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

Gopalarathnam Sambasivan s.gopalarathnam at gmail.com
Tue Aug 7 09:39:00 UTC 2007

 Hello All,
UAC sends a REGISTER with expires=1800 to UAS which has say
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.

UAC sends a REGISTER with expires=7600 to UAS which has say
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?

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?

Thanks & Best Regards,

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>
       *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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