Cisco router configuration for VoIP
I would like to set up Voice over IP on the Cisco 3640 router. We have an office in the U.S. and one in India. We would like to implement VoIP to reduce phone calls. How do I configure the router.

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In India you cannot connect a data link along with a Voice link. So at your India end you will need a seperate router. If you have a very limited need than you can use VoIP with FXS ports on the router itself. On both sides you need to create dial-peers and assign a dialing scheme. An indicative configuration is here for your reference. Use it judiciously because it is not tested on a live set up. 
US end
!configue pots
dial-peer voice 1 pots
 destination-pattern +1408.......
 port 1/0/0

! Configure voip dial peer 2
dial-peer voice 2 voip
 destination-pattern 9........... (india end number)
 session target ipv4:172.16.65.182 (india end IP address)

! Configure the serial interface
interface serial 0/0
 clock rate 2000000
 ip address 172.16.1.123
 no shutdown

India end Router 
! Configure pots dial peer 1
dial-peer voice 1 pots
 destination-pattern 9...........(India end number)
 port 1/0/0

! Configure voip dial peer 2
dial-peer voice 2 voip
 destination-pattern +1408(US number)
 session target ipv4:172.16.1.123 

! Configure the serial interface
interface serial 0/0
 ip address 172.16.65.182
 no shutdown

This was first published in July 2003

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