Secure Computing SnapGear Application Note page 12

Setting up SnapGear for VoIP
Using QoS traffic shaping
Figure 4: Summary table
12
3 Set the
Outbound Speed
a If you are running a DSL/ADSL connection to the Internet, enter
bandwidth numbers approximately 80-90% of the most conservative
measured speed.
b If you have a cable modem or other type of direct IP connection to the
Internet, enter values much closer to 90-100%.
Use inbound or outbound speeds provided by your ISP, or tune these val-
ues by measuring actual conditions using your PC and any one of the free
sites listed below. These sites allow you to select local or distant test serv-
ers to get a practical snapshot of how your VoIP bandwidth may be effected
by call destination. It is good practice to use the most conservative figures
for the most distant call destination that is used during routine business.
This prevents other outbound applications from using too much of the avail-
able bandwidth and degrading call quality.
http://www.speedtest.net/
http://myvoipspeed.visualware.com/
http://www.speakeasy.net/speedtest/
On a cable modem, several sites provided a measured download (Inbound)
speed of 6300 kilobits per second and an upload (Outbound) speed of 360
kilobits per second. In the example shown Figure 3 on page 11, you would
set an Outbound Speed of
4 Setting the inbound speed has a less pronounced effect on call quality
because the SnapGear must begin processing everything it receives in the
order it is received, even if it is at different prioritized rates. You may wish to
determine if your ISP offers inbound QoS options that will let you prioritize
VoIP traffic over other inbound applications before the packets are sent to
the SnapGear.
5 Set the full Inbound speed, for example 6300 Kbps, and click
6
Review the Summary table.
7
Repeat the steps listed above for each Internet connection.
according to your ISP type.
(international)
(limited international)
(U.S. national)
Kbps (360 Kbps x 0.9).
324
Finish .
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