# Point-to-point switching service definition

The Point-to-Point Switching (PPX) service is a Natural Access service that enables you to make switch connections between boards connected by a telephony bus without having to specify the intervening bus timeslots
. The PPX service maintains an internal database that records the switching configuration for the system and the state of all the timeslots.

To make a switch connection using PPX, specify the two endpoints for the connection. The PPX service manages the telephony bus timeslots and controls the underlying hardware switches to make the connections. The PPX service can be used with any board that has an FMIC or HMIC type switch.

In the following example, a connection is required between a DSP
resource on an AG 4040 board and a T1 channel on an CG 6000 board. The DSP resource on the AG 4040 board is used to play an on hold message for all incoming calls.

Using the PPX service, the application calls one function specifying both the location of the DSP resource (board number, local stream, and timeslot) and the location of the caller (board number, local stream, and timeslot). The PPX service determines the required telephony bus timeslots and makes the necessary switch connections.

In contrast, when using Natural Access Switching (SWI) service functions to make the connection, an application is required to:

1. Determine if the switch connection can use the local bus or if it requires telephony bus timeslots.

2. Determine which telephony bus timeslots are available for the connection.

3. Send the switch commands to connect the caller to an available timeslot on the telephony bus.

4. Send the switch commands to connect the DSP resources to the telephony bus.

When using the PPX service, all streams and timeslots are addressed using the MVIP-95 switch model. The Switching service provides additional functions for configuring telephony bus clocks and stream speed. Use these commands to configure the bus before making any connections. Refer to the Switching Service Developer's Reference Manual for more information.

Caution: | When using the PPX service, do not use the SWI service to make switch connections. The PPX service maintains an internal connection database to determine local resource and telephony bus usage. Since connections made with the SWI service are not recorded in this database, you can have unpredictable results. The PPX service could use timeslots already used by the SWI service and the SWI service could use timeslots already used by the PPX service.