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DCN Next Generation Open Interface Release 2.4 General

en | 23

Bosch Communications Systems | 2007 February | SRS_INF | Du010933

• An expected sequence number

The receiving side is expecting either a data-packet or a heartbeat message. In this case

the receiving side has no pending message (see Figure 3 where no message is marked),

so no acknowledge is expected.

The sending side of the communication line responds on this NAK-packet by

retransmitting the data-packet. When no data-packet is pending a heartbeat should be

retransmitted.

The sequence number passed is the packet sequence, which the receiver size expects to be

received. This number can be wrong if the received packet is out of number synchronization.

4.1.2.4.2 Timing values

This section presents the different value and time-limits needed for handling the protocol.

Description Value

The maximum delay between two consecutive bytes of a message 50 ms

The number of outstanding messages for which the transmitter is waiting for

acknowledge.

The number of retries applied before discarding the message. This number

includes the number of retransmissions after the reception of NAK packets.

The time to start a retry of a message. (The time is measured after the last

byte of the packet is sent)

2 sec.

The time between two consecutive heartbeat's transmissions. Note that any

message is a valid heartbeat.

5 sec.

The time for heartbeat time-out. The time without receiving any packet. 10 sec.

The maximum message data length 5000 bytes

Typical remote function execution time (exclusive the time needed for

transmission of the data).

< 0,5 sec.

Note that the timing value for the ‘heartbeat-time’, the ‘retry-time’ and the ‘number of retries’

can be changed by sending the special message-type MDSC_COMMUNICATION_PARAMS.

The layout for that message type is described in §3.2.4.

The values given in the table are the default value for the communication parameters.

Note that setting the communication parameters with excessive values could lead to

malfunction of the protocol.

4.1.2.4.3 Special Conditions

Using the protocol described above. Special attention must be taken for the following points:

• Transmission errors in the length field of a message

This kind of error can result in very long message-data (length received much larger than

actual transmitted). This results in losing information over several blocks.

With help of the limited length, any length above this limit can be rejected, followed by a

negative acknowledge. Also is stated that a packet should be sent as a continuous stream

(§4.1.2). Therefore when during the reception of a message the transmission is halted, the

message may be considered having errors.

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