Comtech EF Data DD240XR Rev Е - Manual (Page 48)

User Interfaces DD240XR High-Speed Digital Demodulator
4-28 MN-DD240XR – Rev. E
Ethernet Data Interface will resolve the Destination MAC
using ARP for Unicast IP Addresses and automatic
construction for Multicast IP Addresses.
ETH TEST DATA {ENABLED / DISABLED}
This field allows the operator to test LAN connectivity
and routing without requiring an input IF signal for the
DD240 to demodulate. When enabled, the Ethernet
Data Interface will generate a test MPEG stream at the
programmed data rate. This test stream consists of
MPEG packets with the following contents:
 Sync byte (0x47)
 Second byte that increments once per MPEG
packet
 186 data bytes that are a running counter that
increments each byte across all MPEG packets
The Ethernet Data Interface will lock to this stream as
though it were actual demodulated data and generate the
appropriate UDP, RTP, and FEC packets depending up
the operational mode.
4.3 Host Computer Remote Communications
Control and status messages are conveyed between the DD240 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.
4.3.1 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.
4.3.2 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 one 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: