Cisco Unified SRST Configuration in CUCM SRST Reference Definition: SRST reference comprises the gateway which can provide limited CUCM functionality when all other CUCM Servers for IP Phones are unreachable.Also question is, what does Srst mean?
Survivable Remote Site Telephony
Beside above, which is the default SRST Certificate Provider Port? 2445
Besides, how does Cisco SRST work?
SRST Function of Switchover Signaling When the WAN link fails, the IP Phones lose contact with the central CUCM but then register with the local Cisco Unified SRST gateway. The Cisco Unified SRST gateway detects newly registered IP Phones, queries these IP Phones for their configuration, and then autoconfigures itself.
How long is the default keepalive period for Srst in Cisco IOS?
The default keepalive period is 30 seconds. If the phone has an active standby connection established with a Cisco Unified SRST router, the fallback process takes 10 to 20 seconds after connection with Cisco Unified CM is lost.
What is Cisco cube?
Cisco Unified Border Element (CUBE) is a unified communications border element that bridges voice and video connectivity between two separate VoIP networks. It is similar to a traditional voice gateway, except for the replacement of physical voice trunks with an IP connection.What is Call Manager fallback?
MGCP fallback enables a gateway to act as local call control when the CUCM server to which the remote site phones and gateway register is offline or WAN connectivity is lost (in which case, Cisco Unified SRST kicks in and offers call control functionality).What is Cisco CME?
Cisco Call Manager Express (CME) is an enhanced IP telephony solution that is integrated into Cisco IOS. It is an ideal solution for small business customers to efficiently use their existing IP data connectivity to incorporate the deployment of voice and IP telephony.What is Cisco Unity Express?
Cisco Unity Express gives your organization a quick, convenient way to manage voicemail, auto attendant, and interactive voice response (IVR). As a simple addition to voice-enabled integrated services routers, Cisco Unity Express provides: Affordable voicemail and greeting services. Voice mailboxes for up to 500 users. 
