1.  Field of the Invention
The present invention relates to telecommunications.  More particularly, the present invention relates to an ATM-based distributed network switching system for use within a public switched telephone network (PSTN). 
2.  Background Information
Today""s network backbone is a consolidation of dissimilar networks, including, for example, asynchronous transfer mode (ATM), frame relay, time division multiplex (TDM), private line, etc.  The variety of networks is necessary to accommodate different types of access, e.g., xDSL, ISDN, line access, etc. 
The present day network backbone employs numerous protocols because each type of network requires its own protocols.  Even within the voice network alone, there are multiple protocols and thus protocol conversions are required.  That is, an incoming protocol, e.g., Bellcore GR-303, communicates with digital loop carriers (DLCs) to control voice channels coming into the switch.  Within the switch, a different switch protocol transfers the traffic through the switch.  To further complicate the situation, the internal switch protocol of each vendor is proprietary.  Another protocol, i.e., a trunk protocol (e.g., Signaling System 7 (SS7)), is necessary to move the traffic from the originating switch to the destination switch.  The large number of protocols operating within the network backbone complicates communications across the backbone. 
The present day backbone has disadvantages other than a plethora of protocols.  For example, each type of network is managed in a different manner with its own management system, often from a different location.  Thus, many areas of expertise are required to manage the network backbone.  In other words, a large number of engineers, having different skill sets, is required to manage the heterogeneous network. 
The present day central office architecture also demands burdensome engineering and management.  More specifically, each central office must be managed separately.  To compound the problem, each central office has a unique configuration, different from each other central office.  For example, different central offices may have different vendor""s switches (switch types), as well as different switch hardware configurations.  Thus, a variety of personnel, with different skill sets is required to manage a unique central office.  In addition, the engineering of facilities and trunks between central offices and their switches consumes a large number of personnel with unique skill sets as well as physical resources. 
It has been proposed to replace tandem switches with a distributed architecture, referred to as Voice Trunking over ATM (VTOA), to reduce the number of trunks between central offices and accordingly engineering of trunks between end offices.  VTOA is, however, limited to trunk interconnection (that is, service provider""s switch interconnection as opposed to customer""s access) and still requires the services of Class 5 switches.  Consequently, even with VTOA, the network backbone requires multiple protocols and additional hardware to provide all the necessary switch interconnection. 
Another problem with today""s voice network is that end office Class 5 switches, such as the Lucent 5ESS and Nortel DMS 100, are proprietary switches employing proprietary hardware and software.  That is, upgrading and replacing of switches is not an easy task, in part due to this proprietorship.  Thus, a need exists for components with a generic hardware implementation that relies upon software and personality cards to provide specific functionality. 
The current network architecture does not distribute well within a metropolitan area due to the transport requirements and technology base of the current Class 5 switches.  Thus, the current central office based telephony topology is constrained to geographical boundaries and often requires digital loop carriers (DLCs) and other remote telephony units.  Therefore, a need exists to replace today""s end office Class 5 switches with a distributed switching system.  This will allow the extension of the central office switch boundaries to the controlled environment vault (CEV) of the carrier serving area (CSA) or even to the customer premises for medium and large customers. 
Thus, a need exists for a streamlined network backbone that allows all kind of access and is managed by a single management system from a single location or a limited number of locations.  The management system should be able to converse with all components of the network using a single standardized protocol, significantly reducing the need for protocol conversion.  It would also be desirable if proprietary hardware could be eliminated.  Such a network would only require expertise in a single area and thus would reduce the personnel required for network management. 
A-IWF Access Interworking Function
AAL ATM Adaptation Layer
ABR Available Bit Rate
ACM Address Complete Message
ADPCM Adaptive Differential Pulse Code Modulation
ADNSS ATM Based Distributed Network Switching System
ADSL Asymmetric Digital Subscriber Line
AIN Advanced Intelligent Network
ANM Answer Message
ANSI American National Standards Institute
ATM Asynchronous Transfer Mode
BAF Bellcore AMA Format
B-ISUP Broadband ISDN User Part
CAS Channel Associated Signaling
CBR Constant Bit Rate
CCS Common Channel Signaling
CES Circuit Emulation Service
CEV Controlled Environment Vault
CIC Circuit Identification Code
CSA Carrier Serving Area
CS-IWF Control and Signaling Interworking Function
DLC Digital Loop Carrier
DPC Destination Point Code
DS0 Digital Signal Level 0 (64 Kbps digital signal format)
DS1 Digital Signal Level 1 (1.544 Mbps digital signal format)
IAM Initial Address Message
IP Internet Protocol
IPM Impulses Per Minute
ISDN Integrated Service Digital Network
ISUP ISDN User Part
ITU-T International Telecommunications Unionxe2x80x94Telecommunications
IWF Interworking Function
IXC Interexchange Carrier
LA-IWF Line Access Interworking Function
LA-CPS Line Access Call Processor Server
OAMandP 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
OSS Operations Support Systems
PCM Pulse Code Modulation
PLA-IWF Private Line Interworking Function
PNNI Private Network-Network Interface
POTS Plain Old Telephone Service
PSTN Public Switched Telephone Network
PVC Permanent Virtual Connection
SS7 Signaling System 7
SSP Service Switching Point
STP Signal Transfer Point
STS1 Synchronous Transport Signal, level 1
SVC Switched Virtual Connection
TACPS Trunk Access Call Processing Server
TA-IWF Trunk Access Interworking Function
TDM Time Division Multiplexing
UBR Undefined Bit Rate
UNI User-to-Network Interface
VPI/VCI Virtual Path Identifier/Virtual Channel Identifier
VTOA Voice and Trunking over ATM
xDSL Digital Subscriber Line