Telecommunication trunk circuit reporter and advisor

A telecommunication network includes a number of switches interconnected by groups of trunk circuits. Trunk traffic data is generated by the switches and transmitted to a network control center where it is stored in a traffic database. The network control center includes a system for mechanically generating periodic traffic reports and performing calculations leading to recommendations pertaining to additions or deletions of the number of trunks in a group necessary to maintain an optimum size network.

FIELD OF THE INVENTION 
This invention is concerned with telecommunication networks and, more 
particularly, is concerned with control centers for such networks. 
CROSS REFERENCE TO RELATED APPLICATIONS 
Co-pending U.S. patent application Ser. No. 439,470, filed Nov. 5, 1982, 
for "Private Interconnect Network" is directed towards a tandem switching 
network. 
The following co-pending U.S. patent applications pertain to other features 
of a network control center. 
Ser. No. 446,072, filed Dec. 1, 1982 herewith in the name of Jonas R. 
Bielkevicius, entitled "Network Control Center Alarm Message Detector". 
Ser. No. 445,867, filed Dec. 1, 1982 herewith in the name of Richard E. 
Little, entitled "Telecommunication Network Display System". 
Ser. No. 445,866, filed Dec. 1, 1982 herewith in the names of Samuel J. 
Kline and Richard E. Little, entitled "Network Control Center Call Trace". 
Ser. No. 445,868, filed Dec. 1, 1982 concurrently herewith in the name of 
Samuel J. Kline, entitled "Network Control Center Trouble Ticket". 
Ser. No. 445,861, filed Dec. 1, 1982 herewith in the name of Richard E. 
Little, entitled "Internodal Conference Call Administrator". 
REFERENCE TO RELATED PUBLICATIONS 
A detailed description of the GTD-4600 exchange referred to herein will be 
found in a paper entitled "Evolution of the GTD-4600 PABX Tandem Switching 
System" given at the National Telecommunications Conference in New Orleans 
on Dec. 3, 1981. The last portion of this paper provides a list of 
additional published references concerning the GTD-4600. 
The telecommunication network described herein is described in more detail 
in a paper given at the same conference and on the same date given above 
and entitled "Private Interconnect Networks Overview". 
The network control center disclosed herein is described in another paper 
entitled "Network Control Center" and given at the same conference and on 
the same date given above. 
Additional papers describing the network control center and the connections 
between the exchanges and the center have been published in the GTE 
Automatic Electric World Wide Communications Journal, January-February 
1982. Titles of these papers are as follows: "Network Control Center 
Interface for the GTD-4600 Tandem Switch Enhancement" and "GTD-4600 Tandem 
Switching and Feature Enhancements". 
The contents of all of these papers and the list of references identified 
above are incorporated by reference herein. 
BACKGROUND OF THE INVENTION 
Medium to large corporations and governmental agencies may have a number of 
locations scattered across the country. The amount of voice and data 
information to be rapidly transferred between locations is increasing each 
year. This increase in transferred information coupled with increased 
rates charged by common carriers has caused many users to purchase or 
lease private telecommunication networks. These networks may include 
network control centers which provide important network administration, 
control, and maintenance functions. 
SUMMARY OF THE INVENTION 
In one aspect of the invention, a telecommunication network has a plurality 
of tandem node switches interconnected by groups of trunks. Each switch 
generates trunk group management data which is transmitted to a network 
control center system where the data is stored and read. Days for which 
the average usage of a selected set of trunk groups exceeds a specified 
level are identified as data days. 
The system determines the average busy hour and the average offered load. 
The system then calculates the amount of busy hour average blocking. The 
amount of trunks to be added to or deleted from a trunk is calculated for 
the condition where the actual busy hour blocking is approximately the 
same as a target busy hour average blocking.

For a better understanding of the present invention, together with other 
and further objects, advantages and capabilities thereof, reference is 
made to the following disclosure and appended claims in connection with 
the above-described drawings. 
DESCRIPTION OF THE INVENTION 
I. Overview of Network 
FIG. 1 shows an example of a private telecommunication network 
configuration. Several tandem node switches 10 serve as traffic 
concentrators and are used to direct traffic through the network. The 
tandem node switches are interconnected by intermachine trunks 11. These 
tandem node switches are generally located at the customer's major 
locations and may also provide private automatic branch exchange (PABX) 
capability. Since the tandem node switch generally provides major tandem 
capability and serves the stations at major locations, these switches must 
have a capacity to serve thousands of stations and hundreds of trunks 
(intermachine, access lines, and off-net). Satellite PABXs 12 are homed to 
one or more tandem node switches by access lines 13. Traffic to locations 
not served by the network is called off-net traffic and is served by 
common carriers on the public networks. 
The private network configuration also includes a centralized network 
control center (NCC) 14, which provides network administration, control, 
and maintenance functions. 
Each tandem node switch 10 may serve a large geographical area. The access 
lines 13, the intermachine trunks 11 and off-net facilities are leased 
from common carriers. Mixtures of satellite and terrestrial circuits are 
available. 
One such tandem node switch is the GTD-4600-TSE manufactured and sold by 
GTE Corporation. This switch can function as a large PABX utilizing a 
digital network as well as function as a tandem node in a private 
interconnect telecommunication network. The tandem node switch can be 
configured to have one or more customer groups as mains. These mains can 
be stand-alone switches or can have subtending satellite PABXs 12 or 
tributary PABXs 15. Each main can also have any or all of the features of 
a tandem node switch and may or may not be part of the network served by 
the tandem node customer group. 
