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A virtual path identifier (VPI) is a data communication identifier that uniquely identifies a network path for an asynchronous transfer mode (ATM) cell packet to reach its destination node.
VPIs are eight- to 16-bit numeric headers in ATM cell packets. ATM cells typically pass through ATM switches. VPI headers tell the switches where to route the packet. Each path has a specific proportion of bandwidth allocated to it. The number of paths depends upon the available bandwidth. Every newly created path has a VPI assigned to it.
VPIs work in collaboration with virtual channel identifiers to enable the whole ATM cell switching network. ATM cells create virtual circuits and paths leading to different networks within the whole channel communication capability. The virtual channel identifier referrs to the circuit/channel in use, while VPI matches the appropriate path to the desired destination host.
ATM cells enable direct and rapid communication. They also create a symmetry and provide identification while managing access control. A numeric identification is given to all the circuits and paths created by the ATM switch, they are known as virtual channel identifiers and virtual path identifiers.