling
`transfer point 18.
`The signaling transfer point receives the ACM message
`and forwards it to the originating end office 20 that receives
`the ACM message. The originating end office 20 then
`connects the calling telephone number line to the selected
`trunk. Consequently, the caller of the calling number hears
`a ring tone and the called party at
`the called telephone
`number picks up the phone. The destination end office 22
`detects the off hook on the called telephone number 23 and
`removes the ring tone. The destination end office 22 then
`initiates an SS7 ANM (answer) message to the signaling
`transfer point 18. The signaling transfer point 18 receives the
`ANM message and forwards it to the originating end office
`20. The originating end office 20 receives the ANM message
`and starts necessary billing measurement. Ultimately, the
`caller speaks with the called party.
`Another call flow scenario according to the prior art is
`now described with reference to FIG. 2. Initially, a caller,
`e.g., 235—1111 dials a destination, e.g., 676—2222. The
`originating end office 20 (end office A) collects digits of the
`called number and checks routing tables to determine which
`end office handles 676. The originating end office 20 finds
`that 676 belongs to a destination end office 22 (end office B).
`End office Athen locates a direct trunk group 14 to end office
`B. Assume in this example that no idle trunk exist within the
`direct
`trunk group 14. Thus, end office A chooses and
`reserves a first tandem trunk group 12, and a selected trunk
`from the first reserved trunk group 12. Subsequently, end
`office A initiates an SS7 IAM message containing the
`following: signaling transfer point routing address of the
`tandem; calling telephone number; called telephone number;
`and trunk identification (CIC) for the selected trunk of the
`first reserved trunk group 12.
`The signaling transfer point 18 receives the IAM message
`and forward it to the tandem switch 16. The tandem office 16
`
`receives the IAM message and utilizes the CIC information
`to reserve the selected trunk of the first reserved trunk group
`12. The tandem office 16 then checks a routing table to
`determine the destination and reserves a selected trunk of a
`
`second trunk group 12, which connects to the destination.
`Subsequently, the tandem 16 initiates an SS7 IAM message
`to the signaling transfer point 18 with the following infor-
`mation: signaling transfer point routing address of end office
`B; calling telephone number; called telephone number; and
`trunk identification (CIC) for the selected trunk of the
`second trunk group 12.
`The signaling transfer point 18 receives the IAM message
`and forwards it to end office B. End office B receives the
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`IAM message and utilizes the CIC information to reserve the
`selected trunk of the second trunk group 12. End office B
`checks whether the called telephone number is on-hook and
`holds the line, assuming that 676—2222 is on-hook. End
`office B applies ringing to the line and a ring tone to the
`selected trunk of the second trunk group 12. End office B
`then connects the line to the selected trunk of the second
`
`trunk group 12 and initiates an SS7 ACM message to the
`signaling transfer point 18.
`The signaling transfer point 18 receives the ACM mes-
`sage and forward it to the tandem switch 16. The tandem
`switch 16 receives the ACM message from the signaling
`transfer point 18 and consequently, the tandem switch ini-
`tiates an ACM message to the signaling transfer point 18.
`The signaling transfer point 18 receives the ACM mes-
`sage and forwards it to end office A. End office A receives
`the ACM message and connects 235—1111 to the selected
`trunk of the first reserved trunk group 12. Next, the caller at
`235—1111 hears a ring tone and the called party at 676—2222
`picks up the phone.
`Consequently, end office B detects an off-hook on
`676—2222. Accordingly, end office B removes the ring tone
`and initiates an ANM message to the signaling transfer point
`18. The signaling transfer point 18 receives the ANM
`message and forwards it
`to the tandem switch 16. The
`tandem switch 16 receives the ANM message from the
`signaling transfer point 18 and the tandem switch 16 initiates
`an ANM message to the signaling transfer point 18.
`The signaling transfer point 18 receives the ANM mes-
`sage from the tandem switch and forwards it to end office A.
`End office A receives the ANM message from the signaling
`transfer point 18 and starts necessary billing measurement.
`Finally, the calling party at 235—1111 talks to the called party
`at 676—2222.
`
`The current system has disadvantages. In order to mini-
`mize overflow call volume, the size of a trunk group needs
`to be forecast so that the trunk group can handle the expected
`call volume. Then, appropriately sized trunk groups are
`preprovisioned, each having a dedicated bandwidth. The
`process of forecasting and preprovisioning is expensive.
