SIMPLE chat: Status codes

The SIMPLE chat draft, draft-ietf-simple-chat-13t.txt, went through the 
Apps review. The reviewer had a comment that requires a bit of discussion 
in the working group before we take an action. Here is the issue.

---
In Section 7.1:

      The reservation of a nickname can fail, e.g. if the NICKNAME request
      contains a malformed or non-existent Use-Nickname header field, or
      if the same nickname has already been reserved by another
      participant (i.e., by another URI) in the chat room.  The
      validation can also fail where the sender of the message is not
      entitled to reserve the nickname.  In any of these cases the MSRP
      switch MUST answer the NICKNAME request with a 423 response.  The
      semantics of the 423 response are: "Nickname usage failed; the
      nickname is not allocated to this user".

It would be better to use different response codes for different error
conditions.
---

So, here is the discussion I would like to have. Do we need different 
response code for each of these issues? We can do:

a) Do nothing and motivate why a single response code is sufficient

b) Create a response code for each error situation. This could be, e.g.:

    424 Malformed nickname
    425 Nickname already in use
    507 Not allowed to reserve a nickname

Notice that the "Not allowed to reserve nickname" should have a 500-class 
response to indicate a permanent failure, as opposed to the other two 
error codes, where a new request fixing the problem may succed.

Note: i just noticed that the 423 status code is already allocated (see 
http://www.iana.org/assignments/msrp-parameters/msrp-parameters.xml ) so 
I have chosen the next available status code.


And while composing this e-mail, I revised the rest of the status codes 
that we are requesting, and we have requested a status code 428 for 
indicating "Private messages not supported". I think this should be a 
500-class status code as well, since it is a permanent failure. Can we 
also move this one to 508?

Please comment.

/Miguel



-- 
Miguel A. Garcia
+34-91-339-3608
Ericsson Spain