Problem description:
On the condition of EtherChannel function of AIX, when the data exchange between the nodes on the network, there sometimes lost datat packets and cause the application failed. Once we deconfig EtherChannel and use the single adapter configuration, the application works normally. Anyone can analysize and propose any suggestion? The following are the environment of our onsite system:

Hardware:
4*p630 + 3*p615
dual network adapter for each machine(10/100M Auto Negotiate);
2*Cisco 3550 switch;
Software:
AIX 5.2 , xlC 6.0
Application

Network required: adapter and switch redundance.
If one network adapter on host or on Cisco switch failed, the other one can take over without disrupting our application.

Application:
In the application, we used multiplecast (IP:228.228.228.228) mechanism to send and receive the data packets between the servers and workstations on the network.

Switcth configuration :
using default configuration. nothing added.

system and network connect scenario :
Using AIX EtherChannel to config each server' or workstation' network adapter. On each host, we select one adapter as EhterChannel's primary channel and select the other one as EtherChannel's backup channel. At the same time ,these two adapter connect to two different Cisco 3550 switch. The speed and mode of all of the adapters set to Auto Negotiate. In order to attach the other route while the adapter or switch is failing,there is a Gigbit Fiber link between two switch.