ISDNin

ISDNin is not a widely recognized term in telecommunications and does not denote a standard specification or protocol. In most references, the topic is ISDN, or Integrated Services Digital Network. The term "ISDNin" may appear only as a typographical variant of ISDN, or as part of a product name, project, or internal designation in some documents. For clarity, discussions should be anchored to ISDN.

ISDN defines a set of ITU-T standards that enable digital transmission of voice, data, and signaling over traditional copper telephone networks. It provides end-to-end digital connectivity and supports multiple channels on a single line, allowing simultaneous voice and data sessions. Two parts of the signaling and data structure are the B channels, which carry user data at 64 kbit/s each, and the D channel, which carries control and signaling information.

Two main interface types are used: Basic Rate Interface (BRI) and Primary Rate Interface (PRI). BRI offers 2B+D, totaling 144 kbit/s, typically used for home or small office deployments. PRI provides higher capacity, with 23B+D in North America and Japan, or 30B+D in Europe. PRI delivers a dedicated signaling channel and multiple B channels for higher bandwidth needs.

ISDN also supports standards for call setup and teardown (such as Q.931 signaling) and various LAN-to-network and terminal equipment options. Over time, ISDN has been largely supplanted in many regions by broadband technologies like DSL, cable, and fiber, and is now mostly deployed for legacy systems or specific applications with compatible equipment.