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106 •
LON
4.5.3 Protocol
Individual network nodes communicate via one common communication pro-
tocol, the so-called LonTalk protocol.
The LonTalkprotocol is based on the OSI reference model (ISO 7498).
It is part of the Neuron chip as a complete communication protocol and makes
services available for the transmission of data to other nodes. For this reason,
there is no need to program the sequence of these services. All the program-
mer has to do is select among them and to concentrate on the programming of
measuring and control algorithms.
Following each task, the LON technology offers four different transmission
services:
• Request/Response(confirmation of receipt only once the message has been
• Acknowledged (always simultaneously with the confirmation of receipt,
• Unacknowledged Repeated
• Unacknowledged Service
The Acknowledged transmission service is typical for the LonTalk protocol.
To exclude transmission errors, the messages can be sent together with the ac-
knowledgement request. It is also possible to repeat their transmission.
With the Unacknowledged transmission service, the receivers do not supply a
confirmation of receipt.
4.5.4 Channel access method
The channel access method, also termed access or control method, represents
one variant of the CSMA method (Carrier Sense Multiple Access ~ free chan-
nel access with data traffic detection on the bus) of the LonTalk protocol. The
channel access is performed without the assignment of an access authentica-
tion, and only if the channel is free.
LON offers the additional possibility to assign message priorities which can
be useful for alarms or critical events. A special authentication process guar-
antees an optionally increased access reliability, for which reason LON can
also be used in special safety relevant applications, such as, for instance in fire
alarm and burglar alarm systems.
The channel access method of the LonTalk protocol allows the communica-
tion through various media with a good data throughput both with a low and
with a high channel load. This also applies to large networks.
processed)
the safest method of data transmission)
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