CTI Products NCB/EM with External PSTN Modem - Manual (Page 59)

CTI Products, Inc. NCB-EM User Guide
Appendix H. Ring Mode 53
A PPENDIX H. R ING M ODE
The NCB-International module can be configured to allow a group of NCBs to be connected in a ring topology
via their RS232 serial ports as shown in Figure 11 (note that the external modems are not shown but are
implied):
Figure 11 NCB Modules Connected in Ring Mode
Up to 64 NCB modules can be connected together in such a ring. Connection order is not significant (“PORT
1” of one unit can be connected to either “PORT 1” or “PORT 2” of the other unit). Using this topology, any
LonTalk message entering one NCB unit is distributed to all of the other NCB units in a redundant manner such
that the communication system will remain functional even if the ring is broken in any ONE place. The status
of the ring (open or closed) is available by request from the control neuron of any of the NCB members.
Note: If a set of NCB-International modules are connected as shown in the figure above with
all of the NCB units configured for NON-RING mode, a single LonTalk message entering any
one of the NCB units will "loop forever" in the ring, causing saturation of the communication
system. THEREFORE, ALWAYS BE CERTAIN TO CONFIGURE AT LEAST ONE OF THE
NCBs TO ENABLE RING MODE (as explained below) BEFORE COMPLETING THE RING
AS SHOWN ABOVE. For Ring Mode to function properly, ALL NCB modules in the ring
must be configured with Ring Mode Enabled. Additionally, messages placed on the ring by
NCB modules configured in non-ring mode will be ignored and dropped from the ring by
NCB modules configured in ring mode, and vice-versa.
For operation in ring mode, all NCB modules in the ring must be configured to enable ring mode.
Each NCB module in the ring must be assigned a unique Unit Number from 1 to 64. An NCB can be set to Unit
Number 0 in order to connect it into the ring as a "non-participatory" unit. This can be used to determine what
other unit numbers already exist in the ring in order to choose one that will not conflict with any others. This
"non-participatory" unit can be changed to an active unit by then changing its unit number to some non-zero
value that is not already in the ring.
Additionally, the maximum expected ring propagation delay and desired test interval parameters must be
specified. The ring propagation delay is used to set timeout values for ring maintenance packets and must have
a value between 1000 and 7500ms. The test interval sets the frequency of ring maintenance packets that
determine ring status, duplicate unit number faults, and sequence number resynchronization. The test interval
must have a value between 10000 and 65000ms.
The NCB/Plug plug-in can be used to set Ring Mode parameters.
The NCBCON.EXE DOS utility can be used to set Ring Mode parameters and also to query the ring status. See
Technical Note TN023, “Using NCBCON to Configure an NCB”.
NCB A
PORT 1 PORT 2
NCB B
PORT 1 PORT 2
NCB C
PORT 1 PORT 2