`Moreover, the current trunking architecture requires a large
`number of small trunk groups to link end offices because of
`the large number of end offices that each end office must
`connect with. This form of trunking leads to inefficiencies
`due to the relatively small size of a significant number of the
`trunk groups. That is, the small size reduces the call carrying
`capacity per trunk and therefore requires a larger percentage
`of overflow trunking. In addition, the large number of trunk
`groups requires huge investments in hardware and software
`for systems that keep track of individual interoffice trunks.
`Further, the trunk forecasting and provisioning is necessary
`for thousands of individual trunk groups.
`The ATM Forum’s VTOA Group has attempted to solve
`the problems associated with voice trunking over ATM. The
`VTOA Group developed a specification for carrying voice
`over ATM in a private network environment. For example,
`see ATM Forum Technical Committee, “Circuit Emulation
`Service Interoperability Specification Version 2.0” (January
`1997). That specification allows private businesses to
`employ an ATM network to establish voice channels across
`the ATM network using a protocol, such as private network-
`network interface (PNNI), which facilitates moving cells
`from one point in the ATM network to another point in the
`ATM network. However,
`the specification is limited to
`application within a private environment, which is not
`appropriate for applications in the PSTN. That is, interaction
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`US 6,169,735 B1
`
`5
`include out-of-band
`is not supported with systems that
`signaling, e.g., Signaling System 7 (SS7), which is essential
`to supporting capabilities such as an advanced intelligent
`network
`Within these private networks, the signaling is typically
`in-band signaling. Thus, no interface with an out-of-band
`signaling network would be required. Moreover, if a calling
`party within the private network would like to contact
`someone outside of the private network, the calling party
`must communicate over the normal PSTN, thus leaving the
`scope of the VTOA Group’s system.
`US. Pat. No. 5,483,527 addresses voice trunking within
`the PSTN. The patent discloses a system that interposes an
`ATM network between two central offices. Signaling is sent
`from the central office via a signaling transfer point (STP) to
`the ATM switch. Within each ATM switch, a processing
`system is provided for interfacing the ATM switch with the
`STP. Thus, the ATM switches are modified to be able to
`communicate with the signaling transfer point, which is a
`very expensive process. Furthermore, due to the interface
`being provided within each ATM switch, the path across the
`ATM network is established relatively slowly. Finally, the
`distributed placement of the interface between the signaling
`transfer points and the ATM network has its own disadvan-
`tages.
`
`Glossary of Acronyms
`
`ATM Adaptation Layer
`AAL
`Address Complete Message
`ACM
`ADPCM Adaptive Differential Pulse Code Modulation
`ADSL
`Asymmetric Digital Subscriber Line
`AIN
`Advanced Intelligent Network
`ANM
`Answer Message
`ANSI
`American National Standards Institute
`ATM
`Asynchronous Transfer Mode
`B-ISUP
`Broadband ISDN User Part
`CAS
`Channel Associated Signaling
`CBR
`Constant Bit Rate
`CCS
`Common Channel Signaling
`CES
`Circuit Emulation Service
`CIC
`Circuit Identification Code
`CS-IWF
`Control and Signaling Interworking Function
`DPC
`Destination Point Code
`D50
`Digital Signal Level 0 (64 Kbps digital signal format)
`D51
`Digital Signal Level 1 (1.544 Mbps digital signal format)
`IAM
`Initial Address Message
`IP
`Internet Protocol
`ISDN
`Integrated Service Digital Network
`ISUP
`ISDN User Part
`ITU-T
`International Telecommunications Union -
`Telecommunications
`Interworking Function
`IWF
`Interexchange Carrier
`IXC
`OAM&P Operations, Administration, Maintenance, and Provisioning
`OC12
`Optical Carrier level 12 signal (622 Mbps)
`OC3
`Optical Carrier level 3 signal (155 Mbps)
`OPC
`Originating Point Code
`PCM
`Pulse Code Modulation
`PNNI
`Private Network-Network Interface
`POTS
`Plain Old Telephone Service
`PSTN
`Public Switched Telephone Network
`SS7
`Signaling System 7
`SSP
`Service Switching Point
`STP
`Signal Transfer Point
`SVC
`Switched Virtual Connection
`TDM
`Time Division Multiplexing
`T—IWF
`Trunk Interworking Function
`UNI
`User-to-Network Interface
`VTOA
`Voice and Telephony over ATM
`
`SUMMARY OF THE INVENTION
`
`In view of the foregoing, the present invention is directed
`to providing a replacement for the current trunking system
`
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`operating between end offices, as well as between end offices
`and an interexchange carrier network.
