KNX devices can retransmit telegrams if no positive acknowledgement has been received.
Telegram retransmissions improve operational reliability during temporary communication faults but may increase bus traffic if faults persist.
The retransmission parameters can be configured independently for both communication directions:
-
On the superordinate side
-
On the subordinate side
Overview
Contents
Group Telegrams
No distinction is made between Main Groups 0–13 and 14–31 for group telegrams.
|
Setting |
Behavior |
|---|---|
|
Do not repeat |
The coupler does not check whether a positive acknowledgement has been received for group telegrams. This setting is particularly useful during commissioning or when group telegrams are temporarily forwarded without filtering. |
|
Repeat |
The coupler checks whether a positive acknowledgement has been received. If no acknowledgement is received, or if a Busy or NACK response is received, the telegram is retransmitted. The maximum number of retransmissions is configured using the "Number of Retransmissions" parameter. This setting improves operational reliability during temporary communication faults. |
Physical Addresses
Physically addressed telegrams are used for commissioning and diagnostics.
|
Setting |
Behavior |
|---|---|
|
Do not repeat |
The coupler does not check whether a positive acknowledgement has been received for physically addressed telegrams. This setting is particularly useful during commissioning when a programming interface is temporarily connected to different bus lines. |
|
Repeat |
The coupler checks whether a positive acknowledgement has been received. If no acknowledgement is received, or if a Busy or NACK response is received, the telegram is retransmitted. The maximum number of retransmissions is configured using the "Number of Retransmissions" parameter. This setting improves operational reliability during temporary communication faults. |
Broadcast
Broadcast telegrams (address 0/0 or 0/0/0) are used during commissioning and diagnostics.
|
Setting |
Behavior |
|---|---|
|
Do not repeat |
The coupler does not check whether a positive acknowledgement has been received for broadcast telegrams. This setting is particularly useful during commissioning when a programming interface is temporarily connected to different bus lines. |
|
Repeat |
The coupler checks whether a positive acknowledgement has been received. If no acknowledgement is received, or if a Busy or NACK response is received, the telegram is retransmitted. The maximum number of retransmissions is configured using the "Number of Retransmissions" parameter. This setting improves operational reliability during temporary communication faults. |
Number of Retransmissions
The "Number of Retransmissions" parameter is displayed as soon as Repeat is selected for at least one telegram type.
|
Setting |
Description |
|---|---|
|
1 |
Provides a good compromise between reliable communication during temporary faults and low bus traffic when filter functions are disabled. |
|
3 |
Provides the highest level of communication reliability when filter functions are enabled. If filtering is disabled, the additional retransmissions may significantly increase bus traffic. |
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