Assuring Constant User Connectivity to CallManager
To lose connectivity to CallManager would trigger intermittent loss of call
ability, or cause the phone to lose its settings and possibly reboot the phone.This
doesn’t mean the phones will always have a TCP session to CallManager, but that
by picking up the handset, it will result in a dial tone provided by CallManager.
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410 Chapter 11 • Designing and Implementing Multisite Solutions
Interesting solutions for call backups for the branch offices to the head office
network include using dial backup provided by ISDN, or perhaps using a 0 Kbps
CIR Frame Relay backup circuit to the head office network. If the primary site
connection were to fail, then the routing protocols would detect this and know
that the 0 Kbps CIR link was active and available.
Because this failure recovery is automatic and performed without the users’
knowledge, it is almost a seamless recovery mechanism. It is only almost seamless
because calls in progress would be lost since that call setup was performed across
the original circuit. Figure 11.11 shows how this backup connectivity might look.