PBX circuit cards are based on solid-state integrated circuitry mounted on printed wiring boards. A label, usually color coded to simplify installation and maintenance operations, identifies each circuit card. The circuit cards usually have fault, test, and busy multicolor LED indicators. A metal latch for electrostatic discharge protection is typically included. Circuit cards can be categorized into three basic types: control, service, and port. Control circuit cards support PBX call processing and switching functions. Service circuit cards enable some call processing features and functions. Port circuit cards serve as connection gateways between peripheral equipment and the PBX call processing, switching network, and power distribution systems.
Each port circuit card supports a unique type of peripheral endpoint, but all share several common design elements. Each port circuit card has a TDM bus buffer, control channel interfaces, an onboard microprocessor controller with limited memory storage, and additional processing elements to perform functions such as voice quality control.
Port circuit card bus buffers are the digital interface between the backplane TDM transmission line wires and the onboard integrated circuitry. The buffers have wire leads that transmit or receive electrical signals from the transmission line. The control channel interfaces access signaling information on the TDM bus. Control channel interface wire leads interface to the TDM bus, pickup common channel information intended for the port circuit pack, and transmit it to the onboard microprocessor controller. When the microprocessor controller transmits information to the TDM bus control channel, it is transported by the control channel interface. In addition, the control channel interface initiates power-on start-up procedures, performs diagnostics tests on the onboard microprocessor controller, and follows Main System Processor instructions to disable the port circuit pack in case of onboard problems. It also can perform several localized processing functions at the station user desktop, such as control of voice terminal LED/LCD status indicators.
The main responsibilities of the onboard microprocessor controller are relatively low-level processing and monitoring functions, such as scanning for changes and relay operations. It generally carries out the instructions of the Main System Processor and reports back status changes. Additional onboard processing elements are responsible for voice quality control, such as conference and gain-adjust functions, and port circuit termination access to the TDM bus time slots based on instructions from the onboard microprocessor controller. Figure 1 shows a Siemens Digital Line Card with the various design elements of a port interface card.
The following section contains descriptions of circuit interface cards typically used in PBX systems. Some PBX systems may combine the functions for several circuit cards into single multifunction card.
Control Cards
Processor. The processor card has the main Central Processing Unit (CPU) microprocessor chip that controls the entire system and executes the stored program control commands to perform call processing operations and administrative control functions. Integrated memory chips store the generic system program. In a duplicated control system design, the card allows the memory of the passive standby processor to be continuously updated to reflect the memory in the active processor. Additional card functions usually include provisioning of alarm LEDs for system status; monitoring and control of all port circuit pack conditions; and an interface to systems management and maintenance systems.
The processor card may also perform the following functions: transmission of control channel messages to the port circuit cards over the TDM bus; control signaling to customer-provided equipment, such as CDR and accounting devices; time-of-day clock; battery backup; and monitoring of system clocks. Some PBX systems may use an additional system control card for these functions, if not performed by the processor circuit card.
Power system monitor. A power system monitor card monitors the status of power-related hardware elements, such as power supplies, fan operation, power failure transfer, circuit breakers, and LEDs. Power error messages may be routed to the processor card for subsystem switchover operations or to the administration and maintenance system to generate alarms.
System memory. The system memory card has one or more memory chips for storage of the generic system program. The system memory may be partitioned to also support the customer database. Small and intermediate line size PBX systems may include the memory chips on the processor card, instead of having a dedicated memory card. Some systems require multiple system memory cards.
Memory storage drives. The PBX memory storage system usually requires a tape drive circuit pack or a floppy disk unit. The memory drives load the generic system program into system memory.
Switch network. The switch network cards may include the center stage switch network and/or local TDM bus switch network interfaces to the center stage switch network.
Local Loop Interfaces: Maintenance/Diagnostic
The maintenance/diagnostic card performs basic maintenance and diagnostic operations, such as monitoring of port circuit packs, TDM bus interfaces, and power distribution.
Service Cards
Tone clock. The tone clock supplies a variety of tones, including call progress tones, touch tones, answer-back tones, and trunk transmission tones. The card provides multiple clock signals for transmission over the TDM buses. Tone clock cards may also provide an interface to the external Stratum 3 synchronization clock. interface cards can support signaling interfaces to multiple LAN-connected servers.
Serial data interface. The serial data interface card can provide interfaces to the main processing element for one or more I/O devices. interface cards can support signaling interfaces to multiple LAN-connected servers.
