Rich, 

--- Here is the detail from the manual. I have first cut & pasted the "graceful 
degradation" math detail:

Graceful Degradation Limit (AU only)
Sets the limit on using the graceful degradation algorithm. In cases of over
demand, the performance of all SUs is degraded proportionally to their CIR
(IR=(100%-k%) x CIR). The graceful degradation algorithm is used as long as
k ≤ K, where K is the Graceful Degradation Limit. Beyond this point the simple
"brute force" algorithm is used. The Graceful Degradation Limit should be raised
in proportion to the demand in the cell. The higher the expected demand in a 
cell,
the higher the value of the Graceful Degradation Limit. Higher demand can be
expected in cases of significant over subscription and/or in deployments where a
high number of subscribers are in locations without proper communication with
the AU at the highest data rate.
The available values range from 0 to 70 (%).

--- And here is the whole bit about how the mechanism works

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 inTable 4-12. The actual value will be the 
entered value rounded to the nearest multiple of 128 (N*128).

4.2.6.6.2.2 MIR: Uplink (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. 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).

4.2.6.6.2.3 CIR: Downlink (SU only)
Sets the Committed Information Rate of the downlink from the AU to the SU. The 
CIR value cannot be higher than the corresponding MIR value. Available values 
range and default value are shown inTable 4-13. The actual value will be the 
entered value rounded to the nearest multiple of 128 (N*128).

4.2.6.6.2.4 CIR: Uplink (SU only)
Sets the Committed Information Rate of the uplink from the SU to the AU. The
CIR value cannot be higher than the corresponding MIR value. Available values 
range and default value are shown in Table 4-13. The actual value will be the 
entered value rounded to the nearest multiple of 128 (N*128).

Table 4-12: MIR Ranges and Defaults
MIR Uplink MIR Downlink
Unit
Type
 Range (Kbps) Default (Kbps) Range (Kbps) Default (Kbps)
SU-3 128-2,048 2,048 128-3,072 3,072
SU-6 128-4,096 4,096 128-6,016 6,016
SU-54 128-53,888 32,896 128-53,888 32,896

Table 4-13: CIR Ranges and Defaults
CIR Uplink and Downlink
Unit Type Range (Kbps) Default (Kbps)
SU-3 0-2,048 0
SU-6 0-4,096 0
SU-54 0-45,056 0

4.2.6.6.2.5 Maximum Burst Duration (SU and AU)
Sets the maximum time for accumulating burst transmission rights according to 
the Burst Duration algorithm. Available values range from 0 to 2000 
milliseconds). The default value is 5 (milliseconds), enabling a maximum burst 
of (0.005 X CIR) Kbps after a period of inactivity of 5 milliseconds or more.

4.2.6.6.2.6 Maximum Delay (SU only)
Sets the maximum permitted delay in the buffers system. As certain applications 
are very sensitive to delay, if relatively high delays are permitted, these 
applications may suffer from poor performance due to data accumulation in the 
buffers from other applications, such as FTP. The Maximum Delay parameter 
limits the number of available buffers. Data that is delayed more than the 
permitted maximum delay is discarded. If the SU supports applications that are 
very sensitive to delay, the value of the Maximum Delay should be decreased. 
Valid values range from 300 to 10000 milliseconds. The default value is 5000 
(milliseconds).

4.2.6.6.2.7 Graceful Degradation Limit (AU only)
Sets the limit on using the graceful degradation algorithm. In cases of over 
demand, the performance of all SUs is degraded proportionally to their CIR
(IR=(100%-k%) x CIR). The graceful degradation algorithm is used as long as
k ≤ K, where K is the Graceful Degradation Limit. Beyond this point the simple 
"brute force" algorithm is used. The Graceful Degradation Limit should be 
raised in proportion to the demand in the cell. The higher the expected demand 
in a cell, the higher the value of the Graceful Degradation Limit. Higher 
demand can be expected in cases of significant over  subscription and/or in 
deployments where a high number of subscribers are in locations without proper 
communication with the AU at the highest data rate. The available values range 
from 0 to 70 (%). The default value is 70 (%).

4.2.6.6.2.8 MIR Only Option (AU only)
When the MIR Only Option is enabled, it forces the MIR/CIR algorithm to use
MIR values only. The MIR/CIR algorithm determines the actual information rate 
for each of the supported SUs under changing conditions of demand, based on the 
configured CIR and MIR values. When the MIR Only Option is enabled, the MIR/CIR 
algorithm is overridden and forced to operate with MIR values only. For 
example, the AU attempts to enable all SUs to transmit/receive information at 
the specified MIR value. When enabled, the graceful degradation algorithm, 
which is a part of the CIR/MIR algorithm, is also disabled. The default is 
Enable.

4.2.6.6.2.9 Show MIR/CIR Parameters
Displays the current values of the MIR and

----
Patrick Leary
AVP WISP Markets
Alvarion, Inc.
o: 650.314.2628
c: 760.580.0080
Vonage: 650.641.1243
[EMAIL PROTECTED]

-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Rich Comroe
Sent: Wednesday, January 24, 2007 4:01 PM
To: WISPA General List
Subject: Re: [WISPA] Advanced Bandwidth Management

Fascinating.  I only spoke of leaky bucket because that's practically a match 
to what Jason originally described to the list (and I happen to know of radios 
that have this algorithm internally programmed -- happens to be Canopy).  But I 
presume there are other algorithms programmed to different manufacturer's 
radios.  Patrick, is it possible to share details of the Alvarion implemented 
4th gen algorithm you spoke of? 





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