it depends where the connection was broken. In general the migration is divided into 4 parts. Getting the source data by querying the source database, translating it into an Oracle model and generating the Oracle model, finally the data move.
You can restart each step individually which means when the source model information was successfully collected, then you can just create the Oracle model without collecting the source info again. When it for example failed during the data move, then it depends how many data you got migrated so far. Sometimes it is more efficient to manually copy the data (right mouse click on the table) for the missing and the failing table rather then performing the whole data move again.
BTW, you can also use the offline options just in case you have frequently some networking issues.