If a SIP Servlet acting as a User Agent Client (UAC) sends a REGISTER request with the headers required for RFC 5626 support, on receiving a 200 response to such a request, if that response contains an outbound option-tag in the Require header field, Converged Application Server starts sending keep-alive messages. These keep-alive messages may be double Carriage Return Line Feeds (CRLFs) for connection-oriented transports, such as TCP and Session Traversal Utilities for NAT (STUN) binding requests as described in RFC 5626.

Example 8-1 shows an implementation of such a UAC:

void sendRegister(SipServletRequest register) throws Exception {
  register.setHeader("Supported", "path,outbound");
  // Add the instance ID...
  Parameterable contact = register.getParameterableHeader("Contact");
  contact.setParameter("+sip.instance", <instanceId>);
  // Add the registration ID...
  contact.setParameter("reg-id", <registrationId>);
  register.send();
}

// The container starts sending keep-alive messages...
@SuccessResponse
public void handle200ok (SipServletResponse resp) {
  Flow flow = resp.getSession().getFlow();
}