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Telephony Control Protocol Specification Profile Group

The Telephony Control Protocol Specification (TCS), shown in Figure 5, defines ways to send audio calls between Bluetooth devices. Bluetooth pundits have suggested that it can be used to create a three-in-one phone:

  1. On the move, a mobile phone connected to a cellular network

  2. At home, a cordless phone connected to a PSTN via a gateway or base station

  3. At the office, an intercom

Feature 1 simply uses the mobile phone's existing capabilities as a cellular phone, but features 2 and 3 rely on Bluetooth profiles.

Feature 2 uses the Cordless Telephony Profile. This enables a gateway connected to a telephone network to relay calls to a handset via a Bluetooth link. Why use this instead of the mobile network? First, very cheap handsets could be made using just Bluetooth links. Second, battery life should be longer than that of cellular phones. Third, savings are a result of not paying for cellular air time.

Feature 3 uses the Intercom Profile. This provides a basic point-to-point audio service allowing direct voice calls between Bluetooth handsets. This profile is likely to prove most useful with +20dBM radios that have a range of up to 100m.

A weakness of all the Bluetooth telephony profiles is that no handover facilities are defined in TCS. This means that you can connect a terminal to one gateway, but if you walk out of range of that gateway—even if you are in range of another gateway connected to the same telephone network—there is no way to hand your call to a second gateway. The call is dropped, and you must start again.

Figure 5

Telephony Control Protocol Specification Profile Group

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