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5.5. Packet Resend

Due to the fact, that the GigE Vision

datagram protocol - for data transfer, a mechanism for saving the "lost" data needs to be

employed.

Here, a resend request is initiated if one or more packets are damaged during transfer

and - due to an incorrect checksum - rejected afterwards.

On this topic one must distinguish between three cases:

5.5.1.

In the case of unproblematic data transfer, all packets are transferred in their correct order

from the camera to the PC. The probability of this happening is more then 99%�

5.5.2.

Fault 1:

Lost Packet within Data Stream

If one or more packets are lost within the data stream, this is detected by the fact, that

packet number n is not followed by packet number (n+1). In this case the application

sends a resend request (A). Following this request, the camera sends the next packet and

then resends (B) the lost packet.

In our example packet no. 3 is lost. This fault is detected on packet no. 4, and the re-

send request triggered. Then the camera sends packet no. 5, followed by resending

packet no. 3.

5.5.3.

Fault 2:

Lost Packet at the End of the Data Stream

In case of a fault at the end of the data stream, the application will wait for incoming pack-

ets for a predefined time. When this time has elapsed, the resend request is triggered and

the "lost" packets will be resent.

standard stipulates using a UDP - a stateless user

◄ Figure 43

Data stream without

damaged or lost pack-

ets.

◄ Figure 44

Resending lost packets

within the data stream.