You have to set the port forwarding on the home router (check the router's manual, or google for how to), by selecting for the internal IP assigned by router to camera an external port, a random number like 3xxxx. Then identify the router's WAN IP. From the office network type in the IE address bar xxx.xxx.xxx.xxx:3xxxx
where xxx.xxx.xxx.xxx is the home WAN IP and 3xxx the port you set on router for forwarding.