GTI, a Graphical Telephone Interface

Konrad Froitzheim
Peter Schulthess

Department of Distributed Systems
University of Ulm

Abstract: The Graphical Telephone Interface (GTI) is a screen-based telephony application for Telecommunication services. It provides an intuitive user interface to the myriad of services and features in state of the art communication systems such as the ISDN or a digital (ISDN) PBX. As a high end telephony user interface, GTI controls voice and data connections with the comfort and ease of use of todays graphical user interfaces.


Dialling accessories for personal computers have been floating around as long as modems exist. With the appearance of telephony features such as conference, transfer, and redirection on Private Branch Exchanges (PBX) and on the emerging Integrated Services Digital Network (ISDN), screen based telephony applications were implemented. Most of them simply mimic a featurephone with keypad, call appearance buttons, and a small display. This featurephone paradigm is often combined with a computer based 'phonebook', for example mimicking a rolodex. Some allow access to phone numbers stored in PC-databases [BM]. The look of a typical dialing application is given in figure 1.

Figure 1: Feature phone emulation

We think that the conventional feature phone and its graphical equivalent on a computer are no longer adequate to take advantage of the wealth of services and features offered by modern communication systems:

* Memorizing telephone directory numbers will become obsolete. We have to deal with more and more numbers as connectivity increases. A sequential or pseudo-sequential approach to electronic phonebooks is also insufficient.

* A common complaint about telephony features like conference or call transfer is that they are to complicated. Advanced features in PBXes are rarely used. We think not the feature itself is complicated, but the procedure necessary to invoke it with buttons.

* Another problem is the representation of the communication partners. A two-line alphanumeric display on a feature phone is just not adequate to reflect the connection topology.

Probably the only advantage of the button-telephone is the low usage-hurdle, the time and effort needed to learn how to build a simple connection. Conventional screen based telephony applications exploit this instant familiarity but they sacrifice the option to manage the new features in an intuitive way.

The Graphical Telephony Interface (GTI) presented here takes a different approach in order to present services and features of modern communication systems to the user. GTI is built on three basic assumptions:

* Easy directory (phonebook) access is crucial for convenient connectivity.

* Features are easy to use, as long as an intuitive, single step operation is provided to invoke them. We will present such an operation for the conference feature later.

* Seamless integration into the Graphical User Interface (GUI) of the workstation is the key to the instant familiarity, that feature phone and their software emulations enjoy.

* GUI concepts like see, point, and click operations on objects are more intuitive than buttons and keypads on a workstation.

Before we present a user interface that takes these fairly generic assumptions into account, we should classify the functionality of screen-based telephony for advanced communication systems briefly.

1. Call Origination

The user should be able to initiate connections by selecting a communication partner out of his personal directory (phonebook). The growing size and complexity (multiple numbers) of the directory make unstructured phonebooks hard to use in the context of a computer-displayed directory. A personal directory should be structured in a hierarchically fashion to avoid information overload. Furthermore the computer user is already accustomed to this way of representing directories. The user obtains the power to organize the directory according to his own needs and preferences. Some criteria to arrange the directory are:

	- text-based list, sorted by:
		most recently called,
		call frequency,

	- symbolic:
		position in the window,
		groups (companies, departments, ...),

	- database:
The public directories (white and yellow pages) are integrated as subdirectories. They are not stored locally but accessed as a network service (provided either by the phone company, corporations or by private service suppliers).

2. Call Management

ISDN allows several connections to exist in parallel: two active calls on the two B-channels (voice or data), several calls on hold, and incoming calls waiting to be accepted. Managing multiple simultaneous connections is a nontrivial task requiring a sophisticated representation of the call scenario. The GTI's graphical display has the power to provide such a representation.

3. Call Logging

Another useful function of the GTI is recording important call data like calling or called party, number, time and duration, notes etc. This log is also useful to originate calls, a powerful variant of the call back feature. It should be treated as a subdirectory of the hierarchical user-phonebook.

