The function of the MSRD service is comparable with the SDR service. Slaves are differentiated between 'publishers' and 'subscribers'. A master sends an MSRD telegram to the publisher. The publisher then releases it previously prepared answer in the form of a broadcast telegram, so that all stations can receive the answer. One or more slaves can now subscribe to this telegram and adopt the data contained.
MSRD: Send and Request Data with Multicast Reply
The MSRD service is part of the DP-V2 protocols and so only optional. A field device can also support just the publisher function, or just the subscriber function, or both simultaneously. This service is used in direct data exchange .