ISUP (ISDN User Part)

What is an ISUP?

In the realm of telecommunications, ISUP, which stands for ISDN User Part, plays a crucial role in establishing, controlling, and terminating voice calls over digital networks. ISUP is a signaling protocol used primarily in Integrated Services Digital Network (ISDN) and Signaling System 7 (SS7) networks. It is essential to the overall telephony infrastructure, ensuring efficient call routing and handling.

ISUP serves as the backbone of the telecommunication system, responsible for the signaling necessary for call setup and teardown between different network nodes. It operates at the network layer of the OSI model, specifically in the Signaling Connection Control Part (SCCP) of the SS7 protocol suite. ISUP carries information about call progress, such as the initiation of a call, its progress, and the release of the call. It provides a standardized communication mechanism between switches and network exchanges.

How do you use an ISUP?

When a user initiates a voice call, the ISUP protocol facilitates the necessary signaling exchanges between the originating and terminating switches or exchanges. Here's a simplified overview of how ISUP works:

Call Setup: The process begins when the originating switch receives a request to establish a call. It sends an ISUP Initial Address Message (IAM) to the destination switch, indicating the call's destination and relevant information.

Call Progress: As the call progresses, the originating and terminating switches exchange ISUP messages to convey call progress updates, such as call ringing, call acceptance and call forwarding.

Call Termination: Once the call is completed or terminated, the switches exchange ISUP messages to release the call resources and inform each other about the call's end. The ISUP Release Message (REL) is sent to indicate the termination of the call.

ISUP messages carry information about call control, routing, and management throughout these stages. These messages include parameters such as called party number, calling party number, call reference number, and more, enabling effective communication between network elements.

Advantages of ISUP

ISUP brings several advantages to the telecom industry, making it an essential protocol for voice call signaling. Some key advantages of ISUP include:

Standardization: ISUP is a standardized protocol ensuring interoperability between different vendors and network elements. This standardization facilitates the seamless integration of various switches and exchanges within a telecom network.

Efficient Call Handling: ISUP optimizes call setup and teardown processes, enabling efficient call routing and management. Providing standardized signaling mechanisms ensures that calls are established and terminated reliably, minimizing call setup delays and failures.

Scalability and Flexibility: ISUP supports a scalable architecture, allowing telecom networks to simultaneously handle a large volume of voice calls. It provides the flexibility to route calls across different network elements, including switches, exchanges, and international gateways.

Network Management: ISUP includes features for network management and monitoring. Operators can use ISUP messages to gather call statistics, monitor network performance, and detect and troubleshoot call-related issues.

Compatibility with SS7: ISUP seamlessly integrates with the SS7 protocol suite, enabling efficient communication between different network layers. This compatibility enhances the overall reliability and robustness of the telecommunication infrastructure.