The desc explicitly states this is the count of IPsec bytes before decompression — bytes received still compressed, before the optional IPComp decompression step that expands payloads compressed before encryption to save WAN bandwidth. A nonzero value here confirms IP compression is actually negotiated and active on at least one tunnel, which trades a small amount of CPU overhead for reduced bandwidth usage on the WAN link carrying that tunnel, useful context when diagnosing unexpectedly high CPU on a gateway with slow WAN links. e.g. cpvIpsecDecomprBytesBefore = 500MB received compressed, expanding to a larger figure once actually decompressed.