The message ID is represented by msgId=value.
The message ID is the LDAP operation identifier generated by the client. The message ID can have a different value to the operation number, but identifies the same operation. The message ID in an ABANDON operation specifies which client operation is being abandoned.
The operation number starts counting at 0. However, in many client implementations the message ID number starts counting at 1. This explains why the message ID is frequently equal to the operation number plus 1.