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SRST - phone register rate

I am trying to understand how the phones register with the local SRST router during WAN failure. For example, what mechanism causes some phones to register with the local SRST router before others? Why not all at the same time? Is it the router hardware limitation? Or is it some timing variable that varies with phones?


Re: SRST - phone register rate

Cisco CallManager SRST is unique in the industry because it provides backup redundancy for broad deployment of IP telephony to small branch offices. Small offices under normal operation can now take advantage of the call-processing servers, unified messaging servers, and other IP telephony equipment maintained at a central site and use the converged voice and data network to transmit the calls to distributed, intelligent Cisco IP phones. In the event of a WAN failure, SRST enables the local router to provide basic call processing and allows access to telephony features through the duration of the failure. "Companies can install one of these systems at a central location and use it to serve IP phones at remote locations over an IP network. ... This is one of the key economic advantages of IP telephony" (The Phillips Group InfoTech 2000).

Centralized IP telephony call processing delivers these benefits:

 Reduced administrative costs:

 Centralized IT staff

 Centralized call-processing equipment

Availability under normal operations of Cisco CallManager features and associated applications across all branches and to all users, such as Web-enabled call centers, unified messaging services, embedded directory services, mobility, and Cisco IP SoftPhones

Increased end-to-end quality of service (QoS) using the industry-leading capabilities embedded into Cisco IOS. Softwa

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