Code change:
Retransmission and deduplication of messages is provided by the TCP/ TLS protocol. <ins> 2.4. Empty messages (Code 0.00) can always be sent and MUST be ignored by the recipient.  This provides a basic keep-alive function that can refresh NAT bindings. If a client does not receive any response for some time after sending a CoAP request (or, similarly, when a client observes a resource and it does not receive any notification for some time), it can send a CoAP Ping Signaling message (sec-ping) to test the connection and verify that the server is responsive. </ins> 3. <ins> CoAP over WebSockets is intentionally similar to CoAP over TCP; therefore, this section only specifies the differences between the transports. </ins> CoAP over WebSockets can be used in a number of configurations.  The most basic configuration is a CoAP client retrieving or updating a <del> CoAP resource located at a CoAP server that exposes a WebSocket </del> <ins> CoAP resource located on a CoAP server that exposes a WebSocket </ins> endpoint (arch-1).  The CoAP client acts as the WebSocket client, establishes a WebSocket connection, and sends a CoAP request, to which the CoAP server returns a CoAP response.  The WebSocket

Related discussion:
text: Connection Health There is no way to retransmit a request without creating a new one. Re-registering interest in a resource is permitted, but entirely unnecessary. (See the discussion we already had.) [Brian] - The reference is
Closing the Connection Does this mean, only the client must cancel the requests? Or should the server do this also? Then a clarfication may be useful.
The original - URL - was specific to Observe: ~ All updates to Observe are now captured in a single place - Appendix A. This specific case is in URL At this point, I think that Closing the Connection could simply be deleted because there are no specific changes required.
Let's say a client has sent one or more requests to a server but hasn't received any response yet, and/or is observing a resource at a server. If the client or the server closes the connection or if the connection goes down unexpectedly, then the client will never receive the responses or any further notifications. The client has to reconnect and send new requests. Neither the client nor the server needs to send anything to cancel active requests before closing the connection; when a connection closes, all active requests are canceled automatically. The client should signal that to the code waiting for the responses, e.g., by throwing an exception. The server should abort processing the requests or at least discard the responses once the requests have been processed. The server also should remove the client from the lists of observers (at latest when it tries to send the next notification and it notices that the connection is down).
URL General - It's not clear "how" mandatory the use of the CSM is. Clause 2.3 on TCP/TLS indicates that the CSM message must be sent at the start of the connection. Clause 3.1 on Websockets makes no mention of CSM messages. Clause 4.3 indicates that the CSM MUST be sent at the start of the connection also and makes no distinction between TCP/TLS and Websockets. Clause 2.3 also indicates that the connection must be aborted if the CSM is missing or invalid as the first message on the connection. Given the discussion about address changes does more information need to be provided what start of connection means?
In the , the intent of this statement is unclear: There is no way to retransmit a request without creating a new one.