Call Manager Express is the new name for ITS.
Cisco has added new features to ITS and has re-branded ITS as Cisco Call Manager Express targeted for small businesses. CCME is an add-on feature to the router. Unity Express for Voice Mail solution is add-on hardware/software to the router to provide voice mail solution for the small office. This is a standalone solution for a small office.
URL for CCME and Unity Express:
http://www.cisco.com/en/US/netsol/ns110/ns163/ns359/ns331/netbr09186a00801c63a1.html
SRST - Survival Remote Site Telephony
This is an add on feature to the router. You will use this feature on the routers that are installed in a remote site connecting back to a central site where the call managers are installed. In a centralized call processing deployment model, call managers are installed at the central site and all the remote sites IP phones register to the call manager at the central site. If the WAN Link goes down, the phones will register to the local router to get basic ip telephony functions, to support the IP Phones during WAN Link failure the router should be SRST capable.
URL for SRST
http://www.cisco.com/en/US/products/sw/voicesw/ps2169/products_feature_guide09186a008018912f.html
SRST is used at remote sites in a failover scenario for enterprise wide IPT deployment but CCME is for standalone small offices.
Number of phones supported by SRST and CCME various based on Router Hardware Platform
