ATM connections

ATM architecture has two kinds of virtual circuits: permanent (PVCs) and switched (SVCs).

Item	Description
Permanent Virtual Circuits	PVCs are statically and manually configured. The switches forming the ATM network must first be set up to recognize the VPI:VCI combination of each endpoint and to route the endpoint ATM cells to the destination endpoint through the ATM network. Once a link connection through the network has been established from one endpoint to another, ATM cells can be transmitted through the ATM network and ATM switches. The network switches translate the VPI:VCI values in the appropriate way so as to route the cell to its destination.
Switched Virtual Circuits	SVCs are dynamically set up on an as needed basis. The ATM end stations are assigned 20-byte addresses. SVCs use a control plane and a data plane. The control plane uses a signaling channel VPI:VCI 0:5. SVCs involve on demand call setup, whereby an ATM station sends information elements specifying the destination ATM address (and optionally, the source ATM address). In general, calling station, network, and called station participate in a negotiation. Finally, a call is either accepted or rejected. If a call is accepted, network assigns VPI:VCI values for the data plane to the calling station and called station. In the control plane, the ATM network routes (or switches) signaling packets on the basis of the ATM addresses. While these packets are being routed, the switches set up data plane cell routing tables. In the data plane, ATM networks switch cells on the basis of VPI:VCI much like in the case of PVCs. When data transfer is over, connection is terminated.

Item

Description

Permanent Virtual Circuits

PVCs are statically and manually configured. The switches forming the ATM network must first be set up to recognize the VPI:VCI combination of each endpoint and to route the endpoint ATM cells to the destination endpoint through the ATM network. Once a link connection through the network has been established from one endpoint to another, ATM cells can be transmitted through the ATM network and ATM switches. The network switches translate the VPI:VCI values in the appropriate way so as to route the cell to its destination.

Switched Virtual Circuits

SVCs are dynamically set up on an as needed basis. The ATM end stations are assigned 20-byte addresses. SVCs use a control plane and a data plane. The control plane uses a signaling channel VPI:VCI 0:5. SVCs involve on demand call setup, whereby an ATM station sends information elements specifying the destination ATM address (and optionally, the source ATM address). In general, calling station, network, and called station participate in a negotiation. Finally, a call is either accepted or rejected. If a call is accepted, network assigns VPI:VCI values for the data plane to the calling station and called station. In the control plane, the ATM network routes (or switches) signaling packets on the basis of the ATM addresses. While these packets are being routed, the switches set up data plane cell routing tables. In the data plane, ATM networks switch cells on the basis of VPI:VCI much like in the case of PVCs. When data transfer is over, connection is terminated.

The ATM address is constructed by registering with the ATM network and by acquiring the most significant 13 bytes. The next six bytes contain the adapter's factory-assigned, unique MAC address. The least significant byte is the selector. Use of this byte is left to the discretion of the end station. ATM networks do not interpret this byte.