Wireless Future - Telenor

5 How should the System
Architecture be?
In order to realise the Virtual Terminal concept
as described in the aforementioned visions and
demands a terminal management and co-ordination
function called Virtual Terminal is needed.
In short, such a function should have the following
capabilities: It should continuously maintain,
monitor and update the configuration of the Virtual
Terminal, i.e. it knows exactly what devices
are present and active in the Virtual Terminal.
It should also be able to multiply and deliver
streams from applications to respective devices
and to unify and deliver streams from devices
to respective applications.
There are three alternatives concerning the location
of this Virtual Terminal:
• On a user’s mobile device;
• On a user-owned stationary device such as
a PC;
• On a server somewhere in the network, owned
by a service provider.
The first alternative has the advantage that it is
closer to the devices and hence easier to implement.
The major drawback lays in the fact that
the mobile device might lose contact with the
system and it is more exposed to damage or
theft. The second alternative is not convenient
since it requires the user to have an expensive
stationary device, which is not always the case.
Finally, although most challenging to realize, the
last alternative proves to be the best since it is
the most flexible. It does not require that the user
owns an expensive terminal, and roaming is provided
to allow the user to move away from his
home domain while keeping in touch with his
Virtual Terminal. This conclusion regarding
location is in agreement with other research
projects’ conclusions [6].
Figure 7 shows the proposed system architecture
of the Virtual Terminal. Other applications are
only aware of the Virtual Terminal and not of
the user’s many devices. Applications will deliver
services to the Virtual Terminal, which
again has the responsibility to ensure that the
delivery to the user is done via the most appropriate
device. From a technological viewpoint,
the Virtual Terminal object could reside on a
standard server that is connected to an IP-based
network as shown in Figure 8. All the networks
are connected together by gateways.
Telektronikk 1.2001
6 How could the Virtual
Terminal be Implemented?
In this section we will study successively the
five main use cases and discuss the possible
implementation alternatives.
6.1 Initiating Services
By service is meant both communication and
computing services. The user has at his disposal
a set of devices and can initiate services from
any of them. For the use cases Initiating data service
and Initiating directly communication service
no additional functionality than the existing
ones on the device is required. The user can just
select the device he wants to and initiate service
directly from there without going through the
Virtual Terminal. However, if he later on wants
to swap to another device the initiation must
have been done through the Virtual Terminal in
the first place or this will not be possible.
Further, for the use cases Initiating communication
service via address book and for a group,
additional functionality is required if a common
address book for all devices is wanted.
User
X:User
1:Device
2:Device
3:Device
ISUP
PSTN/ISDN
Gateway
The Virtual
Terminal
ISUP
Gateway
Gateway
Mobile Network
Figure 7 The Virtual
Terminal Architecture
Application
Virtual Terminal
Telecom system
Figure 8 Physical network connection of the Virtual Terminal
SIP/H323
IP-based
Network
X:Virtual
Terminal
111