Lifetime Packet Discard for Efficient Real-Time Transport over Celullar Links
Andrei Gurtov
Reiner Ludwig
ACM Mobile Computing and Communications Review, 7(4):32-45, October 2003
[Full Text in PDF Format, 700KB] [Older version in PDF Format, 700KB]
Abstract
Mobile cellular users often experience significant delay jitter
that undermines quality of real-time applications. Delay jitter can
cause
unnecessary delivery of stale packets with passed playback deadline and
duplicate packets retransmitted by the end host after experiencing a
timeout. With Lifetime Packet Discard (LPD) a flow adaptive link can
tailor the trade-off between the maximum delay jitter and reliability if
quality of service requirements of a flow are known. We propose using an
IP option to communicate the flow requirements to the link layer.
Packet
lifetime is set to the minimum of data lifetime determined by
application
and the retransmit timeout value determined by the transport protocol if
selective reliability is supported. For congestion-responsive flows, the
link transmits only headers of expired packets to prevent unnecessary
triggering of end-to-end congestion control. Our simulations show that
LPD
is efficient in reducing stale data delivery and increases the number of
packets delivered in time for real-time flows. For semi-reliable flows
throughput and goodput are improved because duplicate packet delivery is
prevented.