Operating instructions

User Interfaces DVB3030/DVB3030L Digital Video Broadcast Modulator
4-28 TM052 - Rev. 3.5
When Radyne 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 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 might 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.
4.3.8 RLLP Summary
The RLLP is a simple send-and-wait protocol that automatically re-transmits a packet
whenever 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>.
If an acknowledgment (response) packet or a NAK 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 <FSN>. 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 <FSN> to the same receiver and
waits once again for an acknowledgment or a NAK packet.
To reiterate, the format of the message block is shown in Table 4, Link Level Protocol
Message Block.
Table 4. Link Level Protocol Message Block
SYNC COUNT SRC
ADDR
DEST
ADDR
FSN OP
CODE
DATA
BYTES
CHECKSUM