WO1994000958A1

WO1994000958A1 - Method of controlling the traffic in a communications network

Info

Publication number: WO1994000958A1
Application number: PCT/GB1993/001306
Authority: WO
Inventors: Brian Charles Tester; Donald Fisk; Charles Arnold Swaine
Original assignee: British Telecommunications PLC
Current assignee: British Telecommunications PLC
Priority date: 1992-06-19
Filing date: 1993-06-21
Publication date: 1994-01-06
Anticipated expiration: 1994-12-19
Also published as: AU4349393A; GB9213033D0

Abstract

A method of controlling the traffic in a network, which includes at least one local exchange connected by one or more routes to one or more parent trunk exchanges, each parent trunk exchange being one of a plurality of trunk exchanges interconnected by trunk routes. The method consists in that controls are applied: (a) whenever the Percentage Overflow (OFL) for one or more traffic routes from a parent exchange to the local exchange has stayed above a first threshold for the duration of a measurement period; and (b) whenever the All Circuits Engaged (ACE) parameter for one or more traffic routes from a far-end trunk exchange to a parent exchange of the local exchange has increased from above a second threshold to above a third threshold greater than the second threshold during a measurement period. The control which is applied when condition (a) is met and the said OFL has stayed above the first threshold as required is route gapping to affect the relevant traffic route or routes. The control which is applied when condition (b) is met and the ACE parameter for a traffic route has remained above the third threshold as required is call gapping for the number range of the local exchange and the control is applied at the relevant far end trunk exchange or exchanges.

Description

METHOD OF CONTROLLING THE TRAFFIC IN A COMMUNICATIONS NETWORK

This invention relates to a method of controlling a communications network which includes at least one local exchange connected by routes to one or more parent trunk exchanges each being one of a plurality of trunk exchanges interconnected by trunk routes. It is particularly concerned with the control of a network following detection of a local exchange failure.

Commonly a local exchange is associated with a home exchange, through which incoming calls to the local exchange are routed, and a security exchange, through which outward calls from the local exchange are routed, in normal operation. The security exchange is so called because it can also be used to route incoming calls to the local exchange if the home exchange fails. The security and home exchanges are collectively referred to as the parent exchanges of the local exchange. Exchanges other than the parent exchanges are referred to as far end trunk exchanges of the local exchanges. Near real-time network traffic management (NTM) is an essential component of network management if optimal traffic performance in terms of call throughput is to be ensured. To give an indication of the volume of traffic which may be involved, BT' s trunk network in the United Kingdom currently handles approximately six million call attempts per hour during the busy periods which is equivalent to 1, 700 call attempts per second. Given such a volume of traffic it is essential that any network difficulties are detected and controlled as quickly as possible. For example, difficulties are often encountered by network traffic managers due to abnormal traffic patterns which can be caused by events such as ' phone-ins, tele-votes and public holidays (for example Christmas Day and New Year's Eve/Day). In all these cases traffic in the network varies widely from the normal level, sometimes quite spectacularly, and the network must be controlled to maintain the best overall network performance. With the introduction of digital switches such as System X it is possible to monitor closely the performance of each exchange and the routes between them and to the subscribers. BT' s Network Traffic Management System (NTMS) currently receives statistics on upwards of 37, 000 routes from 490 exchanges in the UK every five minutes, which measurement period was chosen to be a long enough period to be able to obtain a statistically reliable measurement of the network performance whilst being short enough to allow effective real-time control of the network.

The information received by the NTMS is processed to provide CCITT recommended parameters. For instance, these include the Percentage Overflow (OFL) and All Circuits Engaged (ACE) parameters. The parameter values are then compared with thresholds to determine if any difficulties exist on the monitored network elements.

