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XStream-PKG-R™ RS-232/485 RF Modem – Product Manual v5.x00

5.3.2. Multi-Streaming Mode

Characteristics: Enables exclusive connections (refer to Theory of Operation section for

definition)

Supports the passing of large data streams (> 256 bytes) from multiple

remote modems to a base modem (If a complete data stream from a remote

modem is less than 256 bytes, data can be sent from several remotes to a

base location without enabling this mode and latencies will be much less.)

Transmissions never acknowledged (ACK) by receiving modem(s)

Required Parameter Values (TX Modem): MD = 1 (Base), MD = 2 (Remote), RN > 0, RR > 0,

MY ≠ 0xFFFF

Recommended Use: Use this mode in point-to-multipoint networks where remote modems

initiate communications and require exclusive (uninterrupted) connections to the base modem.

Table 5.5. Sample Network Profile

Modem

Parameter Settings (assume default values for parameters not listed)

Base

ATMD 1 (configure modem as Multi-Stream Base) *

Remotes

ATMD 2 (configure modem as Multi-Stream Remote) *

* When Multi-Streaming is enabled, the following parameters are consequently modified (if they have not

already been modified from their default states): RR, RN, MY, CD, AT and BT. (refer to Table 5.6)

Theory of Operation

When in Multi-Streaming Mode, all remote modems can initiate communications with the base

modem at the same time, but only one remote is granted an exclusive connection. After an

exclusive connection begins, data is transferred exclusively between two modems without

interruption from any other modems in the network.

An exclusive connection is a bi-directional connection that can only be established when in Multi-

Streaming Mode. An exclusive connection is immune to other remote modems interrupting the

connection and interleaving data (The interleaved data potentially renders the base modem

unable to discern from which remote modem the data was transmitted).

When an exclusive connection is granted to a single remote, the other remotes are notified that

the connection exists. The notification causes the remote modems to postpone transmissions

until the base modem sends notification that the exclusive connection has ended.

Figure 5.7. Sample Connection Sequence Diagram

In the connection sequence above, an exclusive connection is first granted to “Remote m”. The

CGP (Connection Grant Packet) is broadcast to all remote modems in the network to

communicate the base in engaged in an exclusive connection. Upon receipt of the CGP

notification, remote modems will wait for a DGP (Disconnect Grant Packet) before attempting

again to send data to the base modem.

CRP = Connection Request Packet

CGP = Connection Grant Packet

DRP = Disconnect Request Packet (not

shown in diagram – applicable when

remote connection is disconnected using

the pin sleep I/O line.

DGP = Disconnect Grant Packet

ACK = Acknowledgement of reception.

Base modem = The central

transmitting/receiving modem in a network

of modems that maintains communications

with remote modems.

Remote modem = A modem in a network

that sends data to and receives data from a

base modem.

Payload = Data contained inside the RF

Data of the RF Packet that originates from a

host to be transmitted over-the-air.