Cellular Network Infrastructure » Core Network (CN) » OsmoGGSN (former OpenGGSN)

h1. 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:]]

h2. 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:

<pre>

sudo apt install libtalloc-dev libpcsclite libmnl-dev

</pre>

Please follow instructions provided at [[cellular-infrastructure:Build from source]] in order to install following library and projects :

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

* libgtpnl

<pre>

  sudo make install

  sudo ldconfig

</pre>

* libosmocore 

* openggsn

<pre>

./configure --enable-gtp-linux

make 

sudo make install

sudo ldconfig

</pre>

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

<pre>

openggsn Configuration:

  GTP Linux kernel support:			yes

</pre>

This means that appropriate header files are available.

h2. 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:

<pre>

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

</pre>

Output below shows that gtp.ko module is present:

<pre>

/lib/modules/4.8.0-30-generic/kernel/drivers/net/gtp.ko

</pre>

We are loading module gtp from kernel issuing command: <pre>sudo modprobe gtp </pre> 

when you enter: 

<pre>

lsmod | grep gtp

</pre>

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

<pre>

gtp                    28672  0

udp_tunnel             16384  1 gtp

</pre>

Some helpful tools are available in: @libgtpnl/tools@

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

<pre>

sudo ./gtp-tunnel list

</pre>

Output will be similar to:

<pre>

version 1 tei 1/0 ms_addr 192.168.0.2 sgsn_addr 127.0.0.2

</pre>

Furthermore we can use: <pre> sudo strace ggsn --gtp-linux -c ggsn.conf -f -d </pre>  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: 

<pre>

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

</pre>

-d option is useful for debugging purposes. 

Related output should be similar to the one shown below: 

<pre>

conf: ggsn.conf

fg: 1

debug: 1

qos: 0x0b921f

apn: internet

net: 192.168.0.0/24

pidfile: /var/run/ggsn.pid

statedir: /var/lib/ggsn/

gtp_linux: 1

timelimit: 0

cmdline_parser_configfile

listen: 127.0.0.1

conf: ggsn.conf

fg: 1

debug: 1

qos: 0x0b921f

apn: internet

net: 192.168.0.0/24

pidfile: /var/run/ggsn.pid

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 127.0.0.1 4257

</pre>

osmosgsn can be started with: 

<pre>

sudo osmo-sgsn -c sgsn.cfg    

</pre>

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

Additional information related to setup of openbsc and GPRS setup is available [[cellular-infrastructure:OpenBSC GPRS]]

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