Nortel DMS-100 Series Maintenance Manual page 38

1-22 Maintenance overview
Control messaging between the SMS and the RCS
The derived data link (DDL) is the message protocol that transfers messages
from the SMS to the RCS. The DDL transfers messages from the RCS to
the SMS. The DDL is a 2.2 Kbit/s data path. The system robs frame
signaling (Fs) bits to form the DDL.
A Superframe includes 12 193-bit frames. A framing bit precedes each
frame. These framing bits are Ft or Fs bits. In the SMS-RCS subsystem,
two Superframes pass unchanged. The system robs the next four
Superframes of Fs bits. The DDL bits replace the robbed F bits. The DDL
link has 24 bits. The system robs the Fs bits at a card in the RCS, or at the
time switch card in the SMS.
The DDL messaging The 8085 microprocessor of the A/B-DDL message
card sends DDL messages to the time switch. The DS-1 PCM data stream
includes these messages. The 8085 microprocessor extracts the DDL
message from incoming PCM. The DDL facility processes DDL messages.
The DDL facility is software in the SP.
The DL message has 24 consecutive bits. The arrangement of the bits
appears in the following table.
297-8231-550 Standard 09.01 August 1998
The DDL message bits and field names
DDL bits
Bits 1 through 11
Bits 12 through 14
Note: If the M-, A-, or S-fields do not change between messages, the 8085
microprocessor sends the previous field patterns. The RCS, at the other
end, also sends the same patterns. The 8085 microprocessor sends
information to the UP when a DDL field changes. The RCS does not
transmit idle patterns.
Field name
Concentrator field (C-field). When a
C-field is not available to send on
the DDL link, the 8085
microprocessor sends an idle
pattern on the DDL link. The RCS
sends an idle pattern when a new
C-field is not present.
Spoiler bits (fixed pattern of 010).
Spoiler bits are inserted at set
positions in the DDL to make sure
that the DDL never duplicates a
signaling pattern.
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