Tone receiver. The touch-tone receiver card supports multiple channels of DTMF or multi frequency (MF) detection for analysis and interpretation of incoming tone signals from 2500-type terminals and certain DID and tie trunks. General-purpose tone receivers detect call progress tones and answer tones, modem answer-back tones, transmission test tones, and noise. Tone detection capability is usually required for ARS and OPX dialing applications. Tone receivers also detect answer on outgoing analog trunk (CO, FX, WATS) calls so that CDRs can be generated. More than one tone receiver card may be required per system, based on port size requirements and customer applications. interface cards can support signaling interfaces to multiple LAN-connected servers.
Conference. The conference card supports the multiparty conference feature. Only a select number of PBX system models require a dedicated card to implement a conference call among three or more system ports. interface cards can support signaling interfaces to multiple LAN-connected servers.
Speech synthesizer. The speech synthesizer card stores customerprogrammed audio messages that are required for several PBX features, such as automatic wake-up, voice message retrieval, and call intercept treatments. The speech synthesizer card supports a limited number of communications channels, usually between two and eight. interface cards can support signaling interfaces to multiple LAN-connected servers.
Call classifier. The call classifier card supports tone detectors that are used for call prompting applications. The call prompt feature prompts callers to input touch-tone digits for call screening and analysis purposes. It is generally used in ACD system configurations instead of a stand-alone automated attendant, VMS, or IVR system for digit collection, analysis, and call redirection applications. The card can also detect special intercept tones for outbound call management applications. interface cards can support signaling interfaces to multiple LAN-connected servers.
Expansion interface. The expansion interface card extends internal system buses (call processing, switch network) between stackable carriers and/or cabinets. interface cards can support signaling interfaces to multiple LAN-connected servers.
Control buffer. The control buffer card is housed in a port carrier card slot and provides an interface between the local TDM bus and the center stage switch network complex. The card may also include a microprocessor that supports local processing control and maintenance functions. interface cards can support signaling interfaces to multiple LAN-connected servers.
Announcer board. An announcer board stores customer-programmed recorded announcements. PBX/ACD features requiring an announcer board may include call intercept treatments, estimated wait time, and the number of callers in queue. The number of distinct announcements per announcer board varies by manufacturer, but most boards can support between 32 and 128 announcements. The total recording time for announcements is usually limited to between 4 and 10 minutes per board. The number of communications channels per board varies by manufacturer, but is typically between 16 and 32 channels. Several callers can usually listen to the same channel announcement. interface cards can support signaling interfaces to multiple LAN-connected servers.
CTI link. The CTI link card supports a signaling interface link between the PBX system and a CTI applications server or host. First-generation CTI signaling links were based on proprietary PBX interface protocols. Current PBXs commonly use a TCP/IP signaling link and an Ethernet LAN interface connection supporting CTI applications. The TCP/IP interface cards used for CTI application requirements can be used for a variety of other PBX applications, such as VMS signaling interface, adjunct ACD MIS reporting system server signaling interface, and IP call control signaling to IP station/trunk peripherals. The first-generation proprietary CTI link cards were usually limited to a signaling interface link for a single server; the current TCP/IP LAN interface cards can support signaling interfaces to multiple LAN-connected servers.
Port Cards
Analog line. The analog line card provides the interface to the local TDM bus for analog communications terminals and devices. These terminals and devices include 500-type rotary dial telephones, 2500-type DTMF dial telephones, facsimile terminals, modems, external alerting devices, paging systems, dictation machines, and recorded announcements. Analog line cards may also provide PBX system communications links to external VMSs, IVR systems, and wireless communications system controllers. One or more analog line cards may be required to support any or all of the listed peripherals. The port density of current PBX analog line cards is typically 16 or 24 single bearer communications channel circuit terminations. the actual numbers depend on each manufacturer’s PBX system platform. Some IP line cards may function as universal IP port cards, and support IP trunks (see discussion below).
OPX line. The OPX line card provides the interface to off-premises wiring with rotary or DTMF dialing in support of an OPX. The port density of a current PBX OPX line card is typically 16 single bearer communications channel circuit terminations. the actual numbers depend on each manufacturer’s PBX system platform. Some IP line cards may function as universal IP port cards, and support IP trunks (see discussion below).
Digital line. The digital line card provides the interface to the local TDM bus for proprietary digital telephones or data modules. For many PBX systems, the digital line card also can be used to support proprietary attendant consoles. Each digital circuit port interface supports a 2B+D transmission protocol to the desktop device. The port density of a current PBX digital line card is typically 16 or 24 dual bearer communi-cations channel circuit terminations. the actual numbers depend on each manufacturer’s PBX system platform. Some IP line cards may function as universal IP port cards, and support IP trunks (see discussion below).
