/** Starts a new call, inviting a remote user (<i>r_user</i>) */
public void call(String r_user, String from, String contact, String sdp)
{ printLog("calling "+r_user,LogLevel.MEDIUM);
if (username!=null) dialog=new ExtendedInviteDialog(sip_provider,username,realm,passwd,this);
else dialog=new ExtendedInviteDialog(sip_provider,this);
if (from==null) from=from_url;
if (contact==null) contact=contact_url;
if (sdp!=null) local_sdp=sdp;
if (local_sdp!=null)
dialog.invite(r_user,from,contact,local_sdp);