Avaya Application Solutions Deployment Manual page 250

Reliability and Recovery
IP endpoint recovery
The Avaya server is designed to have a scalable architecture with different server components.
These components provide processing and relay signaling information between Communication
Manager and the Avaya IP endpoints. The architecture is inherently distributed, thus allowing
the system to be scalable to handle large number of endpoints, and flexible to work in different
network configurations.
This distributed nature of the architecture introduces additional complexity in dealing with
endpoint recovery, since failure of any element in the end-to-end connectivity path between an
IP endpoint and the switch software can result in service failure at the endpoint.
The recovery algorithm that is outlined here deals with detection and recovery from the failure of
signaling channels for IP endpoints. Such failures are due to connectivity outages between the
server and the endpoint, which could be due to failure in the IP network or any other component
between the endpoint and the server.
In the S8700 Server configurations the connectivity path between the endpoint and the server
is:
Endpoint
In this configuration, IP endpoints register to C-LAN on the PN. The DEFINITY platforms G3r,
G3si, and G3csi, which support Avaya Application Solutions features, also use C-LAN for
signaling connecting to IP endpoints.
A C-LAN provides two basic reliability functions:
A C-LAN hides server interchanges from the IP endpoints. The signaling channels of the
endpoints remain intact during server interchanges, and do not have to be reestablished
with the new active server.
A C-LAN terminates TCP keepalive messages from the endpoints, and thus frees the
server from handling frequent keepalive messages.
Recovery algorithm
The recovery algorithm is designed to minimize service disruption to an IP endpoint in the case
of a signaling channel failure. When connectivity to a gatekeeper is lost, the IP endpoint
progresses through three phases:
Recognition of the loss of the gatekeeper
Search for (discovery of) a new gatekeeper
Re-registration
When the IP endpoint first registers with the C-LAN, the endpoint receives a list of alternate
gatekeeper addresses from the DHCP server. The telephone uses the list of addresses to
recover from a signaling link failure to the C-LAN/gatekeeper.
250 Avaya Application Solutions IP Telephony Deployment Guide
IP network C-LAN PN backplane IPSI IP network S8700