Processing redirection (3xx) response


This article is about processing SIP redirect (3xx) response in outgoing calls, and not about sending redirection/3xx response. Sending 3xx response in PJSUA-LIB can be accomplished by calling pjsua_call_hangup() and with the new targets in Contact header in pjsua_msg_data parameter.


  • It is implemented all the way from PJSIP to PJSUA2 API level, to allow the usage on non-PJSUA-LIB based applications.

  • Handles multiple targets in the 3xx response (and targets that are returned in 3xx response of subsequent INVITE).

  • Allows application to accept or reject the redirection request on a per-target basis.

  • Allows application to defer the decision to accept or reject the redirection request, for example, to ask for user confirmation in the UI.

  • Remembers which targets have been sent INVITE and not retry the INVITE to these targets

  • Prioritize targets based on the q-value

  • Allows keeping or replacing the To URI in the subsequent INVITE requests, while keeping the same From, and Call-ID as the original INVITE.

Redirection with PJSIP API

Application MUST implement pjsip_inv_callback::on_redirected callback to handle redirection. If this callback is not implemented, the invite session will be disconnected upon receipt of 3xx response.

Redirection handling is controlled by the return value of this callback. See pjsip_redirect_op for possible actions.

If application wishes to defer the redirection decision, it must return from the callback with PJSIP_REDIRECT_PENDING and call pjsip_inv_process_redirect() once it has decided how to process the redirection.

The redirection usage scenarios will be explained below.

Accept redirection to this target

Return PJSIP_REDIRECT_ACCEPT from the callback to accept the redirection to this target. And INVITE session will be sent immediately to the target.

Alternatively PJSIP_REDIRECT_ACCEPT_REPLACE can be returned to accept the redirection to the current target and replace the To header in the INVITE request with the current target.

Reject redirection to this target

Return PJSIP_REDIRECT_REJECT from the callback to reject the redirection to this target. If there is another target to try, then the callback will be called again with this next target, otherwise the invite session will be disconnected immediately.

Stop redirection

Return PJSIP_REDIRECT_STOP from the callback to stop the redirection process and disconnect the call immediately, regardless of whether there are more targets to try.

Defer the Decision

Return PJSIP_REDIRECT_PENDING from the callback to tell the invite session that a decision cannot be made that this time (for example to ask for user approval), and the application will notify the invite session about the decision later.

Once the application gets the user approval (or disapproval), it MUST call pjsip_inv_process_redirect() function to notify the session about the decision. It may accept or reject the target, or stop the redirection altogether by setting the appropriate value to the cmd argument. It must not set PJSIP_REDIRECT_PENDING to this argument.

Failure to call pjsip_inv_process_redirect() will cause the invite session to be kept alive indefinitely until the library is shutdown.

When the pjsip_inv_process_redirect() function is called for the next target in the context of this function (that is when this function is called with reject command and next target is selected, hence the callback is called), the event (e) argument passed to this function will be passed down to the callback. And similarly when the disconnect callback is called. If NULL is given to the event argument of this function, this function will create a PJSIP_EVENT_USER event with NULL values, to be passed to the callbacks.

Because of this, application MUST be prepared to handle these type of events in both the pjsip_inv_callback::on_redirected and pjsip_inv_callback::on_state_changed callbacks. Traditionally only PJSIP_EVENT_TSX_STATE event is passed to pjsip_inv_callback::on_state_changed callback.

Redirection with PJSUA-LIB API

Use the pjsua_callback::on_call_redirected callback and pjsua_call_process_redirect() API to handle redirection.

See the PJSIP section above on how to use this feature.

Redirection with PJSUA2 API

Use the pj::Call::onCallRedirected() and pj::Call::processRedirect() methods to handle redirection.

See the PJSIP section above on how to use this feature.

Redirection in pjsua application

Call redirection handling in pjsua is as follows:

  • Use command line argument --accept-redirect, with valid values:

    • 0: reject/stop,

    • 1: follow automatically (default),

    • 2: ask

  • the default behavior is to follow redirection automatically

  • when --accept-redirect is set to 2 (ask), user can enter Ra, Rr, or Rd to accept, reject, or stop/disconnect the redirection.