I have a Cisco CME running SCCP with a few phones located across an Internet L2L VPN. The Internet router at the main site is an 1841 with a high bandwidth cable connection. I have successfully implemettned QoS on this router to mark and class outbound VoIP while policing inbound ftp/http. The remote phones work well with the CME system.
I implemented a Switchvox system at the main office which uses SIP for call control. I applied the same style QoS policies to that traffic as that of the CME. File downloads interfere with outbound audio to the remote site on the SIP system while simultaneous calls on the CME SCCP system to the remote site are perfect.
I'm having difficulty determining why the SIP based and SCCP based systems react differently under the same circumstances. In theory, the RTP streams function similarly, while the call control is different. Any opinions or advise would be appreciated.