The DCPS layer disseminates data from publishers to interested subscribers. It is
implemented using the concepts of publisher and data writer on the sending side and subscriber and data reader on the receiving side. The DCPS layer consists of one or more data domains, each of which contains publishers and subscribers that communicate via DDS. Each publisher and subscriber belongs to a domain. Within any data domain, data is identified by a topic, which is a type-specific domain segment that allows publishers and subscribers to refer to data unambiguously.
Within a domain, a topic associates a unique topic name, data type, and a set of
quality of service (QoS) policies with the data itself. Each topic is associated with
one data type, although many different topics can publish the same data type. The behavior of publishers is determined by the QoS policies associated with the
publisher, data writer, and topic elements for a particular data source. Likewise, the behavior of subscribers is determined by the QoS policies associated with the subscriber, data reader, and topic elements for a particular data sink. A few of the QoS policies and operations specified in the language and used in the case study are as shown in Table1 and 2 respectively. The QoS policies and operations.