Blocked call notification system

A method and a system allow an inbound telecommunications subscriber to receive notification of blocked calls directed to that subscriber and other information associated with calls that are blocked due to lack of available egress facilities at the subscribers' premises communications systems.

TECHNICAL FIELD 
This invention relates to communication systems. More specifically, this 
invention relates to a method and a system for notifying a called party of 
blocked calls. 
BACKGROUND OF THE INVENTION 
Network and premises communications systems--even robust ones--are 
typically engineered to handle the so-called "average busy hour" traffic 
load because it is uneconomical to design communications systems to handle 
worst case "peak" loads. Thus, when the arrival rate of calls is beyond 
the average busy hour system capacity, calls are simply blocked resulting 
in the application of a busy tone to callers' telephone sets. 
To reduce incidences of call blocking, large inbound telecommunications 
service subscribers usually lease bulk facilities, such as DS-1 lines that 
connect those subscribers' premises equipment to a communications 
carrier's terminating switch using a common interface such as, the Primary 
Rate Interface (PRI) of the Integrated Services Digital Network (ISDN) 
standards. A call directed to those inbound subscribers is blocked when 
the terminating switch determines that no circuit is idle in the leased 
facility. 
Blocked calls directed to inbound telecommunications service subscribers 
result in economic losses for all parties involved. Callers are frustrated 
by their inability to communicate with the subscribers (or their 
representatives) to complete or inquire about commercial transactions of 
interest. From the subscribers' perspective, blocked calls represent 
potential losses of business. A more concrete economic loss is the 
uncompensated use of the switching and transmission facilities of the 
carrier or carriers that attempted to complete the blocked calls. Adding 
further economic injury is the fact that Interexchange carriers (IXC) 
incur access and/or egress charges for blocked calls. The problem is 
further compounded when repeated call attempts from persistent frustrated 
callers result in repeated blocked calls. 
SUMMARY OF THE INVENTION 
The present invention is directed to a method and a system that allow an 
inbound telecommunications subscriber to receive a) notification of 
blocked calls directed to that subscriber and b) other information 
associated with calls that are blocked due to lack of available egress 
facilities at the subscribers' premises communications systems. 
In preferred embodiments of the invention, signaling information associated 
with incoming calls destined for a customer premises equipment, are 
received in a network switch connected to that customer premises equipment 
via a facility. The latter is comprised of one signaling channel and at 
least one communications channel. When no communications channel in that 
facility is available to complete an incoming call to the customer 
premises equipment, the switch sends the signaling information for that 
incoming call to the customer premises equipment via the signaling channel 
of the facility. 
The network switch can be connected to a different facility which is 
assigned to, but not connected to the customer premises equipment. In 
accordance with a feature of the invention, an announcement from a voice 
information system connected to the different facility, may be presented 
to the caller indicating that his or her call cannot be completed. The 
announcement may prompt the caller for a callback number and/or other 
information. Alternatively, a conventional busy tone may be applied to the 
caller's telephone set.

DETAILED DESCRIPTION 
FIG. 1 shows in block diagram form, a configuration for a communication 
switching system designed to provide blocked call notification to an 
inbound subscriber. In FIG. 1 a Customer Premises Equipment (CPE) 101 is 
shown connected to a network 102 via PRI ISDN circuits 103. The CPE 101 is 
comprised of a PBX 104 and a Channel Service Unit 105. PBX 104 is a 
telecommunication switching system which interconnects station sets at the 
premises, such as sets 120 and 121, and allows them to communicate between 
themselves and with other non-premises telephone sets via the digital 
circuits 103 to the switched telephone network 102. The central nerve of 
the digital PBX 104 is a communication processor 1040 which receives 
signaling messages from the D channel 1041 off Channel Service Unit (CSU) 
105 and processes those signaling messages to direct incoming calls to 
particular idle telephone sets. CSU 105 terminates the digital circuits 
103 at the subscriber's location and performs certain line conditioning 
functions and bipolar violation correction. 
