Technical data

VoIP Service 254
SBX IP 320 Features & Operation Guide
At low loads, the traffic is not significant enough for the TOS to have any effect on the ping as
the packets will get through anyway. Similarly at high loads, the TOS will not have an effect on
the ping statistics but in this case there's too much traffic & there will be a significant amount
of packet loss & elongated round trip times irrespective of the precedence set. Somewhere in
between these two extremes we expect to see a window where the TOS actually has an effect
on the RTT/packet loss (high RTT/Packet loss at TOS=0 & low RTT/Packet loss at TOS=224).
Executing "ping2" for different TOS with no load.
The modified NIKHEF ping code was run from nereus.slac.stanford.edutonocdev1-qos.es.net
with TOS: 0, 32, 64, 96, 128, 160, 192, 224 & No TOS specification. The code was run for
10,000 packets of each TOS. The TOS numbers represent the precedence bits as follows.
PRECEDENCE BITS (0,1,2) TOS
00000
100132
201064
301196
4 100 128
5 101 160
6 110 192
7 111 224
Precedence 0 (TOS 0) is NORMAL PRECEDENCE (low precedence) while precedence 7
(TOS 224) is called network control (High precedence).
Since there is no load on the line, one would expect the TOS to have no effect on the ping
statistics. Rightly so, we see from the chart that the obtained results are similar to the predicted
results.
Admin Programming
• Precedence value (PGM 340 - FLEX 21)