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The CS-USC is a multi-tiered, distributed software system that executes on commercial SUN Netra servers, interconnected over an underlying IP data network. The ControlSwitch is designed with a highly scalable and fault-tolerant architecture. A service provider can elect to start with a small system and grow it to a very large one, spanning multiple geographic centers, by adding components as their traffic and end-user volume increase.
At a high level the CS-USC can be described as a distributed IP-network-based system providing traditional switch functions of call control, call routing, signaling gateway, and media device control, in addition to support of provisioning, billing, and network operations. The CS-USC functional blocks are depicted in the graphic.
The elements described below are logical functions (not devices), and service providers can implement a specific combination of functions that better meet their business needs.
Serving Call Session Control Function (S-CSCF): Registers users, providing service to them even when these services reside on separate application platforms. It performs routing and translation, provides billing information, maintains session timers, and interrogates the HSS to retrieve authorization, service triggering information and user profile.
Interrogating Call Session Control Function (I-CSCF): Resides within the home network; it determines the S-CSCF with which a user should register. It is also used in call setup in the called party's network to resolve the called party's S-CSCF.
Home Subscriber Server (HSS): Houses the database for all subscribers and services data. HSS is a realtime processing element.
SIP Application Server (SIP AS): This is an IMS compliant platform for SIP application development and operation. It provides services logic and multimedia services, and it resides in the user's home network or in a third-party location. It provides SCIM functions to manage interactions.
Service Capability Interaction Management (SCIM): Uses realtime service management and delivery, and enables blended services and legacy services integration. As it is based on the Interaction Model, it facilitates planning, implementing and service interactions at the service design stage.
Subscriber Location Function (SLF): Houses multiple HSSs; helps to find a HSS instantly and locate subscribers’ profiles. The SLF locates the database containing subscriber data.
Presence: Conveys a user availability to communicate. The information supplied by the user is stored in the user personal availability record and can be made available for distribution to other users to convey the user’s availability.
Device Manager (DM): Links users and network service environments. Configuration and software updates are also performed on administrator initiative and on client request. It is used for downloading and configuring softclients / IAD automatically via Internet browser and administrative GUI interface. It scales up to 250,000 devices per server.
Charging Data Function / Charging Gateway Function (CDF/CGF): CDF is used for offline charging. It reports accounting information and uses this information to construct and format CDRs. The CGF extracts usage information from multiple sources and uses rules to distribute the data records in realtime. It is compliant with the DIAMETER protocol and interoperates via SIP.
Online Charging Function (OCF): Collects online charging information in the network. The charging events are transferred to the OCF using CAP or Ro reference points.
Media Gateway Control Function (MGCF): Communicates with S-CSCF and controls the connections for media channels in the MGF. The MGCF performs protocol conversion between ISUP and the IMS call-control protocols.
Breakout Gateway Control Function (BGCF): Controls the transfer of calls to and from the PSTN; provides the interface between IMS and legacy call processing functions. It processes all calls routed from the IMS to the PSTN or coming from the PSTN to the IMS.
Proxy-CSCF (P-CSCF): This is the first point of contact within the IMS user; can be located in the home or visited network; ensures that SIP registration is sent to the correct home network and messages are sent to the correct S-CSCF. It detects services which should be hosted by the visitor's network. This is important in terms of content services and provisioning of emergency call handling. It provides defense against SIP signaling attacks.
Element Management System (EMS): Provisions all CS-IC components and enables the modular and distributed network solution to be easily managed from a single switch. It proactively monitors the status of the system’s elements.
Subscriber Manager (SM): Manages subscriber and subscription data; binds subscriber, resources and services; and delivers Customer Relationship Management (CRM) functions. All aspects of users’ interaction use software and Internet capabilities.
Policy Control and Charging Rules Function (PCRF): Based on 3GPP v7 standard, it coordinates network resources; authorizes users’ access to their services; and determines parameters as to what users may do and what content of an application they may use. It determines the bandwidth and resources required to deliver a determined service. It set policies for admission and QoS and allows the application layer to be access technology agnostic, allowing a given application to operate seamlessly across the various access technologies.
Access Gateway Control Function (AGCF): Enables multiservice access equipment housing PSTN users to be controlled by IMS SIP-based call control equipment. It enables PSTN service emulation over IMS.
Veraz Interconnect Border Control Function (IBCF): Enables global carrier IP peering, protects the carrier network against malicious attacks, and provides key security features including topology hiding, access control lists for “denial of service” attack prevention, and far-end and near-end NAT traversal to avoid NAT/Firewall complications.
Policy Decision Function (PDF): Controls traffic entering the packet-switched network by allocating or denying IP bearer resources. It assigns network bandwidth and resources in realtime, according to demand and QoS requirements.
Signaling Gateway Function (SGF): Provides both directions signaling conversion between SS7 and IP networks. It allows for the access and utilization of the STP and SCP resources of the SS7/C7and intelligent networks.
Portal Connect: This is a third-party call control application server. It enables web portals to initiate call-backs to users or even send MMS/SMS to a user. This application server also integrates these functionalities with prepaid and postpaid billing services available in the CS-USC.
Media Gateway Function (MGF): Terminates bearer channels from a switched circuit network and media streams from a packet network. It can support media conversion, bearer control, and payload processing such as codec, echo canceller, etc.
Virtu: This is a softclient that provides users with the enhanced phone capabilities such as dial pad, dial tone, unified messaging including video, conference calls, voice mail, etc.
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