The network can process both private and public dialing. In the case of 
public dialing, a route will be established through the network to the 
closest location to the dialed number and the call dropped off the private 
network to the public network at that point. 
The network dialing plan consists of a seven digit code. The first three 
digits are a unique RNX code which determines the location of the main 
within the network. The remaining four digits are the station number of 
the party dialed and correspond to his extension number or the listed 
number of the PABX. Within a main/sat/trib complex, each satellite and/or 
tributary can have a unique RNX code or may have the same RNX code as the 
main. If an entire main/sat/trib complex has the same RNX code, then the 
four digit station number or the listed number must be unique within that 
main/sat/trib complex. 
The tandem node switch also processes on-network ten digit calls. Based on 
the area and office codes dialed, the closest tandem node will be selected 
by a translator and a route established through the network until the last 
tandem node is reached. The last tandem node will outpulse off-net either 
seven or ten digits, depending upon the NPA area. 
In addition to network routing and translation functions of a tandem node 
switch, it has network control features which dynamically control the 
routing and translation, and for providing information on the level and 
type of traffic through the switch. These controls can be activated via 
either the network control center (NCC) or a designated local control 
terminal at each switch. Features such as trunk direction, dynamic route, 
time-of-day override and code blocking are all used to dynamically alter 
the routing and translation capabilities of the tandem node switch. Short 
register timing changes the holding time for receivers while station 
message detail recording (MDR), traffic data recording and 100 second 
trunk data provide periodic messages to the NCC for use in determining 
traffic data. 
Centralized administration and maintenance is accomplished by providing the 
tandem node switch with a high speed data-link interface to the network 
control center (NCC) 14. The data-link interface provides transmission and 
processing of such data as 100 second update of trunk data, traffic data, 
message detail recording (MDR), as well as the other maintenance and 
administration information previously provided locally. There is a need to 
send considerable amounts of full period data, the transmission of which 
requires framing, error checking, retransmission for error conditions, and 
a number of other communications tasks which require the tandem node 
switch to include a network control interface (NCI) which includes 
software and a communications front end 17 seen in FIG. 2. 
The NCI provides the centralized administration and maintenance features 
associated with interfacing the corresponding tandem node switch with the 
network control center. 
The NCI is structured around standard data communications protocol levels. 
A modem interface (level 1) was chosen as EIA RS232C. The transmission 
protocol (level 2) is a subset of HDLC/SDLC (the X.25 transmission level 2 
protocol). Since full period point-to-point circuits are required, a data 
switching level is not used. Therefore, the next level is an application 
dependent protocol established between the tandem node switch and the NCC. 
This level is implemented entirely in software and runs on the 
communications front end (CFE) 17. 
A brief overview of the GTD-4600-TSE hardware as seen in FIG. 2 should 
serve to better understand the network control interface (NCI). The 
GTD-4600-TSE 10 is a central processor based PABX with tandem switch 
enhancement which utilizes a general purpose sense and control structure 
termed the peripheral unit matrix (PUM) 16 to address the peripheral 
hardware. The entire complex is duplex for high reliability. There are a 
variety of peripherals associated with the system such as the input/output 
(I/O) interface, telephony circuit interfaces, and network control 
interfaces. The switch has a fully duplex digital network. 
The network control requirements are partitioned from the primary function 
of the switch. These requirements, having a major real-time impact, allow 
the use of distributed processing. This is achieved in hardware by the 
addition of the communications front end (CFE) 17 as part of the I/O 
facilities of the GTD-4600-TSE. 
An Intel 8085 controller serves as the main CFE microprocessor 18. An Intel 
8273 programmable HDLC/SDLC protocol controller 19 interfaces a data-link 
modem by means of an EIA RS232C driver and receiver 20. 
The modem configuration between the tandem node switch and the NCC is 
illustrated by FIG. 3. Communication between the tandem node switch and 
the NCC is through dedicated 4-wire 4800 b/s data-links 21. The data-link 
protocol is the International Telephone and Telegraph Consultative 
Committee (CCITT) specified LAP-B. 
Referring again to FIG. 2, a unique 16K by 32 bit "common memory" 
arrangement 22 is configured to accommodate the 32 bits bus of the 
GTD-4600 and the 8 bit bus of the CFE microprocessor 18. 
The "common memory" functions are to buffer messages received from (or sent 
to) the data-link, provide program store and provide interprocessor 
communications between the GTD-4600 central processing unit (CPU) and the 
CFE microprocessor 18. The system hardware to permits the GTD-4600 to 
write into the "common memory" via the peripheral control interface (PCI) 
data bus 23, and read from it via the existing PCI return bus 24. Reading 
or writing of "common memory" by the GTD-4600 CPU is controlled by two 
hardware pointers 25, 26 in conjunction with specifically selected 
peripheral matrix words. Auto-incrementing of the hardware pointers occurs 
on reads or writes to the peripheral matrix words. This permits the 
GTD-4600 CPU to automatically write (or read) into (or from) any of eight 
2K by 32 pages of consecutive addresses of "common memory". The CFE 
microprocessor 18 views the same memory as a 64K by 8 RAM within its 
addressing range and as such, can contain executable code. 
II. Overview of Network Control Center 
FIG. 4 is a block diagram of the physical layout of a network control 
center (NCC) 14 for practicing the invention. FIG. 5 is a functional block 
diagram of the NCC. 
The network control center is a stand-alone facility, and need not be 
co-located with a tandem node switch, nor for that matter housed at a 
location connected into the network. Thus, the network control center may 
be located to accommodate administrative concerns rather than technical 
constraints. 
