Instruction manual

Menus and Parameters
2-93
BreezeACCESS Version 4.5 System Manual
Under normal conditions, the actual Information Rate (IR) will be
between the applicable CIR and MIR values: IR=CIR+K(MIR-CIR),
where K is between 0 to 1 and is determined dynamically by the AU
according to overall demand in the cell and the prevailing conditions
that may influence the performance of the wireless link. In some
situations the minimum rate (CIR) cannot be provided. This may
occur as a result of high demand and poor wireless link conditions
and/or high demand in cells with over subscription (total CIR higher
than 1600Kbps). When this happens, actual information rate will be
lower than CIR. The simple solution for managing information rate
in such cases results in an unfair allocation of resources, as
subscribers with higher CIR can actually get an IR lower than that
given to subscribers with lower CIR. A special algorithm for graceful
degradation has been incorporated into the AU, ensuring that the
degradation of performance for each individual subscriber will be
proportional to its CIR.
The MIR/CIR algorithm uses buffers to control the flow of data. To
average the performance over time, a special Burst Duration
algorithm is employed to enable higher transmission rates after a
period of inactivity. If no data was 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 an inactivity time of
0.5 second, a unit with CIR = 64 Kbps can transmit up to 64 Kbits x
0.5 = 32 Kbits without any delay.
" MIR/CIR Option – Enables or disables the CIR/MIR support
feature. In cells where the AU and all SUs use SW version 4.0
and higher, the MIR/CIR Option in the AU controls the
operation of the whole cell. The MIR/CIR Option in the SU is
thus meaningless, as the setting of the option in the AU will
override possible conflicting setting in any of the served SUs.
The option is available in the SUs only for compatibility with
previous versions to support operation in cells where the AU
uses SW version 3.X and lower.
Default selection is Disable.
" MIR: AU to SU (SU only) – Sets the Maximum Information Rate
of the down-link from the AU to the SU. The MIR value cannot
be lower than the corresponding CIR value.
Valid values are from 32 to 2200 Kbps.
The default value is 128 Kbps.
" MIR: SU to AU (SU only) – Sets the Maximum Information Rate
of the up-link from the SU to the AU. The MIR value cannot be
lower than the corresponding CIR value.
NOTE:
The value of the MIR/CIR option parameter must be the same for all Subscriber
Units served by the same AU (i.e. Enable for all SUs or Disable for al SUs).
Otherwise, throughput to/from all SUs in the cell may be reduced significantly.