Proximity detection for telecommunications features

A switching system in which telecommunications features are improved by the use of the proximity status of a telephone station set user. The status is transmitted to the switching system over the same telephone line used for the station set. The proximity status information simply defines the presence or absence of a person to answer calls to the station set without identifying a particular person.

TECHNICAL FIELD 
This invention relates to telecommunications. 
BACKGROUND AND PROBLEM 
A multitude of customized services are presently available for serving 
telephone customer needs. Illustrative of such a service is a call 
forwarding feature which enables a customer to control the forwarding of 
her incoming calls to a designated telephone station instead of her 
regular telephone station. Typically, the service is activated by the 
customer dialing a prearranged code plus the directory number of the 
telephone station designated to receive the forwarded calls. In many 
situations, the call forwarding service is activated before the customer 
leaves the home or business environment of her regular telephone station. 
The service is usually deactivated when the customer returns to the 
environment of the regular telephone station. Again, the deactivation is 
generally controlled by the customer dialing another prearranged code. 
While such a service has enjoyed widespread commercial success, a common 
problem facing the art is that a customer often does not remember to 
deactivate the service when she returns to her home or business 
environment. Obviously, such a situation results, for example, in the 
undesired forwarding of calls, wasted time, customer frustration and many 
times, unnecessary other calls to receive information about who called and 
finally to return the missed calls. 
One known advanced communication arrangement, disclosed in U.S. Pat. No. 
4,275,385 issued to L. L. White on June 23, 1981, is based on an infrared 
personnel locator system using a periodic unique infrared identification 
code emitted from a battery-powered transmitter unit to identify the 
person carrying the transmitter unit to an overhead infrared receiver as 
the person enters the receiver's monitoring zone. The transmitter unit 
identification code together with the receiver identification code is 
communicated to a common control unit which displays the location of all 
of the transmitter units. For paging, the system provides alerting units, 
e.g., telephone station sets, which are selectively operated in the zone 
closest to the person being paged. As disclosed in the above-referenced 
U.S. Pat. No. 4,275,385, the common control unit may be implemented as 
part of the control unit of a telephone switching network and call 
forwarding to the nearest telephone station set may be effected based on a 
person's location. Although the advanced services afforded by this known 
arrangement are very useful, the cost and complexity associated with 
providing an additional wiring arrangement, separate from the telephone 
wiring, to connect the infrared receivers to the common control unit, and 
monitoring the location of particular individuals based on unique 
identification codes, are undesirable and unnecessary in many 
applications. 
SOLUTION 
These deficiencies are eliminated and a technical advance is achieved 
consistent with the principles of the invention in an exemplary switching 
system in which telecommunications features are improved and extended by 
the use of proximity status information defining the presence or absence 
of a person to answer calls to a telephone station set, where the status 
information is transmitted to the switching system advantageously over the 
same telephone line used for the station set. Illustratively, the 
proximity status information simply defines the presence or absence of a 
person to answer calls to the station set without identifying a particular 
person. 
A method in accordance with the invention is used in an arrangement 
comprising a telephone station set, a telephone switching system, access 
means, e.g., a telephone line, interconnecting the station set and the 
switching system, and a proximity detector. The proximity detector has a 
first state corresponding to the presence of a person to answer calls to 
the station set and a second state corresponding to the absence of a 
person to answer calls to the station set. The switching system receives 
information via the telephone line defining the state of the proximity 
detector. The switching system responds to incoming signaling requesting 
service by determining the state of the proximity detector based on the 
received information. 
For a first exemplary feature of the invention, the incoming signaling 
defines a telephone call and that call is selectively extended to the 
station set based on the state of the proximity detector. The call is 
extended to the station set when the proximity detector is in the first 
state, i.e., a person is present to answer calls. The call is forwarded to 
another station set when the proximity detector is in the second state, 
i.e., no one is present to answer calls. Illustratively, the call is 
selectively extended or forwarded also based on the availability status of 
the station set to receive calls. 
