System information

H-2 INSTALLING TELEVANTAGE
Setting the Layer 3 QoS TOS Octet for higher VoIP quality
VoIP traffic on the Internet is flagged with a special byte, called the Layer 3 Quality of Service
(QoS) Type of Service (TOS) Octet, that gives it higher priority over other traffic as it is routed
to its destination. Not all routers on the Internet recognize the Layer 3 QoS TOS Octet, but those
that do (DiffServe routers) prioritize the traffic according to the byte’s value, helping to maintain
high quality of service for VoIP traffic.
By default, TeleVantage Internet spans (SIP and H.323) set a value of
184 (decimal) for the TOS
Octet, which maps to IP Precedence 5 (Express Forward) and DiffServe 46 (RFC 2598
Expedited Forwarding.)
You can modify this value via the parameter
Layer 3 QoS TOS Octet on the Tuning tab, which
will adjust the quality of service on outbound VoIP traffic from TeleVantage. Changes to
Layer
3 QoS TOS Octet
take place immediately; no restart of the span or Server is needed.
Notes
Q To adjust the TOS Octet on incoming VoIP traffic to TeleVantage, you must adjust it at the
end-point sending the traffic, for example, the IP phone.
Q Not all Dialogic boards that provide IP telephony resources support the TOS Octet. See
Installing Dialogic Telephony Components for details.
To enter a value for the Layer 3 QoS TOS Octet
1. Determine the 8-digit binary number that you want. The first three bits (Bits 0-2)
correspond to Precedence and are set as follows:
Q 111 - Network Control
Q 110 - Internetwork Control
Q 101 - CRITIC/ECP
Q 100 - Flash Override
Q 011 - Flash
Q 010 - Immediate
Q 001 - Priority
Q 000 - Routine
The next five bits are set as follows:
Q Bit 3 - Delay. (0 = Normal Delay, 1 = Low Delay)
Q Bit 4 - Throughput. (0 = Normal Throughput, 1 = High Throughput)
Q Bit 5 - Reliability. (0 = Normal Reliability, 1 = High Reliability)
Q Bit 6 - Cost. (0 = Ignore Cost for Routing, 1 = Minimize Cost)
Q Bit 7 - Ignored. (Reserved for Future Use)