OpenGGSN and Linux Kernel accelerated GTP-U

OpenGGSN has support to use the Linux kernel GTP-U code to accelerate the data/user plane while still implementing the control plane (GTP-C) in userspace in OpenGGSN.

For more information about the Linux kernel GTP-U code, please see linux-kernel-gtp-u

Building OpenGGSN with kernel which has GTP-U support

At the time of writing (2017-01-09) of this wiki, below listed distributions have support of GTP kernels :

  • Debian 4.9.1-1~exp1 - Debian's latest experimental build
  • Ubuntu 16.10 kernel 4.8
  • OpenSUSE Tumbleweed (stable) 4.8 (.12)
  • Fedora 25 kernel 4.8

Following two Debian kernels do not activate GTP kernel module during build: 4.8.0 and 4.9.0.

It is expected that complete openbsc project and related dependencies are pre-installed.

Check if package libc-ares-dev is installed and if not please add it.

Ubuntu 16.10, kernel 4.8.0-30-generic is used.

  • Installing dependencies and build library libgtpnl

You can install those packages with:

sudo apt install libtalloc-dev libpcsclite libmnl-dev

Please follow instructions provided at Build from source in order to install following library and projects :

Information about dependencies between Osmocom projects is given at the above link:

  • libgtpnl
  sudo make install
  sudo ldconfig
  • libosmocore
  • openggsn
./configure --enable-gtp-linux
sudo make install
sudo ldconfig

Following message is shown at end of the command: ./configure --enable-gtp-linux

openggsn Configuration:
  GTP Linux kernel support:            yes

This means that appropriate header files are available.

Using OpenGGSN with kernel which has GTP-U support

In order to find out whether gtp.ko module is available we can enter following command:

find /lib/modules/`uname -r` -name gtp.ko

Output below shows that gtp.ko module is present:


We are loading module gtp from kernel issuing command:

sudo modprobe gtp 

when you enter:

lsmod | grep gtp

then more information about gtp and related udp tunnel can be obtained:

gtp                    28672  0
udp_tunnel             16384  1 gtp

Some helpful tools are available in: libgtpnl/tools

you can get more details about gtp-tunnel, entering command from the OpenGGSN shell:

sudo ./gtp-tunnel list

Output will be similar to:

version 1 tei 1/0 ms_addr sgsn_addr

Furthermore we can use:

 sudo starce ggsn --gtp-linux -c ggsn.conf -f -d 
to determine if Ubuntu 16.10, kernel 4.8.0-30 is in use.

Next two cases shall be considered as an indication whether gtp kernel module is active:

  • If gtp kernel module is active then we can see the strace output just when PDP context activation or deactivation is done.
  • If gtp kernel module is not active then we can see the strace output constantly running on the screen.

Note: OpenGGSN is started by:

sudo  ggsn --gtp-linux -c ggsn.conf -f -d

-d option is useful for debugging purposes.

Related output should be similar to the one shown below:

conf: ggsn.conf
fg: 1
debug: 1
qos: 0x0b921f
apn: internet
pidfile: /var/run/
statedir: /var/lib/ggsn/
gtp_linux: 1
timelimit: 0
conf: ggsn.conf
fg: 1
debug: 1
qos: 0x0b921f
apn: internet
pidfile: /var/run/
statedir: /var/lib/ggsn/
gtp-linux: 1
timelimit: 0
<000c> gtp.c:701 GTP: gtp_newgsn() started
<0002> gtp-kernel.c:123 Using the GTP kernel mode (genl ID is 27)

<0002> gtp-kernel.c:156 GTP kernel configured

<000b> control_if.c:693 CTRL at 4257

osmosgsn can be started with:

sudo osmo-sgsn -c sgsn.cfg    

- d option is also available ins osmo-sgsn command.

Additional information related to setup of openbsc and GPRS setup is available OpenBSC GPRS

For clarity purposes configuration files of openbsc, OpenGGSN, osmosgsn and sysmoBTS are added.

osmo-pcu.cfg (79 Bytes) laforge, 02/23/2017 05:56 PM

osmo-bts.cfg (1.65 KB) laforge, 02/23/2017 05:56 PM

sgsn.cfg (2.28 KB) laforge, 02/23/2017 05:57 PM

ggsn.conf Magnifier (441 Bytes) laforge, 02/23/2017 05:57 PM

openbsc1.cfg (2.55 KB) laforge, 02/23/2017 05:57 PM