Usually the first: indication of a network problem is when an ' exception' is displayed on a wall-board, or on a graphical interface at an individual manager' s workstation, at a Traffic Management Centre. Exceptions are those parameter values, calculated from network element measurements, which deviate sufficiently from a predetermined threshold for that value. The exceptions are ranked in a priority order with the top 20 displayed. However, due to the manner in which the thresholds are set by the network traffic managers, some exceptions do not necessarily indicate a difficulty as thresholds are percentage-based and set a value which ensures all potential difficulties are captured. This results in exceptions being displayed that are occasionally spurious or insignificant. The exceptions therefore need to be examined in more detail to determine if a real difficulty exists and whether it warrants any action. To help in this activity several information sources are currently used by the network traffic manaσers. The NTMS provides near real-time surveillance and monitoring of the network' s status and performance. It provides the network traffic managers with information to enable them take prompt action to control the flow of traffic to ensure the maximum utilization of the network in all situations. The NTMS allows network traffic managers to look at the raw statistics as well as derived generic parameters and to compare traffic patterns over the last few measurement periods to isolate any trends. An On-Line Traffic Information System (OTIS) takes the measurement of statistics from the NTMS system and processes them to provide summarised historical data for daily and weekly traffic patterns. This system allows the network traffic managers to examine historical traffic patterns to detect any radical shifts in traffic.

A data management system provides the network traffic managers with an up-to-date copy of the routing tables at all trunk exchanges. This information is used to check the routes to which calls can be routed, which controls are in force and the routing algorithms being used.

There is also a broadcast speaker facility which connects the world-wide network management centre to all the regional centres.

Once a potential difficulty has been detected, acknowledged and analyzed, it is characterised and a decision made whether to control it using the available range of expansive and restrictive controls to either allow alternative traffic paths through the network or to restrict or block call attempts to particular areas, respectively. The situation must then be monitored to ensure ^the controls are having the desired effect and that they are removed as soon as a problem has been dealt with effectively.

One class of exception associated with telecommunications networks is the failure of a local exchange. - A -

Although local exchange failures occur relatively frequently they rarely result in a problem that requires intervention from the network traffic managers. This is because of the unit' s built-in self-correcting mechanisms. For example, if a problem occurs at a System X exchange there are a number of stages it will go through to try and recover. These are: a) Process Rollback - this is a software routine and service is not affected. A Rollback shows on the NTMS as an exchange alarm; b) Restart - the exchange automatically restarts and service is affected; c) System Initialisation - the software is initialised from a backing store; and d) Manual Reload - part or all of the system is reloaded manually.

When a unit is in trouble it will first try four or five Rollbacks and only if these are unsuccessful in curing the problem will it perform an automatic Restart. If a Restart occurs this can be detected from NTMS statistics.

Normally a Restart is sufficient to return the unit to a fully working condition. However, sometimes when the unit returns it still does not perform correctly so it needs to be monitored to ensure that it is handling calls correctly. The last two stages, c) and d), occur only rarely when a Restart fails.

In the majority of cases no action is therefore necessary. However, when it is, route gapping is a control that may be used but it is present practice only to apply route gapping if the exchange is likely to be isolated for another five minutes and the calling levels are high.

Controls available might comprise not only route gapping but also other forms of call gapping, and code blocking. Route gapping however affects all calls down a particular route. Call gapping and code blocking can be applied to be more destination specific. When an exchange is in difficulty the first function it stops is the production of performance statistics. (In System X exchanges these are known as MSS statistics, from the Management Statistics Subsystem. ) In some cases this means the statistics from the affected exchange are all zero even when it is in fact handling calls correctly. In such cases it is therefore necessary to monitor the network to determine at which particular trunk exchanges controls should be applied and for how long other than by looking at the parameters issued by a local exchange which has failed.

According to the present invention, there is provided a method of controlling a network, which includes at least one local exchange connected by one or more routes to one or more parent trunk exchanges, each parent trunk exchange being one of a plurality of trunk exchanges interconnected by trunk routes, the method being characterised in that controls are applied: a) whenever the Percentage Overflow (OFL) for a traffic route from a parent exchange to the local exchange has stayed above a first threshold for the duration of a measurement period; and b) whenever the All Circuits Engaged (ACE) parameter for a traffic route from a far-end trunk exchange to a parent exchange of the local exchange has increased from above a second threshold to above a third threshold greater than the second threshold during a measurement period.

When the above condition a) is fulfilled, and the OFL for a traffic route from a parent exchange to the local exchange has remained above the first threshold as stated, the control which might be applied is route gapping to affect the appropriate traffic route or routes. When condition b) is fulfilled, the control which might be applied is call gapping to the number range of the local exchange, and it s applied at the relevant far end trunk exchange or exchanges. It might be noted that, for the purpose of the present specification, "traffic route" or "route" is used to describe a route in a network primarily between exchanges and does not normally include the link between a subscriber' s customer premises equipment and the local exchange.

