  BitTorrent developers have recently introduced a new application layer
congestion control algorithm based on UDP framing at transport layer and
currently under definition at the IETF LEDBAT Working Group. LEDBAT is a
delay-based protocol which aims at offering a "lower than Best Effort" data
transfer service, with a lower priority with respect to elastic TCP and
interactive traffic (e.g., VoIP, game). However, in its current specification,
LEDBAT is affected by a late-comer advantage: indeed the last flow arriving at
the bottleneck is more aggressive due to a wrong estimation of the base delay
and finally takes over all resources. In this work, we study several solutions
to the late-comer problem by means of packet level simulations and simple
analysis: in the investigation process, we individuate the root cause for
LEDBAT unfairness and propose effective countermeasures.
