This counts BTUs that were discarded specifically because the outbound link the traffic needed to egress on was down at the time. This isolates a very specific failure mode, traffic correctly identified a valid circuit but couldn't be forwarded because the destination port or link itself was inactive, which helps an admin distinguish a fine circuit configuration with a failed physical link from a VC-lookup or provisioning problem. For example, this counter spikes during a fiber cut on an egress trunk, then flatlines again once the link is restored, cleanly correlating the discard period with the outage window.