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Net-Traces-TSH-0.01
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/ Net::Traces::TSH

NAME

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

SYNOPSIS

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

  # Enable progress information display
  #
  verbose;

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

  # Then, write a summary of the trace contents in some_trace.csv, in
  # Comma-Separated Values (CSV) format
  #
  write_trace_summary 'some_trace.csv';

ABSTRACT

Net::Traces::TSH provides methods to analyze IP packet traces in Time Sequenced Headers (TSH) format. The trace summary statistics are stored in comma separated values (CSV), a platform independent text format. Use Net::Traces::TSH to gather general information about a TSH packet trace, measure Transport protocol, DiffServ and ECN usage, and generate packet and segment size distributions. In addition, you can extract all TCP traffic present in a TSH trace in a tcpdump-like text format.

INSTALLATION

To install Net::Traces::TSH type the following:

 perl Makefile.PL
 make
 make test
 make install

In addition,

 perldoc perlmodinstall

will provide more information and options about installing Perl modules.

DESCRIPTION

Net::Traces::TSH provides methods to analyze IP packet traces in Time Sequenced Headers (TSH) format. TSH is a binary trace format. Each trace record corresponds to an IP packet passing by a monitoring point. A TSH record is 44 bytes long can be viewed as being composed of three essentially distinct 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.

IP

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

TCP

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 (at least to me) how to interpret the last section (remaining 16 bytes). As such, Net::Traces::TSH makes no assumptions, and does not analyze in detail packets from protocols other than TCP. That is, Net::Traces::TSH reports on protocols other than TCP based on the second section (IP header) only.

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 a modified version 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. Keep in mind that recent RFCs have modified the meaning of the IP header Type of Service field to accommodate Differentiated Services and Explicit Congestion Notification.

You can use Net::Traces::TSH to gather information from a TSH packet trace, and perform a statistical analysis on Transport protocol usage, the usage of DiffServ and ECN, get packet and segment size distributions, and more. The trace summary statistics are stored in comma separated values (CSV), a platform independent text format. In addition, you can use Net::Traces::TSH to extract the aggregated "good" and "bad" transmission periods in the packet trace.

Data Structures

The data collected from a trace is stored is a hash called %Trace_Summary, the main data structure in Net::Traces::TSH. %Trace_Summary is initialized and then populated by "process_trace". The recommended way to get the trace summary information is by calling "write_trace_summary" to write the contents of %Trace_Summary in a CSV formated text file, as shown in "SYNOPSIS".

%Trace_Summary is not exported by default and it is not intended to be accessed directly by user code. However, if you know what you are doing, you can get a reference to %Trace_Summary by calling "get_trace_summary_href". If you choose to do so, the following subsections explain how you can access some of the information stored in %Trace_Summary, but they are not an exhaustive list. See also "Taking advantage of %Trace_Summary".

General Trace Information

$Trace_Summary{filename}

The trace FILENAME.

$Trace_Summary{log}

The trace summary FILENAME.

$Trace_Summary{starts}

The first timestamp in the trace.

$Trace_Summary{ends}

The last timestamp in the trace.

$Trace_Summary{records}

Number of records in the trace.

$Trace_Summary{unidirectional}

True, if each interface carries unidirectional traffic.

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

undef if process_trace() did not examine the direction of the traffic

The capacity of the monitored link in bits per second (b/s). If not specified it is initialized by process_trace() to 155,520,000.

Internet Protocol

$Trace_Summary{IP}{'Total Packets'}
$Trace_Summary{IP}{'Total Bytes'}

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

Fragmentation

$Trace_Summary{IP}{'DF Packets'}
$Trace_Summary{IP}{'DF Bytes'}

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

$Trace_Summary{IP}{'MF Packets'}
$Trace_Summary{IP}{'MF Bytes'}

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

Differentiated Services

$Trace_Summary{IP}{'Normal Packets'}
$Trace_Summary{IP}{ 'Normal Bytes'}

Number of IP packets and bytes, respectively, with no DiffServ and no ECN bits set. These packets request no particular treatment (best effort traffic).

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

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

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

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

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

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

Explicit Congestion Notification

$Trace_Summary{IP}{'ECT Packets'}
$Trace_Summary{IP}{'ECT Bytes'}

Number of IP packets and bytes, respectively, with either of the ECT bits set. These packets carry ECN-capable traffic.

$Trace_Summary{IP}{'CE Packets'}
$Trace_Summary{IP}{'CE Bytes'}

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

Transport Protocols

Besides the summary information about the trace itself and statistics about IP, %Trace_Summary gathers information about transport protocols based on the IP header. %Trace_Summary maintains the same statistics mentioned in the previous section for TCP, UDP and all transport protocols with an IANA assigned number, provided that the trace contains packets of that protocol. For example,

$Trace_Summary{Transport}{TCP}{'Total Packets'}
$Trace_Summary{Transport}{TCP}{'Total Bytes'}

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

$Trace_Summary{Transport}{UDP}{'Total Packets'}
$Trace_Summary{Transport}{UDP}{'Total Bytes'}

Ditto for UDP.

