Cabletron Systems 04-0053-01 manual Creating Virtual Ports, Available VPIs = 2MaxVpiBits

Virtual Ports Virtual Ports and Static Connections

5.3.1Creating Virtual Ports

Virtual ports are created on physical ports by first allocating a range of Virtual Path Identifiers (VPIs), and then distributing the VPIs among the virtual ports. The number of VPIs used depends on the number of virtual ports needed and the range of VPIs controlled by each virtual port.

When creating virtual ports, it’s important to remember that the virtual port number represents the Base VPI used by the virtual port. For example, the virtual port 5b1.3 uses Base VPI = 3.

Creating virtual ports on an ATM SmartSwitch consists of the following basic process

•Create a traffic descriptor for the virtual port that meets its bandwidth and service category requirements.

Note To assure that virtual ports receives the exact bandwidth required, you may want to assign them traffic descriptors that specify CBR as the service class.

•Use the set portconfig command to turn off signaling on the physical port on which you are creating the virtual ports.

Note Signaling is usually not used on physical ports on which virtual ports are created. However, you can leave signaling active on the physical ports if necessary.

•Use the MaxVpiBits parameters of the set portconfig command to set the number of bits to use for VPIs for virtual ports on this physical port:

Available VPIs = 2MaxVpiBits - 1

For example, if MaxVpiBits is set to 3, then the number of VPIs available for virtual ports is:

Available VPIs = 23 - 1 = 8 - 1 = 7

Note The value for Available VPIs is also the highest number that can be used to specify a virtual port on the physical port. For instance, in the example above, 7a1.7 is the highest virtual port that can be created using MaxVpiBits = 3.

•Use the add port command to create the virtual port and to specify the number of VPIs used by the virtual port. Note that the add port command also uses the MaxVpiBits parameter, however, here it’s used to define the number of VPIs the virtual port uses, based on the equation:

VPIs Used by Virtual Port = Base VPI + (2MaxVpiBits-1)

For example, if the virtual port number is 5b2.1 (Base VPI = 1), and MaxVpiBits = 1, then the total number of VPIs used by this virtual port is:

Base VPI + (21-1) = 1 + (2-1) = 1 + 1 = 2 VPIs

So port 5b2.1 controls VPI 1 (the Base VPI) and VPI 2.

5-8 SmartSwitch ATM User Guide