[Freeswitch-users] Don't deprecate this option - useful for buggy user agents

[Martin Paterson]

I had a problem which I solved by turning on a FreeSWITCH option that logs a warning: "Enabling reg-deny-binding-fetch-and-no-lookup - this functionality is deprecated and will be removed - let FS devs know if you think it should stay". So here is me letting the FS devs know.

The problem is to do with buggy user agents and their handling of multiple Contact headers in the 200 OK response to their REGISTER.

My FreeSWITCH system uses mainly Snom phones and Zoiper soft phones. I allows multiple registrations and I have two sip profiles that the user agents connect to, one for Snoms and one for Zoiper. They share a registration database with the dbname option.

When multiple user agents register with the same credentials, the correct behaviour in the 200 OK to a REGISTER is to list all the user agents in multiple Contact headers with their individual registration expiry times. This is exactly what FreeSWITCH does. However both clients (Snom and Zoiper) fail in a similar way:

For their own reasons (https://www.zoiper.com/en/support/home/article/205/Zoiper%20Push%20Proxy) Zoiper clients register with a 1 month expiry time. If in the 200 OK to a Snom the Zoiper contact header is first, then the Snom assumes that the header is meant for it, reads the large expiry time and uses it (and complains in its log if it's over 14 days). The FreeSWITCH registration for the Snom then expires after 1 hour, which what the Snom asked for in the first place. The Snom then doesn't receive calls.

Annoyingly a similar thing happens the other way round - if the Snom Contact header is first in the 200 OK sent to Zoiper, then the Zoiper client just looks at the first header, and complains that the expiry time is too short with a message "You are connecting to a server with a low re-registration time. Battery life will not be optimal. Please contact your VoIP provider or PBX server administrator."

(An aside: it would be interesting to know why returning multiple Contact headers is the defined behaviour, and what a user agent is supposed to do with the others headers, and therefore what the consequences of not having them might be.)

We are contacting both Snom and Zoiper about this, but for the moment this is a useful FreeSWITCH option to cope with these user agents' behaviours.

Martin

Martin Paterson
Development Team
Phone: 0207 953 8840
Email: martin.paterson at technologywithin.com
Chevron Business Park, Limekiln Lane, Southampton, Hampshire, SO45 2QL
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