brianraymor
commented
8 years ago https://trac.tools.ietf.org/wg/core/trac/ticket/394#comment:1 Here is the story for adding keep-alive functionality to the CoAP over TCP document.
After reaching out to folks measuring TCP usage I was told that the use of TCP keepalive messages is often unreliable since network operators deploy middleboxes, which suppress these messages.
For this reason we are suggesting to add a ping/pong message to the CoAP over TCP document. Here is how this could look like.
First, we define a new CoAP Method Codes (for the request) and CoAP Response Codes (for the responses). Let us give them new numbers, such as 7.01 (for PING) and 7.02 (for PONG).
Here is an example message exchange:
Client Server
| |
| <--- TCP ---> |
| Connection Setup |
| |
| NON |
| GET /temperature |
| (Token 0x74) |
+----------------->|
| |
| NON [0x23bc] |
| 2.05 Content |
| (Token 0x74) |
| "22.5 C" |
|<-----------------+
| |
| ...... |
| time passes |
| ...... |
| |
|7.03 Ping |
|(Token 0x7f) |
+----------------->|
| |
|7.02 Pong |
|(Token 0x7f) |
|<-----------------+
| |
| <--- TCP ---> |
| Conn. Teadown |The PING packet would look as follows:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x01 | 0xe1 | 0x7f |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Len = 0 ------> 0x01
TKL = 1 ___/
Code = 7.01 --> 0xe1
Token = 0x7f
Figure: PING Encoding Example.The PONG packet has the following structure:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x01 | 0xe2 | 0x7f |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Len = 0 ------> 0x01
TKL = 1 ___/
Code = 7.02 --> 0xe2
Token = 0x7f
Figure: PONG Encoding Example.
Captured from Ticket 394:
Do we need ping/pong messages to keep an idle connection alive through NATs?