This specifies the class of service or service type 'cbr (1)' : Constant Bit Rate. 'vbr-rt (2)' : Variable Bit Rate 1 (Real Time) although, VISM does not do any kind of traffic shaping, the PVC has to be specified as vbr-rt for PXM to treat the connection as a VBR1 connection. Variable Bit Rate is not currently supported. 'vbr-nrt (3)' : Variable Bit Rate 1 (non real time) the service type of the connection cannot be modified once the PVC is added. 'vbr3-rt (4)' : Variable Bit Rate 3 (Real Time) although, VISM does not do any kind of traffic shaping, the PVC has to be specified as vbr3-rt for PXM to treat the connection as a VBR3 connection. Variable Bit Rate is not currently supported. 'vbr2-rt (5)' : Variable Bit Rate 2 (Real Time) although, VISM does not do any kind of traffic shaping, the PVC has to be specified as 'vbr2-rt' for PXM to treat the connection as a VBR2 connection. Variable Bit Rate is not currently supported. 'vbr2-nrt (6)' : Variable Bit Rate 2 (non real time) the service type of the connection cannot be modified once the PVC is added. 'vbr3-nrt (7)' : Variable Bit Rate 3 (non real time) the service type of the connection cannot be modified once the PVC is added.