General Concepts

Classes Overview

Here are the main classes of the PJSUA2:


This is the main class of PJSUA2. You need to instantiate one and exactly one of this class, and from the instance you can then initialize and start the library.


An account specifies the identity of the person (or endpoint) on one side of SIP conversation. At least one account instance needs to be created before anything else, and from the account instance you can start making/receiving calls as well as adding buddies.


This is an abstract base class that represents a media element which is capable to either produce media or takes media. It is then subclassed into pj::AudioMedia, which is then subclassed into concrete classes such as pj::AudioMediaPlayer and pj::AudioMediaRecorder.


This class represents an ongoing call (or speaking technically, an INVITE session) and can be used to manipulate it, such as to answer the call, hangup the call, put the call on hold, transfer the call, etc.


This class represents a remote buddy (a person, or a SIP endpoint). You can subscribe to presence status of a buddy to know whether the buddy is online/offline/etc., and you can send and receive instant messages to/from the buddy.


Class Usage Patterns

With the methods of the main classes above, you will be able to invoke various operations to the object quite easily. But how can we get events/notifications from these classes? Each of the main classes above (except Media) will get their events in the callback methods. So to handle these events, just derive a class from the corresponding class (Endpoint, Call, Account, or Buddy) and implement/override the relevant method (depending on which event you want to handle). More will be explained in later sections.

Error Handling

We use exceptions as means to report error, as this would make the program flows more naturally. Operations which yield error will raise pj::Error exception. If you prefer to display the error in more structured manner, the pj::Error class has several members to explain the error, such as the operation name that raised the error, the error code, and the error message itself.

Asynchronous Operations

If you have developed applications with PJSIP, you’ll know about this already. In PJSIP, all operations that involve sending and receiving SIP messages are asynchronous, meaning that the function that invokes the operation will complete immediately, and you will be given the completion status in a callback.

Take a look for example the pj::Call::makeCall() method of the pj::Call class. This function is used to initiate outgoing call to a destination. When this function returns successfully, it does not mean that the call has been established, but rather it means that the call has been initiated successfully. You will be given the report of the call progress and/or completion in the pj::Call::onCallState() callback method of pj::Call class.


For platforms that require polling, the PJSUA2 module provides its own worker thread to poll PJSIP, so it is not necessary to instantiate own your polling thread. Application should be prepared to have the callbacks called by different thread than the main thread. The PJSUA2 module itself is thread safe.

Often though, especially if you use PJSUA2 with high level languages such as Python, it is required to disable PJSUA2 internal worker threads by setting EpConfig.uaConfig.threadCnt to 0, because Python doesn’t like to be called by external thread (such as PJSIP’s worker thread).

Problems with Garbage Collection

Garbage collection (GC) exists in run-time such as Java and Python, and there are some problems with it when it comes to PJSUA2 usage:

  • it delays the destruction of objects (including PJSUA2 objects), causing the code in object’s destructor to be executed out of order

  • the GC operation may run on different thread not previously registered to PJLIB, causing assertion

Due to problems above, application ‘’’MUST immediately destroy PJSUA2 objects using object’s delete() method (in Java)’’’, instead of relying on the GC to clean up the object.

For example, to delete an Account, it’s NOT enough to just let it go out of scope. Application MUST delete it manually like this (in Java):


Objects Persistence

PJSUA2 includes pj::PersistentObject class to provide functionality to read/write data from/to a document (string or file). The data can be simple data types such as boolean, number, string, and string arrays, or a user defined object. Currently the implementation supports reading and writing from/to JSON document (RFC 4627), but the framework allows application to extend the API to support other document formats.

As such, classes which inherit from PersistentObject, such as pj::EpConfig (endpoint configuration), pj::AccountConfig (account configuration), and pj::BuddyConfig (buddy configuration) can be loaded/saved from/to a file. Heres an example to save a config to a file:

EpConfig epCfg;
JsonDocument jDoc;
epCfg.uaConfig.maxCalls = 61;
epCfg.uaConfig.userAgent = "Just JSON Test";

To load from the file:

EpConfig epCfg;
JsonDocument jDoc;