# Fax application overview

A NaturalFax application uses Natural Access functions to control the PSTN
and NaturalFax functions to manage fax sessions and related tasks. The Natural Call Control service is responsible for establishing and disconnecting the calls.

Natural Access functions:

- Initialize and tear down the application.

- Perform call control.

NaturalFax functions:

- Build and destroy document queues.

- Transmit or receive faxes.

- Perform image format conversions.

- Monitor fax session status.

- Monitor fax document status.

A fax session begins when a transmit or receive operation is initiated, and ends when the application receives the corresponding NaturalFax DONE event. A document queue contains a list of one or more document files (the document files must be in TIFF-F or TIFF-S format). NaturalFax functions operate on document queues, not on individual files. You must use document queues for all fax operations, including transmitting and receiving single documents.

The following illustration shows how Natural Access and NaturalFax are used in a basic NaturalFax application:

## Natural Access components

A Natural Access service is a group of logically related telephony functions. NaturalFax is a Natural Access service that provides functions for sending and receiving Group 3 faxes.

Within Natural Access, services and accompanying resources are organized around a single processing entity called a context
. A context usually represents an application instance controlling a single telephone call. Some Natural Access contexts are not associated with a call. For example, an operation performing fax file conversions does not require a telephone line.

Note: Only one asynchronous fax operation per context can be active at one time.

A service can only be opened once on an individual context. For example, in order to send faxes using all eight channels of an AG 2000 board, an application needs to create eight Natural Access contexts, and open the NaturalFax service on each context.

An event queue
is the communication path from a service to an application (such as NaturalFax). A service generates events indicating certain conditions or state changes. An application retrieves the events from the event queue.

You can alter the characteristics of services by modifying associated parameters. Each NaturalFax parameter structure has default values that are sufficient for most configurations. NaturalFax applications typically need to set the subscriber ID (the telephone number) to comply with FCC or other local regulations, but may not need to modify other parameters.

Natural Access manages parameters for services on a context-by-context basis. The context maintains a copy of the parameters for all services opened on the context, allowing each fax operation to have its own characteristics. Refer to the Overview of NaturalFax data structures for detailed descriptions of NaturalFax parameters and their default values.

For detailed information about Natural Access, refer to the Natural Access Developer's Reference Manual.

## Preparing the hardware environment

You must initialize and load all boards before you can run NaturalFax. Use NMS OAM to perform hardware configuration and initialization. For more information, refer to the NMS OAM System User's Manual.