Commit c44540fd authored by Mac Newbold's avatar Mac Newbold

Small tweaks. I lost a commit race with Leigh, and had to resolve a bunch

of conflicts. Changes that are new include a couple of typo fixes,
replacing the tb-set-ip-routing command with the rtproto style, and adding
a "Long Answer" version of the round-trip vs one-way question,
since I already had it written.
parent 95d1601f
......@@ -87,7 +87,7 @@
<li> <a href="#TR">Troubleshooting</a>
<ul>
<li> <a href="#TR-1">My experiment is setup, but I cannot
<li> <a href="#TR-1">My experiment is set up, but I cannot
send packets between some of the nodes. Why?</a>
<li> <a href="#TR-2">I asked for traffic shaping, but everything
seems to be going at full LAN speeds.
......@@ -1017,8 +1017,8 @@
</p>
<p>
If you have requested automatic routing on your nodes with the
<code>tb-set-ip-routing</code> command in your NS file, this will
If you have requested automatic routing on your nodes with
<code>$ns&nbsp;rtproto&nbsp;Session</code> in your NS file, this will
start <code>gated</code> on all of your nodes.
</p>
......@@ -1054,7 +1054,7 @@
<h3>Troubleshooting</h3>
<ul>
<li><a NAME="TR-1"></a>
<h3>My experiment is setup, but I cannot
<h3>My experiment is set up, but I cannot
send packets between some of the nodes. Why?</h3>
<p>
The most common reason is that your topology
......@@ -1112,6 +1112,29 @@
<h3>I set a non-zero packet-loss (or delay) but 'ping'
shows a different packet-loss (or delay). Why?</h3>
<p>
Ping is round trip, PLR and delay are "one way".
Short answer: Ping is round trip, PLR and delay are "one way".
</p>
<p>
Long Answer: If you're not seeing any traffic shaping at all
(100Mbps, 0ms, 0plr), see <a href="#TR-2">this FAQ entry</a>. If
you are seeing shaping, but something different than you
expected, it is probably because link characteristics are one
way, and you're measuring them over the round trip.
</p>
<p>
For instance, if you asked for a link that was 100Mbps, 30ms,
with 5% (0.05) packet loss rate (plr), you may expect ping to
show 30ms ping times and 5% loss rate. But what you should see
is 60ms latency for the round trip, and a loss rate of
9.75%. Latencies can be added, therefore 30ms + 30ms gives
60ms. However, loss rates are probabilities, and must be
multiplied. The chance of a packet making it across a 5% lossy
link is 95%, so with a 95% chance of arriving at the
destination, and a 95% chance of returning if it made it there,
and the total chance of making a round trip is .95 * .95 = .9025 or
90.25%, or a round trip loss rate of 9.75% on a 5% lossy link.
</p>
</ul>
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