This read-only counter tracks how many times this modem has had to retrain, meaning renegotiate its modulation parameters with the far end, since it was last initialized. Admins treat frequent retraining as a sign of unstable line conditions, since each retrain typically causes a brief data interruption and often a reduced connect rate afterward. For example, a modem accumulating many cmmRetrainEvents during a single call would explain choppy, inconsistent throughput reported by users on that session.