Physically, the NCC consists of a main processor and memory 28, disc 29, 
operator terminals 30, alarm and exception character printer 31, dynamic 
color graphics display 32, remote trunk testing system 33, magnetic tapes 
35, system line printer 36 and data-link communications interface 37. 
The main processor and memory 28 is based on a microcomputer such as the 
Digital Equipment Corporation PDP-11 series of minicomputers and can range 
from the PDP-11/34 to the PDP-11/70, depending on network characteristics. 
The main processor, memory, disc and operator terminals accommodate the 
data manipulation, intermediate storage and human interface necessary to 
support the central control functions. The color graphics display 32 
provides a real-time, global view of network traffic and switch equipment 
status. The trunk test system 33 consists of software on the NCC computer 
and communications hardware that transmits control signals via direct 
distance dialing (DDD) lines 38 to remote office test lines (ROTLs) 39 
located at switch sites. The line printer 36 is used to output high-volume 
reports. A character printer, designated as the "alarm and exception" 
printer 31, outputs messages of critical importance. The magnetic tapes 35 
store message detail record (MDR) data and traffic data for processing on 
a separate computer facility. 
The NCC communicates with the tandem node switches using corresponding 
dedicated, 4-wire, 4800 b/s data-links 21 as seen in more detail in FIG. 
3. The data-link protocol (level 2) is preferably the CCITT specified 
LAP-B and was chosen for its throughput efficiency, error control and the 
availability of devices for implementation. This protocol can be enhanced 
to X.25 to be compatible with public data networks such as that offered by 
GTE-Telenet Communications Corporation. 
In the event of a data-link failure, dial-up lines 34 can fully restore 
functionality. In the event of catastrophic failure at the NCC, simple 
hardcopy terminals can be connected to switches via the dial-up lines to 
continue a degraded monitoring and control operation. Network call 
processing is in no way hampered by the loss of the NCC. In case of a link 
or NCC failure, MDR data from the tandem node switches are stored on 
magnetic tape 42 (FIG. 7) at the tandem node switch site, and can be read 
back to the NCC when the failure has been corrected. 
The important NCC capabilities are summarized below: 
1. Trunk testing is a tedious manual task and thus often not adequately 
scheduled. With software and hardware at the NCC, and remote office test 
lines (ROTLs) at the switches, trunk testing can be scheduled and 
automatically carried out under NCC control for all inter-machine trunks 
(IMTs) and satellite PABX access lines. The NCC analyzes the test results 
and prepares reports showing, for example, which trunks need immediate 
attention. Trunk testing can also be manually initiated. These 
capabilities ensure maximum trunk availability and avoid expensive 
over-dimensioning of network transmission facilities. 
2. Switch node maintenance is centralized at the NCC by remoting all tandem 
node switch craftsperson terminal functions to the NCC. As multiple 
switches are monitored the volume of maintenance messages and status 
reports would become overwhelming for manual scanning and, without 
computerized assistance, important messages would be overlooked. The NCC 
accepts and stores all switch messages from each network switch, scans 
them in the process, and alerts the operator immediately when critical 
messages are detected. Database utility software is provided for later 
sorting and selective retrieval to make the remaining messages useful. 
Maintenance costs are reduced and rapid restoral of network service is 
gained by these capabilities. 
3. Network user complaints can provide valuable maintenance information to 
an NCC operator. The NCC call trace feature provides a capability from an 
NCC resident database of MDR data to precisely reconstruct the path of any 
network call. The MDR record format includes identification of incoming 
and outgoing trunk groups as well as individual circuit identification. 
Further, other information can be selectively acquired from the MDR 
database; for example, a specific circuit can be examined for short 
holding times. These call trace features allow the telecommunication 
manager to be responsive to user complaints and improve service. 
4. Centralized real-time monitoring of network traffic conditions would be 
virtually impossible without computer assistance. The tandem node switch 
reports occupancy on each trunk group to the NCC at 100 second intervals. 
The NCC displays this information using color graphics techniques. When an 
all-trunks-busy condition persists too long, a threshold report is 
generated. Such timely information supports effective use of the numerous 
traffic control features provided by the tandem node switch and 
controllable from the NCC to mitigate traffic congestion. Optimal service, 
even during unusual traffic conditions, can be assured. 
5. The extensive traffic measurement features of the tandem node switch are 
designed to accommodate automated centralized traffic data collection at 
the NCC. The NCC analyzes the traffic data from all nodes in the network, 
and produces trunk group grade-of-service reports with add/delete-circuits 
recommendations to meet specified traffic objectives. In addition, traffic 
data is recorded on magnetic tape for subsequent off-line analysis. These 
features ensure that the desired grade-of-service is achieved at the 
lowest transmission costs. 
6. By providing for centralized switch database administration, 
particularly in regard to switch database changes involving network-wide 
operations or features, the NCC facilitates improved coordination of 
technical and administrative tasks required for economical, high-quality 
network operation. FIG. 6 illustrates the centralized switch control of 
the NCC. 
7. The NCC centrally collects all MDR data from all tandem node switches 
and records the data on magnetic tape for off-line processing. This avoids 
the operational costs of manual MDR tape collection. 
8. The NCC provides management aids to track alarms and trouble reports, 
and produces summaries of MDR and traffic data. These reports help the 
telecommunications manager "monitor the pulse" of network activity. 
