CoAP.Net Documentation
About
This library encodes and decodes CoAP protocol packets that is transport agnostic. IT also provides a CoapClient and CoapServer for communicating over CoAP
Since CoAP is designed for unreliable transport layers. (6LoWPAN, UDP, etc...) it made sense to not worry about the transport implementaions and allow the applicatrion to provide their own.
If you're after a UDP transport example, see CoAPNet.Udp ()