9XTend™
OEM
RF
Module
–
Product
Manual
v1.2.4
©
2005
MaxStream,
Inc.
Confidential
&
Proprietary
39
4.3.
Acknowledged Mode
Attributes:
Reliable delivery through positive acknowledgements for each packet
Throughput, latency and jitter vary depending on the quality of the channel and
the strength of the signal.
Required Parameter Values (TX Module):
RR (Retries) >= 1
Related Commands:
Networking (DT, MK, RR), Serial Interfacing (PK, RN, RO, RB, TT)
Recommended Use:
Use for applications that require Reliable Delivery. If messages are smaller
than 256 bytes, use RB and RO commands to align RF packets to application packets.
4.3.1.
Acknowledged Mode Connection Sequence
Figure
4.4.
Acknowledged
Mode
State
Diagram
P
t
f
After sending a packet while in
acknowledged mode, the
transmitting module listens for
an acknowledgement. If it
receives the ACK, it will either
move on to sending a
subsequent packet (if more
transmit data is pending), or will
wait for exactly RN random d
slots before allowing anothe
transmission (if no more data is
pending to be transmit
If the transmit
elay
r
ted).
ting module does
lot.
t
of
s.
not receive the ACK within the
allotted time, it will retransmit
the packet with a new RF
initializer following the ACK s
There is no delay between the
first ACK slot and the first
retransmission. Subsequen
retransmissions incur a delay
a random number of delay slots,
between 0 and RN. If RN is set
to 0 on the transmitting module,
there are never any back-off
delays between retransmission
Note that during back-off delays,
the transmitting module will go into Idle Mode and may receive RF data. This can have the effect
of increasing the back-off delay, as the radio cannot return to RF transmit (or retransmit) mode
as long as it is receiving RF data.
After receiving and acknowledging a packet, the receiving module will move to the next
frequency and listen for either a retransmission or new data, for a specific period of time. Even if
the transmitting module has indicated that it has no more pending transmit data, it may have not
received the previous ACK, and so may retransmit the packet, possibly with no delay after the
ACK slot. In this case, the receiving module will always detect the immediate retransmission,
which will hold off the communications channel and thereby reduce collisions. Receiving modules
acknowledge each retransmission they receive, but they only pass the first copy of a packet they
receive out the UART.
Events through the “Transmit
acket” process are common to all
RF communication options. Refer to
he Transmit Mode section [p11]
or more information.
