User Manual

Table Of Contents
Menus and Parameters
Operation and Administration
187
4.2.6.6.1.5 DHCP Unicast Override Filter
When user filtering is activated, unicast DHCP messages are filtered out;
therefore the unit cannot communicate with the DHCP server. The DHCP Unicast
Override Filter option enables to overcome this problem. When enabled, unicast
DHCP messages pass, overriding the user filtering mechanism.
The default is Disable DHCP Unicast.
4.2.6.6.1.6 Show User Filtering Parameters
The Show All User Filtering Parameters option displays the current value of the
User Filtering Option and the list of User Filtering addresses, subnet masks and
ranges.
4.2.6.6.2 MIR and CIR Parameters
The CIR (Committed Information Rate) specifies the minimum data rate
guaranteed to the relevant subscriber. The MIR (Maximum Information Rate)
value specifies the maximum data rate available for burst transmissions,
provided such bandwidth is available.
Under normal conditions, the actual Information Rate (IR) is between the
applicable CIR and MIR values, based on the formula IR=CIR+K(MIR - CIR).
In this formula K is between 0 and 1 and is determined dynamically by the AU
according to overall demand in the cell and the prevailing conditions that
influence the performance of the wireless link. In some situations the minimum
rate (CIR) cannot be provided. This may result from high demand and poor
wireless link conditions and/or high demand in over-subscribed cells. When this
occurs, the actual information rate is lower than the CIR, and IR = (1+K)*CIR,
where K < 0. The K value to be used in the cell is advertised by the AU in every
beacon, and it is changed every second based on comparison of the traffic during
the last one second interval with the traffic during the previous previous one
second interval. The advertised K value is used by each SU to calculate the
amount of data that can be transmitted. This algorithm ensures fair resource
distribution among SUs, based on their configured CIR/MIR values.
The MIR Threshold Percent parameter determines the level of wireless link
utilization above which the MIR/CIR mechanism is activated. A Threshold of 0%
allows CIR only. A threshold of 100% means MIR only. For other values, if the
actual wireless link utilization is below the threshold, K is set to 1. As the link
utilization increases above the threshold, K is decreased as described above.
The simple solution for managing the information rate in such cases can result in
an unfair allocation of resources, as subscribers with a higher CIR actually
receive an IR lower than the CIR designated for subscribers in a lower CIR
bracket.