Digital attendant console. The attendant console card provides the interface to the local TDM bus for proprietary digital attendant consoles. (A digital line card, instead of a dedicated digital attendant console card, currently supports most PBX attendant consoles.) Each digital circuit port interface supports a 2B+D transmission protocol to the attendant console. The port density of current PBX digital attendant consoles is usually limited to one or two dual bearer communications channel circuit terminations. the actual numbers depend on each manufacturer’s PBX system platform. Some IP line cards may function as universal IP port cards, and support IP trunks (see discussion below).
Data line. The data line card provides the interface to the local TDM bus for proprietary data modules. Data modules support a modemless communications link between customer-provided Data Terminal Equipment (DTE) or Data Communications Equipment (DCE) and the PBX system. There are a variety of data line cards; each data line card is designed to support asynchronous and/or synchronous data endpoints at different transmission rates. The port density of a current PBX data line card is typically 16 single bearer communications channel circuit terminations. the actual numbers depend on each manufacturer’s PBX system platform. Some IP line cards may function as universal IP port cards, and support IP trunks (see discussion below).
Power failure transfer. The power failure transfer card provides direct physical connections between central office trunk line circuits and analog station equipment in the event of a failure of the PBX power system. The power failure transfer lines function as normal CO trunks in the normal PBX state. Power failure transfer cards typically support a limited number of central office trunk connections, such as two or four lines. the actual numbers depend on each manufacturer’s PBX system platform. Some IP line cards may function as universal IP port cards, and support IP trunks (see discussion below).
ISDN BRI line. The ISDN BRI line card provides the interface to the local TDM bus for DTE conforming to National ISDN standards. There are two types of ISDN BRI line cards: U-interface and S/T-interface. A U-interface line card supports a 1B+D transmission protocol to the desktop device; an S/T-interface supports a 2B+D transmission protocol to the desktop device. The port density of a current PBX ISDN BRI line card typically supports 16 single or dual bearer communications channel circuit terminations. the actual numbers depend on each manufacturer’s PBX system platform. Some IP line cards may function as universal IP port cards, and support IP trunks (see discussion below).
IP line. The IP line card provides the interface to the local TDM bus for IP telephones and IP PC client softphones. The IP line card functions as a media gateway to convert IP communications signaling format to TDM/PCM communications signaling format and may be used to convert proprietary PBX signaling protocol to an IP call control protocol, such as H.323 supported by the IP telephone. A dedicated port circuit card may also support call control signaling transmission to and from the IP telephone. The IP line card is embedded with numerous DSP resources that function as the media gateways. IP line cards may support more physical IP telephones than available media gateway channel connections to the local TDM bus. The number of local TDM channel connections depends on available DSP resources and the type of audio coder used by the IP telephone. Current IP line cards support between 24 and 500 IP telephones and between 24 and 64 channel connections; the actual numbers depend on each manufacturer’s PBX system platform. Some IP line cards may function as universal IP port cards, and support IP trunks (see discussion below).
CO trunk. CO trunk cards provide interfaces to the local TDM bus for the following types of local exchange carrier trunk circuits: loop-start or ground start CO, FX, or WATS. The CO trunk card may also be used for paging systems or other external communications systems, such as IVR systems. The port density of a current PBX CO trunk card is typically 8 or 16 communications channel circuit terminations. cations channels and one signaling channel (23B+D); an E1-based ISDN PRI trunk card supports 30 bearer communications channels and one signaling channel. Some PBX systems require a dedicated circuit card to support D-channel signaling protocol. The D-channel handler card, as it is sometimes called, supports a manufacturer-defined, limited number of ISDN PRI trunk cards. An ISDN PRI trunk card supports one ISDN PRI service T1/E1trunk circuit.
DID trunk. DID trunk cards provide interfaces to the local TDM bus for immediate-start or wink-start DID trunks. The port density of a current PBX DID trunk card is typically 16 communications channel circuit terminations. cations channels and one signaling channel (23B+D); an E1-based ISDN PRI trunk card supports 30 bearer communications channels and one signaling channel. Some PBX systems require a dedicated circuit card to support D-channel signaling protocol. The D-channel handler card, as it is sometimes called, supports a manufacturer-defined, limited number of ISDN PRI trunk cards. An ISDN PRI trunk card supports one ISDN PRI service T1/E1trunk circuit.
