Arrangement for public safety answering points

Emergency service calls, such as 911 calls, are routed to specially trained operators at public service answering points (PSAPs). A PSAP switch, a special focus private branch exchange (PBX), is provided for interconnecting incoming PSAP calls to a PSAP position staffed by a PSAP operator. The PSAP position comprises a telephone facility for talking to the caller, and a PC for accessing and displaying data about the caller, i.e., the caller's address, and any special characteristics such as a caller's disability, etc. An ISDN, (Integrated Services Digital Network), line connects a tandem access switch used for routing PSAP calls with the PSAP switch. The ISDN facility is used for conveying information about the caller for display at the PC of the answering PSAP position. Advantageously, this arrangement provides an integrated system for communicating both the voice of the caller, and the data describing the caller to a PSAP operator.

TECHNICAL FIELD 
This invention relates to arrangements for more efficient facilities for 
public safety answering points (PSAPs). 
PROBLEM 
Emergency service calls such as 911 calls are routed to specially trained 
operators at public service answering points (PSAPs). It is important that 
calls to these agents be handled expeditiously and that the location of 
the caller be provided to the PSAP operator as quickly as possible. It has 
also been found desirable that PSAP operators be familiar with the 
territory from which the calls they serve originate. Consequently, 911 
calls are normally routed to small groups of PSAP operators, typically, 
two to four, although 911 calls in large cities may be routed to much 
larger groups. 
In the most common PSAP arrangements, 911 calls are routed from end offices 
to a tandem office for collecting the traffic from many such end offices, 
and thence, routed from the tandem office to a PSAP position. The caller 
is identified using automatic number identification to pass the caller's 
telephone number to the PSAP position. A personal computer (PC) is then 
used by the PSAP operator to access an automatic location identifier (ALI) 
database to provide the PSAP operator with location information for the 
caller. 
In addition, some people choose to call Police or Ambulance service using a 
conventional telephone number instead of 911. Calls to these telephone 
numbers are also routed to a PSAP operator over usually "administrative 
lines", to a different telephone. The present prior art, PSAP 
arrangements, are inefficient and costly. 
SOLUTION 
Applicants have analyzed the prior art PSAP arrangements, and have 
concluded that they present a number of problems. First, a PSAP position 
receives 911 calls from only a single tandem switch. Because of the 
importance of 911 calls, it would be desirable to have at least two 
switches for handling 911 calls, and to be able to route traffic from 
either of these switches to a PSAP operator. Second, calls for PSAP 
operators which are dialed using a conventional telephone number instead 
of 911 require the use of a separate administrative line and telephone for 
the PSAP operator. Third, the facility for accessing the ALI database is 
completely separate from the voice facilities associated with PSAPs. 
An analysis of these problems has led Applicants to propose the solution 
disclosed herein which represents an advance over the prior art. The 
solution involves the use of a PSAP switch, a private branch exchange 
(PBX), connected on the input side to the 911 tandem switches and to the 
administrative lines, and on the output side to the telephone portion of 
PSAP operator positions. Advantageously, this arrangement allows more than 
one 911 tandem access switch to be connected to a group of PSAP operators 
and allows administrative lines to be connected to the same PSAP operator 
positions, including the same telephones. 
In one preferred embodiment the processor of the PSAP switch receives ANI 
(automatic number identification) data from the 911 tandem access switch 
or, for administrative lines, from a local switch. This information is 
transmitted over a Computer Telephony Interface (CTI) to a server PC, 
thence to other PC's of the PSAP operator group. The server PC accesses 
the PC's of the various PSAP operator positions via a local area network 
for interconnecting the PC's. 
In Applicants' preferred embodiment, the tandem access switch is connected 
to the PSAP switch via an ISDN, (Integrated Services Digital Network) 
facility; in Applicants' initial embodiment this facility is terminated on 
a basic rate interface (BRI).

