As the day begins, Karmen is visiting Lee Strum in his office three doors from her own. Heard above the sounds of the office is a simple melody that Karmen recognizes as her personal ring tune, or motif. A few seconds later, Kim Bagley's motif joins in, in counterpoint to Karmen's tune. So that Karmen need not rush down the hallway to answer Kim's call, Lee turns to his workstation and registers Karmen as a visitor (Figure xx). Immediately, Lee's own telephone repeats the ring-duet, Lee's workstation presents a description of the call (Figure xx), and Karmen lifts the receiver with a friendly "Hi, Kim, what's up?" During Karmen's meeting with Lee, two additional calls find her in a similar way, and Lee also answers one that rings with his own motif. An additional call to Karmen after she has returned to her office reminds Lee to terminate the visiting arrangement (Figure xx). Had the visit to Lee's office been a scheduled meeting, Karmen's appointments calendar would have made and cancelled these arrangements automatically.

Karmen uses the morning hours for activities requiring intense concentration that the disturbance of frequent telephone calls would disrupt. Yesterday, she modified her personal profile to reject all normal-urgency calls altogether for several hours (Figure xx). For the remainder of that morning, internal callers were given a visual explanation for being turned away, while outside callers were routed to an attendant.

Today, Karmen simply wants to reduce the annoyance level of the telephone without ignoring it altogether. She again changes her personal profile (Figure xx) to request subdued ringing. When Frances Brodsky calls, Karmen hears only a single, short, soft tone. On her screen appears the usual visual information: Frances' name and an indication that it's neither extremely urgent nor merely a social call. If she were to ignore the call completely, it would be handled as if Karmen were not there at all. Frances would have the standard options of speaking to an attendant, composing and sending a voice message, negotiating a later call with Frances' calendar, or simply trying again later. This time, she indicates (Figure xx) to Frances that she'll take the interruption if it's important enough. Frances, after a moment's thought, decides that it is and reissues the call at a higher priority, backed up by a short statement of the subject of the call (figure xx). Karmen answers, and they agree to meet later in the day to resolve a budget crisis.

After lunch, Karmen takes advantage of Brett Kornwald's temporary absence to spend an hour preparing a presentation at Brett's full-color workstation. Logging in tells the telephone system where Karmen is. For the duration of Karmen's occupancy, although Brett's incoming calls still ring there, so do Karmen's. Outgoing calls are identified as hers; in fact, the workstation and associated telephone behave in all ways as if they belonged to Karmen.

For their mid-afternoon budget discussion, Karmen and Frances remain in their own offices, connected by a background telephone call. Both of them place and receive several calls to other parties during this meeting, sometimes adding them to the background call, sometimes superceding it. The system knows enough about the background connection to reestablish it, in a speakerphone configuration, whenever the standard behavior would otherwise be to hang up the phone. By remaining in their own offices, the participants have full access to their paper documents, workstation documents, policy manuals, etc. Using teleconferencing capabilities such as those described by Sarin [14] ,Lantz [7], or Stefik et al [17], they can view a shared budget document, discussing changes as they make them. Karmen and Frances create, edit, and attach voice annotations to specific locations in this document [2], combining these annotation into a narrative intended to convince their manager that several proposed new projects, although expensive, will be well-worth it (Figure xx). When the manager later plays this list of annotations, the corresponding budget document locations will be brought into view on his workstation, in synchrony with the audio presentation [29].

Following the budget discussion, Karmen wants to advise her own team of the outcome. She turns to her workstation and composes a request to set up a conference telephone call, to take place ten minutes later. The call will involve Karmen, Lee, Kim, Pat Fisher, and Frances. Karmen selected their names from a hierarchical telephone/personnel directory that merges Karmen's personal entries with organizational and community directories (Figure xx). Each participant or his workstation agent is consulted to determine if they will be available. Pat's calendar system accepts on his behalf, since it knows that he will be in his office, accepting visitors, and not otherwise engaged. Similarly, Frances already knows about the call, and has indicated a willingness to participate. The others must be consulted. Reacting to a distinctive melody on their telephones, Kim and Lee independently consult their workstations to learn of the proposed call. Each of them indicates whether he or she will be available (Figure xx: Kim can make it; Lee cannot). Meanwhile, Karmen engages in other activies, undisturbed until the scheduled time arrives, when another distinctive tone advises all parties that the conference connection has been established among all their telephones.

As the call begins, Karmen has the "floor": hers is the only voice that will be transmitted to the other conference participants. After her opening introduction, she grants the floor to each of the other participants in turn for a reaction to the budget proposal, then opens the conference up for the remainder of the call to full interactive discussion [18, 7]. During the conversation, she lets all the participants see and hear the narrated document that she and Frances prepared earlier. A copy of the document itself appears on each workstation, and sections appear, as before, in synchrony with the narration.

