Signalling System No. 7 (SS7) networks are used to transport call control messages for both traditional telephony and advanced intelligent network (IN) based services. A large number of IN implementations have been successfully deployed, however a key factor in ensuring their ongoing commercial success will be that they continue to meet specified performance targets. Because network congestion may have a serious adverse effect on IN service performance, much research effort has been focused on IN congestion control. However, in general, this research has not taken into account operation of the standardised congestion controls operating at the SS7 plane of the network. This paper outlines an investigation that demonstrates that the interaction between SS7 and IN congestion controls is not always harmonious and can lead to serious performance degradation. A congestion control strategy, which resolves the problems identified, is presented and evaluated.