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User Manual V
2
IU 4350 Converged Network Appliance
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ToS Byte Setting
Since the Internet itself has no direct knowledge of how to optimize the path
for a particular application or user, the IP protocol provides a limited facility
for upper layer protocols to convey hints to the Internet Layer about how the
trade-offs should be made for the particular packet. This facility is the “Type
of Service” or ToS facility.
ToS settings allow the service provider to prioritize time sensitive traffic, such
as voice plus video to ensure minimized packet loss and delay through their
network. When providing end-to-end QOS, it is important that the voice plus
video traffic be placed in the correct queues to deliver a higher QOS than
regular traffic. Regular traffic, that is not time sensitive, can be delayed with
little or no indication to the user, while the slightest delay in voice plus video
can cause auditable differences. The ToS byte setting helps prioritize traffic
going to the WAN so a provider can prioritize the traffic correctly in its
network.
Although the ToS facility has been a part of the IP specification since the
beginning, it has been little used in the past. However, the Internet host
specification now mandates that hosts use the ToS facility. Additionally,
routing protocols (including OSPF and Integrated IS-IS) have been developed
which can compute routes separately for each type of service. These new
routing protocols make it practical for routers to consider the requested type
of service when making routing decisions.
How the ToS Byte Setting Works
For all RTP traffic (voice and video), the Polycom V
2
IU 4350 marks the ToS
byte in the IP header as “High Priority,” and strips (set to 0) the ToS byte for
all other traffic. Unchecking the “Enable ToS Byte Stripping” option means
that the ToS byte will not be stripped from non-RTP traffic, but will remain
unchanged.
Note: For most situations, you should leave this setting as it is. Only change it
if your provider indicates that you should do so.
Viewing or Changing the ToS Byte Setting
To view or change the ToS byte setting, use the following steps:
1. Using the configuration graphical user interface, from the Configuration
Menu on the left-hand side, click Traffic Shaper.
2. Scroll down the area of the screen shown below.