The value of tnOamPingCtlMtuStartSize specifies the size of the first OAM Echo message sent as part of an 'mtuPing' test. Setting this object to a non-zero value is a prerequisite for starting an 'mtuPing' test. Its value must be less than or equal to the value of tnOamPingCtlMtuEndSize. An attempt to set this object from a non-zero value to zero will fail with a wrongValue error. Changing the message size is a method of checking the ability of an SDP to support a particular path-mtu value. The size of the message does not include the SDP encapsulation, VC-Label (if applied) or any DLC headers or trailers.