Proxy and Caching considerations

[bsilverajan]

The draft describes conditional notification attributes for observation as well as binding methods (GET, GET+Observe, POST, PUT).

However, there is little, if any, information regarding any potential challenges that could arise particularly with proxying and caching.

We have 3 choices:

1. Add a new section to explore these considerations
2. Expand the text under the current Implementation Considerations
3. Omit adding anything

Your comments?

[bsilverajan]

I'm proposing the following text as an Implementation Consideration:

"This specification defines conditional attributes that can be used with CoRE Observe relationships between CoAP clients and CoAP servers. However, it is recognised that the presence of 1 or more proxies between a client and a server can interfere with clients receiving resource updates, if a proxy does not supply resource representations if the value remains unchanged (eg if pmax is set, and the server sends multiple updates when the resource state contains the same value). A server MAY use the Max-Age option to mitigate this by setting Max-Age to be less than or equal to pmax.”

Additionally we can also include a pictorial representation of the issue as follows:

00 00 00 00 00 00 01 01 01 01 01 01 01 01 01 02 02 02 02 03 03 03 03        SERVER
|     |     |     |     |     |     |     |     |     |     |     |
|     |     |     |     |     |     |     |     |     |     |     |    pmax 2
|     |     |     |     |     |     |     |     |     |     |     |
00    00    00    01    01    01    01    01    02    02    03    03        PROXY
|                 |                             |           |
|                 |                             |           |          pmax 2
|                 |                             |           |
00                01                            02          03              CLIENT

Comments?

[bsilverajan]

The text has now been included into -02