One of the most powerful iptables match is the u32 module.
Using the u32 match you are able to write a firewall rule matching against a single bit of a network packet.

If you wanna play with u32 module you have to be prepared to deal with a syntax very ...

SIPp is a real SIP swiss army knife. You can create various SIP scenario and test your devices and environments.

I never found a SIPp scenario implementing an UAs (User Agent server) registrar with authentication.

Following you can find this scenario:

The SIPp XML scenario file: sipp_register_auth_uas.xml

<?xml version ...

This little piece of extensions.conf implements a callback from a failed transfer (attendant and unattendant/bind)

exten => _1XX,1,Dial(SIP/${EXTEN},20,tT)
exten => _1XX,n,GotoIf($[ "a${BLINDTRANSFER}" = "a" ]?TransferFailed)
exten => _1XX,n,Set(CALLER=${CUT(BLINDTRANSFER,-,1)});
exten => _1XX,n,Goto(CallBack)
exten => _1XX,n(TransferFailed ...

Using directmedia=update or (canreinvite=update in old-sytle configuration) in chan_sip.conf Asterisk sends SIP UPDATE request to refresh SIP session.

If this UPDATE requests refers to an inactive call the phone reply with SIP/2.0 481 Call Leg/Transaction Does Not Exist.

In this situation Asterisk continue in ...