Another important component of digital PBX 104 is a high-speed digital 
multiplexed interface 1043 that allows communications between the PBX 104 
and the network 102 carried over digital circuits 1043 comprised of 23 
bearer (B) channels 1040-1 to 1040-n and one data (D) channel 1041. The 
bearer channels 1040-1 to 1040-N also called "communications channels" 
carry user-information to PBX 104 while the data channel, also called 
"signaling channel", carries signaling information such as call set up 
information to PBX 104. The digital multiplexed interface 1043 conforms to 
PRI ISDN standards adopted by international standard bodies, such as the 
International Telecommunications Union Telecommunications Standardization 
Sector, better known by its acronym "ITU-T". Digital circuits 103 also 
conform to the PRI ISDN standard. One of the key attributes of the PRI 
ISDN standard is the support for twenty-four 64 Kbps channels over a 
standard DS-1 facility. Of particular importance is the portion of the 
standard requiring the use of twenty-three of those channels to carry 
voice or data information (communications or bearer or B channels 1030-1 
to 1030-n) and one common channel (data channel or D channel 1032) to 
exclusively carry signaling information for the other twenty-three 
channels. The ITU-T standard also allows the D channel 1031 to carry 
signaling information for more than the 23 channels in more than one DS-1 
facility. The signaling channel 1031 can be used, for instance, to carry 
user information (ANI, calling party name) and terminating supervisory 
signals, thereby, allowing additional flexibility in call SETUP and 
termination procedures. Further information regarding ISDN standards in 
general, and PRI interface in particular, can be found in AT&T Technical 
Journal, Vol. 65, No. 6, Issue 1, pp. 1-55 January/February 1986. The PBX 
104 may be implemented using for example, the AT&T Definity.RTM. digital 
PBX. 
Also shown in FIG. 1 is a public switched telephone network 102 to which, 
telephone sets 111, 112 and 113 are connected. Public switched telephone 
network 102 may be a Local Exchange Carrier (LEC) network or an 
Interexchange Carrier (IXC) network. In the latter case, network 102 is 
connected to a LEC network which provides communications services to 
telephone sets 111, 112 and 113, which may be ISDN telephone sets. Public 
switched telephone network 102 is comprised of switching complexes 106, 
109 and 110 that are interconnected via a) Intermachine trunks (IMT) 1110, 
1111 and 1112, and b) a signaling network represented in FIG. 1 by STP 117 
which is described in further detail below. In this example, the switching 
complex 106 is the terminating switching complex to which CPE 101 is 
connected. Switching complexes 106, 109 and 110 include communications 
switches, such as switch 107 in switching complex 106, that are 
processor-controlled, software-driven switching systems that operate as 
points of access and egress to network 102 for incoming and outgoing 
calls, respectively. Switching complexes 106, 109 and 110 exchange call 
handling messages via a data network called the Common Channel Signaling 
network. The latter is a packet switching network composed of a plurality 
of interconnected nodes called Signal Transfer Points (STP) that exchange 
call handling messages between switching complexes according to a specific 
protocol, such as CCS7. However, for the sake of simplicity, the signaling 
network is represented in FIG. 1 by a single Signal Transfer Point, namely 
STP 117. The features and functionality of an STP are described in the 
book "Engineering and Operations in the Bell System", Second Edition, 
published by AT&T Bell Laboratories, at pages 292 through 294. 
Switch 107 is comprised of a processor 1078 which is a wired-logic 
processing unit arranged to provide path information to route a call over 
the network. In particular, processor 1074 performs the functions 
necessary to interface incoming data signals with time-slot interface 
ports in the switch. Processor 1078 also insures that all received DS-1 
level signals are frequency-locked to the switch 107 network clock. 
Processor 1078 includes a memory 1077 which contains the stored programs 
for all the control, call handling and administrative maintenance 
functions for the switch 107. In addition, the memory 1077 also stores 
routing tables, such as the one shown in FIG. 2, to translate routing 
numbers to channel identification numbers and interface identification 
numbers. 
Switch 107 within switching complex 106 may be implemented using the AT&T 
No. 4ESS.RTM. switch or the AT&T 5ESS.RTM. switch. A detailed description 
of the inner workings of the AT&T No. 5ESS.RTM. is provided in AT&T 
Technical Journal, Vol. 64, No. 6, part 2, pp. 1305-1564, July/August, 
1985. The features and functionality of the AT&T No. 4ESS.RTM. are 
explained extensively in Bell System Technical Journal (BSTJ), Vol. 56, 
No. 7, pp. 1015-1320, September, 1977. 