For a second exemplary feature of the invention, the incoming signaling 
defines a person status request from another telephone station set. The 
switching system first determines whether the other station set is 
entitled to receive information concerning the state of the proximity 
detector. Upon determining entitlement, the switching system transmits 
information defining the state of the proximity detector to the other 
station set. Illustratively, if the other station set remains off-hook 
after receiving the proximity state information, the switching system 
attempts to complete a telephone call between the two station sets. 
For a third exemplary feature of the invention, the incoming signaling 
defines a telephone call and alerting is selectively effected at the 
station set based on the state of the proximity detector. For example, 
audible alerting is effected at the station set when the proximity 
detector is in the first state and silent alerting is effected at the 
station set when the proximity detector is in the second state. Silent 
alerting is effected at another station set when the proximity detector is 
in the first state and audible is effected at the other station set when 
the proximity detector is in the second state. This feature is effective 
to facilitate the efficient answering of calls, for example, to an 
executive having a primary secretary and a backup secretary. 
For a fourth exemplary feature of the invention, the incoming signaling 
defines a telephone call and an automatic call distribution function is 
performed by selectively extending calls to station sets based on 
proximity detector state. 
For a fifth exemplary feature of the invention, the incoming signaling 
defines an automatic callback request and the switching system attempts to 
complete a call between the station set and another station set when the 
proximity detector is in the first state. The proximity state 
determination is repeated at regular time intervals as long as the 
proximity detector is in the second state. Alternatively, rather than 
attempting to complete a call, the requesting party is simply notified 
when the proximity detector returns to the first state. 
Apparatus in accordance with the invention is used in an arrangement 
comprising a telephone station set, a telephone switching system, and 
access means interconnecting the station set and the switching system. The 
apparatus comprises a proximity detector for detecting the presence and 
absence of a person within a predefined area. The proximity detector has 
first and second states and is for location with respect to the station 
set such that the first state corresponds to the presence of a person to 
answer calls to the station set and the second state corresponds to the 
absence of a person to answer calls to the station set. The apparatus 
further comprises means responsive to the proximity detector for 
transmitting state information of the proximity detector via the access 
means to the switching system. 
An essential part of the invention is a device that responds to the 
presence of a person. Many such devices are marketed, for various 
purposes, such as intrusion detection and turning on lights or opening 
doors automatically. One type of device which is well suited, but is not 
the only choice, is one based on detection of infrared radiation from the 
human body. One example is a unit marketed by the RCA Company, intended to 
turn on lights in a home, either as a convenience for the residents, or to 
repel intruders. It is called the Plug-In Security Switch Model c-21. It 
is sold in retail hardware stores, and is manufactured by RCA New Products 
Division, New Holland Avenue, Lancaster, Pennsylvania, 17604-3140. 
Another device, in a relatively small package (1.5.times.1.5.times.0.5 
inches), intended to be built into other equipment, is the Digital Passive 
Infrared Sensing Module, model IR1000, manufactured by Infrared, 
Incorporated, P.O. Box 47, Parlin, N.J. 08859

DETAILED DESCRIPTION 
Referring to FIG. 1, the principles of the invention are described in the 
context of a distributed control, integrated services digital network 
(ISDN) switching system 100. An integrated services digital network is 
defined as a network evolved from the telephony integrated digital network 
that provides end-to-end digital connectivity to support a wide range of 
services, including voice and non-voice services, to which users have 
access by a limited set of multipurpose customer interfaces. System 100 is 
connectable to analog or digital terminals such as analog terminal 161 and 
digital ISDN terminals 171, 181-1, 181-2 and 181-3 of FIG. 1. Each of the 
terminals 161, 171, 181-1, 181-2 and 181-3 is assigned a unique directory 
number illustratively DN1, DN4, DN15, DN16 and DN17. (Although not shown 
in FIG. 1, system 100 is also connectable via trunks to terminals 
associated with other switching systems.) System 100 includes a number of 
switching modules (SMs) each associated with a different subset of 
terminals. For example, switching module 110 is associated with terminals 
161 and 171 and switching module 120 is associated with terminals 181-1, 
181-2 and 181-3. Each such module includes a control unit, or switching 
module processor (SMP), for controlling connections to and from its 
associated subset of switch terminations. Module 110, for example, 
includes control unit 111, and module 120 includes control unit 121. 
