[FROG] BGP Updates every minute

Hello, I am working on a topology which has 6 AS systems in Mininet. BGP is running between AS systems. The topology is not connected to any external network (internet/ISP). I want to get BGP updates every minute. I understand that updates are sent when there is some change in the topology. I wrote a script that advertised its network, then withdrew it next minute and then advertises again. When there is an advertisement, updates are sent but they are overwritten by the previous updates. I am getting just one update each time I view a dump file. For update i am using " dump bgp updates router.dump 60" command. I am a newbie in networking stuff. Please help!