Runtime considerations for SIP application developers
We should consider certain product runtime behaviors when we are writing 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. We 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 later. See the information center topic Premigration considerations for more information.trns
Directing requests in a multiple-container environment
In a multiple-container environment (SIP proxy plus SIP containers), when the 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 using in the application the method shown in Table 1.
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.
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