Esa Operation - Nortel DMS-100 Series Maintenance Manual

3-12 PRLCM overview

ESA operation

The PRLCM enters ESA mode when the PRLCM determines that it can no
longer communicate with the host site. The two situations that cause entry into
ESA mode at the PRLCM are as follows:
•
•
When the PRLCM enters ESA mode, all active calls are taken down. This is
called a cold enter.
The ILCM detects the loss of communication with the host. When the ILCM
determines the ESA mode is required, the ILCM switches the C-side links
from the host to the ESA processor. The ESA processor detects the switching
of links through the clock and tone card.
When the ESA processor detects the switching of links, ESA-enter is initiated.
The time between loss of communication and ESA mode depends on the type
of failure situation.
The ESA processor has a nailed-up (direct) communication link with the DMS
CC at all times. The ESA processor is the only processor at the PRLCM that
can communicate with the DMS CC during ESA exit. The DMS CC must
instruct the ESA processor to exit ESA.
During ESA mode, call processing is done through the ESA processor. The
ESA processor contains a module of software, called the ESA CC, that
emulates the DMS CC and handles line-to-line call processing. The ESA CC
contains a subset of the translation data found in the DMS CC.
This subset is a snapshot of the DMS CC data needed for ESA call processing.
The translation data in the snapshot data are known as static data. PRLCM
ESA mode is not entered until the ESA processor is loaded with static data.
The download of the static data to the ESA CC from the DMS CC truncates
some translation data; thus static data are not true subsets of the DMS CC and
only basic calls are supported. During PRLCM ESA mode, plain old
telephone service (POTS) and Meridian Digital Centrex (MDC) subscriber
lines are supported.
297-8361-550 Standard 04.01 September 2000
unusable communication links
looparound message audit failure