Upon completion of a call which passes through the network, each of the 
involved tandem node switches creates message detail record (MDR) data 
which identifies the called number, the incoming and outgoing trunk groups 
and circuit number, authorization code (if applicable), the date, 
beginning and completion times, and call disposition. In the case of an 
originating node, the station on the tandem node switch or the access line 
from a satellite PABX would be identified. A station on a remote PABX 
could also be identified if equipped with automatic identification of 
outward dialing (AIOD). 
The collection and magnetic tape storage of message detail record (MDR) 
data is important to many network customers, as it allows for equitable 
proration of telecommunications costs and supports network traffic 
engineering activities. MDR data can be accessed on-line for maintenance 
purposes. Referring to FIG. 7, the NCC collects MDR data in an MDR 
database 40 from all network node switches 10 and creates a single, 
uniformly formatted magnetic tape 41 convenient for off-line processing. 
The centralized collection of MDR records avoids the problems of physical 
transportation of locally created MDR tapes. A single tape eases the 
off-line merging problems, and a single format eases the off-line 
pre-processing problems. In case of a data-link failure, data from a 
switch produced tape 42 can be entered through an MDR consolidation and 
reformatting module 43. 
A report generation unit 45 produces an MDR summary report 49 to provide 
NCC operators with an overview of network traffic. 
With reference to FIG. 9, automatic circuit assurance (ACA) reports are 
sent by the tandem node switch 10 to the network control center, 
identifying trunks with either long or short holding times. These reports 
can also indicate trunk problems and can be used in conjunction with other 
NCC features to assist in localization of a problem. 
The network control center makes valuable use of network user experience 
and complaints as a source of maintenance information. The NCC provides a 
call trace capability as well as database access to all past automatic 
circuit assurance reports and recent MDR records. 
The NCC call trace feature would typically be used in response to a network 
user complaint. Complaints may result from noisy lines, insufficient 
volume, call cutoffs, etc. Based upon the called and calling number and 
the approximate time of the call, call trace will sort the MDR records and 
determine the exact circuit path (trunk group and circuit identification) 
taken by the call through any number of tandemed switches. FIG. 15 is an 
information flow diagram of the call trace feature. This information may 
be used to initiate further maintenance activity. The NCC also creates a 
log of all call traces and their results, which can be studies to identify 
facilities common to a number of complaints. The call trace log can often 
reveal an intermittent or subtle problem undetectable via other 
mechanisms. 
To uncover problems not otherwise apparent, additional features allow an 
operator to selectively search a database of MDR records based upon time, 
date, switch, incoming or outgoing trunk, called or calling number, and/or 
call disposition. For example, a specific trunk can be examined for short 
holding times. Adjunct to these search/sort/select features (which can be 
applied to switch messages, MDR, ACA, and traffic data) is the capability 
of requesting printed reports of the results in operator-definable 
formats. 
The network control center provides two powerful trouble tracking 
mechanisms: an alarm log and trouble tickets. These computerized 
facilities, illustrated in FIGS. 8 and 9, respectively, support the 
network operators and their management by simplifying and assisting in 
trouble followthrough. This avoids previous manual methods which were 
usually ad hoc and often incomplete. 
In a centralized control center environment, the operator must be made 
aware of critical maintenance conditions rapidly. The network switches 
remote all maintenance information to the network control center. However, 
in a multiswitch network the volume of maintenance information (e.g., 
switch status and error messages) can be so large that critical messages 
get overlooked. To ensure that critical conditions are not overlooked, the 
NCC alarm feature identifies messages requiring immediate operator 
attention. 
Every message from each tandem node switch in the network is transmitted by 
a computerized filter 66 to the NCC and compared with predefined alarm 
conditions. If there is a match, an alert is immediately generated and the 
alarm message is printed by the alarm and exception printer 31. Further, 
many categories of messages are not of alarm priority unless their 
frequency of occurrence reaches a certain threshold. This would apply, for 
example, to intermittent hardware or software failures. In such instances, 
the NCC also alerts the operator when a predefined frequency-of-occurrence 
threshold has been exceeded. 
An alarm log 44 is a computerized database, automatically updated each time 
an alarm is detected by the NCC. Included in the alarm log format are the 
date and time of occurrence, switch identification, message type, status, 
alarm log entry number, and space for an operator-entered free-format text 
area. The operator is given wide-ranging ability to print, display or 
update alarm log entries at any time through the terminal 30. 
To maintain visibility of alarms, there is a periodic open alarm summary 
report 46 which, on an operator-selected schedule, reminds him with a 
short summary of open alarms. Also provided is a printed management 
summary report 47 which, for a specified reporting period, summarizes the 
alarms opened and closed, and the dates and times of their opening or 
closing. 
Analogous to the alarm tracking mechanism, the NCC provides a computerized 
trouble ticket log 63 to coordinate and track general troubles. The 
trouble ticket format, displayed upon operator request, provides a time, 
date and trouble ticket number field already entered by the system. In 
addition, there are fields for the switch identifier, the operator's name, 
the site telephone number, an area for trouble descriptions and a status 
field (open and closed). As with the alarm log, entries may be sorted by 
time, date, switch, trouble ticket number or status. Also provided is a 
printed trouble ticket summary report 64. 
Both the alarm and trouble ticket management summary reports provide 
management with visibility and documentation of problems handled by the 
staff, and may be used as a gauge of switch and transmission performance. 
