How to configure Elesign ESC-2420 (SIP)

Hello,

We would appreciate if somebody help us to know the configuration of Elesign ESC-2420 Gateway (SIP Version) that will be connected to one extension of a traditional PBX.
In the head quarters we have installed ESC-2420 (SIP Version) that is connected to one extension of our traditional PBX. As well the PBX has connected traditional telephone lines. In the branch office we have installed Elesign ESP-1202 IP telephone (SIP Version) that would have to be able to call to the extensions of the traditional PBX of our head quarters and as well to take line (traditional telephone line) of the same PBX. In addition this equipment would have to be able to receive calls from the traditional PBX.
Summarized we have to configure both equipments to the ESP-1202 (SIP Version), that is installed in the branch office, acts like one remote extension of our PBX.
At the moment we only can make calls from a traditional telephone connected to the VOIP1 of the ESC-2420 (SIP Version) to the ESP-1202 (SIP Version).

Thanks in advance.

Regards,
Facundo Demian Gómez.