UDP Channel Timeout

[mchlnix]

UDP Channels can only be opened implicitely by sending the first message, but not closed explicitely or implicitely.

There should be a timeout for connections, which haven't sent in a certain time interval.

It should also be thought about a signaling mechanism to let the client know. Or should a new channel just be opened transparently?

[mchlnix]

This would also apply to the Mix Messages in the MixMessageStores in the Entry and ExitPoint. After a time out the message should be seen as lost and removed. Otherwise a lot of memory would pile up for lost fragments.