The simplicity of the ROSE protocol underscores the role of the service provided. ROSE delivers the information required to cause a remote execution of an operation and to return a result or error response. The responsibility to execute an operation rests with the remote peer of the ROSE service user. Since the services provided by ROSE are all unconfirmed and require no state information kept by ROSE, the protocol machine is very simple. Each service maps to a corresponding PDU, which in turn requires a service to provide delivery. Two types of delivery service are called for - one for ordinary data delivery and one for reliable transfer of bulk data. The Presentation Layer provides access to ordinary data delivery; the common application service, RTSE, offers delivery of bulk data.