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7. Glossary
Step
Manual Function
ACK
An ACK is a positive IACK frame . If the sender detects an ACK, then the sender´s data has been received correctly, i .e . been
successfully transmitted to the receiver .
Acknowledgement frames
Acknowledgment on the KNX Link Layer is also called Immediate ACK (IACK) in KNX jargon, presumably to differentiate it from
other ack methods on the upper layers . In practice, IACK frames are used to confirm to a sender the transmitted data was
correctly received by the receiver (ACK) or not (BUSY/NACK) . Furthermore, a receiver cannot respond by sending back an IACK
when a frame is damaged or incorrectly addressed (missing IACK) .
BUSY
A BUSY is a negative IACK frame . If the sender detects a BUSY, then the receiver was not able to process the received frame .
Consequently, the sender waits for a short period and re-sends the frame (up to three times) .
Communication Object
same as Group Object
Extended Frames format
An extended frame has a maximum APDU length of 254 octets and a maximum length of 263 octets (incl . checksum) .
Filtering
Filtering of telegrams can be accomplished according to the topology via Individual Addresses (Physical Telegrams) and accor-
ding to filter tables for group communication (Group Telegrams) via Group Addresses .
Group Object
A data point in KNX is called a ‘Group Object’ or short an ‘Object’ .
Group Telegram
Group-oriented telegrams are named Group Telegrams . Filtering of Group Telegrams is accomplished according to the built-in
filter tables for group communication .
IACK
see Acknowledgement frames
Individual Address
The Individual Address of a device defines the location of the device within the topology .
Long Telegrams
Long telegrams or long frames are telegrams having an APDU length that exceeds 15 octets . Long telegrams use the extended
frame format .
NACK
A NACK is a negative IACK frame . If the sender detects a NACK, then the sender´s data has not been received correctly, i .e .
successfully transmitted to the receiver . Consequently, the sender re-sends the frame (up to three times) .
Physical Address
same as Individual Address
Physical Telegram
Individually addressed telegrams are named Physical Telegrams .
Repetition of telegrams
When there is no positive IACK on the TP line (e .g . NACK, BUSY, missing IACK), couplers usually repeat messages up to three
times . For all MEC couplers, the number of repetition is configurable .
Security functions
For using ETS Security functions, a minimum ETS version is necessary . Security functions have been available since ETS version
5 .7 .2 (ETS Inside 1 .4 .0) .
Short Telegrams
Short telegrams or short frames are telegrams having an APDU length that is not exceeding 15 octets . Short telegrams use the
standard frame format .
Standard Frame format
A standard frame has a maximum APDU length of 15 octets and a maximum length of 23 octets (incl . checksum) .
Glossary