A study of congestion in SS7 signalling links of an intelligent network

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A study of congestion in SS7 signalling links of an intelligent network


Author: Yeung, Ric-shang Alex
Title: A study of congestion in SS7 signalling links of an intelligent network
Degree: M.Sc.
Year: 2000
Subject: Telephone systems
Telephone -- Signaling
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Dept. of Electronic and Information Engineering
Pages: 39, [56] leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1517719
URI: http://theses.lib.polyu.edu.hk/handle/200/3205
Abstract: Although the signalling components of a modem day telephone network are usually precisely dimensioned with sufficient margin, there is still the possibility that the signalling traffic momentarily rises to a level beyond the capacity of the network. To cater for such situations, several congestion control measures for the SS7 signalling links have been suggested in the ITU-T Recommendations. As for the Intelligent Network (IN) environment, there are also various methods suggested for preventing the overloading of the Service Control Point (SCP). Most of the methods for IN are based on controlling the signalling traffic offered to the SCP. The interworking of the SS7 controls and the IN controls of congestion is important to the performance of the overall signalling network. In order to investigate the effects of interworking between SS7 and IN, a simulation study is carried out. In the study, a model network is built to represent a typical signalling network with IN components. The model consists of 4 local exchanges as signalling points. They are connected to a Signal Transfer Point (STP). The STP also provides the functions of Service Switching Point (SSP). An SCP is connected to the SSP for providing the IN services. All these components are connected by SS7 links. Two congestion control measures are applied in the model network. For the SS7 signalling links, the ITU-T International Option of congestion control is applied on the MTP level, and the ISUP congestion control is applied on the User Part level. For the IN components in the network, the Window Method is used to control congestions in the SCP. The total simulated time is 900 seconds. Mass call-in occurred at the 300th second and ends at the 540th second. When mass call-in occurs, traffic equivalent to over 300% of the normal level is generated from three of the exchanges towards one. Two aspects of the congestion are investigated. First, the impact on network performance is studied by observing the throughput of the signalling links. Second, the impact on subscribers is studied by observing the call completion rate. It is found that both the congestion control for the SS7 links and that for the SCP work well on their own. Traffic is throttled and both the congested SS7 links and the SCP are offered with signalling traffic not more than their capacities. Optimal network throughput is maintained. As for the congestion control on the SS7 links, it is found that the IO/ISUP mechanism only controls the traffic of the non-IN calls and it has no effect on the messages for the IN services. As for the Window Method, it is found that the control parameters could affect the response time to the congestion situation. Since non-IN calls towards the congested destination are throttled by the SS7 control while IN calls are sent through the congested link, there is an issue of fairness and improvement on the congestion control methods is necessary.

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