Once route or call gapping has been applied it should be removed when the failed local exchange has been brought back into service. Again, it is necessary to monitor the network to determine when this has occurred. It has been determined that preferably the route gapping is removed from a parent exchange once the Circuits In Service (CCTS

IS) on the traffic route(s) from the parent exchange to the local exchange has been greater than a first proportion of the available circuits on that route (or those traffic routes ) for the duration of a measurement period and the call gapping is removed from a far-end trunk exchange once the ACE from the far-end trunk exchange to the parent exchange of the local exchange has stayed below a fourth threshold for the duration of a measurement period.

The first threshold may be set to a value larger than the highest normal value of OFL for the network, for example 30%.

The second threshold may be set to a value approximately equal to the normal expected daily maximum of

ACE for the network, generally greater than 10%.

Preferably the third threshold is greater than 20% and the first proportion is 95%.

- The fourth threshold is preferably set approximately equal to the normal expected daily maximum of ACE for the network,— for example 10%.

According to a second aspect of the present invention there is provided apparatus, for use with a telecommunications network including at least one local exchange which is connected by routes to one or more parent trunk exchanges, each parent trunk exchange being one of a plurality of trunk exchanges, interconnected by trunk routes, and control means for applying controls to the trunk exchanges of the network, which apparatus is characterised in that there is included a system responsive to the Percentage Overflow (OFL) for a traffic route from a parent exchange to the local exchange and the All Circuits Engaged (ACE) parameter for one or more traffic routes from a far-end trunk exchange to a parent exchange of the local exchange, which system: a) whenever the Percentage Overflow (OFL) for one or more traffic routes from a parent exchange to the local exchange has stayed above a first threshold for the duration of a measurement period, indicates the need for a control such_ as route gapping to affect those traffic routes; and b) whenever the All Circuits Engaged (ACE) parameter for one or more traffic routes from a far-end trunk exchange to a parent exchange of the local exchange has increased from above a second threshold to above a third threshold greater than the second threshold during a measurement period, indicates the need for a control such as call gapping to the number range of the local exchange at the far end trunk exchange.

The apparatus provides to the network controller a recommendation to apply appropriate controls when it is determined by the system that controls should be applied to any exchange of the network.

According to a third aspect of the present invention a communications network, including at least one local exchange which is connected by routes to one or more parent trunk exchanges, each parent trunk exchange being one of a plurality of trunk exchanges interconnected by trunk routes, and control means for applying controls to the trunk exchanges of the network, is characterised in that there is included a system responsive to the Percentage Overflow (OFL) for one or more traffic routes from a parent exchange to the local exchange and the All Circuits Engaged (ACE) parameter for one or more traffic routes from a far- end trunk exchange to a parent exchange of the local exchange, which system: a) whenever the Percentage Overflow (OFL) for a traffic route from a parent exchange to the local exchange has stayed above a first threshold for the duration of a measurement period, causes the control means to apply a control such as route gapping to affect that traffic route; and b) whenever the All Circuits Engaged (ACE) parameter for one or more traffic routes from a far-end trunk exchange to a parent exchange of the local exchange has increased from above a second threshold to above a third threshold greater than the second threshold during a measurement period, causes the control means to apply a control such as call gapping to the number range of the local exchange at the far end trunk exchange.

An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings of which:

Figure 1 is a schematic representation of a network controllable by a method of the present invention;

Figure 2 is a schematic representation of a control system for implementing the method of the present invention; and

Figure 3 is a schematic representation of a control system for implementing the method of the present invention using direct control of a network by a computer. Referring to Figure 1, a telecommunications network comprises a number of digital main switch units (DMSUs) - trunk exchanges - of which only five are shown for clarity and are referenced 100, 102, 104, 106, 108 and 110. Subscribers' customer premises equipment, of which only two are shown referenced 112 and 114, are connected to the trunk exchanges 102 to 110 via respective digital local exchanges (DLE) 116 and 118.

The DLE 116 is connected to the DMSUs 100 and 102 via traffic routes Rl and R2, respectively, through which incoming calls to the subscribers attached to the DLE 116, including subscriber 112, are routed. The DMSUs 100 and 102 are commonly referred to as the home trunk exchanges for the DLE 116. The DLE 116 is also connected to the DMSU 104 through which outgoing calls from the DLE are routed. This is usually called a security exchange as incoming calls to the exchange 116 can be routed through it should one of the DMSUs 100 and 102 fail.

