[SIPForum-discussion] Regarding Re-Register and min-expires

[Abhishek Mishra]

Hi,

Please see my comments inline.

Kind Regards,
-Abhishek

On Tue, 2007-08-07 at 15:09, Gopalarathnam Sambasivan wrote:
> Hello All, 
> Case1.
> UAC sends a REGISTER with expires=1800 to UAS which has say
> min-expires=3600.
[Abhishek] I think Min-Expires: 3600 is too large value, anyways RFC
does not disallow this value so it is OK.
> UAS rejects the REGISTER with 423 (Interval Too Brief) with
> min-expires=3600 - OK.
> A retry of register with min-expires accepted by the server is
> successful.
>  
> Case2.
> UAC sends a REGISTER with expires=7600 to UAS which has say
> min-expires=3600.
> There is no subscribe notify for subsequent registrations and hence
> REGISTER is sent after 
> random time interval between 1 and expires.
>  
> Say there is re- REGISTER s with expires=7600, coming every x secs
> which is less than the
> configured min-expires in the registrar.
>  
> Question 1.
> Can the server reject these frequent re-registers within registration
> expiry with 423 response?
> The min-expires seems to be available for the server to avoid flooding
> of incoming registers.
> But according to RFC3261 sec 10.3 it cannot be done. so what can be
> done?
> what is expected from perspective of UAS testing?
[Abhishek] No, registrar cannot reject REGISTER with 423 for frequent
registrations. Registrar can send 423 only if registration expiry is
less than its configured value.
>  
> Question 2.
> From the perspective of UAC testing, can it be ensured that Re-
> REGISTERS are sent only after min-expiry - 3600 on safer side and
> before Expires - so that UAS will always treat the REGISTER without
> overload?
[Abhishek] Unfortunately it is implementation dependent. Usually sip
phone sends registration refresh slightly before session expiry (or on
session expiry).
>  
> Thanks & Best Regards,
> Gopalarathnam.
>  
>  
> REGISTER which is repeated after every x secs < configured
> min-expires:
> ===========================================================
> REGISTER sip:registrar.biloxi.com SIP/2.0
>        Via: SIP/2.0/UDP bobspc.biloxi.com:5060;branch=z9hG4bKnashds7
>        Max-Forwards: 70 
>        To: Bob <sip:bob at biloxi.com>
>        From: Bob <sip:bob at biloxi.com>;tag=456248
>        Call-ID: 843817637684230 at 998sdasdh09
>        CSeq: 1826 REGISTER
>        Contact: <sip:bob at 192.0.2.4>
>        Expires: 7200
>        Content-Length: 0
>  
> Part from RFC3261 sec 10.3 Processing REGISTER Requests:
> ==============================================
>          The registrar MAY choose an expiration less than the
> requested
>          expiration interval.  If and only if the requested expiration
>          interval is greater than zero AND smaller than one hour AND
>          less than a registrar-configured minimum, the registrar MAY
>          reject the registration with a response of 423 (Interval Too
>          Brief).  This response MUST contain a Min-Expires header
> field 
>          that states the minimum expiration interval the registrar is
>          willing to honor.  It then skips the remaining steps.
>  
> 
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