I CSCF (Interrogating Call Session Control Function)

Introduction:

The Interrogating Call Session Control Function (I-CSCF) is a key component in the IP Multimedia Subsystem (IMS) network. It plays a significant role in the setup, routing, and management of calls in an IMS network. The I-CSCF is responsible for handling incoming requests for IMS services and forwarding them to the appropriate network element. In this article, we will discuss the I-CSCF in detail, including its function, architecture, and deployment.

Function:

The primary function of the I-CSCF is to act as the first point of contact for all incoming requests for IMS services. When a user initiates a session request, such as a voice call or video call, the request is sent to the I-CSCF. The I-CSCF then performs a number of tasks to ensure that the session request is processed correctly.

The first task performed by the I-CSCF is to determine the user's home network. This is done by looking up the user's Public User Identity (PUI) in the Domain Name System (DNS) or using the Diameter protocol. Once the home network has been determined, the I-CSCF forwards the session request to the appropriate Serving Call Session Control Function (S-CSCF) within the user's home network.

The I-CSCF also performs other functions, such as performing security checks on the incoming session request, validating the user's credentials, and verifying that the user has the necessary permissions to access the requested service. Additionally, the I-CSCF may perform functions such as call screening and routing based on various criteria, such as the user's location, time of day, or network conditions.

Architecture:

The I-CSCF is a network element in the IMS architecture that is responsible for handling incoming session requests. It is typically deployed in the edge of the IMS network, where it serves as the first point of contact for all incoming traffic. The I-CSCF communicates with other network elements in the IMS network, such as the S-CSCF, the Home Subscriber Server (HSS), and the Application Server (AS).

The I-CSCF is typically deployed in a redundant configuration to ensure high availability and reliability. Redundant I-CSCFs are typically deployed in a load-balanced configuration, where incoming traffic is distributed across multiple I-CSCFs. This ensures that if one I-CSCF fails, the other I-CSCFs can continue to handle incoming traffic.

Deployment:

The I-CSCF is typically deployed in the edge of the IMS network, where it serves as the first point of contact for all incoming traffic. The I-CSCF is typically deployed in a redundant configuration to ensure high availability and reliability.

The I-CSCF can be deployed in various ways, depending on the operator's network architecture and requirements. Some operators may choose to deploy the I-CSCF as a standalone network element, while others may choose to integrate it with other network elements, such as the Proxy-Call Session Control Function (P-CSCF) or the Border Gateway Function (BGF).

Conclusion:

The I-CSCF is a critical component of the IMS network architecture, responsible for handling incoming session requests and routing them to the appropriate network elements. It performs a number of functions, such as determining the user's home network, performing security checks on the incoming session request, and validating the user's credentials. The I-CSCF is typically deployed in a redundant configuration to ensure high availability and reliability. It can be deployed in various ways, depending on the operator's network architecture and requirements. Overall, the I-CSCF is an essential component of the IMS network, providing a reliable and efficient way to manage session requests and ensure the quality of service for IMS users.