DETAILED DESCRIPTION 
Telephones 1 and 2 are connected respectively to local switches 3 and 4. 
Local switch 3 accesses the PSAP 20 switch via a tandem access switch 5 
whereas local switch 4 accesses PSAP switch 20 via a tandem access switch 
6. The presence of two tandem access switches provide redundancy in case 
of failure; in many cases, local switches are connected via the public 
switched telephone network to two different tandem access switches. Tandem 
access switches 5 and 6 are connected to PSAP switch 20 by an ISDN 
connection 7 and 8 respectively, terminating in a Basic Rate Interface 
(BRI). This in general is likely to be several connections since a PSAP 
operator normally handles several calls simultaneously, and since there 
are typically at least two PSAP operator positions attached to a PSAP 
switch. For much larger PSAP switches, a primary rate interface (PRI) ISDN 
connection can be used. 
The local switches 3 and 4 are also connected, possibly via other switches 
of the public switched telephone network, to PSAP switch 20 over 
administrative lines 9 and 10 respectively. These connections are for 
connecting PSAP operators to customers who have not dialed 911, but have 
directly dialed the telephone number of Police, Fire or Ambulance Service. 
The PSAP switch is a special purpose private branch exchange (PBX) switch 
which interfaces with the public switched telephone network via ISDN lines 
(facilities) used as PBX trunks 7 and 8, and administrative lines 9 and 
10. PSAP switch 20 is connected to PSAP operator positions 21, 25, and 30. 
Each operator position comprises a telephone station (22, 26, or 31) and a 
PC (23, 27 or 32). The PSAP operator stations can be analog or digital 
stations, and the PSAP switch can be an analog or digital switch. In 
Applicants' preferred embodiment, the telephone station and the PC are not 
directly connected, but are connected only by virtue of the fact that the 
same operator hears the caller on the telephone station and controls and 
reads outputs from the PC. 
PSAP switch 20 is controlled by a processor 40. This processor 40 receives 
the ANI information transmitted with each call, and forwards this ANI 
information over CTI link 42 to a server PC, in this example, PC 27. While 
in this case, CTI link 42 is shown as being connected to PC 27, which 
thereby becomes the serving PC, the link could be connected to either of 
the other PCs. If desired, two CTI links might be provided, each connected 
to a different PC, in order to provide additional safety. 
The PCs are interconnected by a local area network 33. PC 27 accesses the 
ALI database 45 via both of the ISDN stations 35 and 36, and via the PC 23 
and 27 connected to those ISDN stations. The D-channel of the ISDN 
connection is used for accessing the ALI database. This arrangement is 
used for accessing the ALI database even when the call that comes in is a 
call over an administrative line which is typically an analog line. The 
ISDN station is connected to a BRI interface with ISDN facility 7 or 8 by 
a multi-point connection. This arrangement allows the ISDN station 35 and 
36 to transmit request data to both of the tandem access switches 5 or 6; 
those tandem access switches can then forward the ALI request to ALI 
databases 45 and 46. ALI database 46 is provided to insure that service is 
not interrupted if ALI database 45 fails, and to increase the number of 
requests that can be processed when both the databases are operative. Only 
one of the ALI databases responds to the request. The ALI databases 45 and 
46 are connected by a data link 47 which allows information to be 
exchanged for the purpose of selecting which ALI database is to respond. 
Only one of the ALI databases responds to the request, and sends that 
response to only one of the tandem access switches. 
The ALI query and response is done by using the ISDN station as modems for 
data. The positions that perform the request, and the position that 
receives the ALI response communicate with the specific operator position 
handling the call via the LAN. 
The multi-point facilities 11 and 12 allow the ISDN stations 35 and 36, 
respectively, to access the D-channel of the BRI interface terminating the 
ISDN lines 7 and 8 between the tandem access switches and the PSAP switch. 
This permits ISDN stations 7 and 8 to insert or extract D-channel signals 
from the D-channel of the BRI facility connected to the PSAP switch, and 
is used for carrying conversations to the PSAP positions; advantageously, 
no additional facility is required to transmit the ALI data to the PSAP. 
FIG. 2 illustrates the method of Applicants' invention. A customer dials a 
911 call which is routed from the local switch via the tandem access 
switch over an ISDN facility to the PSAP switch (Action Block 201). Along 
with the call, the automatic number identification, (ANI), number of the 
calling station is transmitted to the PSAP switch. If the call goes from 
the local switch to the PSAP switch without going through one of the 
tandem access switches, i.e., via one of the administrative lines, 9 or 
10, the PSAP switch may also receive the ANI number for that call. The 
PSAP switch then presents the call to some, or, in the Preferred 
embodiment, to all PSAP positions, (Action Block 203), of which one of the 
positions answers the call (Action Block 205), sometime prior to the 
execution of Action Block 223. The switch transmits the ANI number to the 
server PC, i.e., the PC connected to the CTI link, (PC 27 in the example 
of FIG. 1), (Action Block 207). The server PC transmits ANI to the 
answering PC, (Action Block 209); this step is accomplished when one of 
the positions, the one connected to the answering PC, answers the call, 
which may be at any time prior to, or concurrent with, Action Block 223. 
The server PC transmits an ALI request to the PCs connected to the ISDN 
stations (Action Block 211). In the example of FIG. 1, these two PCs are 
PC 23 and 27. The ALI request is transmitted over the LAN interconnecting 
the PCs. The ISDN stations forward the ALI request via a multi-point ISDN 
facility to the tandem access switches connected to the two multi-point 
ISDN facilities (Action Block 213). The tandem access switches forward the 
request to the ALI databases (Action Block 215). The ALI databases 
communicate with each other to ascertain which database is to respond to 
the query (Action Block 216). One of the ALI databases responds with the 
ALI data to one of the tandem access switches (Action Block 217). The ALI 
response is transmitted from that tandem access switch via its connected 
ISDN facility, and the multi-point facility of the BRI of that ISDN to the 
connected one of the ISDN stations (Action Block 219). That ISDN station 
transmits the ALI response to its connected PC (Action Block 221). The 
connected PC then transmits the ALI response over the local area network 
(LAN) to the answering PC for display to the operator at the answering 
PSAP station, or, if no PSAP position has answered the call, as soon as a 
PSAP position does answer the call, thereby becoming the answering PSAP 
position and having the answering PC, (Action Block 223). 
Because of the nature of the PSAP application, it is particularly important 
that the service be provided in a highly reliable manner. The particular 
duplication scheme described above is one way of achieving this high 
reliability. Other duplication arrangements will be apparent to those of 
ordinary skill in the art. 
The above description is of one preferred embodiment of Applicants' 
invention. Many other arrangements will be apparent to those of ordinary 
skill in the art. The invention is thus limited only by the attached 
claims.