GD-Aggregate: A WAN Virtual Topology Building Tool for Hard Real-Time and Embedded Applications Qixin Wang*, Xue Liu**, Jennifer Hou, and Lui sha* *Dept. of Computer Science, UIUC School of Computer Science, McGill UnivGD-Aggregate: A WAN Virtual Topology Building Tool for Hard Real-Time and Embedded Applications Qixin Wang*, Xue Liu**, Jennifer Hou*, and Lui Sha* *Dept. of Computer Science, UIUC **School of Computer Science, McGill Univ