The graphics display 32 plays an integral part in monitoring and tracking 
both switch alarm messages and traffic conditions. The NCC operator can 
get a rapid overall impression of network traffic from a "global display", 
an example of which is illustrated by FIG. 10, or may choose instead to 
watch a single-node switch as illustrated by FIG. 11. The "single-node" 
images provide, at a glance, the alarm status at all nodes, traffic 
monitoring of all trunk groups connected to the node of interest, 
including IMTs, satellite PABX links (access lines), on-net and off-net 
access lines (DID, CO, FX, WATS), and other details concerning each of 
these trunk groups, such as number of circuits per group and vendor. 
Network alarm status (and traffic) information is dynamically displayed via 
color graphics giving the operator an overview at a glance of current 
networks alarm status (and traffic conditions). This avoids the 
traditional deluge of rows and columns of numbers. The principal display 
consists of a geographic representation of all nodes and inter-machine 
trunks in the network. Immediate recognition of alarm conditions is 
assured by changing the node symbol of the affected node from green to 
flashing red and sounding an audible alert which can only be silenced by 
operator acknowledgement. The node symbol is returned to green when the 
corresponding alarm is retired. The actual message which triggered the 
alarm is printed on the alarm and exception character printer 31. This is 
illustrated by alarm state diagram of FIG. 15. 
The general usefulness and applicability of NCC features may best be seen 
through example. Suppose a PABX attendant calls the NCC operator 
indicating that a number of users have complained of noisy lines or 
interrupted calls when making calls to a particular network switch. The 
PABX attendant provides information regarding the called and calling 
numbers, and the NCC operator logs the trouble indications in a trouble 
ticket. 
A variety of trouble conditions could exist at this point: the problem may 
be intermittent or stable, and may exist in the transmission or switching 
facility. Of course, intermittent problems are the most difficult to 
diagnose, and that is where the NCC features become most useful. The NCC 
operator has a variety of options at this point. 
The operator would probably first examine past trouble tickets and alarm 
logs to see if the problem was already detected, or whether similar 
reports had been logged earlier. Depending on the circumstances, the 
operator may choose to initiate a call trace on one or several of the 
complainer's calls. The call trace will identify specific switch nodes, 
trunk groups and circuits involved in the call setups. The results of the 
call trace will enter the call trace log and common facilities may be 
identified. If a common trunk is found, the MDR database can be sorted to 
see if that particular trunk has recently experienced excessive numbers of 
short holding times. Abnormal holding times may also be found conveniently 
by sorting the ACA reports in the switch message database 65. The NCC 
operator could also initiate a trunk test to measure noise and gain or 
perhaps perform a maintenance call-through on the offending trunk. One or 
several of these features would identify a bad trunk. If a bad trunk is 
found, it may be taken out of service from the NCC. In any case, any 
action taken would be recorded in the trouble ticket. 
Under different circumstances, the NCC operator may take a different course 
of action. If a switch problem instead of a trunk problem were suspected, 
the operator could examine the switch message database 65. The operator 
could select and retrieve the last maintenance summary report from a 
specific switch, or he might choose to see all maintenance messages from 
that switch for the last 30 minutes. In any case, the information is 
conveniently displayed. The operator may then choose to initiate a switch 
diagnostic. Depending on the results, the operator may transfer service to 
a redundant unit or put a unit out of service. If the problem were very 
serious, the operator could even re-route traffic to avoid the problem 
area. Again, actions taken would be tracked using the trouble ticket. 
These are only simple examples of possible NCC activities. However, it is 
seen that from one central location, the NCC operator can localize a 
reported problem, effect required diagnostics, modify the switch hardware 
configuration, and, most important, provide a single maintenance contact 
for network users and provide coordination of repair efforts. The NCC thus 
provides a single center with overall maintenance responsibility. 
Proper and efficient handling of non-alarm messages is also important. 
These messages afford the operator detailed monitoring of switch node 
status, and can assist in diagnostics and trouble localization. All 
messages from all switches are maintained in an NCC switch message 
database. The messages are easily accessible to the operator via database 
utility software capable of sorting and selecting by switch, time period, 
and message type (every message is assigned a message type code by the 
tandem node switch; some message types embrace broad categories of 
messages, while others are unique to a single message format). This 
powerful database capability is a significant improvement compared to 
approaches which involve manually scanning reams of printouts documenting 
the events at each switch from past hours or days. The chances of 
overlooking important symptoms are drastically reduced, and operator 
efficiency in correlating diverse events is greatly enhanced. 
Continual traffic monitoring is necessary to ensure optimal traffic 
handling, especially during unusual conditions. The NCC gives the network 
operator timely traffic information and effective congestion relief tools. 
Traffic monitoring and control capabilities are particularly important in 
a private network, where economics dictate minimal trunk group sizings. In 
such finely optimized networks, localized problems can have network-wide 
consequences. For example, should a common carrier experience a broadband 
failure, all trunks in an intermediate trunk group between two switches 
may be disabled. The NCC operator would be rapidly alerted. The operator 
could temporarily cancel alternate routing from distant nodes which might 
normally be routed through the affected switches. This prevents distant 
traffic from entering the affected region and being blocked when it may 
have had other alternate routing possibilities (such as off-net routing). 
This mitigates the effect of a localized problem on network-wide traffic. 
Further, by preventing distant traffic from entering the affected region, 
local users have a greater opportunity for any remaining alternate paths. 
The network control center monitors the traffic from each trunk group in 
the network on a near real-time basis. Referring now to FIG. 13, this is 
accomplished by each of the tandem node switch network switches sending 
"100-second scan" trunk usage information to the NCC. Specifically, the 
tandem node switches sample each trunk group and send information on the 
number of busy trunks to the NCC every 100 seconds. The information is 
stored in a traffic database 50 and processed by a threshold analysis unit 
51. 
