Some manual documentation on the DMS-100 Message System.
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NTP
NTP 297-1001-100 PAGE 12
PREL., ISSUE 01D03
79 09 21
4. MESSAGE SYSTEM
PURPOSE
4.01 The Message System (MS) provides the media and protocol for
the transmission of inter-module control messages.
TRANSMISSION MEDIA
4.02 The MS consists of hardware units, within each module,
which are inter-connected via the message channels in the message
and speech links.These units, at the terminating points of the
message channels between the modules, have the capability of
accepting and/or originating messages, and thus control the flow
of messages throughout the MS.
MESSAGE PROTOCOL
4.03 Control messages contain a fixed-length header section,
followed by a data section of variable length, depending on the
complexity of the message. Message transmission uses "handshake"
protocol (two-way sequences). No message sequence is sent without
receiving an acknowledgement from the receiver that it is ready to
receive, and no sequence is completed without another
acknowledgement after transmission that the reception was
error-free.
OPERATION
4.04 Via the message system, the CC controls the logic of calls
and directs the action of NM, PM and IOC. The DMS System
structure is based on distributed processing. Microprocessors,
located in the NM, PM, and IOC, relieve the CC of repetitive
real-time consuming functions such as scanning and digit
collection.
4.05 The two CPU are linked to the Central Message Controllers
via the data port bus (which also gives each CPU access to its
private Data Store). CMC connect to NMC and IOC via 2.56 Mb/s
serial data channels on the message links. NMC communicate with
PM via dedicated signalling channels on the speech links at 64
Kb/s per channel.
4.06 The CPU contains firmware which controls the movement of
messages over the data port bus between the CMC and the active
CPU. The CMC scan Network Message Controllers and I/O Controllers
for incoming messages to the CPU and direct outgoing messages from
the CPU to the appropriate controller.
DMS-100 FAMILY SYSTEM DESCRIPTION
(c) NORTHERN TELECOM LIMITED, 1978
NTP 297-1001-100 PAGE 13
PREL., ISSUE 01D03
79 09 21
4.07 Network Message Controllers (NMC) scan the PM for incoming
messages which they pass on to the CMC and receive outgoing
messages from CMC for transfer to the PM. The IOC provide
interfaces between CMC and visual display units, tape units, etc.
4.08 Peripheral Modules have message-handling hardware/firmware
to transfer messages to the NMC and to accept CPU messages from
the NMC.
4.09 All elements of the Message System collection/distribution
system are duplicated. Links also exist so that the failure of a
single unit does not force other units into 'simplex'
(non-duplicated) operation. The path taken by a message is
governed by the CPU master routing algorithm which ensures that
all paths are used. In this way, failures are quickly detected and
the routing modified to bypass the faulty unit or link. Messages
between the CPU and PM normally follow only one path per message.
However, because the duplicate networks operate in step, messages
originating or terminating in one (e.g.: Plane-0) NMC, also
involve the other NMC associated with Plane 1.
DMS-100 FAMILY SYSTEM DESCRIPTION
(c) NORTHERN TELECOM LIMITED, 1978