364662a6_Manager__CallManager_____Cisco_Table_52_Network_Interface_Counter_Descriptions
[Counters] Tx Dropped [Counter Descriptions] 
This counter represents the number of outbound packets that were chosen to be discarded even though no errors were detected. This action prevents the packet from being delivered to a higher layer protocol. Discarding a packet to free up buffer space represents one reason.
Cisco Unified Communications Manager Managed Services Guide, Release 9.1(1) - Cisco Unified Real-Time Monitoring Tool Tracing PerfMon counters and alerts [Cisco Unified Communications Manager (CallManager)] - Cisco