ntrol Functions (CSCFs) Service Delivery Platforms Security server Policy server Wireless client Media server Wireless networks Presence server I-CSCF S-CSCF P-CSCF Fixed client Service orchestration Ethernet passive optical Indirection server network access Network services Ethernet Connection Protection Optical network control and management plane Priority Security Optical ethernet network Figure 9.1 IMS-based testbed system overview. and a Home Subscriber Server (HSS). The Open IMS CSCFs (Proxy, Interrogating, and Serving) form the central routing elements for IMS-based signaling, while the HSS manages user profiles and associated routing rules. The Open IMS Core interfaces with multiple servers such as Security, Policy, Media, Presence, Video, and Application Servers, SO that fixed and wireless clients alike can establish multimedia sessions with them in a standard manner. Lastly, the Core is linked to a SIP-based service orchestration module [13] where the composi- tion logic is stored and executed. This module provides the possibility of rapid service creation and delivery in response to market needs. 9.2.2 Presence Service Our testbed consists of a SIP-based Presence Service [14] that provides presence functionalities to the rest of the application servers using standards developed by the Internet Engineering Task Force (IETF), Open Mobile Alliance (OMA), 3GPP, and ETSI. This service is linked into the IMS core and application servers via the native SIP presence protocol and service building blocks (SBB), respectively. In contrast to the HSS database that contains user information that is short term and transient in nature (e.g., login status and subscription profile), the pres- ence service manages state information which are more static in nature (e.g., resource authorization rules and policy). Design and Implementation of an IMS-Based Testbed The Presence Service actually comprises three separate but interrelated servers. This means that each of these servers can be used independently or combined to pro