McDewey

Preferred Architecture for Cisco Collaboration Release 15 On-Premises Deployments PAGE 18
Call Control

• SIP trunks provide a standards-based environment that reduces operations and maintenance complexity of the end-to-end solution. • SIP trunks are enhanced with presence information. • SIP trunks are recommended for video communications. The Cisco Survivable Remote Site Telephony (SRST) feature is critical for remote sites that require continuation of voice services during WAN outages. SRST runs on the same Cisco ISR that provides WAN and PSTN connectivity for the remote site. Deploy SRST on the Cisco ISR in the following cases: • The remote site has local PSTN connectivity. • The remote site does not have local PSTN connectivity but has more than 25 users. To avoid interruption of external voice services if a WAN outage occurs, provide local PSTN connectivity at the remote site. SRST is required only if the remote site's WAN reliability does not match that site's required service level for voice service availability. If a WAN failure occurs at a site with SRST and local PSTN access, the following services will still be available: • Internal point-to-point voice calls • External voice calls through the PSTN • Call hold, transfer, and conference • Music on hold

Note SRST is not available for Desk Series or Room Series endpoints. See Table 5 for information about endpoints that support SRST.

Dial Plan A structured, well-designed dial plan is essential to successful deployment of any call control system. When designing a dial plan, consider the following main factors: • Dialing habits • Endpoint addressing • Routing • Directory integration • Classes of service Dialing habits