`Accordingly, an Asynchronous Transfer Mode (ATM)
`based distributed virtual tandem switching system is pro-
`vided. The system comprises an ATM switching network, a
`trunk interworking function (T-IWF) device, and a central-
`ized control and signaling interworking function (CS-IWF)
`device. The trunk interworking function (T-IWF) device is
`adapted to receive end office voice trunks from time division
`multiplexed (TDM) channels and convert the trunks to ATM
`cells. The centralized control and signaling interworking
`function (CS-IWF) device performs call control functions
`and is adapted to interface narrowband and broadband
`signaling for call processing and control within the ATM
`switching network. Thus, the ATM based distributed virtual
`tandem switching system replaces a standard tandem switch.
`According to a preferred embodiment, the T-IWF includes
`a circuit emulation service. Further, the T-IWF can include
`ATM adaptation layer 1
`Alternatively, the T-IWF
`adapts circuit traffic to ATM cells utilizing ATM adaptation
`layer 2
`If AAL2 is employed, silence suppression
`and/or voice compression can be supported.
`According to a preferred embodiment, each voice trunk is
`setup dynamically as an individual switched virtual connec-
`tion in the ATM switching network. Moreover, the T-IWF
`and the end office switch are positioned at the same location.
`According to a preferred embodiment, the narrowband
`signaling is SS7 signaling. In addition, the broadband sig-
`naling is preferably PNNI, B-ISUP, and/or UNI.
`A method is provided for transporting voice from an
`originating location to a destination across an Asynchronous
`Transfer Mode (ATM) network. The method includes trans-
`mitting the voice from the originating location to an origi-
`nating trunk that leaves an end office switch; converting the
`originating trunk to ATM cells; and interfacing between
`narrowband and broadband signaling for call processing and
`control within the ATM network. Moreover,
`the method
`includes transmitting the voice within the ATM cells across
`the ATM network utilizing the broadband signaling; con-
`verting the ATM cells to a destination trunk; and transmit-
`ting the voice from the destination trunk to the destination.
`According to a preferred embodiment, the transporting is
`enabled by emulating a circuit by employing a circuit
`emulation service. Further, the voice may be converted to
`ATM cells utilizing ATM adaptation layer 1
`Alternatively, the voice may be converted to ATM cells
`utilizing ATM adaptation layer 2
`If AAL2 is
`selected, silence suppression and/or voice compression is
`employed.
`According to a preferred embodiment, each voice trunk is
`setup dynamically as an individual switched virtual connec-
`tion in the ATM network. Moreover, converting the origi-
`nating trunk to ATM cells occurs in the T-IWF within an
`originating end office and converting the ATM cells to a
`destination trunk occurs in the T-IWF within a destination
`end office.
`
`According to a preferred embodiment, the narrowband
`signaling is SS7 signaling. In addition, the broadband sig-
`naling preferably is PNNI, B-ISUP, and/or UNI.
`According to a preferred embodiment, an Asynchronous
`Transfer Mode (ATM)-based distributed virtual
`tandem
`switching system is provided in which a network of ATM-
`based devices is combined to create a distributed virtual
`
`tandem switch. The system includes an ATM switching
`network setup dynamically with individual switched cir-
`cuits. The system also includes a trunk interworking func-
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`US 6,169,735 B1
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`7
`tion device and a centralized control and signaling inter-
`working device. The trunk interworking function converts
`end office trunks from TDM channels to ATM cells by
`employing a circuit emulation service. The centralized con-
`trol and signaling interworking function device performs
`call control functions and interfaces narrowband signaling
`and broadband signaling for call processing and control
`within the ATM switching network. Consequently, the ATM
`based distributed virtual tandem switching system replaces
`a standard tandem switch.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The present invention is further described in the detailed
`description that follows, by reference to the noted plurality
`of drawings by way of non-limiting examples of preferred
`embodiments of the present invention, in which like refer-
`ence numerals represent similar parts throughout several
`views of the drawings, and in which:
`FIG. 1 shows a prior art system for communicating
`between end offices;
`FIG. 2 shows a known trunk group architecture;
`FIG. 3 shows a known dedicated out-of—band signaling
`network associated with a tandem network and exemplary
`ISUP messages;
`FIG. 4 shows an exemplary architecture of an ATM-based
`distributed virtual tandem switching system according to an
`aspect of the present invention;
`FIG. 5 shows an exemplary architecture of an ATM-based
`distributed virtual tandem switching system including an
`out-of—band signaling network, according to an aspect of the
`present invention;
`FIG. 6 shows an exemplary trunk group architecture
`according to an aspect of the present invention; and
`FIG. 7 shows an alternative architecture for an ATM-
`
`based distributed virtual tandem switching system.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`An ATM-based distributed virtual tandem switching sys-
`tem is provided for replacing standard tandem switches and
`facilitating the reduction of necessary trunk groups without
`decreasing call processing volume.
