Telecommunications network congestion

Details Telecommunications network congestion Telecommunications network congestion

2000-04-27

2004-08-10

Ho, Duc (Department: 2662)

Multiplex communications

Data flow congestion prevention or control

Flow control of data transmission through a network

C370S385000, C379S221010, C379S221050

Reexamination Certificate

active

06775234

ABSTRACT:

This application claims the benefit of the filing date as provided in 35 U.S.C. 119 of United Kingdom patent application number GB 9910026.5 filed on Apr. 30, 1999, the disclosures of which are incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates to congestion in a telecommunications network and more particularly to alleviating congestion during the routing of signalling information between signalling points of a telecommunications network.
BACKGROUND TO THE INVENTION
In a modern telecommunications network, a considerable amount of signalling information is continually being exchanged between signalling points of the network. Examples of signalling points are network switches, databases, etc. The actual signalling information being exchanged may be associated with a specific telephone call, e.g. relating to call set-up or termination, or may relate to network management functions. Complex protocols have been created to deal with the exchange of signalling information. In particular, Signalling System no.7 (SS7) defines (subject to certain national/regional variations) a suite of protocol parts (or levels) capable of dealing with modern network signalling demands.
FIG. 1
illustrates schematically the “structure” of SS7 (it will be appreciated that the SS7 parts are generally implemented by means of software running on computer processors). On top of the SS7 stack sit the user and application parts which are the entities which make use of and provide signalling information. For example, an ISDN User Part (ISUP) controls the setting up and control of inter-exchange connections for subscriber calls whilst a Mobile Application Part (MAP) handles database queries in a mobile network (e.g. to determine the current location of a mobile subscriber).
At the bottom of the SS7 is the Message Transfer Part (MTP) which in fact comprises three distinct levels. Level
1
defines the physical, electrical, and functional characteristics of a digital signalling link. MTP level
1
has a number of different possible forms including the European standard E.1 (2048 kb/s and 32 64 kb/s channels). MTP level
2
takes care of the accurate end-to-end transmission of messages across a chosen signalling link, whilst MTP level
3
handles the routing of signalling messages between neighbouring signalling links based upon information received from higher SS7 a levels concerning the final destination of a signalling message. MTP level
3
handles inter alia re-routing of messages away from failed or congested signalling links.
Routing by MTP level
3
is carried out based on a destination signalling point and subsystem number (SSN), provided to the MTP by a higher SS7 layer. In particular, for the Transaction Capabilities Application Part TCAP (which handles database queries for the MAP, INAP etc) a Signalling Connection and Control Part (SCCP) generates the destination signalling point and subsystem number using a process termed “Global Title translation”. The SCCP typically carries out a Global Title translation on a Global Title (GT), which may be a dialled Intelligent Network (IN) service number, e.g. an 800 number, a subscriber identification number or the like, using a Global Title Routing Case (GTRC) table. This table contains a mapping between GT series and GTRCs (a GTRC typically being one of an ordered series of numbers). A further GTRC translation is then performed to map the determined GTRC to an associated primary destination signalling point (and subsystem number). The destination signalling point is in some cases referred to as a “Destination Point Code” (DPC).
A Global Title routing case defines, by way of the destination signalling point, the route via which signalling information is transmitted. Especially during peak calling times, certain routes may become congested with large volumes of signalling traffic. Indeed, it is often the case that when a call is initiated, the primary destination signalling point generated by the GT and GTRC translations associated with the call, is unavailable. In such a situation (and following the broadcast of a congestion message from a given signalling point to neighbouring signalling points), a secondary destination signalling point, defined as a back-up for the primary destination signalling point, is used to route the signalling information. This procedure is described in ITU-T Recommendation Q.714 (Chapter 5).
It will be appreciated that the secondary destination signalling point handles overflow signalling information which the primary destination signalling point is unable to handle. It will also be appreciated that when overflow occurs, the processor(s) at the primary destination signalling point will be working at maximum capacity whilst those at the secondary destination signalling point may be working well below that maximum capacity. It may also happen that the secondary destination signalling point subsequently becomes congested, requiring the transfer of signalling information back to the primary destination signalling point (if the primary signalling point remains congested, a further switch back to the secondary point may occur, and so on). This switching back and forward between the primary and secondary destination signalling points may result in the loss of signalling information.
SUMMARY OF THE PRESENT INVENTION
It is an object of the present invention to overcome or at least mitigate the disadvantages outlined in the preceding paragraph. In particular, it is an object of the present invention to avoid or mitigate congestion associated with signalling traffic routed by the Signalling Connection and Control Part. It is a further object of the present invention to provide means by which possible congestion at a signalling point can be predicted, thereby enabling signalling traffic to be diverted away from that signalling point before congestion occurs.
These and other objects are achieved in a first aspect of the invention by defining peak periods during which heavy signalling traffic is expected. During these peak periods, a proportion of the Global Titles normally allocated to a given destination signalling point are automatically reallocated to an alternative destination signalling point. The peak periods are defined on the basis of the history of congestion notification messages issued by the given signalling point.
According to a first aspect of the present invention there is provided a method of routing signalling information at a signalling point of a telecommunications network, the method comprising:
providing a Global Title Routing Case (GTRC) table mapping Global Titles to GTRCs;
allocating to a set of GTRCs a primary and a secondary destination signalling point;
defining at least one time period on the basis of a history of congestion notification messages issued by said primary destination signalling point;
swapping said primary and secondary destination signalling points for a fraction of said set of GTRCs for the duration of said at least one time period;
for a signalling transfer request at the signalling point, mapping the Global Title associated with the request to a GTRC using the GTRC table; and
determining the destination signalling point to be used for the request in dependence upon the primary and secondary destination signalling points allocated to the mapped GTRC and signalling point availability.
By carefully selecting said time period(s) to correspond to known peak signalling traffic periods, embodiments of the present invention automatically divert traffic away from the primary destination signalling point without having to wait until congestion of the primary destination signalling point actually occurs. The resulting load sharing reduces the risk of congestion at the primary and secondary destination signalling points. This results in a more optimal use of processor power at the destination signalling points and also reduces the need to transfer signalling traffic from a congested route to a back-up route. Furthermore, as the maximum volume of signalling traffic through a giv

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