This read-write value sets the portion of the port's data rate reserved specifically for ATM QoS Class 2 traffic, one tier below the top-priority class, letting the admin carve out guaranteed bandwidth for that traffic category independent of the reservations made for classes 1, 3, and 4. An admin typically sizes this for a traffic type like interactive video or real-time data that needs better-than-best-effort treatment but does not need quite the guarantees of the top voice/CBR class. For example, an admin supporting videoconferencing traffic might size lportAtmDataRateQoS2 generously enough to prevent video quality from degrading even when best-effort classes 3 and 4 are saturating the rest of the link.