`Referring now to FIG. 4,
`the ATM-based distributed
`virtual tandem switching system according to the present
`invention is described. Originating end office 20 and termi-
`nating end office 22 are similar to the central offices 10
`shown in FIG. 1. The end offices 10 are typically Class 5
`switches such as the 5ESS available from Lucent
`
`Technologies, Inc. of Murray Hill, N]. or the DMS100
`available from Northern Telecom Ltd. (Nortel Networks) of
`Canada. However, any other Class 5 end office switch may
`be substituted for the Nortel and Lucent switches. Also
`
`shown is a signaling transfer point (STP) 18. The signaling
`transfer point 18 is well known in the art and may be
`provided, for example, by Alcatel of France. The signaling
`transfer point 18 communicates with the end offices 20, 22
`via SS7 signaling as described above. An asynchronous
`transfer mode (ATM) switching network 26 is also provided.
`The ATM switches within the network can be provided by
`vendors such as, but not limited to, Lucent, Cisco Systems,
`Inc. of San Jose, Calif., or Nortel.
`A trunk interworking function (T—IWF) device 28 is also
`provided. Although described as a device, the T-IWF 28 can
`be multiple devices or any combination of hardware and
`software. The T-IWF 28 converts end office 20, 22 voice
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`trunks from TDM channels to ATM cells. More particularly,
`the T-IWF 28 segments the 64 Kbps bearer channels into
`ATM cells in one direction and reassembles ATM cells in the
`
`64 Kbps channels in the other direction. Preferably, the
`T—IWFs 28 are distributed throughout
`the PSTN with a
`T-IWF 28 corresponding to each end office 20, 22. An
`exemplary T-IWF 28 is a Succession Multiservice Gateway
`(SMG) 4000, provided by Nortel. However, any other
`T-IWF 28 may be employed.
`The ATM-based distributed network also requires a cen-
`tralized control and signaling interworking function (CS-
`IWF) device 30. Although described as a device,
`the
`CS-IWF 30 can be multiple devices or any combination of
`hardware and software. The CS-IWF 30 performs necessary
`call control functions as well as conversion between a
`
`narrowband signaling, e.g., Signaling System 7 (SS7),
`protocol, and a broadband signaling protocol for call pro-
`cessing and control within the ATM network. Preferably, a
`single CS-IWF 30 serves all the T—IWFs 28 in a metropolitan
`area. An exemplary CS-IWF 30 is a Succession Call Server
`(SCS), provided by Nortel. However, any other CS-IWF 30
`may be employed.
`the ATM switching
`the CS-IWF 30,
`The T—IWFs 28,
`network 26, and the interconnecting links together comprise
`the ATM-based distributed virtual tandem switching system.
`The system is distributed because the tandem functions are
`carried out in part by the T—IWFs 28 that are located near the
`end offices 20, 22 in a distributed manner. The system is
`virtual because as far as the end offices 20, 22 are concerned,
`the ATM-based distributed virtual tandem switching system
`is functionally equivalent to the traditional time division
`multiplexed (TDM) tandem switching system 16. Thus, end
`offices 20, 22 require only slight configuration changes in
`order to utilize the present invention. The virtual aspect also
`refers to the fact that the individual trunks are no longer DSO
`time slots that need to be statistically provisioned. Rather,
`the trunks are realized through dynamically established
`ATM switched virtual connections.
`
`Deployment of the ATM-based distributed virtual tandem
`switching system allows an end office 20, 22 to handle
`normal call volumes while having only one or a few large
`trunk groups connecting to the ATM switching network, thus
`eliminating the need to provision separate trunk groups to
`different destination end offices. In addition, the total trunk-
`ing bandwidth is shared by traffic to all destinations because
`ATM virtual connections are provisioned on demand by
`signaling. Consequently, bandwidth is not dedicated to any
`TDM voice channels between predetermined locations, but
`rather is dynamically shared.
`According to a preferred embodiment, end offices 20, 22
`have a single large trunk group that connects with the virtual
`tandem switch, although exceptions may exist where more
`than one trunk group is needed, for example, if an end office
`limits the number of members in a trunk group connected to