VCI meaning in Computer and Networking ?

Asynchronous Transfer Mode (ATM) is a telecommunications standard defined by ANSI and ITU (formerly CCITT) for digital transmission of multiple types of traffic, including telephony (voice), data, and video signals in one network without the use of separate overlay networks. ATM was developed to meet the needs of the Broadband Integrated Services Digital Network, as defined in the late 1980s, and designed to integrate telecommunication networks. It can handle both traditional high-throughput data traffic and real-time, low-latency content such as voice and video. ATM provides functionality that uses features of circuit switching and packet switching networks. It uses asynchronous time-division multiplexing.

In the OSI reference model data link layer (layer 2), the basic transfer units are generically called frames. In ATM these frames are of a fixed (53 octets or bytes) length and specifically called cells. This differs from approaches such as IP or Ethernet that use variable sized packets or frames. ATM uses a connection-oriented model in which a virtual circuit must be established between two endpoints before the data exchange begins. These virtual circuits may be either permanent, i.e. dedicated connections that are usually preconfigured by the service provider, or switched, i.e. set up on a per-call basis using signaling and disconnected when the call is terminated.

The ATM network reference model approximately maps to the three lowest layers of the OSI model: physical layer, data link layer, and network layer. ATM is a core protocol used in the SONET/SDH backbone of the public switched telephone network (PSTN) and in the Integrated Services Digital Network (ISDN), but has largely been superseded in favor of next-generation networks based on Internet Protocol (IP) technology, while wireless and mobile ATM never established a significant foothold.