[asterisk-dev] Enforce Registrar Stickiness for operation on (3GPP) IMS networks

[Joshua C. Colp]

On Sat, Nov 23, 2019 at 9:37 PM Philipp Schöning <schoening.p at gmail.com>
wrote:

> On IMS networks P-CSCF usually operate stateful, therefore a registration
> is always bound to a specific node.
>
> When RFC3263 is used for a list of possible SIP-Servers/P-CSCF, this list
> of servers might change, if a DNS-based loadbalancing is used.
>
> Asterisk is not taking the statefulness of SIP-Servers (and therefore of
> the registration) into consideration and is immediately sending SIP
> Requests to the new SIP-Server of the DNS result.
>
> AudioCodes introduced with Firmware 7.20 a feature called 'Registrar
> Stickiness' which does the following:
>
> [1] Enable = Enables the Register Stickiness feature. The device always
> routes SIP requests of a registered Account to the same registrar server to
> where the last successful REGISTER request was routed. In other words, once
> initial registration of the Account to one of the IP addresses in the Proxy
> Set (associated with the Account's Serving IP Group) is successful (i.e.,
> 200 OK), binding ("stickiness") occurs to this specific address
> (registrar). All future SIP requests (e.g., INVITEs, SUBSCRIBEs and
> REGISTER refreshes) whose source and destination match the Account are sent
> to this registrar only. This applies until the registrar is unreachable or
> registration refresh fails, for whatever reason
>
> Additionally there is a setting for the 'Registrar Search Mode':
>
> ■ [1] According to IMS Specifications = For the initial registration
> request, the device performs DNS resolution if the address of the Proxy Set
> is configured as an FQDN. It then attempts to register to one of the listed
> DNS-resolved addresses (or configured IP addresses), starting with the
> first listed address and then going down the list sequentially. If an
> address results in an unsuccessful registration, the device immediately
> tries the next address (without waiting any retry timeout). The device goes
> through the list of addresses until an address results in a successful
> registration. If registration is unsuccessful for all addresses, the device
> waits a configured retry time and then goes through the list again. Once
> initial registration is successful, periodic registration refreshes are
> performed as usual. In addition to the periodic refreshes, immediate
> register refreshes are done upon the following triggers according to the
> IMS specification:
> ✔ The device receives a SIP 408, 480, or 403 response from the Serving IP
> Group in response to an INVITE.
> ✔ The transaction timeout expires for an INVITE sent to the Serving IP
> Group.
> ✔ The device receives an INVITE from the Serving IP Group from an IP
> address other than the address to which it is currently registered. In this
> case, it also rejects the INVITE with a SIP 480 response. If the device's
> physical Ethernet link to the proxy goes down, the device re-registers this
> Account with the proxy when the link comes up again. Re-registration occurs
> even if proxy keep-alive is disabled.
>
>
> https://www.audiocodes.com/media/13258/mediant-800-msbr-users-manual-ver-72.pdf
> Page 475 ff.
>
> Is it possible to enforce those two behaviours via settings in Asterisk?
> Or is this impossible in the current Asterisk architecture?
>

There are no settings to enable this, as it is not functionality that
anyone has worked on or added to Asterisk for PJSIP.

-- 
Joshua C. Colp
Senior Software Developer
Check us out at www.sangoma.com
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