RAD Data comm HCD-E1 - Manual (Page 41)

HCD-E1 Installation & Operation Manual Chapter 1 - Introduction
01/01/01 08:07 Functional Description 1-23
HDSL-Related System Functions
The HDSL subsystem performs the following main functions:
•
Mapping of input data bits into HDSL frames, for transmission on the
HDSL lines
•
Start-up process
•
Frame alignment
•
Loop identification and correction
•
System management by means of the eoc channel
•
Collection of performance data.
To achieve proper operation, the management of the HDSL subsystem is
performed under the control of the central unit (LTU) unit, which provides
the timing reference for HDSL line transmission, and manages the
communication on the eoc channel with the remote unit (the NTU) located
on the customer's side.
The transmission of data on each HDSL line is full duplex. To enable duplex
transmission over one pair, the HDSL transceivers use an echo canceler,
based on advanced digital signal processing (DSP) techniques. When starting
system operation, the echo canceler is “trained”, to enable the separation of
the received signal from the transmit signal (near-end crosstalk - NEXT). 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.
Interaction between E1 Port and HDSL Lines
In case the E1 sublink interface loses synchronization, a loss of input data
indication signal is sent via the HDSL lines.
In case an HDSL line interface loses synchronization, idle code is inserted in
the E1 data stream time slots, which have been assigned to this line.