User's Manual

6.1.1 ATM VC & QoS

ATM settings are used to connect to your ISP. Your ISP provides VPI, VCI, settings to you.

In this Device, you can totally setup 8 PVCs on different encapsulations if you apply 8 different

virtual circuits from your ISP. You need to activate the VC to take effect. For PVCs management,

you can use ATM QOS to setup each PVC traffic line’s priority.

Virtual Circuit: Select the VC number you want to setup.

VPI: Virtual Path Identifier. The valid range for the VPI is 0 to 255.

VCI: Virtual Channel Identifier. The valid range for the VCI is 1 to 65635 (0 to 31 is reserved for

local management of ATM traffic).

ATM QoS: Select the Quality of Service types for this Virtual Circuit. The ATM QoS types include

CBR(Constant Bit Rate), VBR(Variable Bit Rate) and UBR (Unspecified Bit Rate). These QoS

types are all controlled by the parameters specified below, including PCR, SCR, and MBS.

PCR: Peak Cell Rate (PCR) is the maximum rate at which the sender can send cells. This

parameter may be lower (but not higher) than the maximum line speed. 1 ATM cell is 53 bytes

(424 bits), so a maximum speed of 832 Kbps gives a maximum PCR of 1962 cells/sec. This rate

is not guaranteed because it is dependent on the line speed.

SCR: Sustained Cell Rate (SCR) is the mean cell rate of a bursty, on-off traffic source that can

be sent at the peak rate, and a parameter for burst-type traffic. SCR may not be greater than the

PCR; the system default is 0 cells/sec.

MBS: Maximum Burst Size (MBS) is the maximum number of cells that can be sent at the PCR.

After MBS is reached, cell rates fall below SCR until cell rate averages to the SCR again. At this