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Replicating SIP sessions

We can set up a replication domain for SIP sessions if we want replication of session, and dialog state information to occur during typical Session Initiation Protocol (SIP) processing. The SIP container typically uses the Data Replication Service (DRS) to replicate all state information. Because DRS does not provide a way to confirm when data replication has completed, the only thing that can be quantified is when a piece of state information is queued for replication. Within this topic, references to replication of data only means that the data has been queued for replication.

The SIP container replicates several different types of information. This data falls into two general categories:

Each of these categories includes a number of different data types, described later in this topic. Each data object is treated independently. Therefore, a change to an application session object, that causes a replication, does not result in the replication of any internal state information.

Replication of internal state information

Internal state information can be defined as anything related to the state of a dialog being handled by the container. It includes things like cseq, dialog state (initial, early, confirmed, terminated), session expiration, local, remote party, etc. Internal state information is only replicated due to the existence of a dialog. Therefore, no internal SIP-related data will be replicated until the dialog with which it is associated is established. The types of SIP requests that can cause the creation of a dialog include:

Replication of internal state happens at well-defined, predictable points in the call flow. For example, a dialog is only established at the container when a 2xx response or a 1xx response with a "To" tag is received or sent due to one of the method types listed previously. Events that can trigger an internal state replication include:

It is important to note that transaction state is not replicated in the WAS 6.1 version of the SIP container, only dialog state. Not replicating transaction state reduces the load on all the servers in the replication domain, but can cause problems in failures that happen in the middle of a transaction (for example, loss of some dialog-related SIP messages).

An important difference between a B2BUA and a proxy application is the number of session objects created and replicated. In both cases only a single application session is created, but for the B2BUA, two session objects are created-one for the inbound leg and one for the outbound leg. For a proxy application, only a single session object is created.

Replication of application state information

Application state information is treated differently from internal dialog state information because it does not rely on the existence of a dialog to be replicated. Application state refers to any data that is being maintained by the application through the use of JSR 116 data constructs. This includes:

Replication of internal state happens at well-defined, predictable points in the call flow, while replication of application state is less predictable because it is generally dependent on when an application creates, invalidates or modifies the session data and timers through JSR 116 APIs. This could be due to the processing of an inbound message, or to the expiration of a SIP timer. All of the following can cause the replication of application-related session data:

Replication can occur for requests that do not establish a dialog if an application calls request.getApplicationSession(true) and if addTimer() and/or addAttribute() are called on the resulting application session object. This is needed so that a listener can be called when the timer expires.

SIP failover and replication setup considerations

A SIP cluster that requires replication and failover can consist of many replication domains, each of which contain a set of SIP containers. There is no limit set on the number of containers in a cluster. For performance reasons, each replication domain should contain only two containers.

The replication domain should be set to the Entire Domain, which means state is replicated to all containers in the replication domain. The replication mode should be Both client and server.

The distributed session for a container needs to be set to Memory-to-memory replication. Any applications that require session replication must include the <distributable /> tag in the web.xml and sip.xml files. Both SIP and HTTP will utilize the same replication topology

(zos) Make sure that the system is configured such that:

(zos) We must also delete and re-create the log stream for a server if any of the following situations occur:

SIP session replication topology

Set up a replication domain for SIP sessions.

  1. In the console, click Environment > Replication domains > New

  2. Click Number of replicas, and then select Entire domain.

  3. In the Container settings section, click Session management.

  4. In the Additional Properties section, click Distributed environment settings, and then click Memory-to-memory replication.

  5. Set Replication mode toBoth client and server.

  6. Save the changes.


Results

  • Memory-to-memory replication is enabled for SIP sessions.


    Related concepts

    SIP session affinity and failover

    SIP high availability


    Related tasks

  • Browse all SIP topics

    1 Causes replication of the SipSession and SipApplicationSession in order to synchronize the "last access timestamp" with the peer containers in the cluster. This is for the integrity of future calls to SipSession.getLastAccessedTime(), and SipApplicationSession.getLastAccessedTime()