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CONCEPT Cited by 1 source

NewReno congestion control

Definition

NewReno is a loss-based TCP congestion-control algorithm standardised in RFC 6582 (2012) — a refinement of Reno (originally 1990) dating back to 1999. It uses additive-increase, multiplicative-decrease (AIMD) with fast-retransmit and fast-recovery to handle packet loss.

By 2024, NewReno is no longer the dominant CC algorithm — it was displaced by CUBIC around 2006 as the Linux default. Yet it remains QUIC's specification-level default.

The QUIC-default paradox

Zalando's 2024-06 post is unambiguous:

"QUIC standard is confusing, it proposes NewReno as default algorithm, although CUBIC is the dominant algorithm for the broad internet traffic today." (Source: sources/2024-06-17-zalando-next-level-customer-experience-with-http3-traffic-engineering)

This is the framing: NewReno is the formal default, but production QUIC deployments run CUBIC or BBR. The specification chose NewReno likely as the most-documented and reference-implementation-friendly CC algorithm — giving implementers a baseline to start from and switch away from.

The fact that it ships in the spec and not in production is another example of the user-space CC mutability that QUIC enables: nothing about the transport requires implementations to actually use NewReno.

5G performance

Same as CUBIC: Zalando cites the 2021 MDPI paper showing NewReno "very poor throughput and latency performance" under 5G physical-failure scenarios (noise, interference, blockage, handover). NewReno is loss-signalled, so it mis-identifies RF loss as congestion.

Mechanics (brief)

  • Slow-start — exponential window growth until a configured threshold.
  • Congestion-avoidance — additive linear growth (1 MSS / RTT).
  • Fast-retransmit — triggered by 3 duplicate ACKs.
  • Fast-recovery — when multiple losses occur in one RTT, continue sending at half rate instead of resetting to slow- start.
  • Multiplicative-decrease — halve the window on congestion signal.

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