Supported OS4K Gateways:

Supported Connections:

Telekom implemented a logic for their SIP-Trunks DeutschlandLAN and CompanyFlex which makes it possible to operate an IP-PBX behind a certified Telekom Router, although IP Network Address Translation is used. The Telekom checks in their Central Office (Backend) whether the received SIP messages originally arrived from a private network (Class A, B or C). If this is the case the communication will be realized with NAT traversal which sends the payload streams on basis of the received RTP packets to the correct ports.

In contrast to direct SIP provider connections; this method is advantageous that the OS4K Gateway must not be served with a dedicated Public IP. The used OS4k gateway is therefore not directly be accessible from the Internet in the NAT scenario. It is enough to route the OS4K gateway into the local network of the certified router. (For a pictorial view refer to Section 5.5.4, “Connection Examples”: Gateway (HG/vHG) in the local network of the Telekom Router (NAT scenario))

All business routers which are certified by the Telekom (LANCOM, AudioCodes, etc.) include a stateful firewall and/or network address translation. These routers will pass through only packets from the WAN side towards the LAN if the used port has already made an outbound connection towards the WAN/Internet (and is counted as active). Everything else is dropped. The used OS4K gateways are therefore “not on the Internet". Connectivity can be compared to a usual Home PC behind a commercial DSL router where a permanent port forwarding and open connection is not necessary. The used port on the WAN interface is set by the router randomly using network address port translation (NAPT) for the SIP communications. Depending on the used router, NAPT can be guaranteed only if the SIP interface on the OS4K is used with port 5060/5061. A modification to a higher port range from the LAN to the WAN interface of the router cannot be excluded (normal NAT).

Furthermore the OS4K Gateways are designed to terminate each SIP and Media session at the gateway itself. Nevertheless in all supported connection scenarios it is possible to connect a session border controller and/or to integrate the scenario into a DMZ.

Connection Scenarios:

Direct Connection OS4K Gateway:

OS4K Gateways connected via Hosted OpenScape SBC / OpenScape SBC:

Refer to chapter Section 5.5.4, “Connection Examples”

See also https://hilfe.companyflex.de/de/einrichtung/anschalteszenarien

Please check also the corresponding hints regarding Emergency Call Routing.