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A number of users have requested the capability for TBB to:

•Call forward first to a number, and then insert additional numbers to access a telephone extension or a cell phone roaming access number.

•Use SpeedDial to dial a number and automatically enter a PIN; perhaps even dialing a second number after this.

Unfortunately, these and other similar scenarios, are not technically feasible within the current Telephony Network.

A typical phone call (direct dial or through SpeedDial) is made through Telephone System switches (aka Bell Central Office or CO). The COs are initially involved in what is called Call-Setup to connect your phone to the phone number you have dialed. Once the call is setup and connected, the CO simply passes the voice signals between these two phones. It then waits for a flash signal, or a phone-on-hook signal before it does anything further.

Once the phone call is setup, any further "PIN numbers" or "extensions" need to be generated by a phone either manually or automatically. It is recommended to program your telephone (or cell-phone) to insert pauses, PINs, or additional numbers where needed. You need to refer to your phone's manual for the detailed programming procedures. If your phone does not have support for long numbers and "pauses", you can program the main number in a SpeedDial number, and the PIN and/or extensions in your phone's memory locations.

Call Setup Simplified Technical details:
  • a phone call is setup between two COs and this is done via protocols like CCS7 (re: BellCore, ITU etc);

  • the LINECARD at the CO connected to your phone listens to the digits you dial (touch-tone)....the CALLED number... seven to ten digits for the North American dial-plan... let us ignore international calls for this example;

  • the LINECARD then gives these CALLED digits to the "CO";

  • your (NEAR END) CO talks to other COs in the PSTN (Network) to find out which (FAR END) CO to terminate at to make the call and ring the telephone you dialled. This is done via the CCS7 protocol or the like (a telco "language");

  • the CO at the FAR END talks to the LINECARD connected to your friend's telephone and the LINECARD causes the phone to ring.

This is what is called "Call Setup". Note that the PSTN consists of many COs and from different companies too. So when a call gets forwarded, this is part of CallSetup and it has to go through the PSTN through many COs perhaps(!).

For the problem at hand, the PSTN only handles 10 digits (incl Area Code). So adding more CALLED digits as in PIN numbers or extensions for roaming numbers or office extensions, cannot be handled by the current PSTN very easily. The system would also have to take into account time for pauses so that the PIN or extension number can be entered correctly.

This would mean the whole network would have to be changed in North America, as well as first getting all the Telcos and equipment manufacturers such as Nortel to agree to add the digits, how many digits, and how to modify the protocols to do this (not just the CCS7 protocol). This is not very likely.

Expand got feedback?

by canoe See Profile
last modified: 2005-05-20 22:30:22