Dario Greggio escreveu:
> Isaac Marino Bavaresco ha scritto:
>   =

>> I use two sequence numbers, one for the packet and other for the command
>> itself. It is useful for networks with routing where the packets may
>> arrive out of order or multiple times due to routing problems.
>>     =

>
> interesting...
>
>   =

>> If the sequence number of the arriving packet if less or equal to the
>> last received one, just ignore it. If it is newer (inside a
>> predetermined window), check the command sequence number. If the command
>> sequence number is exactly equal to the last one, just resend the last
>> answer but don't execute anything. If the command sequence number is
>> newer (inside a window limit), execute it, send the answer and store the
>> answer.
>>     =

>
> ...worth investigating more. I agree on the second part, but why having t=
wo?
>   =


I just sent a post that may explain better it.

>> There must be provision for a synchronization packet which is not
>> sequenced itself.
>>     =

>
> could you explain more this one?
>   =


If the nodes lose connection for too long the sequence numbers may get
very far apart (the sender is using number 2000 and the receiver
received only up to number 100 e.g.).

The window I mentioned, is the maximum difference between the sequence
numbers of two consecutive packets or commands. If a packet arrives with
a sequence number that is 256 (for instance, this is the value I use)
over the previous, it is discarded and the node keeps the sequence
number it had before.

If this happens, the nodes stop sending regular packets and start
sending special packets telling what numbers it is using and asking for
synching. The other node will always respond to these packets, saying it
received the request and providing a challenge (also a sequence number).
After receiving this packet, the sender node answers to the challenge
and assume they are synched again. When the receiver node receives the
correct answer to the challenge, it also assumes they are synched again.

Regards,

Isaac

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