RAD Data comm ASMI-450 operation manual HDSL Signal Structure HDSL-Related System Functions

Introduction

HDSL Signal

Structure

HDSL-Related System Functions

By reducing the line symbol rate, the maximum range that can be reached is increased. This is achieved by offering several versions of ASMi-450, each operating up to a given maximum rate. Together with the advanced digital signal processing techniques implemented in HDSL systems, this results in a robust data transmission system that can reliably operate over regular unconditioned local loops.

The HDSL signal is organized in frames. The HDSL frames carry user data, framing and synchronization data, and overhead data. The overhead data is used for a supervision and management channel, called embedded operations channel (EOC) that serves for status transfer, diagnostic loopbacks and tests, etc.

The HDSL subsystem performs the following main functions:

∙Mapping of input data bits into frames.

∙Start-up process.

∙Frame alignment.

∙System management by means of the EOC channel.

To achieve proper operation, one of the unit<F14P11>s serves as the master that controls the system start-up procedure, provides the timing reference for HDSL loop transmission, and manages the communication on the EOC channel. The master unit is called line termination unit (LTU) and is located at the central office side of the link; the other unit is called network termination unit (NTU) and is located at the remote end of the link.

The transmission of data on the HDSL loop is full duplex. To enable duplex transmission, HDSL transceivers use an echo canceller, based on advanced digital signal processing (DSP) techniques. When starting system operation, the echo canceller is “trained”, to enable the separation of the received signal from the transmit signal. The training is performed by transmitting a special sequence for a predetermined period. This process is called “start-up process”; data transmission can start only after its successful completion.

ASMi-450 Installation and Operation Manual 1-9