Similarly, the DMSU 108 is the home exchange for the digital local exchange 118. The home and security exchanges associated with a DLE are collectively referred to as the parent exchanges of that DLE.

Those exchanges other than the parent exchanges are referred to as the far-end trunk exchanges of a given digital local exchange. For the network of Figure 1 all exchanges other than trunk exchanges 100, 102 and 104 are regarded as far end trunk exchanges for the digital local exchange 116, for example.

The method of controlling a telecommunications network such as that illustrated in Figure 1 according to the present invention will now be described with additional reference to Figure 2 which shows a network control system implementing the method of the present invention.

Referring to Figure 2, the network of Figure 1 is denoted by box 202. Every five minutes, which is the measurement period of the network of Figure 1, a set of statistics is generated by the digital exchanges of the network 202 which is processed by an NTMS system 204 to provide generic measurement values including those of the CCITT recommendation. These parameters are input to a run¬ time system 206 which applies rules to the received parameters from the NTMS 204 by means of an appropriately coded expert system. The run-time system 206 provides recommendations to aid a network traffic manager 208 control local exchange failures in the network 202 according to the method of the present invention.

The run-time system 206 employs a three phase cycle in which recommendations for local exchange failure * control actions are passed to the network traffic manager 208.

The run-time system 206 monitors the exchanges of the network 202 in the manner which will now be described with specific reference to the failure of local exchange 116.

Whenever the Percentage Overflow (OFL) for the traffic routes Rl and R2 from the υarent exchanσes

100 and 102 to the local exchange 116 has stayed above a 30% for the duration of a 5 minute measurement period, route gapping is applied on those traffic routes and whenever the All Circuits Engaged (ACE) parameter for the traffic routes from a far-end trunk exchange 106-118 to a parent exchange 100 and 102 of the local exchange 116 has increased from above 10% to above 20% during a 5 minute measurement period, call gapping for the number range of the local exchange 116 is applied to those far end trunk exchanges.

It is envisaged that the run-time system 206 may directly control the network to apply the method of the present invention as shown in Figure 3 but at present it is expected that it will be necessary for a network traffic manager 208 to implement of the method of the present invention to allow overriding of the recommendations at his or her discretion.

The method of the present invention has been simulated on a computer representation of BT' s UK telecommunications network in which the run-time system 206 comprises a PROLOG-based expert system coded with the rules necessary to provide the recommendations described above in response to the appropriate CCITT parameters from the NTMS 204.

The particular system employed was a QUINTUS PROLOG expert system run on a Sun _ Sparc station. Parameters generated during real network activity were recorded for the entire GB network for fou, 5-minute measurement periods and stored as a data file on the computer.

A C-language program provided an interface between the raw parameters in the computer file and the expert system in that as the expert system required information about the network, the C-language program calculated the data from the raw parameters.

The conditions necessary to implement the method of the present invention were submitted to the expert system, along with other queries about the network performance every five minutes, and where appropriate, the expert system responded to generate the information required for presentation to the network manager.

The particular thresholds adopted in order to determine when a local exchange failure has occurred can be set according to the particular network 202 to which the method is to be applied. The present invention is not restricted to any particular value of threshold adopted in the above described specific embodiment. Although embodiments of the present invention find particular application in the complex telecommunications networks of the PSTNs (Public Switched Telecommunications Networks), they should not be considered to be limited necessarily to networks carrying voice transmissions.

Claims

CLAI MS

1. A method of controlling a network, which includes at least one local exchange connected by one or more routes to one or more parent trunk exchanges, each parent trunk exchange being one of a plurality of trunk exchanges interconnected by trunk routes, the method being characterised in that controls are applied: a) whenever the Percentage Overflow (OFL) for one or more traffic routes from a parent exchange to the local exchange has stayed above a first threshold for the duration of a measurement period; and b) whenever the All Circuits Engaged (ACE) parameter for one or more traffic routes from a far-end trunk exchange to a parent exchange of the local exchange has increased from above a second threshold to above a third threshold greater than the second threshold during a measurement period.

2. A method as claimed in Claim 1, wherein the control which is applied when condition a) is met and the said OFL has stayed above the first threshold as required is route gapping to affect the relevant traffic route or routes.

