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

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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.