Multiple POSIX Timers with handlers: how to?

[jpollard]

And none of them implement reliable delivery over UDP without implementing some form of ACK/NAK and
sending limits.

Reliable delivery of UDP is not a standard...

The problem with UDP is that the senders/receivers cannot assume reliable delivery. Reliable delivery can only
be supported at the application layer.

The original statement was '"pseudo TCP" on top of UDP protocol'.

I know TCP works differently. It implements a reliable delivery. UDP does not. Reliable delivery over UDP must
implement something to support it. Simple ACKs can do that, provided the sender knows to slow down when
congestion occurs. The ACK itself (over UDP) will not be reliably delivered - hence the need to limit the amount
of data being sent - as the application must preserve EVERY packet sent until it receives the corresponding ACK.
The entire exchange must occur from origin host to destination host, not just routers in between (advantage to
TCP).

Thus - a count limit on transmission...

Now, there is still a problem on the receiving side - if a data packet is dropped, there will be a hole in the sequence.
Something must inform the sender that data is missing... Hence, a NAK. Now it is entirely possible to implement this
without a NAK - if the sender ASSUMES the ACK was lost (or the data packet) then it can retransmit in the blind.
That can cause congestion - depending on the size of the data packets...

A timer is still needed in the receiver - otherwise a NAK that gets dropped will not get repeated.

The receiver will also need a count limit - otherwise it must buffer every packet following a dropped packet...
Until it gets the missing packet. The sender gets notified to retransmit (via the NAK for that packet).

Now for simple demonstrations - all of this is not absolutely necessary. local UDP delivery is pretty reliable.

[premudriy]

Oh, yes, I must not implement NAKs in this project, only ACKs. Acknowledgements are cumulative, i.e. if three packets were received, then I'll send ACK for the last (third) packet, which will mean that all tree packets got through.

As for congestion: there's a receiver buffer and ACKs have a special field that tell how much more packets the sender can supply to receiver.