Hi Qiyu,
Just to add a note to the good tips from my friend Joe (+5 Joe)
Each CUCM version since 7.1(5) has both the "normal" Restricted
version and an un-Restricted version available for download (.iso). You
will almost certainly want to run the "Restricted" version
Here are the clip/notes;
Unrestricted Export Support
#The restricted US export classification on Cisco Unified CM meant that governmental and military customers in many countries could not employ Unified CM in their networks.
#In addition to the delay inherent in obtaining export licenses, products classified as restricted by the Department of Commerce (DoC) carry a requirement to allow US government representatives to demand on-site inspections at any time to confirm that the product is being used in accordance with its licensed purpose. This post-shipment verification (PSV) is unacceptable to many customers.
#Additionally, some foreign countries maintain import restrictions which prohibited Unified CM from being available to customers in those countries. Both US export and foreign import issues stem from Unified CM support for strong encryption of signaling and media.
#Unrestricted Classification
#Because Cisco has obtained an unrestricted classification from the DoC for a version of Unified CM, beginning with Unified CM 7.1(5), both restricted and unrestricted versions of Unified CM will be released in parallel.
#Limitations
#Signaling and media encryption is permanently disabled in the unrestricted version, but remains unchanged in the restricted version.
#Migration from the unrestricted version to the restricted version is not supported.
#
Note 
No impact exists to other security features such as HTTP(s), SSH, password encryption and authentication (for example, SIP digest authentication), mechanisms used by unrestricted Unified CM clients such as JTAPI, TSP, encryption of SNMP traffic, encryption of data related to database that is done by using IPSEC and IMS on the server side.
The communication between CTL client and provider remains encrypted.
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/rel_notes/7_1_5/cucm-rel_notes-715.html#wp1768767
Here are two examples;
un-Restricted
UCSInstall_UCOS_UNRST_8.5.1.10000-26.sgn.iso
Restricted
UCSInstall_UCOS_8.5.1.10000-26.sgn.iso
Cheers!
Rob
"Far away from your trouble and worry
You belong somewhere you feel free" - Tom Petty
