We have a Cisco Model ISR4321/K9 router with Cisco IOS XE Software Version 16.09.04 The problem occurs when we make a call forward to an external number. The call made by User A to the destination User B (user B has activated a call forwarding to another external number User C) User C answers the call, user C does not hear anything, User A does not hear anything either, but after 18 seconds the call closes automatically by itself.
User A -->+49xxxxxxx90 ...incoming call
User B--> +49xxxxxxx55 --> call forward to User C
User C--> +49xxxxxxx30 .....Extern number ( external forwarding is configured on the router)
voice service voip no notify redirect ip2ip address-hiding allow-connections sip to sip no supplementary-service sip moved-temporarily no supplementary-service sip refer fax protocol t38 version 0 ls-redundancy 0 hs-redundancy 0 fallback pass-through g711alaw h323
voice register global mode cme source-address 172.20.XXX.XX port 5060 max-dn 10 auto-register ! voice register dn 2 number +49xxxxxx55 call-forward b2bua unregistered +49xxxxxx30