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3.5.2 ATM Settings
The page is for ATM PVCs’ QoS mode setting. The device supports 4 QoS mode — UBR /
CBR /rt-VBR / nrt-VBR. You can click the “ATM Setting” on the WAN Interface setting
screen.
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.
CBR is for connections that support constant rates of data transfer. The only parameter you
need to worry about in CBR is PCR.
UBR is for connections that have variable traffic. The only parameter you need to worry
about in UBR is PCR.
rt-VBR is for connections that, while having variable traffic, require precise timing between
traffic source and destination. PCR, SCR and MBS must all be set for rt-VBR.
nrt-VBR is for connections that have variable traffic, do not require precise timing, but still
require a set bandwidth availability. PCR, SCR and MBS must all be set for nrt-VBR.
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.
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