Both Cell mode and frame mode are stable solutions. But the scenario where we use them are different. I see that Cisco 8540 ATM MPLS Core is used. In this case, I would say that cell mode MPLS is a better solution for the following reason(s); In normal (non-MPLS) ATM core the L2 topology might be different from L3 topology. Say for example, a destination IP (a.b.c.d) might be shown as 3 hops (routers) away but there can be even 10 or more ATM switches in between. In this case the L2 topology might not be an optimal path. Hence we go for cell mode operation, where we form a full mesh topology and hence an optimal path.
