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Line Interface Modules
E1 Network LIM Interface
The E1 Network LIM provides a high-speed aggregate interface for connection to 2.048 Mbps
digital services. It provides the following features:
•
G.703/G.704/G.706 compatibility
•
2.048 Mbps data rate
•
120 ohm balanced or 75 ohm unbalanced interface, jumper selectable
•
Full or fractional E1 services
•
Clock recovery from the E1 line for use in OCM clocking when configured for slave timing
•
Time slot 16 for data use
•
CRC-4 detection and generation.
•
Local and remote loopback capability
•
Front panel LED indicators for local (red alarm), remote (yellow alarm), in service or not in
service, and self-test passed or failed.
•
Redundant or non-redundant operation.
The E1 LIM is fully compatible with ITU-T recommendation G.703 (Physical/Electrical
Characteristics of Hierarchical Digital Interfaces) at 2.048 Mbps. It is compatible with the frame
structure at 2.048 Mbps specified in ITU-T recommendation G.704 (Synchronous Frame Structure
Used at Primary and Secondary Hierarchical Levels).
The E1 LIM supports the use of CRC-4 (Cyclic Redundancy Check - 4) error monitoring capability.
This feature can be enabled or disabled by means of a switch located on the E1 LIM plug-in card.
If it is enabled, and the E1 service does not support CRC-4, no alarms are generated. The spare bits
in time slot 0 are not used and are set to 1. Frame alignment and CRC-4 procedures are compatible
with ITU-T recommendations G.706 (Frame Alignment and Cyclic Redundancy Check (CRC)
Procedures Relating to Basic Frame Structures Defined in Recommendation G.704).
Time slot 16 may be used to carry payload data (TMS subaggregates) or it may be skipped if the E1
line uses time slot 16 for signaling such as Channel Associated signaling (CAS). This is selected
via a switch located on the E1 LIM plug-in card. If the switch is set to CAS (ON), then 30 time slots
are available to carry TMS payload data. If the switch is OFF, then 31 time slots are available to
carry TMS payload data.
When CAS is selected, time slot 16 of frame 0 contains the multiframe alignment word, with the
three x bits set to 1 (not used). The y bit is set to 0 (no alarms). In all other frames, the abcd signaling
bits are sent. These are set to 0. Signaling information received in time slot 16 is ignored.
Plug-in Options
The E1 plug-in card options are typically set at the factory to match your network operation. Check
these settings when you first install the unit. You need not repeat the procedure unless you change
your network.
1. Examine the option switch on the plug-in interface card.
2. Refer to
Figure 4-2
3. When you are satisfied that the plug-in options are set correctly, install the LIM module in the
shelf as described previously in this section under the paragraph on
4-8
for switch location and option descriptions.
Office Connunications Manager OCM-1000/OCM-2000
Installation & Operation
Network Line Interface Modules
LIM Installation
036R340-000
Issue 16
.
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