The architecture of system 100 comprises a communications module (CM) 130 
as a hub for the switching modules 110 and 120, and an administrative 
module (AM) 140. Each switching module includes an integrated services 
line unit (ISLU) which terminates the digital and analog subscriber lines 
and provides access to a time-slot interchange unit (TSIU) and a packet 
switching unit (PSU). For example, in switching module 110, ISLU 112 
terminates the digital and analog subscriber lines 151 and 150, and 
provides access to TSIU 113 and PSU 114, respectively, for 
circuit-switched and packet-switched connections to and from the 
associated terminals under the control of control unit 111. Switching 
module 120 similary includes ISLU 122, TSIU 123, and PSU 124. 
Communications module 130 includes a time-shared, space-division switch or 
time-multiplexed switch, that provides 64 kilobits per second 
circuit-switched paths between switching modules. It supports B-channel 
and analog traffic between switching modules, as well as packet traffic 
between PSUs in different switching modules. The switching module control 
unit, such as 111, provides call processing and overall control and 
maintenance functions for the switching module. Control units, such as 111 
and 121, in different switching modules communicate with each other and 
with the administrative module 140 through a message switch (not shown) in 
the communications module, using an internal message protocol. The 
architecture provides flexibility in placing specific processing functions 
in specific processing elements. The general strategy is to place much of 
the required processing capability in the switching module control units, 
but to reserve the administrative module for those functions that are 
inherently centralized. The call processing functions can for example be 
distributed in a number of ways. In one alternative, most of the call 
processing functions are placed in the switching module control units with 
routing, terminal hunting, and path hunt functions located in the 
administrative module. In another alternative, all call processing 
functions are placed in the switching module control units, with the 
administrative module reserved for truly administrative processing. 
Each analog terminal, such as 161, communicates with system 100 via dual 
tone multi-frequency (DTMF) signals over a standard tip and ring wire 
loop, such as 150. 
Each ISDN user terminal, such as 171, communicates with system 100 over a 
digital line, such as 151, which includes two 64 kilobits per second 
channels conventionally referred to as B-channels (not shown) and in one 
16 kilobits per second channel conventionally referred to as a D-channel 
(not shown). In the present embodiment, one B-channel is used to convey 
digitized voice samples at the rate of 8000, eight-bit samples per second, 
and the other B-channel is used to convey data at a rate of 64 kilobits 
per second. (However, each B-channel could be used for either voice or 
data traffic.) The D-channel is used both to convey signaling packets to 
effect message signaling between ISDN terminals and system 100 and to 
convey data packts between different ISDN terminals. 
Digital line 151 is a four-wire digital line using one pair of wires for 
each direction of transmission. Line 151 transmits a serial bit stream at 
the rate of 192 kilobits per second which comprises 144 kilobits per 
second for the above-mentioned two 64 kilobits per second B-channels and 
one 16 kilobits per second D-channel and which further comprises 48 
kilobits per second used for a number of functions including framing, DC 
balancing, control and maintenance. Line 151 represents what is referred 
to by the International Telegraph and Telephone Consultative Committee 
(CCTT) as the T-interface. The use of the T-interface is only exemplary, 
however, as the invention is equally applicable to systems using other 
access methods. 
Signaling packets are conveyed between an ISDN terminal and system 100 
enclosed in level 2 (link-level) frames in accordance, for example, with 
the standard LAPD protocol. The exemplary signaling messages used for the 
control of circuit-switched voice calls are in accordance with CCITT 
recommendation Q.931. 
