You should consider certain product runtime behaviors when
you are writing Session Initiation Protocol (SIP) applications.
Container may accept non-SIP URI schemes
The
SIP container will not reject a message if it doesn't recognize the
scheme in the request Uniform Resource Indicator (URI) because the
container cannot know which URI schemes are supported by the applications.
SIP elements may support a request URI with a scheme other than sip or sips,
for example, the pres: scheme has a particular meaning
for presence servers, but the container does not recognize it. It
is up to the application to determine whether to accept or to reject
a specific scheme. SIP elements may translate non-SIP URIs using any
mechanism available, resulting in SIP URIs, SIPS URIs, or other schemes,
like the tel URI scheme of RFC 2806 [9].
For transitioning users: When a SIP application sends a request
to a SIP URI over Transport Layer Security (TLS) in version 6.1, the
request URI scheme changes from "sip" to "sips." In the current version,
the scheme does not change. You can reverse the new behavior by changing
the application code. With a "sips" URI, the behavior remains the
same after upgrading from version 6.1 to 7.0 or above. See the information
center topic Premigration considerations for more information.
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Directing requests in a multiple-container
environment
In a multiple-container environment (SIP proxy
plus SIP containers), when your application sends a request intended
initially to be sent externally but later received, it should use
the host and ports of the front-most load balancing element (either
an IP sprayer for multiple SIP proxies, or the SIP proxy if only one
exists). If the application uses the host name of a container instead
of the front-most element, the request may be lost in the event of
a failure.
For example, an application sends an INVITE request
to itself, but the request must pass through an external accounting
system through a pushed Route header. The application should set the
INVITE request's URI to the host and port of the foremost element
to ensure that failover occurs. The request will be routed to the
accounting system via the pushed Route, and then sent back to the
front load balancing element for processing.
Invoking session listener events
SipSessionListener
and SipApplicationSessionListener events are invoked only if an application
requests the corresponding session object. You do this by using in
your application the method shown in
Table 1.
Table 1. Methods that invoke session listener
events. This table lists the methods that invoke session
listener events.
Event |
Method |
SipSessionListener |
getSession() |
SipApplicationSessionListener |
getApplicationSession() |
Session activation and passivation
During normal
operation, this product never migrates a session from one server to
another. Session migration occurs only as a result of a server failure.
Therefore the SipSessionActivationListener method's passivation callback
is never invoked. However, the activation callback is invoked when
a failure forces session failover to a different server.
External resources
If a SIP application performs
intensive I/O or accesses an external database, it may be blocked
for several milliseconds. If possible, use asynchronous APIs for these
resources . Under stress, a blocked SIP application may trigger a
Request Timeout or re-transmission.
SIP application attributes
Avoid hanging large
objects or BLOBs as SIP Session attributes (via SIPSession.setAttribute
API). This may damage the overall performance when combined with high
availability (HA). The same recommendation applies for SIPApplicationSession.setAttribute.
In most cases, the large object can be replaced by several simple
or composed strings.