# Bearer Control Function Library Overview

The application uses the Bearer Control Functions (BCF) library to format and parse Bearer Control messages. In the context of the BCF library, a Bearer Control (BCF) Message consists of the following field sequence:

- APM’2000 Originating Address

- APM’2000 Destination Address

- Bearer Associated Transport (BAT) Application Service Element (ASE) Encapsulated Application Information, as specified in ITU-T Q765.5

The Bearer Control Message types that can be formatted and parsed using the BCF library and the main fields they encapsulate are:

Bearer Control Message Type | Main Fields Encapsulated
FAST_FORWARD_BEARER_SETUP_REQUEST | IPBCP Request Bearer Characteristics
FAST_FORWARD_BEARER_SETUP_ANSWER | IPBCP Answer
DELAYED_FORWARD_BEARER_INFO_REQUEST | Optional Codec List Bearer Characteristics
DELAYED_FORWARD_BEARER_INFO_ANSWER | Optional available Codec List Optional Selected Codec
DELAYED_FORWARD_BEARER_SETUP_REQUEST | IPBCP Request
DELAYED_FORWARD_BEARER_SETUP_ANSWER | IPBCP Answer

The BCF library complies with the following specifications:

- ITU-Q1902.4

- ITU-Q1970, IETF RFC 4566 (SDP), 3GPP TS 29.414

- BICC Bearer Control Tunneling Protocol (ITU-Q.1990)

- BAT ASE (Q.765.5)

The BCF can build and parse Bearer Control messages according to APM’2000 User Application. To send a Bearer Control message, the application needs to:

- Build the Bearer Control message using the BCF library

- Use the Dialogic® NaturalAccess™ BICC Layer to attach the Bearer Control message to a BICC Call Control (usually IAM) or APM message using the Application Transport Parameter IE

To receive a Bearer Control message, the application needs to:

- Use the Dialogic® NaturalAccess™ BICC Layer to get the Bearer Control message attached to a BICC Call Control or APM message

- Parse the Bearer Control message using the BCF library

For more information, refer to the Dialogic® NaturalAccess™ ISUP Layer Developer's Reference Manual.