The 100-second scan information immediately updates graphics displays. 
Specifically, inter-machine trunk group occupancy is shown on the "global" 
display (FIG. 10), and satellite PABX access line group occupancy and 
off-net line group occupancy are shown on a "single node" display (FIG. 
11) available for each node. Colors are used to signify the level of trunk 
group occupancy in three arbitrary ranges; e.g., no traffic to moderate 
traffic (approximately 0-75% busy), heavy traffic (approximately 75-95% 
busy), and all-trunks-busy (ATB= 100% busy). The graphics display 32 
provides the operator with a rapid impression of the overall network 
traffic from the global display and traffic at particular nodes from the 
single-node displays. 
Typically, all-trunks-busy (ATB) conditions are not considered anomalous 
until they persist for several consecutive 100-second scan intervals. 
Although the operator could visually monitor such circumstances on the 
graphics displays, this would be burdensome. Thus, a traffic threshold 
report 52 is printed which identifies trunk groups with more than a 
specified number of consecutive ATB 100-second scans to advise the NCC 
operator of significant ATB conditions. 
The NCC operator is in a unique position: first, to decide if congestion 
relief action is warranted, and second, to take effective action when 
appropriate. Along with the traffic displays and threshold reports, the 
NCC operator also has other information which could bear on a potential 
traffic problem, such as maintenance status (both switch and trunk) and 
administrative information. If the operator decides to take action, 
available traffic control measures include: 
1. Routing and translation table modification 
2. Time-of-day routing 
3. Alternate route controls 
4. Route reservation controls 
5. Code blocking 
6. Queue control 
7. Short register timing 
The operator can watch the results of the action taken on the graphics 
display 32. The graphics display system plays an integral part in 
monitoring and tracking both switch alarm messages and traffic conditions. 
The NCC operator can get a rapid overall impression of network traffic 
from the "global display", or may choose instead to watch a single node 
switch. The "single node" images provide at a glance the alarm status at 
all nodes, traffic monitoring of all trunk groups connected to the node of 
interest including IMTs, satellite PABX links (access lines), on-net and 
off-net access lines (DID, CO, FX, WATS), and other details concerning 
each of these trunk groups, such as number of circuits per group and 
vendor. 
Network traffic engineering for optimum service at minimum cost requires 
considerable traffic data and sophisticated analysis. In most private 
networks, transmission facility costs dominate overall network costs. This 
makes providing the desired grade-of-service with the fewest trunks an 
important goal to the telecommunications manager. The first step toward 
this goal is to properly engineer the overall network; that is, to choose 
the proper number and location of network nodes, and properly dimension 
the interconnecting trunk groups, the satellite PABX trunk groups, off-net 
trunk groups, etc. Once the network is in place, initial traffic 
measurements are necessary to verify that the specified grade-of-service 
on each trunk group is achieved with minimum trunking. Following the 
initial traffic verification period, a plan of regular traffic 
measurements and trunk adjustments is required to accommodate changes in 
traffic patterns arising from network growth and other causes. 
Referring to FIG. 13, the network control center provides a monthly 
grade-of-service report 54 which compares measured traffic statistics with 
the network design objectives for each trunk group, and makes a 
recommendation based on standard traffic engineering formulas of the 
number of circuits to add or remove to bring the group within objectives. 
This report is derived by a traffic analysis unit 55 from traffic data 
routinely collected from all node switches. The traffic analysis unit 55 
extracts trunk usage (in CCS) and event counts data from which busy-hour 
statistics are compiled and compared with the trunk-group design 
objectives. The trunk-group objectives are specified on a per-trunk-group 
basis and can be modified as appropriate. The busy-hour data and 
recommendations are made available at the end of each calendar month, 
along with the previous two months' recommendations. FIG. 16 is an 
information flow chart for this function. 
To support off-line traffic data analysis, a traffic data tape 56 is also 
created at the NCC. The tandem node switch has an extensive repertoire of 
traffic-metering packages, including trunk usage and events (as 
mentioned), switch usage and events, load balancing, business service 
usage and events, load service indicators, inlet usage, customer service, 
MDR studies, and daily totals. These traffic packages can be initiated 
manually or scheduled on a periodic basis as measurement summary 57. In 
either case, the results of all traffic measurements are sent to the NCC, 
stored in the NCC database, made available to the operator, and placed on 
a traffic data magnetic tape for off-line processing. 
The foregoing sections have been an overview of the telecommunication 
network including both the tandem node switches and the network control 
center. Some understanding of the system and its main components is 
necessary to appreciate the present invention which will now be described 
in more detail. 
III. Traffic Analysis 
The objective in traffic engineering is to provide maximum call completions 
with the minimum number of circuits. To reach this objective, the NCC 
regularly evaluates the traffic data, and by using standard traffic 
equations and predetermined blocking and delay targets, decides upon 
changes in the number of circuits required. This is a complex process and 
is in the past was usually done manually quarterly or annually. As a 
feature of the invention, the NCC automatically provides a monthly summary 
report of the traffic data for the network (by trunk group), performs the 
calculations required, and makes recommendations as to additions or 
deletions of circuits necessary to maintain an optimum size (and optimum 
cost) network. 
Traffic data in the form of traffic data administration (TDA) packages is 
collected by the tandem node switches and transmitted to the traffic 
database within the NCC as seen in FIG. 13. All metering package data 
received at the NCC is maintained in detail on a disk for at least 24 
hours in forms suitable for useful access, and are stored on the traffic 
data magnetic tape. Each tandem node switch generates several measurement 
TDA packages pertaining to traffic volume, its distribution on each route 
and circuit group and its variation daily, weekly and seasonally. Only the 
trunk measurement package (MPTK) is used by the NCC to calculate the 
traffic management report and recommendations pertaining to addition or 
subtraction of trunks. 