Terminals 161, 171, 181-1, 181-2 and 181-3 are located in work areas 160, 
170, 181-1, 181-2 and 180-3, respectively. These work areas can be an 
enclosed office or portion thereof, an enclosed laboratory or portion 
thereof, or a small work area within a large open work environment (e.g., 
factory). In this embodiment, the dimensions of the work areas are based 
on the effective range of a proximity detection device. Terminals 161, 
171, 181-1, 181-2 and 181-3 are connected to proximity detection device 
circuitry 162, 172, 182-1, 182-2 and 182-3, respectively. When a person 
enters or leaves work area 160, associated with analog phone 161, 
proximity detection device circuitry 162 initiates a feature activation 
sequence using DTMF. When a person enters or leaves a work area 170, 
180-1, 180-2 or 180-3 associated with ISDN terminals 171, 181-1, 181-2 or 
181-3, proximity detection device circuitry 172, 182-1, 182-2 or 182-3, 
respectively, trigger a special Q.931 message. Work areas 170-1 and 170-2 
also each include an ISDN terminal (not shown) and associated proximity 
detection device circuitry (not shown). 
The exemplary proximity detection device circuitry 162 for analog work area 
160 is shown in FIG. 2. It illustratively includes infrared sensor 201, 
timer 202, OR gate 203, off-hook state sender 204, and tone generator 205 
and dial tone detector 206. When a person enters area 160, sensor 201 
detects that condition and responds by switching to its "on" state. Sensor 
201 remains "on" as long as a person is in work area 160. When a person is 
absent or leaves area 160, sensor 201 switches to its "off" state. 
Commercially available infrared sensors may depend not only on the 
person's body heat, but also on some amount of motion, so there may be 
times when the infrared sensor will momentarily switch to the "off" state 
even though the person is present. There will also be times when the 
assigned person is absent, but another person enters the work area for a 
short time, to leave a note, for example. To avoid inappropriate action 
when someone enters or leaves the work area only temporarily, sensor 201 
is followed by a timing circuit 202 that requires the on and off states of 
the infrared sensor to persist for predetermined periods before the timing 
circuit delivers output signals that report that the person has validly 
arrived or left for purposes of this service. The "arrive" and "leave" 
signals from timer 202 illustratively are short "logic level" pulses 
appropriate to drive standard logic circuits (not shown) in the signaling 
tone generator 205 and "OR" gate 203. When either an "arrive" or "leave" 
signal reaches OR gate 203, it activates the off-hook state sender 204 
which enters a latched state to signal to the switching system 100 over 
line 150 that a service connection is desired. System 100 responds, as it 
does for any request for a connection, by sending dial tone. 
The dial tone, which is normally an audible signal to a person to dial 
digits, is in this case detected by dial tone detector 206 which then 
sends a logic "start" signal to tone generator 205. The latter, in turn, 
sends one of two digit sequences to system 100 for identifying the 
presence or absence of a person in work area 160. 
The digit sequences are illustratively encoded into a dual-tone, 
multifrequency format, which is the same format used to transmit digits 
dialed by a telephone user when dialing a telephone number or activating a 
feature from the key pad on telephone set 161. Although in the majority of 
cases, the digits are sent using standard dual-tone, multi-frequency 
(DTMF) encoding, the "arrive" and "leave" signals could also be sent to 
system 100 using out-of-band tones. After the digit sequence has been sent 
by generator 205, a "complete" signal is sent to the circuit 204 to 
restore it to the on-hook state. To avoid possible interference with calls 
while the person is actually present and using set 161, a switchhook 
control signal is derived from set 161 and delivered to the timing circuit 
202 to inhibit any output from that circuit while set 161 is off-hook. The 
inhibit control signal is based on the flow of "office battery" direct 
current through the line 150 when the analog telephone set is off-hook. 
