You're right. I oversimplified. However when I worked with SDH it was particularly popular because some customers like banks vetoed ATM because they were incre

You're right. I oversimplified. However when I worked with SDH it was particularly popular because some customers like banks vetoed ATM because they were incredibly worried one of their packets would make its way to a third party. At that time encryption was not yet commonplace. I always thought that risk was a bit overblown but they were adamant. SDH was more like a software switched multiplexing (where the previous generation PDH had this in hardware). And it was not exposed to the customer, they just got a symmetric feed of 2mbps or a multiple thereof. Still, technically the same could happen if we configured it wrong. But for some reason the banks were less worried about it. But yes it was not packet by packet switched no. I have to admit my knowledge of ATM was never the best as I worked exclusively on the SDH network.