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The IP Multimedia Subsystem (IMS) was developed by a common initiative of the standardization bodies 3GPP and ETSI TISPAN with the aim to provide a platform for fixed and mobile network operators that supports future communication services. In this article we give an overview about the implications that security threats already known from the Internet have on IMS. We analyze the security requirements of an IMS based network architecture and describe possible security solutions. Finally, we argue that for a secure IMS environment extensive traffic monitoring is required in order to provide IMS-based services in a secure manner. IMS-Sicherheit und was wir vom Internet lernen sollten.Das IP Multimedia Subsystem (IMS) stellt eine gemeinsame Anstrengung der Standardisierungsgremien f€ u ur Festnetz-und Mobilkommunikation dar, deren Ziele sowohl die Entwicklung einer neuen Architektur f€ u ur Betreibernetze als auch die Unterst€ u utzung zuk€ u unftiger Dienste sind. In diesem Artikel geben wir einen € U Uberblick € u uber die Implikationen der aus dem Internet bekannten Sicherheitsproblematiken. Wir analysieren die Sicherheitsanforderungen einer IMS-basierten Netzarchitektur und zeigen m€ o ogliche L€ o osungsans€ a atze auf. Wir kommen zu dem Schluss, dass f€ u ur eine sichere IMS-Umgebung ein € u uber die Standardisierung hinausgehendes Maß an Netz€ u uberwachung unbedingt notwendig ist, damit die grundlegende Funktionalit€ a at sicher gew€ a ahrleistet werden kann. IntroductionThe IMS was originally defined by 3 GPP to support the convergence of data, voice and other services over an IP-based infrastructure for mobile networks. The fundamental motivation behind is the understanding that operators need to fill the gap between the traditional telecommunications services like voice and Internet technology. The ETSI TISPAN NGN initiative extends IMS to support fixed-line access networks (ETSI ES 282 001 v3.4.1., 2009), thus IMS is today the dominating approach towards access-independent Next Generation Networks (NGN). It is designed to be an extremely flexible nextgeneration platform by which operators are enabled to provide new and innovative services. In addition, the NGN is expected to reduce operational expenditure of operators and service providers. To support these goals, the IMS platform offers versatile and generic service enablers, such as mechanisms for session negotiation and management, Quality of Service (QoS), mobility, and security.The IMS is mainly based on IETF protocols, such as IP, DNS, HTTP, and SIP. However, these protocols were designed to offer maximum flexibility and to their users without considering security issues adequately, a strategy that has the potential to backfire in IMS scenarios. Furthermore, they come with security problems that are already well-known from the Internet and which are now inherited by the IMS. These known problems need to be anticipated now, before the widespread deployment of IMS installations, in order to ensure that appropriate protection mechanisms are in place wh...