Example techniques described herein can permit interoperation between network terminals that have different performance characteristics, or that are connected via access networks having different performance characteristics. A calling terminal (or a core network device) can retrieve an indication of functional characteristics associated with a called terminal. The indication can be included in presence information associated with the called terminal. The calling terminal can determine a altered functional specification based at least in part on the functional characteristics and a functional specification of a session. The functional characteristics can satisfy the altered functional specification. The calling terminal can initiate a altered session with the called terminal via the network based at least in part on the altered functional specification. A terminal can detect network service provided by an access network and transmit presence information to a presence-information server. The presence information can indicate a type of the access network.