This article is concerned with protecting service control against interruption attacks. It investigates threats to service control in the Telecommunications Information Networking Architecture. Traditional security services protect message flows, but not service logic. Attackers can still interrupt service control connections and take advantage of the caused influences on service control, even if the messages are cryptographically protected. The focus of this article is to prevent this kind of attack. A protocol for protecting overall integrity of service control by means of a cryptographic protocol is presented and its use is demonstrated.