MaxStream 9XTend-PKG-E Handbuch PDF herunterladen (Seite 47)

9XTend‐PKG‐E™EthernetRFModem–ProductManualv2.x4x[2007.01.04]

©2007MaxStream,Inc.,Confidential&Proprietary‐AllRightsReserved 47

5.2. Basic Communications

Basic Communications are accomplished through two sub-types:

• Broadcast - By default, XTend RF 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 are in order, 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 communica-

tions, meaning that the RF link simply replaces a wired link.

5.2.1. Streaming Mode (Default)

Characteristics:Highest data throughput

Lowest latency and jitter

Reduced immunity to interference

Transmissions never acknowledged (ACK) by receiving module(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.

Connection Sequence

Figure5‐04. StreamingModeStateDiagram(TXModule)

• Events & processes in this mode are common to all of

the other RF Modes.

• When streaming data, RB and RO parameters are only

observed on the first packet.

After transmission begins, the transmission event will con-

tinue uninterrupted until the DI buffer is empty or the

streaming limit (TT parameter) is reached. As with the first

packet, the payload of each subsequent packet includes up

to the maximum packet size (PK parameter).

The TT parameter (streaming limit) is specified by the TX

(transmitting) modem as the maximum number of bytes the

TX module can send in one transmission event. After the TT

parameter threshold is reached, the TX 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

RX (receiving) modems remain synchronized with the TX

modem for the duration of the transmission (from preceding

packet information). However, due to interference, some RX

modems may lose data (and synchronization to the TX

modem), particularly during long transmission events.

Once the TX modem has sent all pending data or has

reached the TT limit, the transmission event ends. The TX

modem will not transmit again for exactly RN delay slots if

the local (i.e. TX modem's) RN parameter is set to a non-

zero value. The RX modem(s) will not transmit for a random

number of delay slots between 0 and (RN-1) if the local (i.e.

receiving module's) RN parameter is set to a non-zero

value. These delays are intended to lessen congestion fol-

lowing long bursts of packets from a single TX modem, dur-

ing which several RX modems may have become ready to transmit.

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