Nortel DMS-100 Series Maintenance Manual page 114

2-6 SMS hardware
An RCS in Mode I has up to four primary DS-1 links to the SMS, plus an
optional protection link. This configuration allows a maximum of four
Mode I remotes, including protection links, to hang off the SMS.
Note: If no protection links are configured, up to five RCS modules in
Mode I may be configured. If fewer than the maximum four primary links
are configured, the SMS may support up to six RCS Mode I modules.
An RCS in Mode II or Mode III has up to two primary DS-1 links to the
SMS, plus an optional protection link. Therefore, the SMS supports a
maximum of six RCS modules in these modes.
Each shelf group in an RCS module can operate independently in one of the
three modes. This mixed mode of operation allows the operating company
to plan for the gradual growth of the SMS-RCS subsystem as dictated by
traffic requirements. For instance, an RCS shelf group operating in Mode I
can be converted to Mode II operation. This configuration frees up a DS-1
link, which can then be used to provide protection switching for the RCS
module. Refer to the Translation Guide for mode conversion procedures.
The derived data link (DDL)
The DDL, as its name implies, is not an actual physical link but is derived
from 24 consecutive supervisory bits to form a special data path with a
transmission rate of 2.2 kilobits/second. This derived data link is present on
the RCS A-link (that is, the DS-1 link terminating at shelf A). If the RCS is
in Mode II, the DDL is present on the C-link.
The DDL is used to send and receive information between the SMS and the
RCS, including control of subscriber assignment and deassignment to
specific DS-1 channels, hook transitions, and activation of the pulse code
modulation (PCM) looping test.
Protection links
Protection switching is a DMS-100 backup feature that ensures continued
communication between an SMS and an RCS if a DS-1 link connecting the
two fails.
A protection link occupies one DS-1 P-side port of an SMS and connects a
single RCS. Each RCS has from one to four primary lines, depending on the
modes of its shelf groups, and at most, one protection line. Each protection
line serves only the RCS to which it connects. A typical protection line
configuration is shown in the following figure.
297-8231-550 Standard 09.01 August 1998