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annotate doc/RTP-analysis @ 4:5216e7fb1c9e

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doc: update for new FR/EFR RTP payload formats
author Mychaela Falconia <falcon@freecalypso.org>
date Sun, 16 Apr 2023 07:55:21 +0000
parents 05ff0f7ac977
children
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1 The present package includes a number of utilities for analyzing RTP streams
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2 that have been captured with tcpdump or equivalent tools in pcap format. In
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3 order to use any of these utilities, you need to have a pcap file (obviously),
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4 and you need to identify the RTP stream to be analyzed or extracted by either
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5 source or destination IP:port. All tools begin by applying a filter,
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6 considering only those packets that are UDP in IPv4 (no IPv6 support currently),
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7 and only those that match the specified source or destination IP:port. Every
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8 matched packet is checked for a valid RTP header, and then the actual RTP stream
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9 analysis or extraction takes place, depending on the specific tool:
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11 rtp-cont-check This program checks the selected RTP stream for continuity. It
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12 verifies that every matched packet has the same SSRC, that the
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13 sequence number always increments by 1 from each individual
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14 packet to the next, and that the RTP header timestamp always
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15 increments by 160 units. (The assumption is that the
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16 application at hand is in the traditional telephony domain,
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17 with a sampling rate of 8000 samples/s and 20 ms packetization
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18 for RTP.) This tool also looks at the capture time deltas
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19 between successive packets and reports the observed minimum and
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20 maximum; by seeing min and max delta-T, a developer can easily
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21 notice timing aberrations that aren't caught by RTP header
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22 sequence number and timestamp checks.
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24 rtp-g711-extr This program focuses on a single selected RTP stream like the
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25 others, enforces its continuity just like rtp-cont-check, and
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26 then further enforces that every RTP packet be a 160-byte
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27 payload, presumed to be either PCMU or PCMA. (The payload type
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28 number is NOT considered, only the payload length.) The
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29 selected G.711 RTP stream is then extracted and written into a
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30 raw binary file.
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31
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32 rtp-gsmfr-dump This program focuses on a single selected RTP stream like the
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33 others, enforces its continuity just like rtp-cont-check, and
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34 then expects the RTP payload to be one of GSM FR or EFR formats
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35 listed in the FR-EFR-formats document. Each recognized FR/EFR
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36 or BFI payload is then dumped in human-readable form on stdout,
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37 similarly to the gsmrec-dump utility from Themyscira Wireless
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38 GSM codec libraries & utilities package.
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39
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40 rtp-gsmfr-extr This program operates like rtp-gsmfr-dump, imposing the same
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41 expectations on the selected RTP stream, but the latter stream
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42 is then extracted and written into a gsmx binary file, as
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43 defined in the GSM codec libraries and utilities package.
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45 rtp-jitter-view This program analyzes a single selected RTP stream just like
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46 rtp-cont-check, but instead of reporting minimum and maximum
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47 time deltas for the entire stream, it prints the individual
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48 capture time delta between every successive pair of packets.