This inhibit control signal prevents call interference that might 
otherwise occur if a person returned to her/his office and made a call 
immediately, before the pre-set time elapses and the "arrive" signal is 
sent. Timer 202 is configured so that the "arrive" signal is subsequently 
allowed to be sent when set 161 is returned to the on-hook state. 
FIG. 3 depicts the exemplary proximity detection device circuitry 172 for 
ISDN work area 170, including an infrared sensor 211, and a timer 212. 
When a person enters or leaves the work area 170, that event is detected 
by sensor 211. However, because of the fact that with an ISDN telephone 
set control messages can be sent via the D channel to system 100 at any 
time, independent of whether telephone set 171 is off hook, the operation 
of the circuitry 172 is substantially simpler than that of circuitry 162. 
When timer 212 times for a predetermined period, it determines at the 
expiration thereof that a person has been consistently present or absent 
long enough for the sending of an "arrive" or "leave" signal, it sends one 
or the other to the ISDN set 171. ISDN set 171 translates each of the 
signals into a distinct digital message and transmits it to system 100 via 
line 151. The off-hook inhibit control signal used in analog telephone 
work area 160 is not needed because the ISDN telephone set can send 
digital messages on line 151 at any time, regardless of whether the set is 
in use or not. 
System 100 responds to the arrive and leave messages from either an ISDN or 
analog line 151 or 150 by toggling back and forth a memory element in a 
memory 115 in the control unit 111 of FIG. 1 between two states that 
represent "person absent" and "person present". These two states are used 
to activate and deactivate other functions, such as call forwarding, work 
position unavailable, or person available for visit. A memory 125 in 
control unit 121 of FIG. 1 functions essentially the same as memory 115. 
The processing of calls to and from terminals that are in work areas 160, 
170, 170-1, 170-2, 180-1, 180-2 and 180-3 are controlled by units 111 and 
121 of FIG. 1. For example, unit 111 processes calls for terminals 161 and 
171. The dynamic busy/idle status and the dynamic proximity status are 
stored in memory 115 as depicted in FIG. 4. The real time busy/idle status 
is maintained in memory 115 for each directory number (illustratively 
DN1-DN8) or equipment location that is connected to SM 110. The real time 
proximity status is stored in memory 115 for the primary user of a 
directory number when the user's terminal equipment is connected to a 
proximity sensor device. Proximity status is set in memory 115 to one of 
four values: in work area, out of work area, private, or unknown. For 
those users that do not employ a proximity sensor device, the proximity 
status field is set to "null". The proximity status is updated under four 
conditions: (1) a person enters the work area, (2) a person leaves the 
work area, (3) a person requests proximity privacy, or (4) an abnormal 
event occurs (e.g., the line is taken out of service) such that the 
proximity status is unknown. 
In FIG. 5, when a person enters the ISDN work area 171, sensor circuitry 
172 detects the presence of a person. After a pre-set time interval, 
circuitry 172 signals terminal 171 that a person has been detected. 
Terminal 171 then sends a Q.931 message to system 100 indicating that a 
person is now in the work area. In response thereto, control unit 111 
updates memory 115--setting the dynamic proximity status field for DN4 to 
"in work area" as shown in FIG. 4. 
Similarly, in FIG. 5, when a person leaves the ISDN work area 170, the 
sensor circuitry 172 detects the absence of a person. After a pre-set time 
interval, circuitry 172 signals terminal 171 that a person has vacated the 
work area. Terminal 171 then sends a Q.931 message to switching system 100 
indicating that the person is no longer in the work area. In response 
thereto, control unit 111 updates memory 115--setting the dynamic 
proximity status for DN4 to "out of work area" as shown in FIG. 4. 
Under certain conditions, the user may not want their proximity status to 
be stored in the switch. To accomplish this, the user can depress a 
feature button 271 on terminal 171, which results in a Q.931 message 
indicating that the button has been depressed. System 100 translates that 
message as "proximity privacy requested," and updates memory 115--setting 
the dynamic proximity status for DN4 to "private." 
