Configuring TOS for SIP

Some networking hardware can prioritize traffic based on TOS (Type of Service), which can result in improved voice quality. This articles describe how to modify the default value of TOS for xMatters SIP. The information in this article applies to xMatters 4.0 (patch 12 and later), 4.1 (patch 4 and later), and xMatters on demand (Sprint 15 and later).

Issue Details

The default value for TOS on SIP is IPTOS_LOWDELAY (0x10) (i.e., 16). Common known values are:

  • IPTOS_LOWCOST (0x02)


NOTE: There is a distinction between SIP messages and the audio (RTP) that is transmitted. While some systems provide TOS configuration for both protocols, the steps below apply only to the audio (RTP) transmitted.

To modify the default value, do the following:

  1. Stop the node.
  2. Open the file (located at <xMHOME>/node/assets/).
    • If the file does not exist, rename to
  3. Add a sipRegistrationAgent.tos= line to the file, where its value is any numeric > -1 and < 255 (for example, sipRegistrationAgent.tos=8).
  4. Start the node.


Note the following verbatim excerpt from an SDN bug detail article:

A number of developers on the JDC have posted comments to indicate that the ToS bits are not set on Windows 2000 and XP. This is not a bug in the setTrafficClass implementation but rather that the IP_TOS option must be enabled by creating a registry setting. The registry setting is :-


It must be created as a REG_DWORD type with a value of 0. xxxxx@xxxxx 2004-08-16 Please note that add [sic] the registry setting and rebooting ceases to be a solution on Windows Vista and Windows Server 2008. The reason is that Microsoft has dropped support for the IP_TOS socket option in favor of newer QoS APIs.

NOTE: Although the xMatters (alarmpoint) engine does not support Windows XP, Vista, or Server 2008, the latter excerpt is likely applicable to Windows Server 2003, which is supported.

You can read the full article here:

Further information

For background on TOS, see:

xMatters Reference

DTN-2424, PRE-3135, JDN-1231

Originally created by Don Clark

Have more questions? Submit a request


Please sign in to leave a comment.
Powered by Zendesk