$Trace_Summary{Transport}{ICMP}{'DF Packets'}
$Trace_Summary{Transport}{ICMP}{'DF Bytes'}

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

Taking advantage of %Trace_Summary

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

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

 use Net::Traces::TSH qw( process_trace write_trace_summary
                          get_trace_summary_href
                        );

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

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

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

FUNCTIONS

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

date_of

  date_of FILENAME

Converts the epoch timestamp, typically part of a TSH trace FILENAME downloaded from http://pma.nlanr.net/Traces to a human readable date. If FILENAME contains a valid timestamp, date_of returns the corresponding GMT date as a string. Otherwise, date_of returns false.

For example

 date_of 'ODU-1073132115.tsh'

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

get_IP_address

 get_IP_address INTEGER

Converts a 32-bit integer to an IP address. For example

 get_IP_address(167772172)

returns "10.0.0.12".

get_trace_summary_href

 get_trace_summary_href

Returns a hash reference to %Trace_Summary.

process_trace

 process_trace FILENAME
 process_trace FILENAME, NUMBER
 process_trace FILENAME, NUMBER, TEXT_FILENAME

If called in a void context process_trace() examines the binary TSH trace stored in FILENAME, and gathers statistics to populate %Trace_Summary. NUMBER specifies the capacity of the monitored link in bits per second. Presumably, NUMBER should equal the capacity of the link where the trace was captured.

If called in a list context process_trace() gathers the same statistics and in addition it extracts all TCP flows and TCP data-carrying segments from the trace, returning two hash references. For example

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

Here $senders_href is a reference to a hash which contains an entry for each TCP sender in the trace file. Each hash entry is a list of timestamps extracted from the trace record and stored after being "normalized" (start of trace = 0.0 seconds, always). In theory, all records 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 hash collision avoidance algorithm. If the collision threshold of trace records with the same timestamp is exceeded, process_trace() aborts as this is a hint that the trace is corrupted. The collision threshold is currently set to 4.

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 10.0.0.12:80 to 10.0.0.14:1080 (in interface 1):

 $senders_href->{1}{167772172,80,167772174,1080}

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

For example, assuming the 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 $packets_href->{$interface}{$timestamp}{bytes};
 print $packets_href->{$interface}{$timestamp}{seq_num};

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

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

Please 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() has not been finalized yet, and as such it is not included in this version. Contact me if you want to to get the most recent version.

If TEXT_FILENAME is specified, process_trace() 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. Here is an example of the contents of such a file:

 0.000000000 10.0.0.1.412 > 10.0.0.2.4400 . ack 1260445590 win 16560
 0.000104547 10.0.0.3.4700 > 10.0.0.4.2783 . 1484823770:1484825230(1460) ack 2722218997 win 17126
 0.000172377 10.0.0.3.4700 > 10.0.0.4.2783 . 1484825230:1484826690(1460) ack 2722218997 win 17126

The format is explained in more detail in TCP/IP Illustrated Volume 1, pp. 230-231. You can use such an output as input to other tools, present real traffic scenarios in the classroom, or simply "eyeball" the trace.

records_in

 records_in FILENAME

Calculates the number to records in FILENAME and returns the "expected" number of records in the trace, which must an integer. If not an integer, records_in() returns false.

verbose

 verbose

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.

write_trace_summary

 write_trace_summary FILENAME
 write_trace_summary

Writes the contents of %Trace_Summary to FILENAME. 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. The summary is stored 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 FILENAME does not need to have a .csv suffix, choosing a FILENAME ending in ".csv" is recommended.

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

DEPENDENCIES

None.

EXPORTS

None by default.

Exportable

date_of() get_IP_address() get_trace_summary_href() numerically() process_trace() records_in() verbose() write_trace_summary()

In addition, the following export tags are defined

:traffic_analysis

verbose() process_trace() write_trace_summary()

:trace_information

date_of() records_in()

Finally, all exportable functions can be imported with

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

VERSION

This is Net::Traces::TSH version 0.01.

SEE ALSO

The NLANR MOAT Passive Measurement and Analysis (PMA) web site (http://pma.nlanr.net/PMA) provides more details on the TSH format and the process of collecting packet traces. The site also features a set of open source tools 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 (http://pma.nlanr.net/Traces). 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.

DiffServ

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 http://www.ietf.org/rfc/rfc2474.txt

S. Blake et al., An Architecture for Differentiated Services, RFC 2475. Available at http://www.ietf.org/rfc/rfc2475.txt

See also RFC 2597 and RFC 2598.

ECN

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 http://www.ietf.org/rfc/rfc3168.txt

AUTHOR

Kostas Pentikousis, kostas@cpan.org

ACKNOWLEDGMENTS

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 AND LICENSE

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.