I have a test setup. At two ends are Cisco2501(IOS 12.05) and Cisco2611(IOS 12.07). The serial link(64kbps) between the two routers has ftp and netmeeting(VoIP) traffic to simulate congestion conditions. According to my test I start the ftp and let it run for about 2 minutes. Then I start VoIP. I have noticed that with WFQ(Weighted Fair Queueing) at the serial interfaces , the VoIP call never gets established(I think the VoIP packets are simply dropped!!!!!!!!). However , with FIFO(First In First Out policy) at the same interface , the VoIP works fine. Could someone explain the observation?