Unified CM Versions
Using the latest Cisco Collaboration Systems Release and SIP trunks across all Unified CM leaf clusters and the SME cluster enables your deployment to benefit from common cross-cluster features such as codec preference lists, ILS, GDPR, and Enhanced Locations call admission control (CAC). If you do not wish to upgrade to the latest Unified CM version on all clusters, the lowest recommended version is Cisco Unified CM 8.5 using SIP trunks because this version includes features that improve and simplify call routing through Unified CM and Session Management Edition clusters.
SME Trunks
Although SME supports SIP, H.323, and MGCP trunks, Cisco highly recommends SIP as the trunk protocol of choice for SME and Unified CM leaf clusters running Cisco Unified Communications System Release 8.5 and later versions.
Using only SIP trunks in the SME cluster allows you deploy a "media transparent" cluster where media resources (when required) are inserted by the end or leaf Unified Communications system and never by SME. Using only SIP trunks also allows you use extended round-trip times (RTTs) between SME nodes when clustering over the WAN.
SME SIP trunks should be configured as Best Effort Early Offer trunks. Leaf Unified CM cluster SIP trunks should also be configured as Best Effort Early Offer.
http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/collab11/collab11/trunks.html
HTH
java
if this helps, please rate