Control unit 111 recognizes certain error conditions in which the dynamic 
proximity status is not determined or guaranteed to be accurate. Under 
these error conditions, unit 111 updates memory 115--setting the dynamic 
proximity status for DN4 to "unknown." Examples of such error conditions 
are: (1) telephone set out of service due to software action or 
maintenance, or administrative action by people responsible for switching 
system; (2) telephone set disconnected by user (the switch monitors the 
status of all ISDN lines); and (3) a unique message sent from the 
telephone set to the switching system to state that the proximity detector 
is inoperative. 
Maintaining dynamic proximity status in memory 115 allows switching system 
100 to provide enhanced call processing capabilities. For example, calls 
can be redirected to other stations depending on whether or not a person 
is within the proximity of the phone for a prescribed time period. The 
application of proximity status to telephone call processing is further 
explained in the following description which is arranged in five parts. 
First, the call processing logic for an improved call forwarding feature 
is described. Second, the call processing logic is described for a call 
processing capability enabling a person to query the switch via a person 
status request about the proximity status of another person. Third, the 
call processing logic for an improved ring transfer feature is described. 
Fourth, the call processing logic for an improved automatic call 
distribution feature is disclosed. Finally, the call processing logic for 
an improved automatic callback feature is described. 
A flow chart for a call processing program used to provide an improved call 
forwarding feature is shown in FIG. 6. The execution of the program begins 
with block 601 when control unit 111 receives a request to terminate an 
incoming call to directory number DN4. Execution proceeds to block 602 
where unit 111 determines whether the primary user of DN4 is present in 
his/her work area. Unit 111 reads the dynamic proximity status field of 
memory 115 and if the proximity status is set to "out of work area" or 
"private," execution proceeds to block 603. Block 603 is executed and the 
call is forwarded to another directory number DN (e.g., DN6) which had 
been previously stored in memory 115. Control unit 111 effects the call 
forwarding by reading from memory 115 the number to which the call is to 
be forwarded and then controlling the call forward establishment of call 
connections to the station associated with that number while concurrently 
sending a special announcement or providing a display to the caller of the 
number to which the call is forwarded. 
If during the execution of block 602, unit 111 determines that the dynamic 
proximity status is "in work area" or "unknown," execution will proceed to 
block 604 with unit 111 examining the busy/idle data in memory 115 (FIG. 
4). If the busy/idle status is set to busy for analog lines, or all CAs 
(call appearances) are busy for ISDN lines, the station set is not 
available to receive calls and execution proceeds to block 605 where 
control unit 111 returns a busy signal to the caller. If the busy/idle 
status is idle for analog lines, or at least one CA is idle for ISDN 
lines, the station set is available to receive calls and execution 
proceeds to block 606 and the called DN will be rung, or alerted, 
normally. 
A flow chart for a call processing program used to provide a new proximity 
query feature is shown in FIG. 7. Execution begins in block 701 when 
control unit 111 receives a person status request comprising a unique 
dialed entitlement code plus a dialed DN (e.g., *58+DN4) from an analog 
terminal, or unit 111 receives a person status request comprising a unique 
feature button entitlement indication and a dialed DN within a Q.931 
message (e.g., button number 18+DN4) from an ISDN terminal. Unit 111 
translates the dial code or feature button indication into a proximity 
query feature request, and performs an entitlement check in block 702. 
Due to the sensitive nature of proximity information, an entitlement check 
is made. This ensures that proximity information is only sent to a 
prespecified set of querying telephone numbers. Memory 115 (FIG. 4) shows 
the list of telephone numbers that are allowed to query about a given 
person's proximity. For example, the owner of DN1 only allows callers from 
DN3 and DN4 to query about his/her proximity status. The owner of DN2 
allows all callers from DN1 through DN50 to query. DN3 denies all users 
from proximity queries. Since any caller using an entitled telephone 
number can make a query, a password may be used to validate the 
entitlement, as is shown with DN4. 
