The 4500-X started shipping in May 2012. From 4500-X white paper Advanced Quality of Service and BufferingAdvanced QoS with up to eight configurable queues per port and customizable queue size per queue Active queue management through dynamic buffer limiting (DBL) to ensure bandwidth protection for low-rate critical and well-behaving flows such as voice traffic 32 mega bytes of centralized buffering optimized to handle bursty video traffic and server microbursts, helping make sure that business-critical packets are not lost because of insufficient buffering |