LiteSpeed QUIC and HTTP/3 Library v4.0

March 8th, 2023 by Company News 0 Comments

lsquic v4.0

After about 2 years of strong stability and performance in production, LiteSpeed’s QUIC and HTTP/3 library gets its first major feature enhancement release: lsquic v4.0. Notable enhancements include:

  • Support for QUIC version 2
  • Version negotiation
  • Packet retry for address validation
  • Handshake improvements under high packet loss
  • Greatly improved QUIC interop results.

Below is the detailed information about the improvements.

QUIC version 2

QUIC version 2 is in draft 10 as of this writing, and will be published as RFC9369 soon. QUIC version 2 is not intended to deprecate version 1. Instead, it is meant to mitigate ossification concerns and exercise the version negotiation mechanisms.

There are a few QUIC implementations that already support QUIC v2 including ngtcp2, Kwik, picoquic, and HAProxy. lsquic might have been a little late to the party, but we are here now with v4.

We also plan to release QUIC v2 into the production environment with our commercial server products very soon.

Version Negotiation

Version Negotiation is pretty much in the same boat as QUIC v2. It is in draft 14, and soon will be published as RFC9368. It updates RFC8999 by defining version negotiation mechanisms that leverage the Version Negotiation packet.

Quote from draft 14:

It is beneficial to avoid additional round trips whenever possible, especially given that most incremental versions are broadly similar to the previous version. This specification also defines a simple version negotiation mechanism which leverages similarities between versions and can negotiate between “compatible” versions without additional round trips.

Version negotiation is a required feature in order to support QUIC v2.

Retry Packet for Address Validation

This feature is defined in RFC9000 section-8.1.2. It is not something new. It has been used in our commercial WebADC product from the very beginning, however this feature was not previously available in the open source lsquic code base. The related code is now published in v4.

Handshake under high packet loss or corruption

In QUIC interop test cases, handshakeloss and handshakecorruption have been two of the toughest tests to pass in our course of improving lsquic interoperability.

The network quality simulated in the test cases is so poor, it is definitely not something a user will come across everyday. However, to make successful handshakes under such conditions, makes a QUIC implementation super resilient to bad network conditions. In the process of testing, many beneficial tweaks have been made, like minimizing server hello return packets, and ACK/PING fine tuning.

You can see how much lsquic has been improved in the next section.

QUIC interop improvements

lsquic was in the first batch of open source QUIC implementations. It has been running in production environments for many years, and is both stable and performant. It has not only been used in LiteSpeed products, but also by other third-parties in large scale deployments.

However, lsquic’s interoperability results have not always been the best. This does not mean that lsquic is not as good as the implementations that have better results. It is just that we do not focus on the interop tests. Some tests were not turned on, and some needed minor tweaks.

Since we are making big improvements to lsquic, it is a good time to take this opportunity to improve interoperability with other implementations. Here is the comparison of before and after.

lsquic 4.0 interop results

Green is passed, gray is not supported by the client, and red is failure. As you can see, there are only a few red ones left. Those failures mostly are due to client side problems. lsquic now joins ngtcp2 and picoquic in the “passes all interop tests” club.

You can check the full results at


The lscquic v4.0 release is a big leap forward in terms of the latest development of the QUIC protocol. The LiteSpeed team is committed to bringing the best QUIC implementation to the public. Stay tuned for what is coming next.

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