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Line Interface Modules
Network Line Interface Modules
There are three models of the Network LIM: T1, E1 and CSU T1. Each model, described below,
employs the use of a line interface plug-in to provide the necessary interface. The Network LIM is
based on the legacy T1, CSU T1, and E1 LIMs (using the same line interface plug-ins), with the
addition of signaling support and the Drop & Insert feature.
•
Signaling support allows the Network LIM to pass signaling information between the line and
the OCM bus for transport to other network compatible cards.
•
Drop and Insert (D&I) is an OCM feature which is available with the Network LIM. D&I
provides the means for a network circuit to bypass from LIM to LIM or drop/insert from LIM
to channel. Drop and Insert is an incremental feature of the OCM and does not reduce any other
features of the OCM. Use of D&I allows the LIM T/S information to be passed from one
Network LIM to another Network LIM. Timeslot information is in two parts, data and
associated signaling.
Table 4-1
and
Table 4-3
lists the pinouts for all Network LIMs.
Signaling
Channel Signaling uses bits associated with the voice circuits to convey call setup and tear-down
information between customer equipment. On-hook, off-hook and ring are examples of signaling
functions. In order to maintain compatibility in both Domestic and International public networks
two basic types of channel associated signaling are supported: Robbed-bit (RBS) and Channel
Associated Signaling (CAS). RBS embeds the signaling bits within the circuit in every sixth frame.
It is used for voice transmissions only. Signaling is disabled for data circuits. CAS uses DS0 16 to
convey the signaling bits.
The Network LIM or other network card uses the signaling bus in addition to the data bus to pass
data and signaling within the OCM. The LIM extracts the associated signaling (ABCD) bits for each
DS0 from the incoming RBS or CAS link and puts them on the signaling bus at the same time it
writes the data bits for that DS0. The LIM also reads the signaling bits from the signaling bus and
integrates them back into the data stream as either RBS or CAS, depending on the type of equipment
configured.
Note
The Network LIM does not perform any conversion of signals.
Signaling transportation (not conversion) from CAS (E1) to T1 (T1) Robbed-bit is supported for
VTP Voice Transcoder Platform) applications only. It is not useful for D&I since the LIM card
hardware does not perform u-law to A-law conversion.
For D&I applications, associated signaling information (ABCD bits) is passed transparently, with
the exception of failure conditioning or diagnostics where signaling bits are forced or conditioned.
For VTP applications the VTP shall provide the necessary signaling bits in the correct format for
the LIM. All signaling protocols and algorithms are performed on the VTP or DPV (Dual Private
Voice) card as necessary. The Network LIM itself is transparent to signaling as in the D&I
application.
Note
The Network LIMs condition channel data/signaling under certain alarm conditions.
4-2
Table 4-2
list the technical specifications for each Network LIM.
Office Connunications Manager OCM-1000/OCM-2000
Installation & Operation
Network Line Interface Modules
036R340-000
Issue 16
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