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annotate doc/RTP-analysis @ 149:95d47a34070a

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gsmefr-dec-parse: add BE support
author Mychaela Falconia <falcon@freecalypso.org>
date Wed, 14 Dec 2022 18:12:55 +0000
parents 8eb0e7a39409
children aaa0380f9958
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136
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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1 The present package includes a utility named rtp-gsmfr-extr; this utility
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
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2 extracts a single RTP stream in either FR1 or EFR codec format from a pcap file,
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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3 presumably captured with tcpdump on an IP network serving either an IP-based BTS
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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4 or a gateway from an E1-based BTS to RTP - the intent is to extract a GSM call
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
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5 uplink that has been rendered into an RTP stream by a BTS. The RTP stream being
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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6 extracted must be fully continuous without any gaps, using Themyscira
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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7 RTP-BFI-extension BFI marker packets in those 20 ms windows where no good
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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8 traffic frame has been received. rtp-gsmfr-extr verifies continuity of the RTP
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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9 stream being extracted: any detected discontinuity (either a sequence number
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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10 jump indicating packet loss or a timestamp jump indicating an intentional gap
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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11 generated at the source) will be reported, and the extraction will stop there.
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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12
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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13 To run rtp-gsmfr-extr, you need to have a pcap file (obviously), and you need to
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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14 identify the RTP stream to be extracted by either source or destination IP:port.
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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15 rtp-gsmfr-extr will look at every UDP packet that matches this src-IP-port or
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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16 dest-IP-port filter, and then check for valid RTP, verify the expected increment
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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17 in sequence and timestamp numbers, check for either FR1 or EFR payload (or a
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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18 Themyscira BFI marker for FR & EFR), and finally write the extracted frame
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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19 stream to a gsmx file. This gsmx output can then be analyzed with gsmrec-dump,
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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20 or decoded to playable WAV with gsmfr-decode or gsmefr-decode.