3. A method as claimed in either one of the preceding claims, wherein the control which is applied when condition b) is met and the ACE parameter for a traffic route has remained above the third threshold as required is call gapping for the number range of the local exchange and the control is applied at the relevant far end trunk exchange or exchanges.

4. A method as claimed in any one of the preceding claims in which the route gapping is removed once the Circuits In

Service (CCTS IS) on the traffic route or routes from the parent exchange to the local exchange has been greater than 0958 _ ^, , PCI7GB93/01306

a first proportion of the available circuits on that traffic route for the duration of a measurement period.

5. A method as claimed in any one of the preceding claims in which call gapping is removed from a far-end trunk exchange once the ACE from the far-end trunk exchange to the parent exchange of the local exchange has stayed below a fourth threshold for the duration of a measurement period.

6. A method as claimed in any preceding claim in which the first threshold is set to a value larger than the highest normal value of OFL for the network.

7. A method as claimed in claim 6 in which the first threshold is 30%.

8. A method as claimed in any preceding claim in which the second threshold is approximately equal to the normal expected daily maximum of ACE for the network.

9. A method as claimed in claim 8 in which the second threshold is greater than 10%.

10. A method as claimed in either of claims 8 and 9 in which the third threshold is greater than 20%

11. A method as claimed in any preceding claim in which the first proportion is 95%.

12. A method as claimed in any preceding claim in which the fourth threshold is approximately equal to the normal expected daily maximum of ACE for the network.

13. A method as claimed m claim 12 in which the fourth threshold is threshold is 10%.

14. A method as claimed in any preceding claim in which the measurement period is approximately five minutes.

15. A method of controlling a telecommunications network substantially as hereinbefore described with reference to the accompanying drawings.

16. Apparatus for use with a communications network including at least one local exchange which is connected by one or more r« s to one or more parent trunk exchanges, each parent r c exchange being one of a plurality of trunk exchange erconnected by trunk routes, and control means for apt .. ' controls to the trunk exchanges of the network, char^* .ised in that there is included a system responsive tc Percentage Overflow (OFL) for a traffic route from a ~ ant exchange to the local exchange and the All Circuit? engaged (ACE) parameter for one or more traffic routes from a far-end trunk exchange to a parent exchange of the local exchange which system: a) whenever the Percentage Overflow (OFL) for one or more traffic routes from a parent exchange to the local exchange has stayed above a first threshold for the duration of a measurement period, indicates the need for a first control in respect of that traffic route or routes; and b) whenever the All Circuits Engaged (ACE) parameter for a traffic route from a far-end trunk exchange to a parent exchange of the local exchange has increased from above a second threshold to above a third threshold greater than the second threshold during a measurement period, indicates the need for a second control with respect t" that traffic route.

17. Apparatus as claimed in Claim 16 wherein said first control comprises route gapping.

18. Apparatus as claimed in either one of claims 16 or 17 wherein said second control comprises call gapping to the number range of the local exchange at the appropriate far end trunk exchange.

19. A communications network including at least one local exchange which is connected by one or more routes to one or more parent trunk exchanges, each parent trunk exchange being one of a plurality of trunk exchanges interconnected by trunk routes, and control means for applying controls to the trunk exchanges of the network, characterised in that there is included a system responsive the Percentage Overflow (OFL) for one or more traffic routes from a parent exchange to the local exchange and the All Circuits Engaged (ACE) parameter for one or more traffic routes from a far- end trunk exchange to a parent exchange of the local exchange which system: a) whenever the Percentage Overflow (OFL) for a traffic route from a parent exchange to the local exchange has stayed above a first threshold for the duration of a measurement period, causes the control means to apply a control with respect to that traffic route; and b) whenever the All Circuits Engaged (ACE) parameter for a traffic route from a far-end trunk exchange to a parent exchange of the local exchange has increased from above a second threshold to above a third threshold greater than the second threshold during a measurement period, causes the control means to apply a control with respect to that traffic route.

20. A network as claimed in Claim 19 wherein, when the condition set out with respect to the OFL is met, the system applies route gapping in relation to the traffic route from the parent exchange to the local exchange.

21. A network as claimed in either one of claims 19 or 20 wherein, when the condition set out with respect to the ACE parameter is met, the system applies call gapping to the number range of the local exchange at the appropriate far end trunk exchange or exchanges.

22. A telecommunications network substantially as hereinbefore described with reference to the accompanying drawings.