Also included in switching complex 106 is a Digital Cross Connect System 
(DCS) 108. The latter is a computerized facility that allows DS-1 
facilities, such as PRI ISDN Trunk SubGroups (TSG) 1070 and 1080 to be 
mapped electronically at the individual (DS-0) channel level. Of 
particular importance is a feature of DCS 108 which allows a signaling 
channel, such as channel 1032 of digital circuits 103 to carry signaling 
information associated with the bearer channels of multiple DS-1 
facilities, such as TSG 1070 and loop back TSG 1080. The latter is a 
digital facility that originates from a digital interface frame of 
communications switch 107, loops back through DCS 108 and terminates on 
communications switch 107. Signaling information associated with the 
channels of loop back TSG 1080 is transmitted to CPE 101 via signaling 
channel (D channel) 1071 of TSG 1070 and signaling channel 1031 of digital 
circuits 103. The bearer channels of TSG 1070 (namely 1070-1 to 1070-N) 
and digital circuits 103 (namely 1030-1 to 1030-N) carry voice traffic 
associated with the incoming calls received by CPE 101. Similarly, bearer 
channels 1040-1 to 1040-N carry voice traffic to PBX 104 while signaling 
channel 1041 carries signaling information to PBX 104. 
FIG. 2 shows an alternative arrangement for the termination switch and the 
CPE of FIG. 1. The major difference between the terminating switch 107 of 
FIG. 1 and the terminating switch 207 of FIG. 2 lies in the termination 
arrangement of Trunk SubGroup (TSG) 1070. Unlike FIG. 1 where TSG 1070 
originates and terminates on switch 107, in FIG. 2, TSG 1071 originates 
from switch 207 but terminates on Digital Announcement System (DAS) 1074. 
The latter is a voice information system which delivers to callers a 
network-based user announcement that is triggered when all the bearer 
channels in TSG 1070 are occupied. Subscribers may wish callers to receive 
either a general announcement indicating that all lines are busy or a 
customized announcement (subscriber-specific) or an interactive 
announcement. Thus, DAS 1074 is arranged to perform specific functions 
depending on subscribers' preference. For example, DAS 1074 can a) prompt 
a caller for specific information by asking questions based on a set of 
modules in a transaction script, b) collect that information by detecting 
and interpreting Dual Tone Multifrequency (DTMF) signals entered by the 
caller or by recognizing speech input from the caller, and c) organize the 
collected information in a specific format and d) forward the collected 
information to CPE 201 via the signaling channels 1071 and 1032. 
DAS 1074 is comprised of a call processing unit (not shown) which executes 
two types of programs, namely user-interface software programs and system 
software programs. User-interface software programs of DAS 1074 include 
modules of a transactions script which is a sequence of questions posed to 
a caller to elicit answers in the form of dual tone multiple frequency or 
speech input. The modules of a transaction script are executed to answer 
incoming calls destined for CPE 201, and to greet callers with 
pre-recorded voice prompts to direct callers to enter specific 
information. System software of DAS 1074, by contrast, include a) 
primitives to detect dual tone multiple frequency signals entered by the 
caller, and/or b) speech recognition software to identify speech input 
provided by a caller. A voice response unit may be implemented using the 
AT&T Conversant.RTM. Voice System, whose architecture and features are 
described in AT&T Technical Journal Vol. 65, Issue 5, pp. 34-47, 
September/October 1986. 
The main difference between CPE 201 and CPE 101 lies in the presence of 
monitor box 202 connected to CSU 105 via a signal channel 1142. Monitor 
box 202 is a device, such as a protocol analyzer or a minicomputer with a 
suitable board arranged to a) detect electrical signals passing through 
the signal channel 1142, and b) decode those signals to extract calling 
party information associated with a blocked call. 
