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Net::Traces::TSH - Analyze IP traffic traces in TSH format


  use Net::Traces::TSH qw(:traffic_analysis);

  # Display progress indicators

  # Process the trace in file some_trace.tsh
  process_trace 'some_trace.tsh';

  # Then, write a summary of the trace contents to some_trace.csv, in
  # comma-separated values (CSV) format
  write_trace_summary 'some_trace.csv';


Net::Traces::TSH can be installed like any CPAN module. In particular, consider using Andreas Koenig's CPAN module for all your CPAN module installation needs.

To find out more about installing CPAN modules type

 perldoc perlmodinstall

at the command prompt.

If you have already downloaded the Net::Traces::TSH tarball, decompress and untar it, and proceed as follows:

 perl Makefile.PL
 make test
 make install


Net::Traces::TSH can assist you in analyzing Internet Protocol (IP) packet traces in Time Sequenced Headers (TSH) format, a binary network trace format. Daily TSH traces are available from the NLANR PMA web site. Each 44-byte TSH record corresponds to an IP packet passing by a monitoring point. Although there are no explicit delimiters, each record is composed of three sections.

Time and Interface

The first section uses 8 bytes to store the time (with microsecond granularity) and the interface number of the corresponding packet, as recorded by the (passive) monitor.


The next 20 bytes contain the standard IP packet header. IP options are not recorded.


The third and last section contains the first 16 bytes of the standard TCP segment header. The TCP checksum, urgent pointer, and TCP options (if any) are not included in a TSH record.

If a record does not correspond to a TCP segment, it is not clear how to interpret the last section. As such, Net::Traces::TSH makes no assumptions, and does not analyze the last section of a TSH record unless it corresponds to a TCP segment. In other words, Net::Traces::TSH reports on protocols other than TCP based solely on the first two sections.

The following diagram illustrates a TSH record.

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1  Section
  0 |                      Timestamp (seconds)                      | Time
  1 | Interface  No.|          Timestamp (microseconds)             |
  2 |Version|  IHL  |Type of Service|          Total Length         | IP
  3 |         Identification        |Flags|      Fragment Offset    |
  4 |  Time to Live |    Protocol   |         Header Checksum       |
  5 |                       Source Address                          |
  6 |                    Destination Address                        |
  7 |          Source Port          |       Destination Port        | TCP
  8 |                        Sequence Number                        |
  9 |                    Acknowledgment Number                      |
    |  Data |       |C|E|U|A|P|R|S|F|                               |
 10 | Offset|RSRV-ed|W|C|R|C|S|S|Y|I|            Window             |
    |       |       |R|E|G|K|H|T|N|N|                               |

This diagram is an adaptation of the original TSH diagram (found on the NLANR PMA web site), which reflects the changes due to the addition of Explicit Congestion Notification (ECN) in the TCP header flags. Also, keep in mind that recent Internet Engineering Task Force (IETF) Requests for Comments (RFCs) have deprecated the IP header Type of Service field in favor of Differentiated Services and Explicit Congestion Notification.

You can use Net::Traces::TSH to gather information from a TSH packet trace, perform statistical analysis on Transport protocol, Differentiated Services (DiffServ) and ECN usage, and obtain packet and segment size distributions. The trace summary statistics are stored in comma separated values (CSV), a platform independent text format.

Data Structures

A single TSH trace may contain records for packets observed on several different interfaces. For example, the daily TSH traces from the NLANR PMA repository typically contain records from two different interfaces. In such cases, incoming and outgoing traffic can be differentiated based on the interface number (despite the scrabbling of IP addresses to protect privacy). Net::Traces::TSH users may be interested in collecting statistical information for each interface separately or aggregating across the entire trace. Net::Traces::TSH uses two hashes to maintain these statistics: %Interfaces and %Trace.

%Interfaces contains counts of several protocol particulars on a per-interface basis. For example, %Interfaces can tell you how many IP packets, TCP segments, and UDP datagrams were recorded in the trace for each interface.