4. Data Functions

ISDN provides the user with digital channels for data transmission. The GTI should allow control of these connections like it does for voice circuits. After the data-connection setup (out of the directory), the user chooses the application for this connection (joint viewing and teleoperation, fax transmission, ...) or configures the workstation network software to use the dialed number for network services like filesharing or printing.

5. Multifunctionality

Several enhancements to the telephone are commonly used: speakerphones, answering machines and voice mail systems. The GTI exploits the resources of the workstation to implement these features (integrated speaker, disk storage for voice recordings). This results in a distributed voice mail system with increased usability (and acceptance) compared to answering machines and voice mail systems.

User Interface Paradigm

Most of the existing screen-based telephony applications for ISDN are modeled on the telephone, giving the user a graphical representation of a featurephone with multiple buttons (digits, speeddialing, hold, drop, conference, etc.). We think that a computer based telephone should give the user a more powerful and comfortable design like GUIs on workstations (Finder for Macintosh, FileManager for Windows, ...). The GTI should compare to the featurephone interface like these 'desktop-managers' compare to command-line interfaces (e.g. MS-DOS).

We have chosen the 'Finder' paradigm for our GTI to maintain instant recognition and usability to the workstation user:

* The phonebook is presented the same way the Finder displays the directory of the local disk.

* Double-clicking or opening a selected entry launches a connection.

* The user can arrange the phonebook like a file-directory by moving icons, sorting lists or creating subdirectories (new 'folders').

* Windows show subdirectories, the active voice connections or data connections.

Figure 2: Directory window

The top level directory shows frequently used communication partners; other possible targets are grouped in subdirectories. Note the subdirectory 'Yellow Pages' representing the public yellow pages.

The left side of the window holds the tools for invoking commonly used functions (from top to bottom): entering and changing the information for an entry (the rolodex-card icon), initiating a call to the selected entry, redirecting calls, or managing the built-in answering machine. The shading on the right sides of the tool-icons indicate further menus or dialogs.

The selected view mode for figure 2 is 'sorted by call frequency'. It is controlled with the view menu (see figure 3). The menu choices reflect the criteria given above.

Figure 3: View Menu

Figure 4: Connection window

The connection window (figure 4) shows three connections: the conference call and the point-to-point call on the left side are on hold, the call to Rolf-Dieter Klein (using an ISDN-workstation) is active, i.e. we are talking to him. Selecting a connection is done by clicking the respective entry (text or icon) with the mouse. The view mode can be changed to the modes in figure 3. The line below the window-name displays the current charges and the total charges in a user selected period (week, month, billing period, ...).

Tools on the left side allow taking notes and changing information, volume control, disconnecting, transfer, or recording the conversation (from top to bottom). There is room for future tools.

The connection window is the base window for managing the connection topology: selecting an icon selects the connection it symbolizes. The GTI-application translates this simple mouse-click into a hold command for the currently active call, which might even be a conference, and a reconnect command for the selected icon (connection). Other procedures to activate communication features are transformed into simple point and click operations of our graphical environment.

Figure 5: Data Connection window

Four data connections are set up and one is selected (i.e. active) in the example for a data connections window in figure 5. Selecting and display control are the same as in the voice connection window. The tools on the left are somewhat different: select an application for the active data call (joint viewing and teleoperation, E-Mail, etc) , disconnect, transfer, and configure the active call as LAN-bridge.

Managing the connectivity situation in the data connections window is performed in the same intuitive way as the voice connections, although the results might of a more permanent nature. This is for example the case when selecting a LAN-bridge: future LAN operations like file-sharing or printing are performed in the selected LAN. The Link Access Protocol driver (LAP) controls the connection automatically according to the LAN-traffic, until we change the setup again in this window.

We will continue the GTI description with example usage procedures for some basic operations.

Call Origination and Termination

A call is originated by selecting an entry in the directory window and opening it. This can be achieved through a menu selection (Open) or a 'double-click', the most common operation in a graphical user interface environment (figure 6a).