Despite her best intentions, Karmen finds herself with so much paperwork to clean up at the end of the day that she cannot attend the late afternoon in-service training session. Instead, she places a call to the training room (Figure xx), which adds her speakerphone to an ongoing conference call carrying the audio portion of the meeting. During the meeting she mostly listens, occasionally obtaining the floor in order to ask a question or clarify a point. Using similar methods, Karmen has access to television and radio broadcasts, shared recorded audio files, etc.

After Karmen has left for the day, George Geargrinder, a salesman from another firm, telephones her. Since Karmen has signed off from her workstation, the call rings immediately at an attendant's workstation. As the attendant converses with Mr. Geargrinder, she uses the voice annotation capabilities [2] to record into a form that has appeared on her workstation his answers to questions such as his name, the reason for his call, and when he might be reached. The attendant also enters his name and telephone number textually. Having assured the caller that the message will be delivered, the attendant sends the message, which is already addressed to Karmen. It is waiting for her in her electronic mailbox the next morning, along with her conventional text-only mail. Having listened to him tell her why he wishes to speak with her, she uses the handy "return call" button on the message border to call him back. Voice mail from internal callers may include their photographs to identify them quickly, in place of the evocative sketch that accompanies the message from George Geargrinder.

Readers familiar with the Phone Slave system [15] will realize that the Geargrinder call follows closely the Phone Slave's automated scenario. We do not consider existing automated answering facilities, even those that are as advanced as the Phone Slave, sufficiently advanced to provide adequate service in the office setting, and therefore have proposed enhancing the role of the attendant rather than eliminating it.

The central facility of the Etherphone software is a system kernel that manages the creation, maintenance, and description of successive states of voice connections (called conversations). Objects denoted as parties represent participants in conversations, for the purpose of either participating in actual voice transmissions, controlling the conversations, or both. Different object classes represent different party types: Etherphone processors, telephone trunks to the public network, channels to the voice file service or to the text-to-speech synthesizers, or workstation control programs supporting the kinds of applications we saw in Section 2. Figure CNV(a) shows the system's representation of a connection between two stand-alone Etherphones; Figure CNV(b) shows a more elaborate configuration, involving several Etherphones, with associated workstations, in a conference arrangement that also includes a channel to the recording service (so that a narrated document can be played to all the participants). Notice the special role of workstation parties as objects that extend and alter the behavior of associated Etherphones [system 2]. This figure corresponds to a conference call that might have taken place place while Karmen Foozle was using Brett Kornwald's workstation (Section 2.2.3). The system prefers the identity of a workstation party to that of the associated Etherphone, so the telephone behaves as if it were Karmen's. Notice also the Visiting association between Kim Bagley and Karmen. Apparently, at the time represented by this figure, Kim was visiting Karmen in Brett's office, so that calls to Kim would also ring there.

At its heart, the system kernel provides programming facilities for

The user interfaces that Karmen and her friends used, along with many of the more elaborate behaviors of Section 2, were implemented not in a server but on the individual workstations. Registration of a workstation sets up associations like the one shown in Figure xx. Subsequently, the implementation of the workstation party object can partipate in the switching control actions and receive the informational reports. Thus, the full status of every call can be reported to users, and calls can be initiated from the workstation. To permit such modifications as call filtering (no ringing), workstation implementations can instruct the telephone party object implementation, through entries in a database maintained by the kernel, to abstain from the normal ringing behavior in response to incoming calls. Inhibition of "ringback" while placing complex conference calls, and a variety of other workstation extensions, are supported in a similar way. Timeout-based safeguards cause a return to conventional telephone behavior if the workstation does not respond to these real-time events in a timely manner.

An important theme in the Etherphone system is the development of enhanced telephone applications as programs that reside on workstations, then the later migration to shared servers of facilities that prove particularly useful. Examples of facilities that have already made this transition are a telephone directory package and the package that manages the editing and storage of recorded voice [2]. A function that would benefit from this kind of migration, but which at present is implemented in workstation code, is the ability to filter incoming calls based on a caller's name, a call's subject, or a call's urgency.

The advantages of development on the workstation are obvious, among them: it can be accomplished without interrupting service to install new software; it better insulates other user from the ill effects of undebugged software; it permits rapid turnaround for changes, extensive debugging facilities, development at one's own terminal, and so on. The advantages to migrating well-understood facilities to reside on a server are perhaps less obvious; in fact, some of them came as a surprise to us. Server residency makes some facilities usable directly through the telephone touchpad, for telephones that are not located near workstations, or whose workstations are not active. It may reduce the performance requirements of the workstation. Most importantly, it reduces the complexity of software that must be redeveloped for a new programming environment or workstation type.

However, migration to servers also introduce new problems. For applications, such as custom-tailored call filtering, that ought to continue to operate when the workstation is not functioning, a method is need a way to record the user's specifications. In cases like this, we have found that it is a simple matter to record the specifications in the kernel-maintained database mentioned in the previous section. The normal migration path is to the server that implements the kernel system, but this is not required, since all of the kernel's facilities are available through network communications.