Q.931 is a standard protocol for establishing and breaking off voice, video, and data communications over digital networks, including ISDN (Integrated Services Digital Network). This protocol defines the procedures that network devices use to communicate crucial information such as call setup and termination. Q.931 doesn’t carry voice or video itself, but provides the necessary setup and coordination for other protocols that do.


The phonetics of the keyword “Q.931” are: “Cue Dot Nine Three One”.

Key Takeaways

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  1. Q.931 is a standard protocol for initiating and managing network connection sessions. It’s often used in Integrated Services Digital Network (ISDN) systems to establish, maintain, and terminate circuit-switched connections.
  2. This protocol involves multiple types of messages including setup messages, disconnect messages, and status messages. The setup messages are utilized for initiating a call, whereas the disconnect messages are employed to end a call. Status messages are used for error reporting and general status inquiries.
  3. In Q.931, each message contains information elements (IEs) like the called party number or the bearer capability. These IEs provide specific information required for call handling, making the protocol flexible and versatile for different communication scenarios.

“`This HTML when rendered, will explain that Q.931 is a key protocol in ISDN systems for managing connections, uses various types of messages for different processes, and utilizes information elements for more specific call requirements.


Q.931 is a significant technology term as it’s a digital communications protocol primarily used for establishing and terminating voice calls over Integrated Services Digital Network (ISDN). Developed by the International Telecommunication Union (ITU), Q.931 is crucial as it provides the necessary structure for transferring voice and data over digital networks and governs call setup and teardown. Without this protocol, the process of setting up, maintaining, and ending voice calls over ISDN becomes inefficient, leading to poor communication quality and user experience. Therefore, the importance of Q.931 protocol lies in its ability to enable seamless and effective communication over digital networks.


Q.931 is a telecommunications protocol that is primarily used for establishing, maintaining, and terminating connections between different points in a network. Its main purpose is to align call connections and disconnections in ISDN (Integrated Services Digital Network) services. This protocol is central to allowing devices to communicate over digital telephone lines. It helps in setting up a call between two parties, maintaining the call while it is in progress, and properly disconnecting the call once it’s finished. In a literal sense, Q.931 can be seen as the director of a play, ensuring all actors (data packets) in an ISDN line perform their roles at the right time and in the right order for the audience (the receiving device) to process the performance (the data) correctly. It’s vital for efficient and reliable communications. Without a standard like Q.931 to guide the flow of data, digital communications over ISDN would be chaotic and ineffective, resulting in poor quality or even loss of service.


Q.931 is a standard protocol for establishing, managing and terminating connections over a network. Its most common use is in providing voice and video communication services, as well as some types of data communication.1. Integrated Services Digital Network (ISDN): ISDN services, which provide both voice and high-speed data capabilities, use Q.931 to manage the call establishment, management and termination processes. When you make a call using an ISDN line, the Q.931 protocol is used to set up the call and keep it active until it’s terminated.2. Private Branch Exchange (PBX): In businesses with a large number of telephone extensions, a PBX is used to manage internal and external calls. Many PBX systems use Q.931 to support advanced features like call forwarding, call waiting, and conference calls. 3. Video Conferencing Systems: Q.931 is used in many commercial video conferencing systems. In these systems, the protocol handles the call control aspect, i.e., the process of setting up a call between two or more endpoints, establishing the media links for audio and video, and then ending the call appropriately when it’s finished.

Frequently Asked Questions(FAQ)

Sure, here’s a Frequently Asked Questions (FAQ) section for the technology term: Q.931.Q: What is Q.931?A: Q.931 is a protocol for the establishment and termination of circuit-switched connections within an ISDN (Integrated Services Digital Network). It’s used to manage call setup and teardown procedures.Q: Who developed Q.931 protocol?A: The Q.931 protocol was developed by the ITU-T, previously known as the International Telegraph and Telephone Consultative Committee.Q: What are the uses of Q.931?A: Q.931 is used extensively within telecommunication systems for regulating communication sessions, especially in VoIP technology where it helps provide connection services over IP networks.Q: What does a Q.931 message contain?A: A Q.931 message contains information for call setup, management and teardown. It might include the called party number, calling party number, cause of cancellation, among others.Q: Is Q.931 still in use today?A: While ISDN and its associated protocols like Q.931 have been largely replaced by newer technologies such as VoIP, they are still in use in certain applications and systems.Q: How does Q.931 work?A: Q.931 works by sending packets of information between the network and the user at the start, during, and at the end of a call. This information includes the number being called and the user’s own number for identifying and regulating communication sessions.Q: Does Q.931 work with other protocols?A: Yes. Q.931 often works in conjunction with other protocols like DSS1 (Digital Subscriber Signalling System No. 1) in ISDN networks, and H.225.0 in VoIP services to differentiate and manage traffic.

Related Tech Terms

  • ISDN (Integrated Services Digital Network)
  • PSTN (Public Switched Telephone Network)
  • Packet switched systems
  • Signalling protocol
  • D Channel

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