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E1/T1 Interface

Why not TDMoIP / CESoIP?

Usual E1/T1 over IP protocols use generic frames over IP transfer that makes more than 2 megabits constant rate with up to 8000 packets per second. That approach:

  • not suitable for distributed sites with limited internet access
  • makes constant parasite load on the servers
  • requires delays to compensate jitters
  • has issues with asynchronous-to-synchronous transition

Fur such kind of integrations we prefer to have our own agent software on-site with hardware E1/T1 interfaces.

  • good timings driven by E1/T1 clock or GPS
  • good framing due to synchronous composition on the site
  • less traffic due to transfer only valuable demultiplexed information



We have chosen Osmocom icE1usb as a primary interface for our projects for several reasons:

  • good compatibility with big range of hardware hosts due to use of USB
  • in opposite to most of DAHDI interfaces it is in production
  • open-source hardware design
  • open-source user-space driver, no need for the kernel driver
  • suitable API for our purposes (at least full-frame mode)
  • available at Sysmocom's web shop

User manual can be found here.


Please be careful! Or your device will be damaged! Front-panel RJ45 connectors accepts 120 Om E1. Back-panel RJ45 is for GPIO and accepts TTL only. Don't try to connect the device to Ethernet. USB-C port should be connected to computer, since it's just an interface. Minijack connector is only to reprogram firmware. Also please configure properly internal jumpers to master (NE) or slave (NT) E1 mode.


Hardware configuration

Almost in all our cases you need this interface in NT (Network Termination) mode. In this mode the interface works as a network side and you can use a normal Ethernet cable for connection (no crossing required).

To change the mode, unscrew the 2 PH0 screws on the side with the 2 RJ45 jacks. You’ll also need to unscrew the nut on the SMA jack on the other side. After that, the cover plate and rubber gasket around the 2 RJ45 jacks can be removed. The PCB can be slid out of the case.

Then swap the jumpers so they match this picture:


Driver installation

You can get Osmocom E1D from Osmocom's Debian repository (amd64, arm64). 

sudo apt install extrepo
sudo extrepo enable osmocom-latest
sudo apt update
sudo apt install -y osmo-e1d

Driver configuration


log syslog daemon
 logging level force-all fatal
 interface 0 icE1usb
  usb-serial [interface serial number]
  line 0
  line 1

More information about logging section can be found here, here and here.
(If you care about configuration file format, please check the sources here).

How to find a serial number of connected icE1usb:

sudo lsusb -d 1d50:6145 -v 2> /dev/null | grep iSerial

Reload a service:

sudo systemctl restart osmo-e1d

You can also test your configuration from the command line:

sudo osmo-e1d -c /etc/osmocom/osmo-e1d.cfg

Recomended settings


if ($programname contains "osmo-e1d") and (($msg contains "Received Only 0 bytes") or ($msg contains "TS read underflow")) then {



Issues with the second E1 port

Please note that on many XHCI host controllers there seem to be implementation flaws in the XHCI host controller firmware preventing the activation of both icE1usb ports simultaneously. The XHCI controller firmware erroneously claims that there is insufficient bus bandwidth. However, the same icE1usb hardware/firmware works perfectly fine with OHCI, UHCI and EHCI host controllers. See for a user-maintained list of USB hosts / controllers and whether or not they work with two E1 ports.

In most installations it's not a real issue, because of need in a single port only.

We have tested it with following equipment:

  • Raspberry Pi 3, 4, CM4 - only first E1 port is working 
  • Raspberry Pi 5 - both E1 ports are working when connected to blue USB port