But how does QUIC actually work?
Well, first, let's take a look at the protocol stack for web delivery over TCP.
Now, application calls and responses are sent to the TLS layer for encryption.
This data is then sent to the TCP stack for segmentation and reliable delivery,
which is then packetized and routed over the IP network.
Now, this is a function that we do every day,
all day, but the QUIC stack looks a little different.
As we've already discussed, QUIC sits on top of the UDP protocol.
One reason for this is to make use of a protocol that's already baked
into the kernel of almost every system on the planet.
If QUIC sat directly on top of IP,
there would be a tremendous learning curve for all aspects of
the local network and the internet, just imagine all the
firewalls you would have to reconfigure.
But with this transport in place, now applications
such as HTTP/3 or other applications, for that matter, can make use of QUIC.
But again, how is QUIC secured?
Well, easy, using TLS 1.3.
But rather than treat it as a separate function that application traffic
sits on top of, QUIC embeds TLS 1.3 into its core function.
So at the start of a QUIC connection,
the TLS handshake happens right away, and then
thereafter, for the rest of that connection,
we no longer have to sit that data on top of the TLS layer. But,
but, but this is still over UDP, so what about packet loss, or
retransmission, or congestion control?
Well, look no further than QUIC.
QUIC is designed with many TCP‑like behaviors when it comes
to congestion control and loss recovery.
Really, to put it simply,
TCP and a lot of its concepts that make data delivery
reliable have simply been formed into QUIC.
So with QUIC coming on the scene at such a rapid pace,
will it completely replace TCP?
Well, no. No, it won't, at least not for a long time.
For many TCP‑based applications,
there will be no immediate need to switch. The engineering
time to re‑port things over to QUIC might not be worth the
performance and the security savings.
TCP has had a long life and will continue to exist for the foreseeable future, but it just has a bright new competitor.