FreeCalypso > hg > gsm-codec-lib
annotate doc/RTP-analysis @ 147:90b9c7c3fa3b
gsmefr-cod-parse: use factored-out ETSI bit reader
| author | Mychaela Falconia <falcon@freecalypso.org> |
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| date | Wed, 14 Dec 2022 08:09:52 +0000 |
| parents | 8eb0e7a39409 |
| children | aaa0380f9958 |
| rev | line source |
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8eb0e7a39409
doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff
changeset
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1 The present package includes a utility named rtp-gsmfr-extr; this utility |
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8eb0e7a39409
doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff
changeset
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2 extracts a single RTP stream in either FR1 or EFR codec format from a pcap file, |
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8eb0e7a39409
doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff
changeset
|
3 presumably captured with tcpdump on an IP network serving either an IP-based BTS |
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8eb0e7a39409
doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff
changeset
|
4 or a gateway from an E1-based BTS to RTP - the intent is to extract a GSM call |
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8eb0e7a39409
doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff
changeset
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5 uplink that has been rendered into an RTP stream by a BTS. The RTP stream being |
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8eb0e7a39409
doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff
changeset
|
6 extracted must be fully continuous without any gaps, using Themyscira |
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8eb0e7a39409
doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff
changeset
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7 RTP-BFI-extension BFI marker packets in those 20 ms windows where no good |
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8eb0e7a39409
doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff
changeset
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8 traffic frame has been received. rtp-gsmfr-extr verifies continuity of the RTP |
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8eb0e7a39409
doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff
changeset
|
9 stream being extracted: any detected discontinuity (either a sequence number |
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8eb0e7a39409
doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff
changeset
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10 jump indicating packet loss or a timestamp jump indicating an intentional gap |
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8eb0e7a39409
doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff
changeset
|
11 generated at the source) will be reported, and the extraction will stop there. |
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8eb0e7a39409
doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff
changeset
|
12 |
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8eb0e7a39409
doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff
changeset
|
13 To run rtp-gsmfr-extr, you need to have a pcap file (obviously), and you need to |
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8eb0e7a39409
doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff
changeset
|
14 identify the RTP stream to be extracted by either source or destination IP:port. |
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8eb0e7a39409
doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff
changeset
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15 rtp-gsmfr-extr will look at every UDP packet that matches this src-IP-port or |
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8eb0e7a39409
doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff
changeset
|
16 dest-IP-port filter, and then check for valid RTP, verify the expected increment |
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8eb0e7a39409
doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff
changeset
|
17 in sequence and timestamp numbers, check for either FR1 or EFR payload (or a |
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8eb0e7a39409
doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff
changeset
|
18 Themyscira BFI marker for FR & EFR), and finally write the extracted frame |
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8eb0e7a39409
doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff
changeset
|
19 stream to a gsmx file. This gsmx output can then be analyzed with gsmrec-dump, |
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8eb0e7a39409
doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff
changeset
|
20 or decoded to playable WAV with gsmfr-decode or gsmefr-decode. |