http://www.rfc-editor.org/rfc/rfc7959.txt
RFC 7959: Block-Wise Transfers in the Constrained Application Protocol (CoAP), C. Bormann, Z. Shelby2016-08-01T23:00:00-00:00A CoAP implementation that does not support these options generally is limited in the size of the representations that can be exchanged, so there is an expectation that the Block options will be widely used in CoAP implementations. Therefore, this specification updates RFC 7252.