Telephonic communications – Concentrator or trunk selector
Reexamination Certificate
1998-09-09
2001-12-11
Matar, Ahmad (Department: 2642)
Telephonic communications
Concentrator or trunk selector
C379S137000, C379S220010, C379S221010, C379S337000
Reexamination Certificate
active
06330329
ABSTRACT:
BACKGROUND
1. Field of the Invention
This invention is related to managing trunk traffic in a telecommunication switch. In particular, this invention involves performing circular hunts for an idle trunk member. With this invention, circular hunts are performed in such away as to reduce the amount of search time and to more evenly distribute traffic across large numbers of trunk groups. The invention supports very large trunk groups that might otherwise encounter trunk timeout, or other conditions before a final disposition of a call is determined. The invention enforces a maximum number of trunk groups or routes searched on a per call basis such that trunk timeout or other anomalies are avoided by returning an all trunks busy condition if no idle members are found within the number of trunks or routes searched.
2. Description of the Problem Solved
The public switched telephone network (PSTN) consists of many switches interconnected by trunks. The trunks which interconnect the switches of the PSTN include multiple trunk groups, each trunk group having many members which can carry calls. Which trunk group is available to a specific call determines the route that the call will take to get to its destination. When a switch handles a call, it must search for an available route, that its, a trunk group with an available channel or member. One type of search used to find a route is called a “circular hunt,” because it can be depicted graphically as a pointer moving around a circle on which the various trunk groups, or available routes, are shown around the circumference of the circle, as shown in
FIG. 1
, where the pointer indicates the current route. When a large number of trunk groups, routes, or channels is involved, a search of this or any type places a burden on the processing resources of the switch which results in a delay until the call can be completed.
With greatly increasing demand being placed on the PSTN, larger and larger numbers of trunk groups are connected to the various switches which make up the PSTN. Much of this demand is due to the growth of the Internet, and many of the trunk groups are connected to Internet access devices. The number of trunk groups can be so large that internal switch limitations can cause software errors and/or trunk timeouts if a free channel or member of a trunk group is not found quickly. Additionally, the usage of the various trunk groups is not evenly distributed, resulting in wasted resources. This problem is illustrated in
FIG. 2. A
trunk group is also called a route (RTE).
FIG. 2
is a table which illustrates the problem in more detail for an ascending sequential search algorithm. A star indicates a particular channel or member of a particular trunk is in use. In this case the trunks are integrated services digital network (ISDN) primary rate interfaces (PRI). Note the upper channels of the higher numbered trunks are not being used at all. The diamond over trunk group PRI
1
/channel
1
indicates where the search algorithm always starts in an ascending sequential search algorithm of the prior art. Traffic must fill all channels in PRI
1
before the algorithm searches PRI
2
. PRI
2
must be completely filled before PRI
3
is used. The result is that trunk groups placed later in a route list are used much less frequently than trunk groups that are early in the route list. The DS-
1
column indicates that a trunk group may have multiple DS-
1
's, or digital signalling-
1
trunks, in the trunk group and is not limited to 23 bearer channels. For this illustration PRI with 23 channels plus one D (signaling channel) is used; as well as the scenario where for PRI
5
four DS-
1
's are used and two D (signaling) channels are used. One D channel is active and one is on standby (or backup). What is needed is a way to limit the number of trunk groups searched, while still insuring even distribution of traffic.
SUMMARY
The present invention solves the above problems by providing a search of only a limited number of trunk groups, and by varying the starting point of a circular hunt each time a new call needs a route. I call this type of search a “circular hunt with window.” The initial maximum number of trunk groups searched, called a maximum trunk group attempt value, can be selected by a network designer of ordinary skill in the art who has become familiar with the invention. The invention limits the amount of time and resources spent searching for available routes and more efficiently distributes traffic across the available trunk groups. At the same time, the probability of finding an idle trunk is high enough so that the number of “all trunks busy” (ATB) conditions returned is limited.
According to the present invention, an initial maximum trunk group attempt value is associated with each new call. The switch initially determines if the trunk group member at the search pointer is idle. If the trunk group member at the pointer is not idle, the switch advances the pointer to the next trunk group member. In the trunk group member is in another trunk group, the maximum trunk group attempt value is decremented. As soon as a trunk group member at the pointer is idle, the switch seizes the trunk group member at the pointer but still advances the pointer so that the next hunt will start at the next trunk group member. If the maximum trunk group attempt value reaches zero, the switch returns an ATB signal. Throughout this disclosure, I illustrate the invention using clockwise circular hunts, but the invention is equally applicable to counter-clockwise hunts.
The invention is typically implemented using a computer program product for the switch involved. A computer program product includes a media with computer program code which causes the switch involved to perform the necessary operations. A switch which implements the invention includes a switching matrix, one or more peripheral modules connected to the switching matrix, one or more input/output devices connect the switching matrix, and a processor core which controls the operation of the switch and, during operation, contains the computer program code which implements the invention. In many cases, a switch with a large number of trunk groups is connected to an Internet access device.
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Bui Bing
Matar Ahmad
Nortel Networks Limited
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