Observe timeout

[dominionish]

##Good day!

I use you library for having comminication with sensortag by Coap protocol.
But I have a problem after long time observe.
I do this:

Request request = GetRequest(type);
request.AckTimeout = -1; //To make timeout unlimit
request.Respond += (s, e) => method(s, e, new Guid(guid));
request.MarkObserve();

So it work, but after 10-12 hours timeout is occured and observer didnt work. I should observe to resource again. Why do it happen?

My sensortag sleep one hour then wakeup, send data by coap to client and sleep again