Issue
Does the ENC maximum number of LON bindings recommendation also apply to the JACE-6, JACE-6E, and JACE-7 platforms as well? The recommendation is not to exceed a total of 1200 bindings on the FTT-10 bus.
Environment
I/A Series G3, ENC and JACE controllers
Cause
LonWorks FTT-10 bus operation
Resolution
The number of bindings on an FTT-10 bus does not change regardless of the platform (e.g. ENC vs. JACE-6/7). The number of LON devices and overall number of bindings is somewhat arbitrary as the actual number is related to bandwidth limitations of the 78K FTT-10 bus. The 1200 binding number is a general rule of thumb. This is the statement from an R2 engineering note that summarizes the basic issue.
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A JACE controller provides a LonWorks FTT-10 port. Electrically, an FTT-10 segment supports up to 63 total nodes (addressable devices). Using repeater(s), a single LonWorks subnet can span multiple segments and have a total of 127 nodes. However, in almost all cases, it is unrealistic to think that a JACE controller can “fully support” anywhere near 126 devices, because of bandwidth limitations. The 78K baud FTT-10 bus can easily become “saturated” with too many messages (as a result of bindings).
Generally, most LON installations reach network saturation at around 1200 bindings (with average messaging). This can easily occur with far fewer than 126 devices. If connections are set to “poll-only," then the network could be sized to agree with the resource count limit of the JACE. However, this configuration puts the JACE in the same category as most other LON interfaces, which poll for values (making for slow updates).
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In summary, the actual number of bindings directly correlates to bandwidth, tuning, and acceptable data update rates. An FTT-10 network can exhibit high bandwidth with less bindings or can be successfully operated at a higher number of bindings. A good rule of thumb is that the average sustained bandwidth on the bus (as measured with a Lon Protocol Analyzer) should not exceed 25 to 28%. This allows for message bursts to be successfully processed when needed. In addition, care must be used when targeting a particular LON node with messages as the Neuron or host processor may not be able to process incoming messages causing lost and missed messages. This includes the ENC or JACE which is why tuning of the individual LON devices is very important.
One alternative is to install two FTT-10 LON cards in the JACE-6E or JACE-7 and run two trunks. The LON network interfaces are configured as LON1 and LON2. Purchase two cards and one driver. Remember to not overload the JACE (e.g. maintain good CPU and memory usage) which is good practice regardless of the communication interface.
