Modem Remote Communications; Host Computer Remote Communications - Radyne DMD15 Installation And Operation Manual

User Interfaces

4.9 Modem Remote Communications

4.9.1 Host Computer Remote Communications

NOTE: This specification is applicable to the DMD15, DMD10 and DMD10L Modems. Any
reference to the DMD15 in this document can be applicable to any one of these three
modems.
Control and status messages are conveyed between the DMD15 and the subsidiary modems and
the host computer using packetized message blocks in accordance with a proprietary
communications specification. This communication is handled by the Radyne Link Level Protocol
(RLLP), which serves as a protocol 'wrapper' for the RM&C data. Complete information on
monitor and control software is contained in the following sections.
4.9.1.1 Protocol Structure
The Communications Specification (COMMSPEC) defines the interaction of computer resident
Monitor and Control Software used in satellite earth station equipment such as modems,
redundancy switches, multiplexers, and other ancillary support gear. Communication is bi-
directional, and is normally established on one or more full-duplex 9600-baud multi-drop control
buses that conform to EIA Standard RS-485.
Each piece of earth station equipment on a control bus has a unique physical address, which is
assigned during station setup/configuration or prior to shipment. Valid decimal addresses on one
control bus range from 032 through 255 for a total of up to 224 devices per bus. Address 255 of
each control bus is usually reserved for the M&C computer.
4.9.1.2 Protocol Wrapper
The Radyne COMMSPEC is byte-oriented, with the Least Significant Bit (LSB) issued first. Each
data byte is conveyed as mark/space information with two marks comprising the stop data. When
the last byte of data is transmitted, a hold comprises one steady mark (the last stop bit). To begin
or resume data transfer, a space (00h) substitutes this mark. This handling scheme is controlled
by the hardware and is transparent to the user. A pictorial representation of the data and its
surrounding overhead may be shown as follows:
S1 S2 B
The Stop Bits, S1 and S2, are each a mark. Data flow remains in a hold mode until S2 is replaced
by a space. If S2 is followed by a space, it is considered a start bit for the data byte and not part of
the actual data ( - B 7).
B0
The COMMSPEC developed for use with the Radyne Link Level Protocol (RLLP) organizes the
actual monitor and control data within a shell, or 'protocol wrapper', that surrounds the data. The
format and structure of the COMMSPEC message exchanges are described herein. Decimal
numbers have no suffix; hexadecimal numbers end with a lower case 'h' suffix and binary values
have a lower case 'b' suffix. Thus, 22 = 16h = 000010110b. The principal elements of a data
frame, in order of occurrence, are summarized as follows:
<SYNC>:
<BYTE COUNT>:
4-44
B B B B
0 1 2 3
The message format header character, or ASCII sync
character, that defines the beginning of a message. The
<SYNC> character value is always 16h.
The Byte Count is the number of bytes in the <DATA>
field, ranging from 0 through 255 for the DMD5000
protocol (1 Byte), or ranging from 0 through 509 for the
DMD15 protocol (2 Bytes).
DMD15/DMD15L IBS/IDR Satellite Modem
B B B S1
4 5 6 7
S2, etc.
TM051 – Rev. 5.8