%Trace contains general information about the trace (date, number of records, duration, number of interfaces, etc.) as well as the aggregate data points across all interfaces. As such, %Trace will report the total number of UDP datagrams in the trace, the total number of TCP SYNs, and so on.

Both %Trace and %Interfaces are initialized and populated by process_trace. The recommended way to get the trace summary information, after processing a trace is to call write_trace_summary, which stores the contents of %Trace in a CSV-formated text file, as shown in SYNOPSIS. Similarly, If you want summaries for the traffic on each interface, use write_interface_summaries.

Neither %Trace nor %Interfaces are exported by default and are not meant to be accessed directly by user code. However, if you know what you are doing, you can get a reference to %Trace by calling get_trace_summary_href, and a reference to %Interfaces by calling get_interfaces_href. If you choose to do so, the following subsections explain how you can access some of the information stored in %Trace. The %Interfaces structure is virtually the same only lacking the "general trace information" part. See also Using the Net::Trace::TSH trace summary hashes.

General Trace Information


The trace FILENAME.


The estimated date of the trace (see date_of).


The trace summary FILENAME.


The first trace timestamp, in seconds, as it is recorded in the trace.


The last trace timestamp, in seconds, after being "normalized". Essentially, the number of seconds since $Trace{starts}.


Number of records in the trace.

Similarly, if $if is the interface number, $Interfaces{$if}{records} contains the number or records corresponding to packets observed on interface $if.


Number of interfaces recorded in the trace.


True, if each interface carries unidirectional traffic.

False, if there is bidirectional traffic in at least one interface.

undef if traffic directionality was not examined.

$Trace{'Link Capacity'}

The capacity of the monitored link in bits per second (b/s).

Internet Protocol


Number of IP packets and bytes, respectively, in the trace. The number of IP packets should equal the number of records in the trace.

As mentioned earlier, %Trace has virtually the same structure as %Interfaces. Therefore, if $if is the interface number, $Interfaces{$if}{IP}{Total}{Packets} and $Interfaces{$if}{IP}{Total}{Bytes} contain the number of IP packets and bytes, respectively, observed on interface $if. The same "rule" applies to all %Trace fields presented below.



Number of IP packets and bytes, respectively, requesting no fragmentation ('Do not Fragment').


Number of IP packets and bytes, respectively, indicating that 'More Fragments' follow.

Differentiated Services


Number of IP packets and bytes, respectively, requesting no particular treatment (best effort traffic). No DiffServ or ECN bits are set.

$Trace{IP}{'Class Selector'}{Packets}
$Trace{IP}{'Class Selector Bytes'}

Number of IP packets and bytes, respectively, with Class Selector bits set.

$Trace{IP}{'AF PHB Packets'}
$Trace{IP}{'AF PHB Bytes'}

Number of IP packets and bytes, respectively, requesting Assured Forwarding Per-Hop Behavior (PHB).

$Trace{IP}{'EF PHB'}{Packets}
$Trace{IP}{'EF PHB'}{Bytes}

Number of IP packets and bytes, respectively, requesting Expedited Forwarding Per-Hop Behavior (PHB)

Explicit Congestion Notification


Number of IP packets and bytes, respectively, with either of the ECT bits set. These packets should be carrying traffic from ECN-aware hosts.


Number of IP packets and bytes, respectively, with the CE bit set. These packets carry ECN-capable traffic that has been marked at an ECN-aware router.

IP Options

$Trace{IP}{'No IP Options'}{Packets}
$Trace{IP}{'No IP Options'}{Bytes}

Number of IP packets and bytes, respectively, carrying no IP header options.

$Trace{IP}{'IP Options'}{Packets}
$Trace{IP}{'IP Options'}{Bytes}

Number of IP packets and bytes, respectively, carrying IP header options.

The following diagram summarizes the %Trace data structure up to here.

