SRX 340 ports

Hi,

Does anyone of you know which port become SRX340's Control Link (fxp1/em0??)  in Cluster Mode. In need this piece of information to finish the LLD.

Unfortunately neither DataSheet nor TechPub Doc (modified month ago ) doesn't explain that:

http://www.juniper.net/techpubs/en_US/junos15.1x49-d40/topics/reference/general/chassis-cluster-srx-series-node-interface-understanding.html

thx in adv