This counts outbound SCTP data chunks explicitly marked for unordered delivery (U bit set), meaning the application told SCTP it doesn't care what order these particular chunks arrive in relative to each other, excluding retransmissions. Voice or telephony signaling applications often favor unordered delivery for latency-sensitive messages where waiting for strict sequencing would add unacceptable delay, so a telephony gateway would typically show significant traffic here. A high proportion of unordered chunks combined with low retransmission rates is consistent with a well-tuned real-time SCTP application prioritizing timeliness over strict ordering.