Avaya ESS User Manual page 72

ESS Design and Planning
An ESS server receives its values when it is administered on the Main server using the
system-parameters ess command. See
system-parameters ess screen.
Figure 26: Administering the ESS servers
Each IPSI maintains its own priority list of available ESS servers in order of highest priority.
Based on the administered community of a particular IPSI Port Network, each IPSI may have a
different list of available ESS servers. Since the Main server defaults to the highest priority in a
system, the Main server holds the highest position on any IPSI's list. The value for the Main
server is not administrable and can never be changed.
In the system-parameters ess form, each ESS server is administered with one of two
preference settings, System Preferred (Sys Prf field) and Local Preferred (Loc Prf field). An
ESS server administered with either the System Preferred or the Local Preferred preference,
can advertise to all IPSIs in the configuration. The preference setting (System Preferred/Local
Preferred), along with a community (Comm field) and a priority value (Pri Scr field), determine
the server's priority on the IPSI's list.
The System Preferred preference has the highest administered value, followed by the Local
Preferred preference, and then an ESS server with no preference setting. The value for the
Local Preferred preference is only used by the IPSIs within the same community as the ESS
server. When the ESS server with a Local Preferred preference advertises to an IPSI outside of
its community, the preference value is the same as an ESS server with no preference.
Local Only works differently than preferences. While the System Preferred preference, the
Local Preferred preference, and an ESS server with no preference, can advertise to IPSIs in all
communities, an ESS server with Local Only administered, can only advertise to IPSIs within its
community. If there are multiple Local Only servers within one community, either the priority
value or setting the Local Preferred preference, can be used to rank one Local Only server
above the other on the IPSI's list. An ESS server administering with both Local Only and the
Local Preferred preference will:
Act like a Local Only server and only advertise to IPSIs within its community.
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Have the preference value of a Local Preferred server.
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72 Avaya Enterprise Survivable Servers (ESS) Users Guide
Figure 26 for an example of the