Unit installation

Installation and Operation Manual Chapter 1 Introduction
FCD-E1 Functional Description 1-13
The operating mode of the LIU receive path, DSU or LTU, is user-selectable.
The HDB3 decoder can provide performance statistics for evaluating line
transmission quality when the CRC-4 option is not used, by collecting data on the
bipolar violations (BPVs) detected in the incoming signal.
Bypass Relays
The bypass relays are normally energized, and connect the external E1 port lines to
the LIU.
When FCD-E1 is not operating, the relays are deenergized, and take the position
shown in Figure 1-3. In this case, for an FCD-E1 with a sublink, the transmit line of
the main link is connected through the optional bypass bridge to the receive path
of the sublink, and vice versa.
• The bypass relays are available only on electrical main link interface boards.
• The bypass bridge is a narrow printed circuit board installed between the main
link and sublink interface boards that plugs into special connectors located in the
center of each board. The bypass bridge is an option available upon order.
• The bypass bridge interconnects only the balanced interfaces.
The use of the bypass bridge is recommended when the FCD-E1 main and sublink
carry inband management traffic destined to additional equipment within the
network. This arrangement enables the management traffic to pass to the other
equipment, irrespective of the state of the FCD-E1. Note however that the bypass
option is useful only when the total attenuation of the lines connected in series
does not exceed the maximum attenuation that can be compensated for by the
other equipment.
Sublink Interface
The sublink interface is similar to the electrical main link interface, except that the
direction of flow of signals is different where the sublink receive data is applied on
the TSER line, and the sublink transmit data is collected from the RSER line.
The sublink interface is an option, installed in accordance with order.
Data Channels
The data channels operate as a synchronous port, which connects to the TDM bus
via a bus interface. The data channels perform two main functions:
• In the output (receive) direction, the bus interface reads the payload data from
the appropriate timeslots of the TSER line, under the control of the
management subsystem, and generates a continuous n×56 kbps or n×64 kbps
data stream. The data stream is accompanied by a clock signal derived from
the internal FCD-E1 system clock.
The transmit data and clock signals are then applied to the channel interface,
which provides the interface to the external (user’s) equipment. The interface
can be ordered from one of the following options: RS-530, V.35, X.21, and
V.36/RS-449.
Notes