title: how to generate graph from trace file in ns2?
body: <p>I am facing a problem in generating <strong>xgraph from .tr file.</strong> The error message is like this:</p>
  
  <blockquote>
    <p>Error in file `voip.tr' at line 610:</p>
    
    <p>Unknown line type</p>
    
    <p>Problems found with input data.</p>
  </blockquote>
  
  <p>The format of .tr file is like this:</p>
  
  <pre><code>+ 1 0 1 sctp 56 -------I 0 0.0 3.0 1 -1 2 65535 65535
  - 1 0 1 sctp 56 -------I 0 0.0 3.0 1 -1 2 65535 65535
  r 1.01224 0 1 sctp 56 -------I 0 0.0 3.0 1 -1 2 65535 65535
  + 1.01224 1 3 sctp 56 -------I 0 0.0 3.0 1 -1 2 65535 65535
  - 1.01224 1 3 sctp 56 -------I 0 0.0 3.0 1 -1 2 65535 65535
  r 1.02448 1 3 sctp 56 -------I 0 0.0 3.0 1 -1 2 65535 65535
  + 1.02448 3 1 sctp 56 -------I 0 3.0 0.0 1 -1 3 65535 65535
  - 1.02448 3 1 sctp 56 -------I 0 3.0 0.0 1 -1 3 65535 65535
  r 1.03672 3 1 sctp 56 -------I 0 3.0 0.0 1 -1 3 65535 65535
  + 1.03672 1 0 sctp 56 -------I 0 3.0 0.0 1 -1 3 65535 65535
  - 1.03672 1 0 sctp 56 -------I 0 3.0 0.0 1 -1 3 65535 65535
  r 1.04896 1 0 sctp 56 -------I 0 3.0 0.0 1 -1 3 65535 65535
  + 1.04896 0 1 sctp 36 -------I 0 0.0 3.0 1 -1 4 65535 65535
  - 1.04896 0 1 sctp 36 -------I 0 0.0 3.0 1 -1 4 65535 65535
  r 1.0604 0 1 sctp 36 -------I 0 0.0 3.0 1 -1 4 65535 65535
  + 1.0604 1 3 sctp 36 -------I 0 0.0 3.0 1 -1 4 65535 65535
  </code></pre>
  
  <p>I have used command like this in ubuntu in ns2.</p>
  
  <pre><code>xgraph voip.tr
  </code></pre>
  
  <p>So how can I generate graph from the trace file?</p>