Now, you've heard me refer to QUIC packets and frames throughout this course,
but let's take a step back for a moment and make sure we have a
clear picture of what these terms are referring to,
which will help us in going forward and understanding QUIC.
Now, historically, if I said the word packet,
we're generally referring to data from the left edge of the IP header,
as we see here, to the right edge of the payload.
That's a packet.
If I said frame, typically, that means the Ethernet frame and also the payload,
so this would be from the left edge of the Ethernet frame all the
way to the end of the frame check sequence.
Now, with QUIC,
there's some new definitions of packets and frames that we need to understand.
While Ethernet frames and IP packets still stay the
same in their overall definition,
those two terms are also used at the transport layer
to define elements within QUIC.
So Ethernet, IP, and UDP, those are the same up to that UDP datagram,
but QUIC packets are encapsulated within the UDP datagram,
and then frames are defined and encapsulated within QUIC packets,
so frames have different functions within the QUIC connection.
So, for example, there can be frames that contain the crypto data,
which could be TLS info at the start of connection,
handshake data, or stream data.
In fact,
there's 20 types of frames that could be contained within a
QUIC packet, so the type of frame will define the data
that's carried within that frame.
Now,
QUIC also allows for more than one packet to be
encapsulated within a UDP datagram,
and this can allow it to take advantage of available
space and make it more efficient.
And we're going to see this in Wireshark in just a moment. And one other
the note about the QUIC packet itself, it has its own header overhead, it
can have either a long or a short header,
and it has its own numbering mechanism so that we can ensure the data that we send within that packet arrives at the other side.