FIG. 3 shows an illustrative routing table that is stored in the memory of 
the terminating switch of FIG. 1. The table of FIG. 3 shows that the 
subscriber routing number RN is associated with a number of channel 
identification numbers within a particular Trunk SubGroup Number. The 
routing number RN is the telephone number of the subscriber. This 
telephone number may be an 800-prefix or 900-prefix telephone number or a 
feature group B number. The channel identification numbers are unique 
identifiers consisting of a) a channel ID within a particular DS-1, such 
as "channel-id-1, and b) an interface ID shown in FIG. 3 as "TSG1" or 
"TSG2". When CPE 101 receives a signaling message, the channel ID and the 
interface ID are included in the message to indicate the particular 
communications or bearer channel (within a DS-1) and the interface through 
which the call is to be received. In this example, the table entry for 
TSG1 represents the regular TSG channels through which, incoming calls are 
routed to CPE 101. TSG2 represents the loop back TSG circuits that 
originate and terminate on the communications switch 107 in FIG. 1 or 
originate on communication switch 207 and terminate on DAS 1074 in FIG. 2. 
When communications switch 107 (207) receives a signal from STP 117 
indicating that an incoming call is destined for routing number RN, switch 
107 (207) accesses the routing table of FIG. 3 to search for an idle 
channel associated with routing number RN. Since multiple channels are 
associated with routing number RN, the channel identification numbers in 
TSG1 and TSG2 are organized in a hunt group arrangement. In particular, 
the search sequence for the first available channel within the hunt group 
is a first listed/first called addressing system. More specifically, in 
the first listed/first called search sequence, communications switch 107 
(207) looks for the first member in the hunt group. If the first member is 
busy, the search proceeds to the second member in the hunt group and so on 
until an available member is found. When all attempts to locate an 
available channel in TSG1 are unsuccessful, the communications switch 107 
(207) looks for an available channel in TSG2. 
A verification table which lists only the channel identifiers of TSG1 is 
also stored in the memory of PBX 104 of CPE 101 (201). 
FIG. 4 graphically portrays the flow of a call and the associated signaling 
messages as the call traverses different links and components of the 
communication system of FIG. 1 or FIG. 2. The description of the call flow 
of FIG. 4 is provided concurrently with a description of the flowchart of 
FIG. 5 that shows a logical sequence of the actions taken and the 
decisions formulated by some components of the communications system of 
FIG. 1 to provide blocked called notification to a called party. 
Looking at FIG. 4 from an horizontal perspective, it can be observed that 
each column in FIG. 4 has a demarcation line indicating a component of the 
communications system of FIG. 1 generating a signaling message. Those 
components include the station set 111 at the upper left hand corner, the 
originating and terminating switching complexes 109 and 106 in the middle 
of the top row, and CPE 101 in the upper right hand corner. For 
illustrative purposes, but without loss of generality, it is assumed that 
telephone set 111 is an ISDN-compatible set. 
When station set 111 dials the inbound subscriber's number, in step 501 of 
FIG. 5, a Q.931 call SETUP message 401 is sent to the originating 
switching complex 109. As is well known to those skilled in the art, Q.931 
is part of the User-to-Network Interface (UNI) of the Digital Subscriber 
Signaling System No. 1 (DSS1) standard that supports exchange of 
information between a communications switch and a terminal device. Because 
communications between switches are supported by the Network-to-Network 
Interface (NNI) of the ISDN User Part standard which is different from the 
DSS1 standard, originating switching complex 109 uses the information 
(called "Information Elements") received in the Q.931 signaling message to 
generate in step 502, an NNI-compliant Initial Address Message 402 that is 
sent to terminating switching complex 106 via STP 117. An Initial Address 
Message (IAM) consists of a set of call handling and user information 
parameters used to transmit signaling information between switching points 
prior to the establishment of a call. It ordinarily consists of Calling 
Party Number, Called Party Number, Carrier Selection, Service Code and 
other user-related types of information. For additional information on 
IAM, see BellCore document TA-NWT-000394 titled "Switching Systems 
Requirements for Interexchange Carder Interconnection Using the ISDN User 
Part." After forwarding the IAM to the terminating switching complex 106, 
originating switching complex 109 also sends a Q.931 CALL PROCEEDING 
message 403 to telephone set 111 to indicate that the call is being 
processed. 
Upon receiving the IAM, switch 107 within terminating switching complex 
106, in step 503, searches for an available channel in the regular Trunk 
Subgroup(s) (TSG) using the first listed/first called searching sequence 
described above. A determination is made in step 504, as to whether a 
channel is available in the regular TSG(s). If a channel is available in 
the regular TSG, in step 505, a Q.931 SETUP message 404 is sent to CPE 
101. As shown in FIG. 4, the 404 SETUP message includes a) the Automatic 
Number Identification (ANI) also called calling party number (or a billing 
number), and b) the identifier of the channel through which the call is to 
be routed. In step 510, CPE 101 checks the validity of the channel 
identifier and upon determining its validity, completes the call in a 
conventional manner. 
