Microhard Systems MHX-900, Руководство по эксплуатации

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12 MHX-900 Operating Manual: Chapter 3 Configuration Options
Each unit must be either a
Master or Slave.
Only one Master can exist
for each network.
S Register 101 - Operating Mode
The Operating Mode (register S101) partly defines the “personality” of the
MHX-900 module. Allowable settings for this register are 1 through 4.
Default is 2 (Slave point to point).
Each unit should be configured as a Master or Slave. The user should
decide, prior to deployment, whether a point-to-point or point-to-multipoint
network is appropriate for the application, and how each unit will be
assigned to terminals.
1)Master - Point to Point
One unit in a point-to-point link
should be set as the Master, obligating the other modem to be used as a
Slave. During operation, it makes little difference which end is which,
especially if data is generally transmitted unidirectionally at any given
moment. When both terminals have data to send, more bandwidth is
dynamically allocated to the Master; otherwise, the transmitting end,
whichever it is at the time, is given the full bandwidth.
* 2)Slave - Point to Point
The terminal in a point-to-point
network which is not set as the Master, is obligated to be the Slave. The
Slave will communicate with the Master, whose network address, unit
address, hopping pattern and hopping interval matches its own.
In point-to-point operation, the Slave modem acknowledges all packets of
data sent by the Master, and vice versa. These acknowledgements, along
with CRC error checking ensure that data is passed through exactly once,
and that the data is not corrupted.
3)Master - Point to Multipoint
In a point-to-multipoint
network, one unit should be set as the Master, obligating all other modems
to be Slaves. The Master designation is generally given to the station which
functions as a hub for all remote nodes, and it is the Master station’s
responsibility to control communications with Slaves.
Point-to-multipoint operation differs from point-to-point operation in many
ways. One key difference is that the Slaves cannot acknowledge packets of
data sent by the Master. Clearly this would cause conflicts when there are
multiple Slaves. The Master does, however, send acknowledgements to all
messages it receives from Slaves. The Master initiates communications by
sending a broadcast message to all Slaves. All Slaves are free to respond in
a “Slotted ALOHA” fashion, meaning that each Slave can choose one of
several windows in which to transmit. If there happens to be two Slaves
attempting to talk at the same time, then the Master would not receive the
data, and the Slaves therefore would not get an acknowledgement. At this
point, the Slaves would attempt to get the information through at random
time intervals, thus attempting to avoid any more conflicts. Special
parameters related to Point-to-Multipoint operation are set in the Packet
Parameters menu, and are described in a later section.
4) Slave - Point to Multipoint
Several Slaves exist in a
point-to-multipoint network, all of which communicate with the common
Master. Slaves cannot directly communicate with other Slaves.