   - filename
   - summary
   - date
   - starts
   - ends
   - records
   - interfaces
   - unidirectional
   - 'Link Capacity'
   - IP
       - Total
           - Packets
           - Bytes
       - DF
           - Packets
           - Bytes
       - MF
           - Packets
           - Bytes
       - Normal
           - Packets
           - Bytes
       - 'Class Selector'
           - Packets
           - Bytes
       - 'AF PHB'
           - Packets
           - Bytes
       - 'EF PHB'
           - Packets
           - Bytes
       - ECT
           - Packets
           - Bytes
       - CE
           - Packets
           - Bytes
       - 'No IP Options'
           - Packets
           - Bytes
       - 'IP Options'
           - Packets
           - Bytes

Transport Protocols

Besides the summary information about the trace itself and statistics about IP, %Trace maintains information about the transport protocols present in the trace. Based on the IP header, %Trace maintains the same statistics mentioned in the previous section for all transport protocols with an IANA assigned number (including, of course, TCP and UDP). For example,


Number of TCP segments and the corresponding bytes (including the IP and TCP headers) in the trace.


Ditto, for UDP.


Number of ICMP packets and bytes, respectively, with the DF bit set.

Using the Net::Trace::TSH trace summary hashes

The following example creates the trace summary file only if TCP accounts for more than 90% of the total IP traffic, in terms of bytes.

 # Explicitly import process_trace(), write_trace_summary(), and
 # get_trace_summary_href():

 use Net::Traces::TSH qw( process_trace

 # Process a trace file...
 process_trace "some.tsh";

 # Get a reference to %Trace
 my $ts_href = get_trace_summary_href;

 # ...and generate a summary only if the condition is met.
    if ( ( $ts_href->{Transport}{TCP}{Total}{Bytes}
           / $ts_href->{IP}{Total}{Bytes}
         ) > 0.9


Net::Traces::TSH does not export any functions by default. The following functions, listed in alphabetical order, are exportable.


  configure %OPTIONS

Used to specify verbosity, the link capacity, and the types of outputs requested. For example,

           # Display progress information, equivalent to calling verbose()
           Verbosity       => 1, # default is 0, no progress information

           'Link Capacity' => 100_000_000, # bits per second

           # Convert the TCP records in the TSH trace to tcpdump
           # format and store in 'trace.tcpdump'.
           tcpdump         => 'trace.tcpdump',

           # Convert the TCP data-carrying segment records to binary
           # ns2 traffic trace format.  Create one binary file per
           # interface and use 'trace.ns2' as the file prefix.
           ns2         => 'trace.ns2',



  date_of FILENAME

TSH traces downloaded from the NLANR PMA trace repository typically contain a timestamp as part of their filename. date_of() converts the timestamp to a human readable format. That is, if FILENAME contains a valid timestamp, date_of() returns the corresponding GMT date as a human readable string. For example,

 date_of 'ODU-1073132115.tsh'

returns Sat Jan 3 12:15:15 2004 GMT.

If the FILENAME does not contain a timestamp, date_of() returns false.

Note that there is nothing special about FILENAME: It can be any string. The goal here is to get an idea of the period the trace was collected.


 get_IP_address INTEGER

Converts a 32-bit integer to an IP address in dotted decimal notation. For example,





Returns a hash reference to %Interfaces.



In list context returns a sorted list of all interfaces recorded in the trace. In scalar context returns the number of unique interfaces in the trace.



Returns a hash reference to %Trace.


 process_trace FILENAME

In a void context, process_trace() examines the binary TSH trace stored in FILENAME, and populates %Trace and %Interfaces.

In a list context process_trace() in addition to collecting summary statistics, it extracts all TCP flows and TCP data-carrying segments from the trace, returning two hash references. For example,

 my ($senders_href, $segments_href) = process_trace 'trace.tsh';

will process trace.tsh and return two hash references: $senders_href and $segments_href.

