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hyuntaek26

BUILTIN_PUBLICATIONS_WRITER in discovery packet.

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Hi, I'm trying to understand helloworld examples's rtps discovery protocol(SPDP and SEDP) using wireshark.

 

I ran pub and sub on different VM connected each other. each VM has only one network interface(enp0s3).

 

tested in ubuntu 16.04 desktop 64bit and DDS Community 6.7

 

1)

 

when I dumped packets, there was a HEARTBEAT packet with writerEntityID 'ENTITYID_BUILTIN_PUBLICATIONS_WRITER' not only 'ENTITYID_BUILTIN_SUBSCRIPTIONS_WRITER'.

 

but that HEARTBEAT packet was sent from helloworld subscriber program. I thought 'BUILTIN_PUBLICATIONS_WRITER' is entity that announces presence of publisher, isn't it?

 

2)

 

and when I ran only one subscriber, there were many SPDP packets with different GUID prefix(more exactly different appId).

 

so, these are intended implementation that creates unused 'BUILTIN_PUB/SUB_WRITER' and many participant with different GUID? or am I misunderstand RTPS spec?

 

 

attached pcap file has two rtps pakcets, one with different guid pakcets and one with HEARTBEAT packets with 'PUB/SUB_WRITER'.

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