Specifies the number of octets by which to increment the OAM Echo message request size for each message request sent when tnOamPingCtlTestMode is set equal to 'mtuPing'. If the next incremented message size is greater than tnOamPingCtlMtuEndSize, the last message has already been sent. The next size message is not sent until a reply is received or three messages have timed out at the current size. This parameter is optional.