$senders_href is a reference to a hash which contains an entry for each TCP sender in the trace file. A TCP sender is identified by the ordered 4-tuple

 (src, src port, dst, dst port)

where src and dst are the 32-bit integers corresponding to the IP addresses of the sending and receiving hosts, respectively. Similarly, src port and dst port are the sending and receiving processes' port numbers. Senders are categorized on a per interface basis. For example, the following accesses the list of segments sent from to (on interface 1):


Each hash entry is a list of timestamps extracted from the trace records and stored after being "normalized" (start of trace = 0.0 seconds, always).

In theory, records corresponding to packets transmitted on the same interface should have different timestamps. In practice, although it is not very likely that two data segments have the same timestamp, I encountered a few traces that did have duplicate timestamps. process_trace() checks for such cases and implements a timestamp "collision avoidance" algorithm. A timestamp collision threshold is defined and is currently set to 3. Trace processing is aborted if the number of records with the same timestamp exceeds this threshold. If you encounter such traces, it is not a bad idea to investigate why this is happening, as the trace may be corrupted.

The second returned value, $segments_href, is another hash reference, which can be used to access any individual data-carrying TCP segment in the trace. Again, segments are categorized on a per interface basis. Three values are stored per segment: the total number of bytes (including IP and TCP headers, and application payload), the segment sequence number, and whether the segment was retransmitted or not.

For example, assuming the first record corresponds to a TCP segment, here is how you can print its packet size and the sequence number carried in the TCP header:

 my $interface = 1;
 my $timestamp = 0.0;

 print $segments_href->{$interface}{$timestamp}{bytes};
 print $segments_href->{$interface}{$timestamp}{seq_num};

You can also check whether a segment was retransmitted or not:

 if ( segments_href->{$interface}{$timestamp}{retransmitted} ) {
   print "Segment was retransmitted by the TCP sender.";
 else {
   print "Segment must have been acknowledged by the TCP receiver.";

Note that process_trace() only initializes the "retransmitted" value to false (0). It is write_sojourn_times() that detects retransmitted segments and updates the "retransmitted" entry to true, if it is determined that the segment was retransmitted.

CAVEAT: write_sojourn_times() is not currently included in the stable, CPAN version of the module. Contact me if you want to get a copy of the bleeding edge version.

Using a TSH trace in ns2 simulations

In addition to extracting %senders and %segments, Net::Traces::TSH allows you to generate binary files suitable for driving ns2 simulations. For example,

 configure(ns2 => 'some.tsh');

 process_trace 'some.tsh';

After the call to configure(), process_trace() will generate a binary file for each interface found in the trace. For example, assume that some.tsh has recorded traffic from two interfaces, 1 and 2. process_trace() will generate two binary files:


Each of these files can be used in ns2 simulations in conjunction Application/Traffic/Trace. For example, the following ns2 script fragment illustrates how to attach some.tsh-if2.bin to a traffic source

 # ...

 # Initialize a trace file
 set tfile [new Tracefile]
 $tfile filename some.tsh-2.bin

 # Attach the tracefile
 set trace [new Application/Traffic/Trace]
 $trace attach-tracefile $tfile

 # ...

Note that both some.tsh-if1.bin and some.tsh-if1.bin include only the TCP data-carrying segments in the trace. If you want to convert the entire TSH trace to Traffic/Trace files, see converters/

Converting TSH to tcpdump

If you would like to extract the TCP traffic and store it in tcpdump format, use

 configure(tcpdump => 'tcpdump_filename');

before calling process_trace(). process_trace() will generates a text file based on the trace records in a format similar to the modified output of tcpdump, as presented in TCP/IP Illustrated Volume 1 by W. R. Stevens (see pp. 230-231).

