A session is defined as an association between two Users, providing the capability to group together the resources needed for the instance of a service. Put another way, a Client accesses a service, say home shopping, by setting up a session with a Server. At the end of the service, when the Client no longer needs an association with the Server, the session is taken down. Rather it is assumed that resources will be acquired when needed to deliver a service, and released after a service has finished. Different services will require different resources.
Resource allocation is tied to sessions.
A Network-wide unique sessionId identifies a session in the network. All resources belonging to an instance of a service are tagged with the sessionId, and can thus be easily identified. This is useful for billing and administration by the Network, and for disposing of all resources associated with a session when the session is torn down. The DSM-CC session setup protocol is designed to allow client authentication by the Network, and to ensure that the client is aware that a session is set up, and thus accepts responsibility for it. In these messages the Server describes the resources it needs from the network using Resource Descriptors.