Threshold-Based Congestion Control for the SS7 Signaling Network in the GSM Digital Cellular Network

This report considers the congestion control scheme for the SS7 signaling network in the GSM digital cellular network. This congestion control scheme is based on monitoring the SS7 link buffer occupancy. In this scheme, a congestion onset message is sent to the user parts of the SS7 network when the buffer occupancy exceeds a certain threshold and then subsequently a congestion abatement message is sent when the buffer occupancy goes below another threshold. Upon receipt of the congestion onset message, the user parts are expected to "intelligently" throttle the user traffic (reduce the traffic rate) so as to yield speedy recovery from congestion. Subsequently, on receipt of the abatement message, the user traffic is restored to pre-congestion levels. This report primarily proposes appropriate choice of throttles and an algorithmic procedure to size the thresholds so as to yield good performance during congestion. The report also addresses some implementation issues related to the throttles and also briefly considers the effects of possible delays for the onset and abatement messages in reaching the user parts on performance and the parameters of the congestion control scheme.