XStream
‐
PKG
‐
T™
Telephone
RF
Modem
–
Product
Manual
v5.x00
[2006.02.24]
4.2.
Basic Communications
Basic Communications are accomplished through two sub-types:
•
Broadcast - By default, XStream Modems communicate through Broadcast communications
and within a peer-to-peer network topology. When any modem transmits, all other modems
within range will receive the data and pass it directly to their host device.
•
Addressed - If addressing parameters match, received RF data is forwarded to the DO (Data
Out) buffer; otherwise, the RF data is discarded.
When using Basic Communications, any functions such as acknowledgements are handled at the
application layer by the OEM/integrator. The Broadcast Modes provide transparent
communications, meaning that the RF link simply replaces a wired link.
4.2.1.
Streaming Mode (Default)
Characteristics
: Highest
data
throughput
Lowest latency and jitter
Reduced immunity to interference
Transmissions never acknowledged (ACK) by receiving modem(s)
Required Parameter Values (TX Modem)
: RR (Retries) = 0
Related Commands
: Networking (DT, MK, MY), Serial Interfacing (PK, RB, RO, TT)
Recommended Use
: Mode is most appropriate for data systems more sensitive to latency
and/or jitter than to occasional packet loss. For example: streaming audio or video.
Streaming Mode Data Flow
Figure
4
‐
04.
Streaming
Mode
State
Diagram
(TX
Modem)
Events and processes in this mode are common to all of the other RF
Communication Modes.
NOTE: When streaming data, RB and RO parameters are only observed on
the first packet.
After transmission begins, the TX event will continue uninterrupted until
the DI buffer is empty or the streaming limit (TT Command) is reached.
As with the first packet, the payload of each subsequent packet includes
up to the maximum packet size (PK Command).
The streaming limit (TT Command) is specified by the transmitting
modem as the maximum number of bytes the transmitting modem can
send in one transmission event. After the TT parameter threshold is
reached, the transmitting modem will force a random delay of 1 to RN
delay slots (exactly 1 delay slot if RN = 0).
Subsequent packets are sent without an RF initializer since receiving
modems stay synchronized with the transmitting modem for the
duration of the transmission event (from preceding packet information).
However, due to interference, some receiving modems may lose data
(and synchronization to the transmitting modem), particularly during
long transmission events.
Once the transmitting modem has sent all pending data or has reached
the TT limit, the transmission event ends. The transmitting modem will
not transmit again for exactly RN delay slots if the local (i.e.
transmitting modem’s) RN parameter is set to a non-zero value. The
receiving modem(s) will not transmit for a random number of delay
slots between 0 and (RN-1) if the local (i.e. receiving modem’s) RN
parameter is set to a non-zero value. These delays are intended to lessen congestion following
long bursts of packets from a single transmitting modem, during which several receiving modems
may have become ready to transmit.
©
2006
MaxStream,
Inc.,
Confidential
and
Proprietary
28
