Quality of Service in RTC 1.5

RTC 1.5 supports quality of service for SIP & audio packets using DSCP and 802.1Q tagging. Windows CE has the following pre-defined DSCP traffic types:

typedef enum _DSCP_TRAFFIC_TYPE {
    DSCPTypeNotSet        = 0,
    DSCPBestEffort        = 1,
    DSCPBackground        = 2,
    DSCPExcellentEffort   = 3,
    DSCPVideo             = 4,
    DSCPAudio             = 5,
    DSCPControl           = 6,
    NumDSCPTrafficTypes   = 6

Check the following link for more info on these traffic types.


By default, RTC uses DSCPAudio traffic type for audio RTP, RTCP and SIP packets.

RTC defines registry keys if user wants to use alternate traffic types for RTP, RTCP or SIP packets. The reg keys are as follows:


DSCPAudioRTP - (DWORD)To change traffic type for Audio RTP packets. Settable to the DSCP enumeration value (0 to 6)
DSCPAudioRTCP - (DWORD)To change traffic type for Audio RTCP packets. Settable to the DSCP enumeration value (0 to 6)
DSCPSIP - (DWORD)To change traffic type for SIP packets. Settable to the DSCP enumeration value (0 to 6)

By setting these traffic types, the DSCP field in the IP header get set to the values that correspond to these traffic types. The DSCP values that go in the header for the above defined traffic types are:

{ 0x00, 0x00, 0x08, 0x18, 0x28, 0x38, 0x38 };

These traffic types also get translated to appropriate 801Q mapping, at layer 2, if the layer underneath supports such a tagging.

User can also disable the whole QOS tagging by setting the following reg


Disabled - (DWORD). If set to 1, RTC Qos will be disabled.