You can use such an output as input to other tools, present real traffic scenarios in a classroom, or simply "eyeball" the trace. For example, here are the first ten lines of the contents of such a file:

 0.000000000 > . ack 225051666 win 65463
 0.000014000 > S 457330477:457330477(0) ack 810547499 win 34932
 0.000014000 > . 3069529864:3069531324(1460) ack 225051666 win 65463
 0.000024000 > F 2073668891:2073668891(0) ack 183269290 win 64240
 0.000034000 > S 3152140131:3152140131(0) win 16384
 0.000067000 > P 3069531324:3069531944(620) ack 225051666 win 65463
 0.000072000 > S 1378088462:1378088462(0) win 16384
 0.000083000 > P 3272208349:3272208357(8) ack 501563814 win 32767
 0.000093000 > S 3127123478:3127123478(0) win 64170
 0.000095000 > R 810547499:810547499(0) ack 457330478 win 34932

Note that this output is similar to what tcpdump with options -n and -S would have produced. The only missing fields are related to the TCP options negotiated during connection setup. Unfortunately, TSH records include only the first 16 bytes of the TCP header, making it impossible to record the options from the segment header.


 records_in FILENAME

Estimates the number to records in FILENAME based on its file size. It returns an integer corresponding to the "expected" number of records in the trace, or false if the file size does not seem to correspond to a legitimate TSH trace.



As you might expect, this function sets the verbosity level of the module. By default Net::Traces::TSH remains "silent". Call verbose() to see trace processing progress indicators on standard error.

As of version 0.13, verbose() is equivalent to

 configure(Verbosity => 1);


 write_interface_summaries FILE_PREFIX

Writes a CSV summary similar to what write_trace_summary() generates for each interface in the trace (see %Interfaces). Each summary file has a .if-X.csv suffix, where X is the number of the interface. If FILE_PREFIX is provided, write_interface_summaries() will append to it this standard suffix (indicative of the interface).


 write_trace_summary FILENAME

Writes the contents of %Trace to FILENAME in comma separated values (CSV) format, a platform independent text format, excellent for storing tabular data. CSV is both human-readable and suitable for further analysis using Perl or direct import to a spreadsheet application. Although not required, it is recommended that FILENAME should have a .csv suffix.

If FILENAME is not specified, write_trace_summary() will create one for you by appending the suffix .csv to the filename of the trace being processed.

If you want FILENAME to contain meaningful data you should call write_trace_summary() after calling process_trace().


Nothing non-standard: strict, warnings and Carp.


None by default.


configure() date_of() get_IP_address() get_interfaces_href() get_interfaces_list() get_trace_summary_href() numerically() process_trace() records_in() verbose() write_trace_summary()

In addition, the following export tags are defined:


verbose() process_trace() write_interface_summaries() write_trace_summary()


date_of() records_in()

Finally, all exportable functions can be imported with

 use Net::Traces::TSH qw(:all);


This is Net::Traces::TSH version 0.16.


The NLANR MOAT Passive Measurement and Analysis (PMA) web site at provides more details on the process of collecting packet traces. The site features a set of Perl programs you can download, including several converters from other packet trace formats to TSH.

TSH trace files can be downloaded from the NLANR/PMA trace repository at . The site contains a variety of traces gathered from several monitoring points at university campuses and (Giga)PoPs connected to a variety of large and small networks.

Net::Traces::TSH version 0.11 was presented in YAPC::NA 2004. The presentation slides are available at .


If you are not familiar with Differentiated Services (DiffServ), good starting points are the following RFCs:

K. Nichols et al., Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers, RFC 2474. Available at

S. Blake et al., An Architecture for Differentiated Services, RFC 2475. Available at

See also RFC 2597 and RFC 2598.


If you are not familiar Explicit Congestion Notification (ECN) make sure to read

K. K. Ramakrishnan et al., The Addition of Explicit Congestion Notification (ECN) to IP, RFC 3168. Available at

The ns2 network simulator

Net::Traces::TSH can convert TSH traces to binary files suitable to drive simulations in ns2. More information about ns2 is available at .


Kostas Pentikousis, kostas AT cpan DOT org.


Professor Hussein Badr provided invaluable guidance while crafting the main algorithms of this module.

Many thanks to Wall, Christiansen and Orwant for writing Programming Perl 3/e. It has been indispensable while developing this module.


Copyright 2003, 2004 by Kostas Pentikousis. All Rights Reserved.

This library is free software with ABSOLUTELY NO WARRANTY. You can redistribute it and/or modify it under the same terms as Perl itself.

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