Figure 6a: Call setup - select target

Figure 6b: Call setup - connecting

The selected icon appears blinking in the respective connection window, while the phone (or computer) on the other side is ringing. As soon as the connection is up (the phone on the other side is picked up), the icon turns steady in the window, thus representing a valid connection (figure 6a). Unselected icons in the connection windows represent connections with inactive status (on hold, figure 4).

Disconnecting an active call is also simple, either click on the scissor or choose the 'Disconnect' menu entry.

Feature Activation

As mentioned above, the connection window and the point-click-and-drag operations of the host workstation graphical user interface are the centerpiece of our intuitive feature control system. The connection window (figure 4) reflects the communication situation (i.e. the connection topology). The user can add new connections - implicitly holding existing connections - just as he originated preceding calls: pointing to a target in the directory window and dragging it into to connection window.

Among the many feature of communication systems, the conference proves to be especially hard to initiate and control. It involves a multistage process to create, namely repeated call-and-hold operations. We want to use this feature to demonstrate the GTI-philosophy to handle features.

Figure 7a: Selecting partners for a conference

The user selects the conference partners in the directory window. This can be done through the shift-select mechanism familiar from the Finder or just by selecting a prefabricated conference represented by a folder (figure 7a). The conference is then built with the 'Open'-menu or double-clicking the selection just as if it were a single conference. The GTI performs the process of calling the participants and switching them into a conference. It plays a prerecorded voice clip to inform the called parties of the conference or prompts the conference moderator to welcome the participants individually. The conference appears in the connections window symbolized through connected icons.

Figure 7b: Conference


A GTI-prototype has been implemented at the department of Distributed Systems at the University of Ulm, Germany. It is based on a NuBus ISDN card [PS, KF, RDK] and the Abstract Personal Communications Manager (APCM) ISDN protocol driver [KF,PS,SS] developed at the department. Since the APCM isolates applications from interface hardware and switch protocols, GTI is available for all the communication systems supported by the APCM, currently the German 1TR6 and AT&T's 5ESS switches.


GTI is structured according to the main functional units of graphical telephony:

* PhoneManager controls the flow of operation and common tasks,

* PhoneWindows is used for all drawing and display operations,

* PhoneGroups manages the operational data (phonebook, log, ...),

* Other modules for complex tools (answering machine, application IF, ...).

Additional modularization is left to the programmer of the respective part as is becomes necessary or useful during development.

Figure 8: Module structure of the GTI-prototype


The prototype is written in MPW Pascal for the Apple Macintosh. It is approximately 56 KBytes big, although this will probably increase with the number of features implemented. It has proven to be a very user friendly and intuitive tool for managing telephone connections. The user friendliness is highlighted by the voice conference, that turns into a very useful tool with the GTI. Another ongoing project at the department augments the GTI application with a management tool for the voice conference itself.


[BM] Bob McNinch: Screen Based Telephony; IEEE Communications Magazine, April 1990, page 34ff.

[PS] Peter Schulthess: Architecture of an ISDN-Workstation, Report #171 des Instituts für Mathematik, Universität Augsburg, Juli 1988.

[PS,KF, RDK] Peter Schulthess, Konrad Froitzheim, Rolf-Dieter Klein: Access to an ISDN-card from Modula-2; 1. International Modula-2 Conference, Bled, 1989.

[KF, PS, SS] Peter Schulthess, Konrad Froitzheim, Steven Sweeney: Abstract Personal Communications Manager (APCM); ACM Computer Science Conference, Kansas City, 1992.


Peter U. Schulthess is full professor at the Department of Distributed Systems at the University of Ulm, Germany. He was professor at the University of Augsburg, Germany. Peter Schulthess received a doctorate from the ETH in Zurich, Switzerland, a MSEE from Georgia Tech, and a diploma in Electrical Engineering from the ETH in Zurich, Switzerland.

Konrad M. Froitzheim works as assistant professor at the Department of Distributed Systems at the University of Ulm, Germany. He spent 1990 at Farallon Computing, Inc. in Emeryville, CA working on ISDN hardware and protocol software. Konrad Froitzheim received a doctorate from the University of Augsburg, Germany and a diploma in Mathematics from the Technical University in Munich, Germany.