Comtech EF Data SFC1800A - Manual (Page 50)

User Interfaces SFC1800A Synthesized Frequency Upconverter
4-26 TM111 - Rev. 1.0
If new device-resident or M&C software receives a message related to an old software
version, new information and processes are not damaged or affected by the omission of data.
The implementation of forward and backward software compatibility often, but not always,
requires the addition of new Opcodes. Each new function requires a new Opcode assignment if
forward and backward compatibility cannot be attained by other means.
When Radyne equipment is queried for bulk 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 the size of the Non-Volatile Section. This count is used by M&C developers to index
into the start of the Volatile Section.
When new features are added to Radyne 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 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 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
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.
4.4.2.7 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 character
and the fields. If this checksum matches the packet , the receiver
processes the packet and responds to the packet sender with a valid response (acknowledgment)
packet.
The response packet is therefore either an acknowledgment that the message was received
correctly. If the sender receives a valid acknowledgment (response) packet from the receiver, the
increments and the next packet is transmitted as required by the sender.
If an acknowledgment (response) packet is lost, corrupted, or not issued due to an error and is
thereby not returned to the sender, the sender re-transmits the original information packet; but
with the same . When the intended receiver detects a duplicate packet, the packet is
acknowledged with a response packet and internally discarded to preclude undesired repetitive
executions. If the M&C computer sends a command packet and the corresponding response
packet is lost due to a system or internal error, the computer times out and re-transmits the same
command packet with the same to the same receiver and waits once again for an
acknowledgment.
Refer to Appendix A for Remote RLLP.