Overview of NOMAD
The NOMAD environment consists of the central voice application and a number of other modules. Figure 1 gives an overview of the current state of the NOMAD test environment.
NOMAD Voice Handler
The NOMAD voice application is the central aspect of the test environment. NOMAD can standard multimedia hardware to capture an audio stream but work is underway in developing a DSP processor baord as an audio capture device. Under software control the audio stream is compressed, packetised and sent to its destination.
NOMAD Voice Transport
The interface between the NOMAD voice application and the hardware depends on the type of call being made. The NOMAD test environment has been designed in a modular fashion to allow the use of a variety of different interfaces. At present Internet and native ATM calls are possible. NOMAD communicates with the appropriate hardware in each case. Work is underway to allow for communication over a variety of wireless networks.
NOMAD Call Control
The NOMAD voice control handler can operate under the control of a call control process. The call control process is responsible for setting up calls and managing the resources associated with the call. There are a wide variety of options for controlling calls in a telephony system.
NOMAD Mobility Control
The mobile control plane is used to allow the user to move freely. Details can be found in mobility considerations.
NOMAD Directory Services
The NOMAD test environment includes a directory services module. Directory services can be used for a number of functions. When the voice application is invoked, the user can register with a directory service. The user can then look up other registered users etc.
To facilitate mobility, directory services can be used to map from a users identity to a routable network address to which the call can be delivered. At present we are experimenting with X.500 directory services using the Lightweight Directory Access Protocol ( LDAP).
One of the main issues which needs to be addressed in a telephony system is the issue of payment . There are a wide number of electronic payment methods which can be used. A payment module associated with NOMAD is used to to demonstrate one such method which involves a pay-as-you-go system. The user pays for number of electronic tokens to spend as desired for telephony services. If payment stops communication is cut off.
At present we are porting NOMAD onto a Windows CE platform. The handheld device will connect with the fixed network via an infrared link.
NOMAD and 4th Generation Telephony
A number of research issues which must be resolved to produce 4th Generation Telephony are discussed in the 4th Generation Telephony Concept pages. The NOMAD Telephony Test Environment provides a suitable framework for experimenting with ideas which can resolve many of those issues. As can be seen from the above description issues such as payment, mobility and interoperability of different network types are being tackled already.