# Developing GR303 applications

Use NMS hardware and software and NMS GR303 library functions to create remote digital terminal (RDT) or integrated digital terminal (IDT) applications that perform the following tasks:

- Configure T1 boards.

- Configure up to four HDLC controllers per GR303 interface.

DS0 and DS1 locations for HDLC links are application-configurable, but for RDT applications must set these links to occupy timeslots 24 and 12 on two different T1 links.

- Perform automatic internal switching between CAS and RAW signaling modes when configuring HDLC channels.

- Send and receive HDLC data and transfer result reports.

- Provide buffering for outgoing and incoming messages on each HDLC data channel.

- Support ABCD robbed-bit signaling on a per timeslot basis.

- Support the switching fabric required for the TSI interface of the GR303 protocol.

- Provide library tracing capabilities.

HDLC device controllers perform the following tasks:

- Dynamically create and destroy HDLC instances.

- Initialize and reset HDLC instances.

- Activate and deactivate HDLC instances.

- Control the transmission and reception of HDLC frames.

- Perform statistics monitoring and configuration tasks.

- Control the transmission of asynchronous events and error reports.

Framer device controllers perform the following tasks:

- Monitor T1 links for alarms and errors.

- Control T1 links statistics queries and configuration.

- Configure signaling operation modes (CAS or RAW mode) on a per-timeslot basis.

The NMS GR303 library also provides physical layer access to the upper layers of the Aztek Access303 protocol stack. NMS GR303 library functions allow applications to perform the following tasks:

Tasks | Library functions
Managing the physical interface | Initialize the software Provision HDLC interfaces Start and stop HDLC interfaces Modify provisioned HDLC interfaces Perform status and statistics queries
HDLC transmit and receive operations | Send LAPD frames to HDLC channels Receive LAPD frames from HDLC channels

Note: The NMS DLCP software is designed to work with the Aztek's Access303 or Exchange303 stack, but can also be integrated with third party GR303 stack software.