Endpoints that do not support presence, including all H.323
endpoints, can have status published on their behalf by the VCS.
The service that publishes this information is called the Presence
User Agent (PUA).
The PUA takes information from the local registration database
and the call manager and determines, for each endpoint that is
currently locally registered, whether or not it is currently in a call.
The PUA then provides this status information via a PUBLISH
message.
In order for the PUA to successfully provide presence information
about a locally registered endpoint:

the endpoint must be registered with an alias in the form of a

•

URI
the domain part of the URI must be able to be routed to a

•

SIP Registrar that has a presence server enabled. (This could
be either the local Presence Server, if enabled, or another
Presence Server on a remote system.)

When enabled, the PUA generates presence information for all
endpoints registered to the VCS, including those which already
support presence. The status information provided by the PUA is
either:

online

•

(registered but not in a call)

in call

•

(registered and currently in a call).

Aggregation of Presence Information

When enabled, the PUA generates presence information for all
endpoints registered to the VCS, including those which already
support presence. However, endpoints that support presence
may provide other, more detailed status, for example

away

not disturb

. For this reason, information provided by the PUA is

used by the Presentity Manager as follows:

Where presence information is provided by the PUA and one

•

other source, the non-PUA presence information will always be
used in preference to the PUA presence information. This is
because it is assumed that the other source of information is
the presentity itself, and this information is more accurate.
Where presence information is provided by the PUA and two

•

or more other sources, the Presence Server will aggregate the
presence information from all presentities to give the ‘highest
interest’ information, e.g.

online

rather than

offline

, and

in call

rather than

away

If no information is being published about an endpoint, either

•

by the endpoint itself or by the PUA, the endpoint’s status will
be

offline

. If the PUA is enabled, the

offline

status indicates

that the endpoint is not currently registered.

FindMe presence

When the Presentity Manager receives a request for information
about the presences of a FindMe alias, it looks up the presence
information for each endpoint that makes up that FindMe alias. It
then aggregates this information as follows:

if the FindMe alias is set to

•

Individual

mode, if any one of

the endpoints making up that FindMe is in a call the FindMe
presentity’s status will be reported as

in call

if the FindMe alias is set to

•

Group

mode, if any one of the

endpoints is online (i.e. not in call or offline) then the FindMe
presentity’s status will be reported as

online

Registration refresh period

The PUA will update and publish presence information on receipt
of:

a registration request (for new registrations)

•

a registration refresh (for existing registrations)

•

a deregistration request

•

call setup and cleardown information.

•

For non-traversal H.323 registrations the default registration
refresh period is 30 minutes. This means that when the PUA is
enabled on a VCS with existing registrations, it may take up to
30 minutes before an H.323 registration refresh is received and

available

presence information is published for that endpoint.

It also means that if an H.323 endpoint becomes unavailable
without sending a deregistration message, it may take up to 30
minutes for its status to change to

offline

. To ensure more timely

publication of presence information for H.323 endpoints, you
should decrease the H.323 registration refresh period (via

VCS

Configuration > Protocols > H.323 > Gatekeeper > Time to live

The default registration refresh period for SIP is 60 seconds, so
it will take no more than a minute for the PUA to publish updated
presence information on behalf of any SIP endpoints.

Presence User Agent (PUA)