I have a UC520 and a 2691. The UC520 has a SIP phone (7940) registered, and the 2691 has an analogue phone connected to its FXS port. The two routers are connected through a crossover ethernet link. Since the SIP phone is registered, the UC520 has a dial peer for it. What should I do to let the analogue phone and the SIP phone call each other? Thanks!