Hi Esko,
Thank you for you email.
I got that the endpiont is identified by IP address (plus port, plus security context), and there may be a number of applicatons in one endpoint.
CoAP URI could indicate an endpiont or an physical resourse.
CoAP could tell the different resours by CoAP contents (Payload).
However, Location option is defined in CoAP šC18.
In CoAP šC18, 5.10.6.1. ETag as a Response Option
If one or more Location-* options are present and thus a location URI is indicated (Section 5.10.7), the tagged
representation is the representation that would be retrieved by a GET request to the location URI.
Why not to use Location opotion?
Regards,
Gengyu
Network Technology Center
School of Computer
Beijng University of Posts & Telecommunications
From: Dijk, Esko
Sent: Thursday, November 28, 2013 5:30 PM
To: weigengyu
Cc: ***@ietf.org
Subject: RE: [core] How to correlate request and responses in group communication
I don¡¯t know the OMA LWM2M details, but the CoAP endpoint is likely to be different šC one Device (=node?) usually supports many endpoints which could correspond e.g. to different applications on the Device. And the CoAP endpoint is identified by IP address (plus port, plus security context) so this is not a suitable UID since the IP address may change over time.
CoAP doesn¡¯t support specific options to communicate a node/Device unique ID back and forth AFAIK. That could be accomplished at lower layer through security (DTLS authentication) or at higher layer in the application-level payloads (e.g. a resource /uid that tells the unique ID of a device, or a UID that is included in the payload of a CoAP response.)
Esko
From: weigengyu [mailto:***@bupt.edu.cn]
Sent: Thursday, November 28, 2013 10:14
To: Dijk, Esko
Cc: ***@ietf.org
Subject: Re: [core] How to correlate request and responses in group communication
Hi Esko,
In OMA LWM2M Requirements,
6. Requirements (Normative)
6.1 High-Level Functional Requirements
LightweightM2MHLF-001 The Lightweight M2M enabler SHALL support a unique ID to identify the LWM2M Device.
It is understood that each device needs a unique ID.
And within a decvice there may have a few of physical resources that can be remotely accessed individually.
Based on CoAP šC18 terminology, it seems that Endpoint is correspondant to the OMA Device.
Whether or not? If it is, attentions need to pay for that.
I think that giving the description how to define and how to access the device or the physical resources is better than leaving that to the application.
By the way, Location option is defined in CoAP šC18.
The current version describes the location-query and location-path used as the response to POST request.
And In CoAP šC18, ¡°
5.10.6.1. ETag as a Response Option
The ETag Option in a response provides the current value (i.e., after the request was processed) of the entity-tag for the "tagged
representation". If no Location-* options are present, the tagged representation is the selected representation (Section 5.5.3) of the
target resource. If one or more Location-* options are present and thus a location URI is indicated (Section 5.10.7), the tagged
representation is the representation that would be retrieved by a GET request to the location URI.
5.10.7. Location-Path and Location-Query
The Location-Path and Location-Query Options together indicate a relative URI that consists either of an absolute path, a query string
or both. A combination of these options is included in a 2.01 (Created) response to indicate the location of the resource created
as the result of a POST request (see Section 5.8.2). The location is resolved relative to the request URI. ¡°
Based on the above text, by the URI the target resource can be accessed.
I got a little confused wether the target resource is a Device or a phiscal resource?
If the URI indicates a Device, the means to access phiscal resources is required.
If the URI indicates a physical resource, CoAP šC18 has the means to tell the differences.
Regards,
Gengyu
Network Technology Center
School of Computer
Beijng University of Posts & Telecommunications
From: Dijk, Esko
Sent: Wednesday, November 27, 2013 11:13 PM
To: Likepeng ; ***@ietf.org
Subject: Re: [core] How to correlate request and responses in group communication
Yes, it¡¯s currently defined to use the UDP layer for that information. At least it¡¯s efficient :)
If information other than IP address is needed, such as a non-volatile GUID, the CoAP server could include this as part of its response payload (in case of GET or PUT).
But that¡¯s not the most beautiful solution I agree.
Esko
From: Likepeng [mailto:***@huawei.com]
Sent: Wednesday, November 27, 2013 09:32
To: Dijk, Esko; ***@ietf.org
Subject: Re: [core] How to correlate request and responses in group communication
Hi Esko,
Post by Dijk, EskoThe identification of the individual response is by the (unicast) IP source address of the responding CoAP endpoint.
In the response, the only place to put the (unicast) IP source address is the UDP layer, right? Because HRI-Host is used to indicate the target node, not the source node.
(CoAP section 5.10.1) The Uri-Host, Uri-Port, Uri-Path and Uri-Query Options are used to specify the target resource of a request to a CoAP origin server.
That means, the requestor has to rely on UDP layer to get the (unicast) IP source address from the response, then correlate the multicast request and the unicast response. But in my opinion, the correlation should be done in the CoAP layer. CoAP layer should provide some information to be used for this purpose.
In CoAP spec, it mentions that Token MUST be used to match the responses with the multicast request. If there are multiple responses, we have to use source endpoint to differentiate. But this information can be only got from UDP layer. That is an issue, in my opinion.
CoAP Section 8.2
When matching a response to a multicast request, only the token MUST
match; the source endpoint of the response does not need to (and will
not) be the same as the destination endpoint of the original request.
Any thoughts?
Thanks,
Kind Regards
Kepeng
·¢ŒþÈË: Dijk, Esko [mailto:***@philips.com]
·¢ËÍʱŒä: 2013Äê11ÔÂ27ÈÕ 15:01
ÊÕŒþÈË: Likepeng; ***@ietf.org
Ö÷Ìâ: RE: [core] How to correlate request and responses in group communication
Hello Kepeng,
The identification of the individual response is by the (unicast) IP source address of the responding CoAP endpoint.
Indeed this would be good to mention somewhere in groupcomm.
Correlation of a single request with a set of responses is via Token; in case there are multiple outstanding multicast requests from a single endpoint.
Also core-coap has some information on use of IP address of the responding endpoint, section 8.2:
For the purposes of interpreting the Location-* options and any links
embedded in the representation and, the request URI (base URI)
relative to which the response is interpreted, is formed by replacing
the multicast address in the Host component of the original request
URI by the literal IP address of the endpoint actually responding.
Esko
From: core [mailto:core-***@ietf.org] On Behalf Of Likepeng
Sent: Wednesday, November 27, 2013 03:50
To: ***@ietf.org
Subject: [core] How to correlate request and responses in group communication
Hi all,
When I read the group communication draft, I come up with one question, how to correlate a multicast request with the multiple responses from different nodes?
For example, a client sends a multicast GET request to a group URI: all.bldg6.example.com, and after some time, it will receive multiple responses from different nodes. In the request, it contains one token. In the responses, I assume that all the responses should use the same token according to the base coap spec. Then how can the client differentiate the different responses from different nodes, corresponding to the same request?
I searched the whole group communication draft, token is not mentioned. So I hope to get opinion from the group.
Thanks,
Kind Regards
Kepeng
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