E&M tie trunk. E&M tie trunk cards provide interfaces to the local TDM bus for two-wire or four-wire E&M trunk circuits. There are several types of E&M tie trunk circuit categories, but the category currently used by most PBXs for networking applications is Type 1. Some PBXs may also use the E&M tie trunk card to support a Centralized Attendant Service (CAS) configuration requiring a Release Link Trunks (RLT). The port density of a current generation PBX E&M Tie Trunk card is typically eight communications channel circuit terminations. cations channels and one signaling channel (23B+D); an E1-based ISDN PRI trunk card supports 30 bearer communications channels and one signaling channel. Some PBX systems require a dedicated circuit card to support D-channel signaling protocol. The D-channel handler card, as it is sometimes called, supports a manufacturer-defined, limited number of ISDN PRI trunk cards. An ISDN PRI trunk card supports one ISDN PRI service T1/E1trunk circuit.
DS1 digital trunk. DS1 digital trunk cards provide interfaces to the local TDM bus for T1 trunk circuits operating at 1.544 Mbps (North America standard) or E1 trunk circuits operating at 2.048 Mbps (Europe standard) digital trunk circuits. Digital T1 trunk circuit cards support 24- to 64-Kbps channels; digital E1 trunk circuit cards support 32- to 64-Kbps channels. The DS1 digital trunk card can be programmed to support voice-grade digital trunks using inband bit-oriented signaling on a per-channel basis or Alternate Voice Data (AVD) digital trunks using common channel signaling. Some DS1 digital trunk cards can also be programmed to support ISDN PRI services over T1/E1 trunk circuits. A DS1 digital trunk card supports one T1/E1 trunk circuit connection and 24 to 32 communications channel circuit terminations. cations channels and one signaling channel (23B+D); an E1-based ISDN PRI trunk card supports 30 bearer communications channels and one signaling channel. Some PBX systems require a dedicated circuit card to support D-channel signaling protocol. The D-channel handler card, as it is sometimes called, supports a manufacturer-defined, limited number of ISDN PRI trunk cards. An ISDN PRI trunk card supports one ISDN PRI service T1/E1trunk circuit.
ISDN PRI trunk. ISDN PRI trunk cards provide interfaces to the local TDM for T1/E1 trunk circuits programmed to support ISDN PRI services. A T1-based ISDN PRI trunk card supports 23 bearer communi- cations channels and one signaling channel (23B+D); an E1-based ISDN PRI trunk card supports 30 bearer communications channels and one signaling channel. Some PBX systems require a dedicated circuit card to support D-channel signaling protocol. The D-channel handler card, as it is sometimes called, supports a manufacturer-defined, limited number of ISDN PRI trunk cards. An ISDN PRI trunk card supports one ISDN PRI service T1/E1trunk circuit.
ISDN BRI trunk. ISDN BRI trunk cards provide interfaces to the local TDM for digital subscriber lines conforming to ISDN BRI signaling standards. An ISDN BRI trunk card supports two bearer communications channels and one signaling channel (2B+D). An ISDN BRI trunk card supports supports one ISDN BRI digital subscriber line. ISDN BRI trunk cards are not commonly available for intermediate/large PBX systems. announcements, and music-on-hold. The port density of current auxiliary trunk cards typically supports 4, 8, or 16 communications channel circuit terminations.
IP trunk. The IP trunk card provides the interface to the local TDM bus for IP trunking services via WAN IP routers. The IP trunk card functions as a media gateway to convert IP communications signaling format to TDM/PCM communications signaling format and may also be used to convert proprietary PBX signaling protocol to an IP call control protocol, such as H.323, supported by IP routers. A dedicated port circuit card may also support call control signaling transmission to and from the IP router. The IP trunk card is embedded with numerous DSP resources that function as the media gateways. The number of local TDM channel connections depends on available DSP resources and the type of audio coder used by the IP telephone. Current IP trunk cards typically support 24 channel connections using the H.323 call control protocol. announcements, and music-on-hold. The port density of current auxiliary trunk cards typically supports 4, 8, or 16 communications channel circuit terminations.
ATM trunk. The ATM trunk card provides the interface to the local TDM bus for ATM trunking services via customer premises ATM switching systems. The card performs a cell assembly/disassembly operation to convert between TDM/PCM communications signals and packeted ATM cells. ATM trunk cards can also be used for T1/E1 Circuit Emulation Service (CES); a single ATM trunk card can support multiple T1/E1 trunk circuit connections. announcements, and music-on-hold. The port density of current auxiliary trunk cards typically supports 4, 8, or 16 communications channel circuit terminations.
Auxiliary trunk. Auxiliary trunk cards provide the interface to the local TDM bus for on-premises trunk connections to customer-provided equipment that supports communications applications, such as loudspeaker paging, code calling, recorded dictation access, recorded announcements, and music-on-hold. The port density of current auxiliary trunk cards typically supports 4, 8, or 16 communications channel circuit terminations.
Pooled modem. The pooled modem card converts resources for switched connections between data modules and modems for off-premises trunking applications. A pooled modem card may support one or two modem connections.
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