All packets within a given channel are ordered by sequence number. It
also happens that a packets is delivered only if all preceding reliable
packets in the sequence have been delivered, with missing preceding
unreliable packets in the sequence simply being ignored, if this
particular packet is ready to be delivered. If some packet later in a
sequence has already been delivered, and the packet being considered for
delivery is earlier in the sequence, it will be discarded; this rule
only really effects unreliable packets, or packets that somehow
duplicated in transit.
The way this works is that a sequence number has, in effect, two
portions X.Y. The X portion being a reliable sequence number, that gets
incremented when a reliable packet is sent, and the Y portion being the
unreliable sequence number, which is reset back to 0. Now, when an
unreliable packet is sent, X does not get incremented, but Y does. This
is how ENet knows if there were any undelivered reliable packets
preceding an unreliable packet in the stream, since the unreliable
packet will have a higher reliable sequence number. So reliable packets
serve as synchronization points in a channel, even across unreliable
packets.
Lee
M. Rijks wrote:
Hi everyone,
A question concerning channels and ordering of guaranteed and
non-guaranteed packets. If I understand Enet well enough, channels can
be considered different queues of incoming packets. Now consider this
scenario: let's assume I'm sending both guaranteed and non-guaranteed
packets on the same channel, and that Enet spends some time receiving
a guaranteed packet (it won't 'give' the packet to me until it is
fully received). What happens for any non-guaranteed packet sent on
the same channel? I suppose the sending end could already have started
to send the non-guaranteed packet, then realizing one of the
guaranteed packets might not have arrived, and trigger a resend. Or
does it stall subsequent packets and wait for confirmation of the
previous message? If it doesn't stall, then on the receiving end will
Enet keep waiting for full delivery of all parts (when the packet is
large) before giving me subsequent packets that may have arrived in
between?
All reactions appreciated!
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