Hi, I have downloaded the source code of "h323plus core"(version:1.23.0) and "PTlib"(version:2.10.1) from the link: *http://www.h323plus.org/source/ * on my X86 Desktop system running ubuntu 10.04 I have followed the tutorial given at link *http://toncar.cz/openh323/tut/index.html* I am able to compile both the source codes without any problems. Then I have downloaded and compiled "oh323tut" (version 1.1-1) source code from the link below: *http://toncar.cz/openh323/tut/files.html* I have got simph323 installed on my system using $ sudo apt-get install simph323 Now when I try to run oh323tut application and simph323 application (in separete terminals) using the commands below: $ ./oh323tut -f audio.wav -n -u 320 $ simph323 -n -u 321 320@127.0.0.1:1820 I am getting the following problem: H323> Could not open sound device Default - Check permissions or full duplex capability. Can anybody please help to solve the above problem. Regards Abdul Moiz