Hardware Projects » E1/T1 Hardware Interface (including icE1usb)

h1. ICE40 based passive tap

In 12/2019, @tnt implemented a bi-directional passive E1 tap device that samples the entire raw 2MBps data stream in both directions.

This is useful in situations where the E1 line is not used channelized, i.e. not with individual 64kBps timeslots, such as in frame relay or 'wideband ISDN' (B-ISDN) use cases, where [[osmo-e1-recorder:]] and re-combining 64k slots in the capture has not always been successful.

Contrary to the "normal" (end-of-line) [[ICE40_E1_USB_interface]], this approach uses actual E1 LIU (Line Interface Unit) hardware in order to use their built-in equalizer and additional gain for passive tapping of long-haul E1 lines.

The setup conceptually looks like this:

{{graphviz_link()

digraph G {

  rankdir = LR;

  e1tap [label="osmocom e1-tap\ninserted into E1 line"];

  xcvr1 [label="osmo-e1-xcvr 1"];

  xcvr2 [label="osmo-e1-xcvr 2"];

  e1tap -> xcvr1 [label="E1 A->B"];

  e1tap -> xcvr2 [label="E1 B->A"];

  xcvr1 -> iCEpick [label="serial bits A->B"];

  xcvr1 -> iCEpick [label="SPI (ctrl)"];

  xcvr2 -> iCEpick [label="serial bits B->A"];

  xcvr2 -> iCEpick [label="SPI (ctrl)"];

  iCEpick -> PC [label="USB (ISO)"];

}

}}

h2. Pictures