-multipoint arrangements, more than two VPC end-points. A VPC end-point is the point where the VCIs are originated, translated, or ter- minated. At the VP level, VPCs are provided for the purpose of user-user, user-network, and network-network information transfer. When VPCs are switched, the VPC supporting the incoming VC links are terminated first and a new outgoing VPC is then created. Cell sequence integrity is preserved by the ATM layer for cells belonging to the same VPC. Thus cell sequence integrity is preserved for each VC link within a VPC. Figure 20.14 is a representation of a VP and VC switching hierarchy where the physical layer is the lowest layer composed of, from bottom up, a regenerator section level, a digital VC switch/cross-connect Endpoint of VPC VCI 21 VPI 1 VCI 22 VCI 23 VCI 21 VC121 VCI 22 VP switch/cross-connect VCI 21 VCI 23 VPI 1 VPI 4 VCI 22 VCI 24 VCI 23 VCI 25 VCI 24 VCI 24 VCI 25 VC121 VCI 24 VCI 22 VP switch/cross-connect Figure 20.14 Representation of the VP and VC switching hierarchy. (a) VC and VP; (b) VP switching. [From ITU-T Rec. 1.311, Figure 4/l.311, p. 5 (Ref. 12).] ASYNCHRONOUS TRANSFER MODE section level, and a transmission path level. The ATM layer resides just above the physical layer and is composed of the VP level, and just above that is the VC level. 20.9 SIGNALING REQUIREMENTS 20.9.1 Setup and Release of VCCs The setup and release of VCCs at the user-network interface (UNI) can be performed in various ways: Without using signaling procedures. Circuits are set up at subscription with perma- nent or semipermanent connections. By meta-signaling procedures, where a special VCC is used to establish or release a VCC used for signaling. Meta-signaling is a simple protocol used to establish and remove signaling channels. All information interchanges in meta-signaling are carried out via single cell messages. User-to-network signaling procedures, such as a signaling VCC to establish or release a VCC used for end-to-end connectivity. User-to-user signaling procedures, such as