Comtech EF Data DM240XR - Manual (Page 60)

DM240XR High-Speed Digital Modulator User Interfaces
MN-DM240XR– Revision 13 4–38
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.
4.4.7 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.
4.4.8 DM240XR Opcode Command Set
Refer to Section 9 for Modem Remote Communications.