Hi, does anyone here have experience with the SIP trunk service from the German Telekom: "DeutschlandLAN SIP-Trunk"? There is little information from Deutsche Telekom on the Internet besides the "Technical Technical Specification of the SIP - 1TR114" As I have read so far, Deutsche Telekom has not necessarily been sticking to the standard. What I know so far Transport protocol is probably TCP instead of UDP Codecs: G. 711a and G. 722 Fax either via G. 711a or T. 38 My Setup Internet <-----> Router/Firewall(NAT) <----> Freeswitch According to the instructions, they require you to open several ports in the firewall. Is that really necessary? Does the Keep-Alive function work without opening any port? At the Federal Office for Information Security (BSI) it is additionally recommended to use a SIP proxy such as kamailio At the moment we are still using an ISDN gateway. I don't like to run into problems when we switch over, because I can't go back then. Best regards, Paul