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Telefax G4

G4 (Group 4) is a rarely-used version of the Telefax service which works only over ISDN. Contrary to the much more commonlty used G3 (Group 3) for analog telephone lines, G4 does not include any Modem. Instead, it natively uses digital transmission for the Telefax data over ISDN B-Channels.

Protocol stack

The protocol stack looks like this:

  • G4 Fax specific data as per T.6, T.563 etc.
  • T.62 Document Layer
  • T.62 Session Layer
  • T.70
  • X.75
  • ISDN B-Channel

B-channel captures

wireshark dissectors for ITU-T T.70 and T.62

simple/basic LUA dissectors for use with current wireshark can be found in https://gitea.osmocom.org/osmocom/wireshark-mate - they make use of the [recently introduced] X.75 dissector in wireshark. Make sure you have a wireshark version that includes the following changes: The are "decode as" dissectors, so you need to
  • select the X.75 payload and "Decode as" T.70
  • then select the T.70 payload and "Decode as" T.62
Files (4)

Updated by laforge 30 days ago · 3 revisions

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