When no channel is available in the regular TSG(s), terminating switch 107 
searches for an available channel in the loop back TSG. Upon finding an 
available channel, terminating switch 107, in step 506, sends a 404 Q.931 
SETUP message (described above) to CPE 101. The latter, in step 507 stores 
the received ANI information and checks the validity of the received 
channel identifier while sending a Q.931 CALL PROCEEDING message 405 to 
the terminating switch. For each ANI information received, a record that 
is comprised of fields for the ANI, the date and the time the ANI is 
received, is created for storage in the CPE 101. When the CPE 101 
determines, in step 508, that the channel identifier that was received as 
part of the Q.931 message, is invalid (i.e., is not a channel identifier 
for the regular TSG), CPE 101, in step 509, sends a Q.931 DISCONNECT 
message 406 to terminating switch 107. The Q.931 DISCONNECT message 406 
includes a field called "cause value" which contains a code associated 
with the reason for generating the DISCONNECT message. 
Once the terminating switch 107 receives the Q.931 DISCONNECT message from 
CPE 101, the processing of that message depends on the subscriber's 
preference for notifying the caller of the subscriber's inability for 
completing his or her call. If the subscriber wishes to have a busy tone 
applied to the caller's telephone set, CPE 101 includes a cause value "17" 
in the Q.931 DISCONNECT message. Thereafter, the terminating switch 107 
forwards a) a RELEASE Q.931 message 409 to CPE 101, and b) an ISUP RELEASE 
message 407 to the originating switch 109 which, in turn, a) returns an 
ISUP release complete message 410 to terminating switch 107, and b) sends 
a Q.931 DISCONNECT message 408 to ISDN telephone set 111 and applies a 
busy tone signal to that set. The latter transmits a Q.931 RELEASE message 
411 to originating switch 109 which returns a Q.931 RELEASE COMPLETE 
message 413 to telephone set 111. Similarly CPE 101, shortly after 
receiving the release message 406 from terminating switch 107 returns a 
Q.931 release complete message 412 to that switch. 
If the subscriber wishes to have an announcement delivered to the caller 
using DAS 1074 of FIG. 2, the terminating switch 207 receives an 
ALERTING/PROGRESS message from the CPE 201, instead of a DISCONNECT 
message. The ALERTING message (not shown in FIG. 4) triggers cut-through 
back to the listen path which is terminated in the DAS 1074. The latter 
delivers the announcement and collects information if needed from the 
caller. Cut-through to the listen path of DAS 1074 is possible only when 
all the loop back channels are terminated at the DAS 1074. Alternatively, 
the CPE 201 may return a DISCONNECT message with a non-standardized cause 
value to trigger cut-through back to the listen path terminated in the DAS 
1074. This alternative offers the advantage of allowing different messages 
to be relayed to different callers based on the cause value output by CPE 
201. For example, a cause value of say `XX` may be generated for preferred 
customers identified by their ANI, while a cause value of `YY` may be 
generated for unknown callers. 
Advantageously, the blocked call notification system of the invention 
allows inbound subscribers to know the number of blocked calls within any 
selected period of time and the phone number of each calling party whose 
call was blocked. A subscriber can use the blocked call ANI information to 
get a more complete profile of their callers and their calling habits. 
Information provided in the profile may include, for example, the 
geographic locations from which blocked calls originate, the distribution 
of the blocked calls at particular times of day, retrial behavior of 
callers whose first calls were blocked, to name a few. 
Furthermore, subscribers can use the blocked ANI information to help 
determine whether their egress facilities are engineered properly by 
analyzing the distribution of blocked calls over different periods of 
time. Blocked Call Notification also gives subscribers a closer idea of 
their true "first-offered traffic load." 
The foregoing merely illustrates the invention. Those skilled in the art 
will be able to devise numerous arrangements which, although not 
explicitly shown or described herein, embody the principles of the 
invention and are within their spirit and scope.