We introduce FLUID (Fountain LiqUId Delivery), a protocol that uses fountain coding and receiver feedback for low-latency delivery of data blocks over lossy networks. Idealized Automatic Repeat reQuest (ARQ) protocols are bandwidth-optimal, but must deliver every packet in a block and therefore can require additional rounds under packet loss. FLUID uses a controlled amount of slack to relax this all-packets requirement, allowing delivery to finish once enough encoded packets have been received. This yields substantially tighter delivery latency while remaining deterministically close to the ARQ bandwidth optimum. FLUID is controlled by a slack parameter $ε$. Under the Loss-Product Rule, delivery finishes once the product of packet loss fractions across transmission rounds falls below $ε$. Thus, FLUID can finish delivery in a small number of rounds even when every round experiences packet loss, while $ε$ controls the gap between FLUID and bandwidth-optimal ARQ.

翻译：我们提出FLUID（喷泉液体传输）协议，该协议利用喷泉编码与接收端反馈机制，在丢包网络中实现数据块的低延迟传输。理想化的自动重传请求（ARQ）协议具有带宽最优性，但必须完整交付数据块中的每个数据包，因此在丢包场景下需要额外传输轮次。FLUID通过引入受控松弛量来放宽"全量数据包"的约束条件，允许在接收端收集到足够数量的编码包后即可完成交付。这使得交付延迟显著降低，同时仍能确定性逼近ARQ的带宽最优性能。FLUID由松弛参数$ε$调控。根据损失乘积准则，当各传输轮次的丢包率乘积低于$ε$时，交付即告完成。因此，即便每一轮传输都遭遇丢包，FLUID仍能在少量传输轮次内完成交付，而参数$ε$则用于控制FLUID与带宽最优ARQ协议之间的性能差距。