This counter tracks the number of CALL PROCEEDING messages, which acknowledge that call establishment for an SVC has begun and is being processed but not yet completed that this port has received, per the description. This PDU marks the handoff point where responsibility for finishing the call shifts from the immediate SETUP handshake to the (typically slower) end-to-end negotiation governed by timer T310, so its count should track SETUP fairly closely on a healthy port. For example, a large gap between SETUP and CALL PROCEEDING counts would suggest calls are being rejected outright rather than accepted for processing.