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osmo-e1-hardware - Collection of various E1/TDM hardware projects

This repository contains a variety of different projects related to E1/TDM hardware interfaces


The Osmocom icE1usb project is an open source hardware, gateware and firmware project implementing a USB-attached interface for E1 circuits. Use this if you want to implement a system speaking to an E1 circuit, such as

  • a GSM BSC (using OsmoBSC) talking Abis/E1 to a GSM Base station,
  • using osmo-gbproxy to convert classing Gb/E1 to Gb/IP
  • talking to legacy ISDN PRI equipment such as PBX, RAS servers, etc.
  • connecting legacy ISDN PRI equipment such as PBX, RAS servers, etc. to the OCTOI comminity TDMoIP network

Depending on your USB host controller, it supports one or two E1 circuits. Most host controllers can only support one E1 circuit.

In order to provide a stable E1 clock reference, it contains a GPS disciplined oscillator.

See for more details.

Fully assembled units can be purchased at the sysmocom webshop

Check the hardware/icE1usb, firmware/ice40-riscv/icE1usb directories in this repository.

The host software is provided either


This is a fully integrated design that allows you to obtain bi-directional high-impedance bitstream E1 traces. It features an iCE40 FPGA with USB + E1 cores from Sylvain Munaut, as well as two E1 LIUs.

See for more details.

Fully assembled units can be purchased made-to-order from sysmocom.

Check the hardware/e1-tracer, firmware/ice40-riscv/e1-tracer and software/e1-tracer directories in this repository.


This was a simple hardware project that aims to generate a reusable module for interfacing E1/T1/J1 lines from various custom FPGA/CPLD/microcontroller projects. Consider it part of an earlier R&D setup before icE1usb and osmo-e1-tracer were around.

The board contains transformers, the analog circuitry, the LIU (line interface unit), an oscillator as well as an integrated transceiver chip.

It exposes the control interface (SPI) as well as the decoded synchronous Rx/Tx bitstreams each on a 2x5pin header.

Framer, Multiplexer, HDLC decoder or anything like that is out-of-scope for now. The idea really is to provide an interface as low-level as possible.

One of the ideas is to create a "soft E1" interface, where the Rx/Tx bitstreams are interfaced with the SSC of an AT91SAM3S and subsequently passed into a PC via USB. The 2Mbps signal is very low-bandwidth, so that a pure software implementation should be absolutely no problem for todays computing power.

See for more details

Check the hardware/e1-xcvr directory in this repository.


This is a small passive board that allows you to perform high-impedance tracing on an E1 or T1 line.

Fully assembled units can be purchased at the sysmocom webshop.

Check the hardware/e1-tap directory in this repository.