“*A problem was reported to the Asterisk project where transactions were not **found when they should have been [1]. In the issue an incoming INVITE transaction is CANCELed but the INVITE transaction cannot be found so a 481 response is returned for the CANCEL. The problematic calls have a
‘_’ **character in the Via branch parameter. *”
–Credit: Richard Mudgett

In the next Asterisk release, we have disabled PJ_HASH_USE_OWN_TOLOWER in the bundled pjproject’s config_site.h file. If you build or package pjproject yourself, we suggest you do the same. We’ve also updated the wiki[2] page.

/*
* Do not ever enable PJ_HASH_USE_OWN_TOLOWER because the algorithm is
* inconsistently used when calculating the hash value and doesn’t
* convert the same characters as pj_tolower()/tolower(). Thus you
* can get different hash values if the string hashed has certain
* characters in it. (ASCII ‘@’, ‘[‘, ‘\\’, ‘]’, ‘^’, and ‘_’)
*/
#undef PJ_HASH_USE_OWN_TOLOWER

[1] https://issues.asterisk.org/jira/browse/ASTERISK-26490
[2]
https://wiki.asterisk.org/wiki/display/AST/Building+and+Installing+pjproject