====== DESTINATION_ORDER QoS Parameter ======
[[ddsf:public:guidebook:06_append:02_quality_of_service:start|return to the Quality of Service (QoS) Parameters ]]

The DESTINATION_ORDER policy controls how each [[ddsf:public:guidebook:06_append:glossary:s:subscriber|subscriber]] resolves the final value of a data [[ddsf:public:guidebook:06_append:glossary:i:instance|instance]] that is written by multiple ''DataWriter''
objects (which may be associated with different ''[[ddsf:public:guidebook:06_append:glossary:p:publisher|Publisher]]'' objects) running on different nodes.
The setting BY_RECEPTION_TIMESTAMP indicates that, assuming the [[ddsf:public:guidebook:06_append:glossary:o:ownership_qos|OWNERSHIP]] policy allows it, the latest received
value for the instance should be the one whose value is kept. This is the default value.

The setting BY_SOURCE_TIMESTAMP indicates that, assuming the OWNERSHIP policy allows it, a timestamp placed at
the source should be used. This is the only setting that, in the case of concurrent same-[[ddsf:public:guidebook:06_append:02_quality_of_service:ownership_strength|strength]] ''DataWriter'' objects updating the same instance, ensures all subscribers will end up with the same final value for the instance. The mechanism to set the source timestamp is [[ddsf:public:guidebook:06_append:glossary:m:midware|middleware]] dependent.

The value offered is considered compatible with the value requested if and only if the inequality ''offered kind >= requested kind'' evaluates to ''TRUE''. For the purposes of this inequality, the values of DESTINATION_ORDER ''kind'' are considered ordered such that ''BY_RECEPTION_TIMESTAMP < BY_SOURCE_TIMESTAMP''. 

Source: [[https://www.omg.org/spec/DDS/1.4/PDF | DDS 1.4 Spec]]

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