If the entitlement check of block 702 reveals no entitlement, an error tone 
or message is sent to the caller per block 703. If there is entitlement, 
call processing proceeds to block 704 where the control unit determines 
the dynamic proximity status. If the proximity status is set to "out of 
work area," execution proceeds to block 705, and the control unit 
transmits an announcement or display message to the calling station set 
indicating that the person is not in the office. A similar procedure (not 
shown in FIG. 7) with an appropriate announcement/message is provided if 
the dynamic status is "private" or "unknown." 
If during the execution of block 704, the control unit determines that the 
dynamic proximity status is "in work area," execution proceeds to block 
706. Control unit 111 then examines the busy/idle status in memory 115 for 
the dialed DN (i.e., DN4). If the busy/idle status is busy (for analog 
lines) or at least one CA is busy for ISDN lines, execution proceeds to 
block 707, and the control unit transmits an announcement or display 
message to the calling station set indicating that the person is in the 
office but is on the telephone. If the busy/idle status is set to idle 
(for analog lines) or all CAs are idle for ISDN lines, execution proceeds 
to block 708, and the control unit transmits an announcement or display 
message indicating that the person is in the office and requesting the 
calling party to stay on the line to complete a call. Execution proceeds 
to block 709 where a branch is effected to either block 710 or block 711 
depending on whether the caller stays on the line. If the caller stays on 
the line, the call is completed in block 711. If the caller does not stay 
on the line, the call is disconnected in block 710. 
A flow chart for a call processing program used to provide an improved ring 
transfer feature is shown in FIG. 8. The execution of the program begins 
with block 801 when control unit 111 receives a request to terminate an 
incoming call to DN4 (Sue Smith) at work area 170. (Since a key-system 
arrangement with shared call appearances (CAs) such as that disclosed in 
U.S. Pat. No. 4,791,662, D. J. Ahnen et al., December 13, 1988, is used, 
Sue's CAs (i.e., DN4 CA1 and DN4 CA2) appear on her secretary's phone at 
work area 170-1. Sue's CAs also appear on a backup secretary's phone at 
work area 170-2.) Execution proceeds to block 802 where the control unit 
determines whether Sue Smith's secretary is present in his/her work area. 
The control unit reads the dynamic proximity status field and if the 
proximity status is set to "in work area," execution proceeds to block 803 
where Sue's secretary's phone rings, and Sue's CA on the backup 
secretary's phone silently flashes. 
If during the execution of block 802, the control unit determines that the 
proximity status is "out of work area" or "unknown," execution proceeds to 
block 804. The control unit then reads the dynamic proximity status for 
the backup secretary, and if the status is "in work area" execution 
proceeds to block 805 where the backup secretary's phone rings, and Sue's 
CA on her secretary's phone silently flashes. 
If during the execution of block 804, the control unit determines that the 
proximity status is "out of work area" or "unknown," execution proceeds to 
block 806, and the call is forwarded to a message center. The proximity 
status of "private" is not supported for this feature. 
A flow chart for a call processing program used to provide an improved 
automatic call distribution (ACD) feature is shown in FIG. 9. In this 
exemplary embodiment a series completion distribution technique is used to 
distribute calls to the agents. More sophisticated techniques are 
available that distribute calls more evenly to groups of agents. The 
execution of the program begins with block 901 when control unit 121 
receives a request to terminate an incoming call to the main DN of a 
business using an ACD (e.g., travel agency). Calls to the main DN are 
distributed to one of many agents (i.e., agents 1, 2, 3, . . . N). A group 
of three ISDN ACD positions are shown as work areas 180-1, 180-2 and 180-3 
in FIG. 1. Execution proceeds to block 902 where the control unit 
determines whether the first agent in the ACD is present in his/her work 
area. 
