Comtech EF Data DD240XR Rev Е - Manual (Page 53)

DD240XR High-Speed Digital Demodulator User Interfaces
MN-DD240XR – Rev. E 4-33
CDS-780 Clock Distribution System 06
SOM-340 Second Order Multiplexer 07
DMD-4500/5000 Modulator Section 08
DMD-4500/5000 Demodulator Section 09
RCU-5000 M:N Switch 10
DMD15 Modulator 20
DMD15 Demodulator 21
DMD15 Modem 22
DVB3030 Video Modulator, DD240 23
Reserved for future equipment types 24-31
When Radyne Corporation equipment is queried for information (Query Mod, Query Demod, etc.)
it responds by sending back two blocks of data; a non-volatile section (parameters that can be
modified by the user) and a volatile section (status information). It also returns a count value that
indicates how large the non-volatile section is. This count is used by M&C developers to index into
the start of the volatile section.
When new features are added to Radyne Corporation equipment, the control parameters are
appended to the end of the non-volatile section, and status of the features, if any, are added at the
end of the volatile section. If a remote M&C queries two pieces of Radyne Corporation equipment
with different revision software, they may respond with two different sized packets. The remote
M&C MUST make use of the non-volatile count value to index to the start of the volatile section. If
the remote M&C is not aware of the newly added features to the Radyne Corporation product, it
should disregard the parameters at the end of the non-volatile section and index to the start of the
volatile section.
If packets are handled in this fashion, there will also be backward-compatibility between Radyne
Corporation equipment and M&C systems. Remote M&C systems need not be modified every
time a feature is added unless the user needs access to that feature.
4.3.7 RLLP Summary
The RLLP is a simple send-and-wait protocol that automatically re-transmits a packet
when an error is detected, or when an acknowledgment (response) packet is absent.
During transmission, the protocol wrapper surrounds the actual data to form information packets.
Each transmitted packet is subject to ‘time out’ and ‘frame sequence’ control parameters, after
which the packet sender waits for the receiver to convey its response. Once a receiver verifies
that a packet sent to it is in the correct sequence relative to the previously received packet, it
computes a local checksum on all information within the packet excluding the <SYN> character
and the <CHECKSUM> fields. If this checksum matches the packet <CHECKSUM>, the receiver
processes the packet and responds to the packet sender with a valid response (acknowledgment)
packet. If the checksum values do not match, the receiver replies with a negative
acknowledgment (NAK) in its response frame.
The response packet is therefore either an acknowledgment that the message was received
correctly, or some form of a packetized NAK frame. If the sender receives a valid
acknowledgment (response) packet from the receiver, the <FSN> increments and the next packet
is transmitted as required by the sender. However, if a NAK response packet is returned the
sender re-transmits the original information packet with the same embedded <FSN>.