Active
Queue Management (AQM) is a queue management feature for the downlink. For
applications using TCP/IP as transmission (e.g. FTP, web browsing, email), it
is important with a rapid feedback of the radio link data rate to the TCP/IP
protocol. Feedback of the radio link data rate is reported to TCP/IP by discarding
IP-packets. In this way the TCP/IP protocol will faster adjust its send rate
according to the radio link capacity and TCP slow-starts are avoided. If the
feature “QoS and Scheduling” in BSC is active (R97 QoS and/or R99 QoS), the
queue management feature is applied to Interactive class and Background class
data. The queue management feature is not applied to signalling messages, SMS,
LLC acknowledged mode data, EIT data or Streaming class data when QoS is
active. For SMS, signalling messages, LLC acknowledged mode data, EIT data and
Streaming class data a maximum buffer is set and when the buffer is overflowed
packets are discarded starting from front of the buffer.
If
the feature “QoS and Scheduling” in BSC is passive, the queue management feature
is applied to all payload data but not to signalling messages, SMS or LLC acknowledged
mode data. For LLC acknowledged mode data and data not handled by AQM a maximum
buffer is set and when the buffer is overflowed packets are discarded starting
from front of the buffer.