This attribute counts the total number of calls from the subnet that were rejected because all of the channels were out-of-service. A channel is considered out-of-service if it is unavailable for any reason other than it is being engaged in handling a call. That is, an operator lock of any of the components required for the channel's operation, or problems which interfere with the connection to the PBX, will cause the channel to be considered out-of-service. When a call is rejected for this reason, the cause code sent back to the originator is 27, destination out-of-service. The value wraps to zero when it reaches its maximum.