Assuming you already have a fully functional Pub server, on a high level follow below procedure:
1) First step add the Subscriber server on the Publisher. Go to System>Server>Add New
2) To install CUCM Sub, Deploy the OVF template for CUCM 11.(From Vspehere Client>File>Deploy OVF Template)
3) Use the bootable file for CUCM and install the subscriber server. The process is pretty much same for Pub installation just when you are asked if this is the first node - just select No. Enter the existing publisher details when asked.
Ref:
http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/install/11_0_1/CUCM_BK_IDF93684_00_installing-cucm_1101/Installation_tasks.html#CUCM_TK_S2EB5F8C_00
Let us know if you are stuck anywhere.
-Terry
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