PSTN Services and Applications

As with almost every industry, it is usually better and easier to acquire additional business from current customers than it is to go out and get new customers. The PSTN is no different. Local Exchange Carriers (LECs) have been increasing the features they offer to create a higher revenue stream per consumer.

Numerous services are now available, for example, which were not available just a few years ago. These services come in two common flavors: custom calling features and CLASS features.

Custom calling features rely upon the end office switch, not the entire PSTN, to carry information from circuit-switch to circuit-switch. CLASS features, however, require SS7 connectivity to carry these features from end to end in the PSTN.

The following list includes a few of the popular custom calling features commonly found in the PSTN today:

• Call waiting—Notifies customers who already placed a call that they are receiving an incoming call.

• Call forwarding—Enables a subscriber to forward incoming calls to a different destination.

• Three-way calling—Enables conference calling.

With the deployment of the SS7 network, advanced features can now be carried end to end. A few of the CLASS features are mentioned in the following list:

• Display—Displays the calling party's directory number, or Automatic Number Identification (ANI).

• Call blocking—Blocks specific incoming numbers so that callers are greeted with a message saying the call is not accepted.

• Calling line ID blocking—Blocks the outgoing directory number from being shown on someone else's display. (This does not work when calling 800-numbers or certain other numbers.)

• Automatic callback—Enables you to put a hold on the last number dialed if a busy signal is received, and then place the call after the line is free.

• Call return (*69)—Enables users to quickly reply to missed calls.

A majority of these features are possible due to the use of SS7 and the IN. Many inter-exchange carriers (IXCs) also offer business features, such as the following:

• Circuit-switched long distance—Basic long-distance services (normally at a steeply discounted rate).

• Calling cards—Pre-paid and post-paid calling cards. You dial a number, enter a password, and then call your destination.

• 800/888/877 numbers—The calling party is not charged for the call; Rather, the party called is charged (normally at a premium rate).

• Virtual Private Networks (VPNs)—The telephone company manages a private dialing plan. This can greatly reduce the number of internal Information Service (IS) telecommunications personnel.

• Private leased lines—Private leased lines from 56 kbps to OC-48s enable both data and voice to traverse different networks. The most popular speed by far in North America is T1.

• Virtual circuits (Frame Relay or Asynchronous Transfer Mode [ATM])—The tele-phone carrier (IXC or LEC) switches your packets. It does this packet by packet (or cell by cell in ATM), not based upon a dedicated circuit.

This list of IXC business features is merely a sampling of the more popular features and applications available in the PSTN. Although the PSTN is evolving and consumers are using more of its features, the basic user experience has remained somewhat consistent since the inception of digital networking for telephony communications.

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