I am working on a project where we have to download videos from DVR box which is at a remote location( Different country). Problem is the client is using 3G router and Cisco vpn client to communicate with their datacenter and application at different stores. They are using IPSec for communication. One more thing, DVR box and application at store is not directly connected. For DVR devices they are using Dynamic DNS. The problem is I dint find anything helpful over the internet to get an idea how Dynamic DNS works with 3G and is this possible to do? Do I need a vpn connection as well to communicate with DVR box? I am very confused, can someone help?
With 3G you are most likely connect via your mobile operator NAT. To check this out - see which external IP address assigned to the 3G router, it's most likely starts with 10., or 172.16.....172.31, or 192.168. In such setup dynamic DNS will cut no ice - DNS in this case will reflect IP of the mobile provider NAT, and you can not forward ports on those.
Mobile operator can probably assign you a real IP, and even static IP, sometimes for some small fee. Either - this, or VPN.