If your network is not dedicated to SIP traffic, but is used for various other purposes in your company, you might want to set the QoS settings on your network so to give SIP packets bigger priority instead of any other traffic. To do that you need to set the following on your network:

• SIP (signalling) - Class 3, AF31, DSCP: 0x1A, TOS: 0x68
• RTP (media) - Expedited Forwarding, EF, DSCP: 0x2E, TOS: 0xB8