A major objective of UMTS is to remove the distinction between the services available to users of fixed and mobile networks. In 2^nd generation systems, the focus has been on providing telephony services to mobile users while non-mobile users resorted to PSTN or ISDN. Universal Personal Telephony (UPT) was an effort to afford personal mobility across fixed and mobile networks in advance of UMTS availability.

The ACTS COBUCO project will demonstrate UMTS features in a mobile environment using DECT as the radio access method but will also have involve fixed terminals attached to a core B-ISDN network with a native ATM interface.

The NOMAD application allows UMTS telephony services to be delivered to fixed terminal users via software operating together with normal multi-media capabilities of a standard workstation. The starting point for NOMAD development is a freely available Internet Telephony package. This software is being re-targeted to setup and receive calls using B-ISDNs Q.2931 signalling.

Users are identified in UMTS by an International Mobile User Number (IMUN). The NOMAD software includes such a number in a Q.2931 call setup request and this triggers software in the mobility enabled switch to invoke UMTS call processing features. An ATM virtual circuit is then set up either between two fixed terminals, or via a gateway (called an ATM Switch Adapter in COBUCO) to a wireless DECT handset.

Initially, the protocol stacks available at the fixed terminal in COBUCO provide only AAL-5 capability. Audio data has been captured in 64Kbps PCM format using the standard PC audio capture capabilities. This data is broken into 40-byte units which are then encapsulated in the payloads of AAL-5 cells destined for other fixed terminals running the same software. An effort has been made to be compatible with the recent ATM Forum standard for "Voice over ATM to the Desktop" . The ATM stack has very low inherent delay, and the quality of the voice connection is substantially better than the typical quality experienced in Internet Telephony applications.

In order to inter-work with wireless handsets in the COBUCO DECT islands, later versions of the software will implement and encapsulation within AAL-1 which is compatible with the COBUCO packetizer/de-packetizer implemented in the gateway system. Within the project other voice encodings supporting either lower bandwidth or higher quality audio connections are possible subject to bilateral negotiation. Future plans also include the support of Voice over IP encapsulation compatible with the work of the ETSI Telecommunications and Internet Protocol Harmonization Over Networks (TIPHON) project.

To be a fully UMTS compliant application, the NOMAD application must allow a user to register to avail of services at a particular terminal. This registration should be accompanied by appropriate positive users authentication. Once registered, incoming calls can be received and outgoing calls made. It common with UPT, a users profile stored in the network by the mobility control server will now become accessible. The NOMAD application will allow a users to interrogate and modify this profile and may also use the contents of the profile to modify the way the application operates. As an example, an examination of the "preferred language" profile attribute could change the language used for all prompts and menus in the system. This would allow a user from (say) France to visit a location in Ireland, register on a terminal and interact with the NOMAD application in French to setup and receive calls.

Since the telephony services are implemented as a normal user program in the Windows NT environment, the NOMAD application provides the basis for a very highly featured telephone. Services such as call screening, call barring and answering machine type service are easy to implement. Multiple simultaneous calls can be supported, each allocated its own window. At any given time, only one will have exclusive use of the audio devices and this is controlled by the user. There is also considerable potential for the use of this facility to implement gateway and conferencing facilities. The integration of more advanced support services e.g. the use of on-line directories is also facilitated by the application structure.

The NOMAD system is currently under active development and will shortly be integrated into the COBUCO UMTS demonstrator. Initially, it will provide simple telephony services to UMTS fixed terinal users. At a later stage, interworking with wireless DECT terminals will be suported using AAL-1 with more advanced features being added as the project develops.