| Summary: |
In a SIP network, call and session state resides in the user agents at
the edge of the network. These user agents can be elements such as
gateways, conferencing servers, and media servers whose availability
is important for service delivery. In order to achieve fault tolerance
for these user agents, this state must somehow be replicated to backup
servers. Traditionally, replication is done through direct memory
copies between a primary and its backup. However, the soft-state
nature of SIP re-INVITEs means that an alternate mechanism for call
state replication is possible. This document proposes mechanisms for
reconstituting call state in a UA through triggered re-INVITEs from a
peer.
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