Connecting KNX and Control 4 with IP Routers - best practice recommendation from Ivory Egg
Historically, KNX and Control 4 systems were linked together with a KNX IP tunnelling connection using a KNX IP interface. The Control 4 driver used for this method is the "KNX Network" driver. In this case, the Control 4 controller running Director is acting as a regular IP device - it communicates with the KNX IP Interface and the C4 controller does not take a KNX Individual Address.
There are various problems related to this method which include:
- historical KNX IP interface/Control 4 compatibility issues;
- occasionally the tunnelling connection will disconnect when idle - potentially causing subsequent loss of telegrams/data;
- it is only possible to connect Control 4 to one KNX twisted pair (TP) line using the C4 KNX Network driver and a KNX IP Interface;
- KNX TP communication is at a very low speed (9,600 bits per second) which is roughly 25-50 telegrams per second.
Taking the last two points above into account, for a KNX installation with more than one TP line there will necessarily be additional traffic passed on to the higher TP lines so that commands and feedback can be transferred between KNX and Control 4. The low communication speed of TP can cause bottlenecks and potential loss of telegrams.
Since Control 4 began marketing their own KNX devices and released the "KNX Routing Gateway" driver, the only recommended connection method is via an IP multicast connection using KNX IP Router(s). In this case, the Control 4 controller running Director is acting as a KNXnet/IP device and takes a KNX individual address.
This gives a much more reliable connection for several reasons:
- multicast is "always-on" and does not periodically drop the IP connection when communication is idle;
- KNXnet/IP communication is several orders of magnitude faster at 10,000,000 or 100,000,000 bits per second - depending on the KNX IP Router and the rest of the IP network;
- using KNX IP Routers, multiple KNX twisted pair lines can simultaneously be linked to Control 4 using the KNX multicast IP address.
Taking the last two points above into account, for a KNX installation with multiple TP lines there are not any "higher" TP lines. Commands and feedback telegrams are transferred between KNX and Control 4 over KNXnet/IP at high speed and are only retransmitted on TP lines where the telegrams are relevant. This eliminates the risk of bottlenecks from additional traffic on higher TP lines.
There are some considerations that must be made with regard to the way that KNX telegrams are filtered across different parts of the topology. Due to project size, many residential projects don’t require the use of couplers however if couplers (TP or IP) are used then the following needs to be configured:
- IP tunnelling with a single line - no issue;
- IP tunnelling with multiple lines including Line Couplers - will require manual filter table entries or use of a Dummy device;
- IP routing with a single TP line - set IP router to route in both directions;
- IP routing with multiple lines - will require manual filter table entries or use of a Dummy device.
The use of dummy devices will be covered in a separate article.
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