This enables Multiclass Multilink PPP (MCML) on this member link, allowing traffic to be split into multiple fragment-interleaving classes for finer QoS control across the bundle; a change takes effect on the next link restart. Admins enable it when a single fragmentation/reassembly stream isn't granular enough for the mix of traffic on the bundle. For example, enabling MCML lets voice, video, and data each get their own interleaving class instead of competing for the same fragment stream.