A bigger role for call processing.

The good news for end users is that the telephone network may now provide features in PBXs and ACDs on a generic rather than a proprietary basis.

The public switched telephone network (PSTN) has undergone significant changes over the past decade. Carriers can process calls and provide network services much more efficiently than in legacy networks.

Although much of this is invisible to end users, the net result is that they can control their telecommunications and information management more effectively. Signaling System Seven (SS7) and the Advanced Intelligent Network (AIN) are key elements in this evolution.

A major side effect of this transformation has been to broaden the role of call processing. Establishing telephone connections traditionally has been hardware intensive. Lines and trunks were monitored for service requests such as an "off-hook" or "circuit busy," dialed numbers were "looked up" in a register, and circuits were established sequentially from switch to switch across the network.

Today carriers carry subscriber-to-the-network signaling through in-band and out-of-band. In-band signaling, the traditional approach, uses the same wires (or communication channel) as voice signals, so these can be used to talk or to signal, not both. Out-of-band signaling is carried on a separate channel, and signaling and communication can occur simultaneously.

With the advent of SS7, dialed numbers are packetized at the local exchange and sent over a separate channel to a host computer containing telephone numbers, routing information, and other service data. This database is constantly updated according to current network status and service profiles. It forms the basis for intelligent networking.

The new systems are more responsive to the needs of diverse customers because they are fast and work with the AIN to bring individually tailored suites of services to both businesses and residences. Some examples being implemented include number portability for those who switch to a new carrier, change their service profiles, or move to a new location.

Together, SS7 and AIN make it possible to control and configure various types of calls, including end-to-end, teleconferencing, call transfer, number portability, personal number allocation, and other services. AIN already supports many of these, and others will be added. Today, service provider number portability is based on AT&T's Location Routing Number (LRN) scheme, which is supported by AIN Issue 0.1.

Although premise switches such as PBXs and ACDs (automatic call distributors) contain many similar features in proprietary form, the significant development for end users is that the new network may now provide these on a generic basis.

As a result, the effectiveness of business applications such as computer telephony integration (CIT), call distributors, and the provision of multimedia services over the Internet/intranet will be enhanced.

Examples of out-of-band signaling are the Q-series protocols defined by the ITU, such as Q.931 (ISDN), Q.933 (frame relay), and Q.2931 (broadband ISDN).

Because the access network is the last portion of the PSTN to be modernized, most network-to-user signaling today is in-band for small and medium-sized businesses. Once new digital access solutions such as xDSL are deployed, this should improve.

Intelligent networking using AIN and SS7 will impact both telecommunications and the management of information services (MIS). The traditional hierarchical switch-to-switch call processing function is now performed through a separate packet network that controls the switching process for each exchange simultaneously and also provides value-added services. This increases network efficiency, decreases post-dial delay, reduces local access charges, provides new services, and reduces the opportunity for fraud.

When a subscriber goes off hook, a special number sequence called a point code is generated. The point code is similar to a telephone number and can be readily processed by the SS7 network.

The point code is packetized and sent to an SS7 packet switch known as a signaling transfer point (STP). The switch communicates with a computer and database jointly known as a service control point (SCP). This contains telephone numbers and other information.

Origination and destination point codes emulate the numbers belonging to the calling party, the called party, and the exchange taking part in the call. In the example shown in Figure 1, the exchanges are numbered 1, 2 & 3. Numbers known as circuit identification codes (CICs) are used to designate the connections between the switches: In the diagram these are circuits 22 and 7.

[Figure 1 ILLUSTRATION OMITTED]

The SS7 network uses these data to talk back and forth between the SCP, the STPs, the originating exchange, and the other exchanges over fast packet connections. The switch and circuit codes change as call processing proceeds, identifying each element in the end-to-end connection. Once the destination exchange and circuits are identified, the end-to-end transmission path is established and the called party is alerted.

The SS7 network provides a platform on which to base intelligent networking. In addition to its call processing functions, the SCP contains a service logic program (SLP) that enables customer to use services such as 800 number translation and calling card verification.

For message-intensive applications, SLP functionality can be located at an exchange nearer to a customer's premises. The adjunct executes programs that provide additional end-user services over an Ethernet-like connection.

To alert end users and keep them informed of call and service status, a device known as an Intelligent Peripheral (IP) is used. This is an AIN network element that facilitates customer interaction with the network. It is controlled by the SLP and incorporates services such as voice and fax storage, voice prompting, tone decoders, voice synthesis, and conferencing circuits.

A related device called a Service Node (SN) facilitates specific customer services such as personal numbering scheduling, screening, and forwarding.

Here are some advantages of AIN and SS7 for carriers and end users:

* New services can be provided consistently across different manufacturers' switches and different switch software releases.

* End-user needs can be met quickly through customizing, creating and introducing service.

* Interswitch services can include automatic recall, automatic call back, call number delivery and blocking, customer originated trace, and selective call forwarding and rejection.

Integrated Services Digital Network (ISDN) gives end users fast digital access to these services. Call processing in both Basic Rate Interface (BRI) and Primary Rate Interface (PRI) is performed on a separate out-of-band channel which is compatible with SS7.

For example, ISDN can provide incoming call management that enables businesses to identify their customers as they call in, using ANI (automatic number identification) (Figure 2).

[Figure 2 ILLUSTRATION OMITTED]

The calling party's AIN is passed through the network and arrives at the called party's on-premise switch. A controller provides an interface between the telephony circuit and a host computer so the caller's account data can be a located and displayed on a workstation. This speeds the transaction and provides the end user with value-added services. A similar service can be offered over BRI to single-line subscribers.

Until recently, however, hundreds of subscription parameters were required to set up ISDN service for BRI users. Because many of these were repetitive, the North American ISDN Users' Forum (NIUF) was able to format a parameter pattern template that simplified service provisioning with a limited number of combinations of line and feature sets:

* Work at home--9

* Transaction services--5

* Videoconferencing--5

* Desktop collaboration--6

* Telemetry--3

* Distance learning--6

* Fax--2

* Telemedicine--6

* LAN to LAN--2

End users can select solution sets best fitting their needs with regard to feature capability, line configurations, and existing ISDN service provider tariffs.

One of the first companies to implement this is Nortel. Its latest DMS-10 software release provides full national ISDN BRI capabilities. The company says the optimum solution set is usually a compromise between the subscriber's needs for features or line configurations and the service provider's ISDN offering.

Signaling and services fall under the broad category of network control. SS7 and AIN give carriers and their subscribers the ability to provide enhanced and value-added services such as number portability. The current weakness of the network is that access for small and mid-sized business customers is mainly analog, making it difficult to combine the strengths of digital telephony and computers. ISDN provides one answer to this dilemma, xDSL another.

What is the future of SS7? First, the network is constantly being upgraded with higher speed links. For example, some STPs and SCPs now communicate at 1.5 Mbps.

A broadband version of the SS7 call control message is under development for ATM switches as part of the Broadband ISDN User Part (B-ISUP). Existing digital switches will continue to use current narrowband messages to support narrowband AIN services.

Finally, interworking is being developed between SS7 and B-ISUP for calls traversing both circuit-switched and AIN networks.