Bosch DCN Next Generation Bedienungsanleitung Seite 18

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DCN Next Generation Open Interface Release 2.4 General
en | 18
Bosch Communications Systems | 2007 February | SRS_INF | Du010933
4. PROTOCOL DESCRIPTION
4.1 Serial Line Protocol Description
The message described in the previous chapter must be transmitted between the CCU and
the remote controller. The transmission mechanism uses a protocol to detect errors on the
communication line.
For the serial communication there are three protocols available:
a ‘terminal’ protocol
This is not actually a protocol used for data communication. This setting is used to connect
a standard ASCII terminal. This setting may be needed for services purposes.
The terminal protocol is not further explained in this document.
a ‘camera’ protocol
This protocol is only used for communication with Allegiant Video-switchers or AutoDome
Cameras by the DCN NG. This protocol is not further explained in this document.
a ‘full’ feature protocol
This includes error detection and retransmissions of messages. Also the communication is
checked using the heartbeat mechanism. For details see §4.1.2.
a ‘simple’ feature protocol
This is the simplified protocol which only checks for transmission errors. The performance
overhead and memory usage is low. For details see §4.1.3.
Note that Appendix A explains how the different protocols could be selected on the LBB4100
and the master CCU of a Multi CCU system (LBB4501).
4.1.1 Data packet format
The actual communication between the CCU and the remote controller is done on packet
base. The data packet used has the following format:
Header Message ChkSum
The protocol only performs actions when a valid header is received. All bytes received before
the header are ignored. The specific header format of the packet is described along with the
protocol (§4.1.2 and §4.1.3).
The message in the packet is the actual data to be exchanged between the remote controller
and the CCU. The general format and various types are described in §3.2.
Note that the message also includes the length of the message-data. This length combined
with the fixed length of the header is used for the checksum calculation.
The package is terminated with a checksum section, which holds the checksum over all data
inside the header and message. The Checksum is described along with the protocol (§4.1.2.2
and §4.1.3.3).
4.1.2 ‘Full’ feature protocol
The ‘Full’ feature protocol is meant to be used within large DCN NG systems. The protocol
provides a full functioning protocol including retransmissions and communication checks.
Due to the great need of memory the ‘Full’ feature protocol is only present on the master-
CCU of a multi-CCU system.
The ‘Full’ feature protocol has the following features:
Unique header detection possible using escape handling (see §4.1.2.3).
Protocol supports related ACK and NAK messages. Only 1 message is sent in advance so
the use of ACK and NAK may be related, because they always react on the last message
transmitted.
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