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Feature #5488

open

create DAHDI mirror sniffer

Added by laforge 11 months ago. Updated 3 months ago.

Status:
In Progress
Priority:
Low
Assignee:
Target version:
-
Start date:
03/13/2022
Due date:
% Done:

80%


Description

For further exploration of a variety of different ISDN equipment and protocols, we need a proper sniffer to trace communication not only on D- but also on B-channels.

Existig systems are not good use cases:
  • osmo-e1-recorder ("owns" the DAHDI devices/channels, for use with passive E1 tap)
  • dahdi_pcap / dahdi_gsmtap (just for D-channel)
  • dahdi_monitor doesn't work
  • dahdi_rawdump works for single B-channel only, and has no signaling integration

The high-level functionality would be:

  • open d-channel in RXMIRROR + TXMIRROR
  • filter out Q.921 I-frames in both directions (ignore everything else)
  • perform simplistic Q.931 decode of message type, call reference and IE iteration
  • maintain table with call references, one entry per callref
    • create on SETUP
    • destroy at RELEASE/RELEASE_COMPLET
    • destroy after timeout?
  • decode/track ChannelID IE
    • store B-channel number with call reference
  • start capturing B-channel on CONNECT
  • stop capturing B-channel when call is destroyed
  • optional: add software HDLC for B channel to avoid transmitting large amounts of flag octets?

The data storage format could very well be the format of osmo-e1-recorder.

Actions #1

Updated by laforge 3 months ago

  • Status changed from New to In Progress
  • % Done changed from 0 to 80

This is basically what became the osmo-isdntap project (see https://gitea.osmocom.org/retronetworking/osmo-isdntap)

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