hi all... I need some links to work together. For example: when link between n3 and n4 is overloaded, link between n1 and n2 will do some reaction, such as drop some packets. Could I add a method drop_packet() to drop-tail.cc and drop-tail.h, and then involk it? (but how? each link has it's own id?) Any other way is better? Thanks a lot... n1 ----> n2 ----> n3 ----> n4