If during the execution of block 902, the control unit determines that the 
dynamic proximity status is "in work area," execution proceeds to block 
903. Control unit 121 then examines the busy/idle data in memory 125. If 
the busy/idle status is set to busy for analog lines, or all CAs are busy 
for ISDN lines, execution proceeds to block 905. If the busy/idle status 
is idle for analog lines, or at least one CA is idle for ISDN lines, 
execution will proceed to block 904 and Agent 1's phone will ring. 
If during the execution of block 902, the control unit determines that the 
dynamic proximity status is set to "out of work area" or "unknown," 
execution proceeds to block 905. 
Starting in block 905 the procedures repeat as the control unit determines 
whether Agent 2 is available to receive a phone call. The execution 
proceeds to block 906 then 907, to block 906 then 908, or directly to 
block 908. The procedures then repeat through as many agents as necessary 
to complete the call; or if none of the agents are available, the 
execution proceeds to block 911, where the control unit transmits an 
announcement or display message indicating that all agents are 
unavailable. 
A flow chart for a call processing program used to provide an improved 
auto-callback feature is shown in FIG. 10. The execution begins when one 
person (Joe) attempts to reach another person (Sally) and fails. In this 
embodiment blocks 1001 and 1002 depict Joe's failed attempt to reach Sally 
because Sally is away from her work area. In block 1003 control unit 111 
receives an automatic callback request comprising a dial code (e.g., *64) 
or feature button indication within a Q.931 message (e.g., button number 
19). The control unit translates the dial code or feature button 
indication to a "notification of availability" feature request. An 
entitlement check (not shown in FIG. 10) is used to ensure that the 
calling telephone number is entitled to use the improved auto-callback 
feature. The procedures used are the same as those used for the proximity 
query feature described earlier. Execution then proceeds to block 1004 
where the control unit determines the dynamic proximity status. If the 
proximity status is set to "out of work area," "private," or "unknown," 
execution proceeds to block 1009. 
If during the execution of block 1004, the control unit determines that the 
dynamic proximity status is "in work area," execution proceeds to block 
1005. Control unit 111 then examines the busy/idle status in memory 115 
for Sally's DN. If the busy/idle status is busy (for analog lines) or at 
least one CA is busy for ISDN lines, execution proceeds to block 1009. If 
the busy/idle status is set to idle (for analog lines) or all CAs are idle 
for ISDN lines, execution proceeds to block 1006 where the control unit 
determines the dynamic proximity status of Joe. If the proximity status is 
set to "out of work area," "private," or "unknown," execution proceeds to 
block 1009. 
If during the execution of block 1006, the control unit determines that the 
dynamic proximity status is "in work area," execution proceeds to block 
1007. Control unit 111 then examines the busy/idle status in memory 115 
for Joe's DN. If the busy/idle status is busy (for analog lines) or at 
least one CA is busy for ISDN lines, execution proceeds to block 1009. If 
the busy/idle status is set to idle (for analog lines) or all CAs are idle 
for ISDN lines, execution proceeds to block 1008. In block 1008, the 
control unit rings Joe's phone. After Joe answers, the control unit sets 
up a call between Joe and Sally and rings Sally's phone. 
If the execution proceeded to 1009 in any of the cases above, the control 
unit will wait "N" seconds. (N is set by the administrator of switching 
system 100 and is approximately 15 to 30 seconds.) Execution then proceeds 
back to block 1004 and the procedures are repeated. Alternatively, upon a 
positive determination in block 1004, the control unit may simply effect 
transmission of information to Joe defining that a person is present to 
receive calls to Sally's station set. Or upon a negative determination in 
block 1005, the control unit may effect transmission of information to Joe 
defining both that a person is present to receive calls to Sally's station 
set and that the person is not busy on another call. 
It is to be understood that the above-described embodiments are merely 
illustrative of the principles of the invention and that other 
arrangements may be devised by those skilled in the art without departing 
from the spirit and scope of the invention. For example, although the 
proximity status information is stored in switching system 100 in the 
present embodiment, such information may alternatively either be stored by 
or in association with the station sets or determined dynamically in 
response to a proximity status request from switching system 100.