2.30 Loop Prevention message (LOP): A message sent to convey information required by the ECT supplementary service. Table 50/Q.763 Message Type: Loop prevention Parameter Reference (subclause) Type Length (octets) Message type 2.1 F 1 Message compatibility information 3.33 O 3-? Parameter compatibility information 3.41 O 4-? Call transfer reference 3.65 O 3 Loop prevention indicators 3.67 O 3 End of optional parameters 3.20 O 1