An event counter is associated with each trunk group. A trunk group is the 
group of trunk circuits connecting one node to another. The event counter 
is incremented each time the particular event occurrence is detected 
(e.g., when all the trunks are busy). The event counter accumulates the 
event occurrences over a specific time interval. At the end of the time 
interval, the value representing the total event occurrences is recorded, 
and the event counter is reset to zero. This data is used to calculate the 
busy hour. 
At least one resource usage counter is associated with each trunk group. 
Trunk group usage is the total time that a trunk group is used to perform 
its designated function over a specific time interval. Actual usage is not 
recorded in the system. By sampling at regular intervals, an approximate 
value for the usage of the trunk group is obtained. The technique of 
sampling requires a busy counter and an accumulator. When an item from a 
particular trunk group is allocated for use, the busy counter is 
incremented. When one of the resource items is released from use, the 
counter is decremented. At regular periods during the time interval, the 
value of the busy counter is added to the accumulator. At the end of the 
specified time interval, the value of the accumulator is recorded and 
reset to zero. 
All usage measurements are reported in hundred call seconds (CCS), where 
the following conditions apply: (a) 1 CCS=1 resource member in use for 100 
seconds; and (b) 36 CCS=1 Erlang. The normal sampling period is 100 
seconds for trunk groups. 
The degree of usage increases as the usage value increases. A maximum of 
100 percent usage occurs when all trunks of a group are in use for the 
entire time interval. The actual numeric value for 100 percent usage 
depends upon the number of circuits contained by the trunk group. 
Average usage of a trunk group during a traffic data administration (TDA) 
reporting interval (RI) is derived by using the following formula: Percent 
average usage=(trunk group usage.div.usage for 100 percent 
usage).times.100. 
Traffic data is held in two distinct forms: intermediate data and complete 
data. The data is accumulated in the intermediate data area with the least 
amount of data processing time required for each data item. At the end of 
each reporting interval (RI), the package is activated and intermediate 
data is transferred to the complete data area in preparation for recording 
the complete data. The intermediate data area for each package is then 
reset to zero to collect data for the next RI. 
The several traffic data administration (TDA) packages must be individually 
activated after which they will generate data messages to the NCC 
according to operator defined schedules until deactivated. Scheduling 
options allow operator selection for each metering package of: 
i. Designated days: Any or all of the 7 days of the week. Typical: Monday 
through Friday. 
ii. Collection interval (CI): Except for the daily totals metering package 
(MPDT) whose CI is always 24 hours, any metering package may have up to 
three scheduled data CIs within a 24 hour period. Data may be collected 
over any one, two, or three non-overlapping CIs such that the sum is equal 
to or less than 24 hours. Each CI must be a multiple of the Recording 
Interval. Typical: One CI: 7 AM to 6 PM. 
iii. Reporting interval (RI): This is the time between scheduled outputs to 
the NCC. The RI must be a minimum of 15 minutes and may be greater in 
increments of 15 minutes. The RIs for all metering packages, except for 
daily totals, are alike for a given switch. 
The MPTK package provides the following measurements for each internode 
trunk group. 
i. INC USAGE--Incoming traffic usage (CCS) during the RI. 
ii. INC ATT--Incoming attempts count during the RI. 
iii. INC HITS--Incoming hits count during the RI, i.e., the total number of 
calling party disconnects before the receipt of digits. 
iv. OGT USAGE--Outgoing traffic usage (CCS) during the RI. 
v. OGT ATT--Outgoing attempts count during the RI. 
vi. OGT OFL--Outgoing overflow count during the RI. 
vii. Q ATT--Attempts count on indicated queue during the RI. 
viii. Q OFL--Overflow count on indicated queue during the RI. 
ix. Q USAGE--Usage (CCS) of the indicated queue during the RI. 
x. OHQ ABAND--Off-hook queue abandon count during the RI. 
xi. RBQ ABAND--Ring-back queue abandon count during the RI. 
xii. OHQ TIMEOUT--Off-hook queue timeout count during the RI. 
Thus, a switch provides per-circuit traffic data and per-queue group data. 
Regarding items i through vi: For one-way trunks, only the appropriate 
three measurements are relevant. Traffic grade-of-service analysis can 
only be meaningful for outgoing service, although the incoming usage on a 
two-way trunk is considered part of the carried traffic load. 
The MPTK package provides items i, ii, iv, and v on a per trunk group 
member basis for one trunk group in the system. 
The NCC operator is able to activate this package as desired, in which case 
the resulting data is stored on the traffic tape. 
The incoming and outgoing usages for two-way trunk groups used is the same 
in MPTK. Two busy counters for each trunk group may be used to calculate 
the incoming and outgoing usages separately. 
The traffic measurement summary report 57 is intended to supplement overall 
network engineering by providing traffic measurement summaries on an 
individual trunk group basis. No attempt is made to correlate whole 
network traffic patterns as the traffic data magnetic tape 56 is created 
for that purpose. 
The traffic measurement report 57 is designed for printing on a monthly 
basis at operator request up to 10 days after the end of the reporting 
period (RP) requested. 
