CODEWITHSUNDEEP
data-distribution-service
user7586189
user7586189

Reputation: 1279

How does DDS/RTPS guarantee Qos?

DDS/RTPS is a peer-to-peer data sharing system. It does not have any centralised control/scheduling. How does it actually guarantee the network related Qos, i.e. transport-priority and latency-budget?

Upvotes: 0

Views: 450

Answers (1)

C Tucker
C Tucker

Reputation: 301

For those network specific QoS, DDS does rely heavily on the services provided by the network.

The specific behavior of the transport-priority QoS is not dictated by the DDS standards. It is considered a 'hint' to the middleware. A typical implementation might map it to the ToS or (DS) field in the IP header, but this is not required. [Consider that DDS can be mapped onto various underlying transports which may or may not support data prioritization.] The effect of this QoS is heavily dependent on the underlying network technology and its configuration. DDS makes no guarantees about the behavior.

The latency-budget QoS is also a hint to the DDS implementation. For exmaple, a larger latency-budget may allow the middleware to make scheduling decisions for optimization purposes (to aggregate several data messages together into one network datagram); while a small budget may force the middleware to send multiple small network packets. An implementation of DDS may attempt to factor in the network transport latency in the overall schedule of data transmissions; but without a deterministic transport, there is no guarantee that the latency budget won't be exceeded.

Based on this question, the deadline QoS may be of interest to you. It essentially requires that each data instance be updated with a certain frequency, and provides a mechanism to alert both the Reader and Writer if this requirement is not met. It does not 'guarantee' data priority or latency, but it provides a mechanism to know if the required data update periodicity is not satisfied.

Also, it might be interesting to look at Time Sensitive Networking (TSN) as a transport for DDS. There has been some recent work in standardizing DDS over TSN. This requires specialized hardware and detailed configuration, but may address your requirements. [I tend to believe that careful architecture of standard ethernet networks is effective and sufficient for the vast majority of applications; so, just make sure you have a good handle on your requirements.]

Upvotes: 1

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