# Network Layer #### ISDN Network Layer The ISDN (Integrated Services Digital Network) Network Layer is responsible for the transmission of data across the ISDN network. It primarily follows the specifications of the ITU-T Q.931 protocol for signaling, which manages call setup, control, and termination. It operates at the third layer of the OSI model, handling logical and physical addressing, ensuring data integrity, and facilitating error handling and correction mechanisms. By leveraging both B-channels for data transfer and D-channel for signaling, the ISDN Network Layer ensures efficient and reliable communication between devices. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://isdn.learn-telecom.com/layers/network-layer.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.