Nortel DMS-100 Series Maintenance Manual page 89

DMS-X protocol
The DMS-X protocol is a state-driven code. The DMS-X protocol requires
handshake messaging between the RLCM EDC and host LTC+ at each stage
of data transfer. This handshake messaging allows the terminals that
communicate to delay the message transfer if one terminal is not ready.
The following figure illustrates a general form of handshaking protocol.
This protocol is part of DMS-X protocol.
DMS-X handshaking protocol
Message header:
DMS-X
Message data
Checksum or cyclic
redundancy check
DMS-X protocol includes a cyclic redundancy check (CRC) code for error
detection. Message time-out and message checksum or CRC calculation
perform message error detection.
If protocol, checksum, or CRC failure occurs on an outgoing message, the
sending node attempts the send sequence again. On an incoming message
failure, the sending node reroutes the message over an alternate central-side
(C-side) link. Hardware redundancies provide a minimum of one alternative
path to and from a node.
The following figure describes the format of DMS-X messages.
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DMS-100 Family Maintenance Manual ABSK007
Signaling for RLCM-EDC 2-5
Link control messages
(request to send, send)
Message
Link control messages
(acknowledgment)