Stack Upgrade - JAVA Dialog Instance

Hi,

I am performing support pack stack upgrade for Netweaver Portal 7.31 SP-5 to SP-17 .Before starting the upgrade, i had kept only Central Instance up and shutdown the dialog instance.

Initial phases of upgrade on SUM completed successfully, Just before execution i get the error:

"Could not check if the instance number 2 on host <dialog-instance host> is started."

This means Upgrade process is looking for Dialog instance also. So my question is:

1. Do i need to keep dialog instance up during SP-upgrade, If not then how to overcome this issue?
2. Do i need to uninstall the Dialog instance and re-install after the completion of upgrade?
3. If i keep the dialog instance down, how are the java local files in /usr/sap/SID upgraded with latest support pack?
   

Thanks

Vik