TCP/IP Active Queue Management added to all Paradise satellite modems

February 22, 2017

Intelligent TCP/IP queue management has been added to all Paradise satellite modems in order to overcome the potential for inconsistent end-to-end packet delays and the problems of 'buffer bloat'. Buffer bloat is where all of the packet buffers in the system are over-sized in order to try to prevent packet loss. The result is often that performance at the application level suffers due to excessive buffering of packets during periods of congestion, leading to extremely high latency levels with old data being kept almost indefinitely in the hope that any overload will ease and extra bandwidth will become available.


Most buffer management in TCP/IP devices is passive and relies on the user setting internal buffer sizes to be consistent with the needs of the application and its data rates. However, TCP/IP is bursty by nature and if the rate of arrival of packets at the satellite modem exceeds its transmission capabilities then packets start to back up and will eventually get dropped if the overload continues. The problem with this is that the end-to-end packet delay can vary greatly and data becomes increasingly stale as the backlog of packets to be transmitted builds up.


Paradise's solution to this problem is Active Queue Management (AQM). This continually measures the packet delay through the modem and rather than let the backlog of packets build up, it ensures that the delay through the modem is kept constant by dropping packets early if required. The effect of this is that transit times through the network continue to be constant even in an overload situation. The use of AQM can be combined with traffic shaping to ensure that high priority traffic is unaffected when demands on bandwidth are exceeded.

The use of active queue management is especially important for latency sensitive applications. AQM is available as a user-selectable menu option from satellite modem software V3.1.3 onwards, which is available for all modem variants.