Alvarion BreezeACCESS VL System Manual page 205

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 following 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.
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.
A special algorithm for graceful degradation is incorporated into the AU, ensuring
that the degradation of performance for each individual Subscriber Unit is
proportional to its CIR.
The MIR/CIR algorithm uses buffers to control the flow of data. To balance the
performance over time, a special Burst Duration algorithm is employed to enable
higher transmission rates after a period of inactivity. If no data is received from
the Ethernet port during the last N seconds, the unit is allowed to transmit N
times its CIR value without any delay. For example, after a period of inactivity of
0.5 seconds, a unit with CIR = 128 Kbps can transmit up to 128 Kbits x 0.5 =
64 Kbits without any delay.
4.2.6.6.2.1 MIR: Downlink (SU only)
Sets the Maximum Information Rate of the downlink from the AU to the SU. The
MIR value cannot be lower than the corresponding CIR value.
Available values range and default value are shown in Table 4-12.
The actual value will be the entered value rounded to the nearest multiple of 128
(N*128).
Operation and Administration
Menus and Parameters
179