All measurement data for the traffic measurement reports are obtained from 
the MPTK metering package. FIG. 16 is an information flow diagram of the 
steps taken to calculate recommendations. First, the MPTK is read and data 
days are selected. The average busy hour is found and other report fields 
are calculated. Then the recommendations are computed using a standard 
blocking formula. In most cases the data required to calculate a given 
monthly (or intermediate) report field can be saved as an accumulated sum, 
thus eliminating the necessity to store vast quantities of detailed data 
items. In addition, the number of trunks in each group, the starting times 
of the busy hours defined above, and the results for the preceding two 
months of the computations for "TIMES ABOVE TARGET" and "ADD/RMV TRUNKS TO 
MEET TARGET" are printed. An example of a traffic measurement report 
format is seen in FIG. 17. 
The report layout shows the report title and date of printing on the first 
line, then the report page number, then the switch number and the 
reporting period, then column headings and report data. TRK GRP identifies 
the trunk group. NUM TKS is the number of trunks in the trunk group. 
For trunk groups with queues, a line showing queue data follows the regular 
traffic measurement data line and be designated by "QUE" in the TRK GRP 
field. 
The remaining report fields are specified in following sections. 
To eliminate averaging-in data from abnormally low traffic days, e.g., 
holidays, a data day is defined as a designated day for which the average 
usage of a selected set of trunk groups (e.g., IMTs) exceeds a specified 
threshold. 
It is necessary to accumulate all of the various MPTK raw data items 
(marked with an * in the following description), and to also accumulate 
the daily computed offered load, blocking, and average queue delay for 
each hour of interest (by switch local time). However, once the busy hour 
is identified after the end of the RP, only the accumulations for the busy 
hour are used in subsequent calculations. 
The "time consistent" busy hour is determined for each trunk group. This 
may be accomplished by accumulating the computed offered load for each 
data day for each hour, and picking the hour with the greatest accumulated 
total (or highest average offered load) for the reporting period. 
The two-way offered load for a given day and hour is given by: 
EQU Offered Load=Carried Load/(1-Blocking) (1) 
where, 
EQU Carried Load=INC USAGE*+OGT USAGE* (2) 
and, 
EQU Blocking=OGT OFL*/OGT ATT* (3) 
For one-way trunk groups, only the appropriate term is used in (2). 
The average offered load for a given hour is then given by: 
##EQU1## 
Doing this computation for the busy hour gives the AVG BSY HR OFFERED LOAD 
to be printed in the report (field 7). 
The accumulated sums of busy hour INC USAGE* and OGT USAGE* data over the n 
data days of the reporting period divided by n give the averages to be 
printed in field 4 (INC) and field 5 (OUT) respectively. The carried load 
(CAR'D LOAD) in field 6 is then just the sum of fields 4 and 5. (Field 7 
OFR'D LOAD was covered in the preceding section.) 
OUTGOING ATMPS (field 8) and OVFL (field 9) are computed in similar fashion 
to average usages by averaging busy hour OGT ATT* and OGT OFL* data over 
the data days in the reporting period. 
Busy hour average blocking (field 10) is given by: 
##EQU2## 
QUEUE ATMPS, OVFL, USAGE, ABND, and TMOTS (fields 11 through 16) are 
averages over the data days in the reporting period (RP) of busy hour data 
items Q ATT*, Q OFL*, Q USAGE*, OHQ ABAND*+RBQ ABAND* and OHQ TIMEOUT* 
respectively. Once again, accumulate and divide by n. 
Average queue delay (field 17) pertains only to off-hook queuing, and is 
given by: 
##EQU3## 
The operator preselects selected busy hour average blocking target on 
regular report lines, or his average off-hook queue delay target on QUE 
lines. 
How many hours during the respective RPs an unqueued trunk group has 
exceeded its blocking target or a queued group has exceeded its delay 
target is calculated. Results for the current and preceding two months are 
entered into the report. Since the busy hour is not known until the end of 
the reporting period, these two above target counters must accumulate for 
all hours. This means blocking and queue delay must be computed for each 
hour. The applicable formulae are: 
##EQU4## 
Recommendations are made for adding or removing circuits, signified by a 
plus or minus sign respectively, to accommodate the target grade of 
service for blocking on unqueued trunk groups or delay on queued groups. 
Recommendations for the current and preceding two months are entered into 
the report. 
These recommendations are computed using a standard blocking formula or a 
customer specified formula. The standard blocking formulae are the Erlang 
B Formula, the Erlang C Formula, and the Poisson Formula. 
Where a is the offered load in Erlangs (1 Erlang=36 CCS) and c is the 
number of trunks, the probability of blocking in an infinite source system 
with blocked calls cleared is given by the Erlang B Formula: 
##EQU5## 
If blocked calls are delayed, the blocking probability (of a delay D=0) is 
given by the "Erlang C" Formula: 
##EQU6## 
and the delay distribution by: 
##EQU7## 
from the previously calculated OUTGOING parameters of fields 5, 8, and 9. 
The Poisson Formula arises from a model with blocked calls held in the 
system and retrials accounted for, and gives a blocking probability 
between the extremes of Erlang B and C. The Poisson Formula is: 
##EQU8## 
The computer iteratively "plugs into" the specified blocking formula 
parameters of offered load, a, and for delay distributions, the average 
holding time, T, computed from the average busy hour figures, and 
increment or decrement the number of trunks, c, until the blocking formula 
yields the result nearest to but not exceeding the specified target. The 
recommendation is then the signed difference between this result and the 
actual circuits equipped. 
While there has been shown and described what is at present considered the 
preferred embodiment of the invention, it will be obvious to those skilled 
in the art that various changes and modifications may be made therein 
without departing from the scope of the invention as defined by the 
appended claims.