On Effectiveness of Application-Layer Coding

The effectiveness of application-layer coding in a system with a large number of users is considered. The end users encode data packets before transmitting them. The effect of additional packets on the system performance is twofold: (i) additional packets increase the offered load, which results in higher drop probability, and (ii) some of dropped packets can be recovered at the receivers after decoding. The paper establishes an asymptotic regime in which systems with and without coding have the same performance. The space of all systems is partitioned into two regions where coding is beneficial and detrimental, respectively. Informally, it is argued that application-layer coding improves the performance only in systems with low loss probabilities (without coding), and employing such coding in systems with high loss probabilities only degrades the performance.