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OsmoGGSN - Open Source GGSN

This repository contains a C-language implementation of a GGSN (Gateway GPRS Support Node), a core network element of ETSI/3GPP cellular networks such as GPRS, EDGE, UMTS or HSPA.

OsmoGGSN is part of the Osmocom Open Source Mobile Communications projects and the successor to OpenGGSN. OpenGGSN was developed until 2004 by Mondru AB.

Homepage

The official homepage of the project is https://osmocom.org/projects/openggsn/wiki

GIT Repository

You can clone from the official osmo-ggsn.git repository using

git clone git://git.osmocom.org/osmo-ggsn.git

There is a cgit interface at http://git.osmocom.org/osmo-ggsn/

Documentation

There currently is no other documentation other than the wiki on the homepage. It would be great if somebody would work towards a user manual that can become part of the osmo-gsm-manuals project.

Mailing List

Discussions related to OsmoGGSN are happening on the osmocom-net-gprs@lists.osmocom.org mailing list, please see https://lists.osmocom.org/mailman/listinfo/osmocom-net-gprs for subscription options and the list archive.

Please observe the Osmocom Mailing List Rules when posting.

Contributing

Our coding standards are described at https://osmocom.org/projects/cellular-infrastructure/wiki/Coding_standards

We us a gerrit based patch submission/review process for managing contributions. Please see https://osmocom.org/projects/cellular-infrastructure/wiki/Gerrit for more details

The current patch queue for OsmoGGSN can be seen at https://gerrit.osmocom.org/#/q/project:osmo-ggsn+status:open

QuickStart

Requirements

Linux OsmoGGSN was originally developed and tested using Redhat 8.0 and 9.0 and is these days mostly developed on Debian GNU/Linux. It should run also on other Linux distributions as well as FreeBSD, but this is untested. Compilation on Solaris 2.8 has also been verified.

Tun The tun driver is required for proper operation of openggsn. For Linux kernels later than 2.4.7 the driver is typically included, but might need to be configured for automatic loading:

  1. Add the following line to /etc/modules.conf: alias char-major-10-200 tun
  2. depmod -a

Installation from binary

OsmoGGSN is built for common versions of Debian and Ubuntu as part of the Osmocom Nightly Builds project. If you don't want to do development, it is suggested to simply use those binary packages, rather than building yourself from source.

Installation from source

  1. ./configure
  2. make
  3. make install

You need to be root in order to install the package, but not in order to compile.

Running

sgsnemu Start the emulator as root using the command:

sgsnemu -l 10.0.0.50 -r 10.0.0.40 --createif --defaultroute

This will cause the sgsn emulator to bind to local address 10.0.0.50 and connect to the ggsn found at 10.0.0.40. It will first send off an ECHO_REQUEST message. After this it will attempt to establish a pdp context. If successful it will create a local interface and set up routing. Now you should be able to ping through the connection. Use a network analysator such as ethereal to monitor the traffic.

sgsnemu -h will show a list of available options.

sgsnemu -c sgsnemu.conf will use sgsnemu.conf as a configuration file. A sample file is provided in examples/sgsnemu.conf.

ggsn Edit the configuration file ggsn.conf found under openggsn/examples. Start the ggsn as root using the command:

ggsn --fg -c examples/ggsn.conf -l 10.0.0.40 --statedir ./

This will run the ggsn in foreground using the local interface 10.0.0.40. If you don't have a GSM network available for testing you can use sgsnemu to test the GGSN.

Support

Please contact the Mailing List above for community-based support.

Features

OsmoGGSN is an open source implementation of GPRS Support Nodes (GSNs). It implements the GPRS tunneling protocol (GTP) version 0 and version 1.

OsmoGGSN provides 3 components: * gtplib * osmo-ggsn * sgsnemu

gtplib This library contains all functionality relating to the GTP protocol. Use this library if you want to implement your own GSN. gtplib supports both GTPv0 (GSM 09.60) and GTPv1 (3GPP 29.060). At the moment no interface documentation is available for download.

osmo-ggsn The osmo-ggsn implements a Gateway GPRS Support Node. The GGSN is a small application which is provided in order to test and demonstrate the use of gtplib. It is fully compliant to the 3GPP standards, but lacks important functionality such as charging and management. Use this application as a starting point if you want to build your own GGSN with your own fancy VPN, management and charging functionality.

sgsnemu This application emulates a Serving GPRS Support Node (SGSN). sgsnemu enables you to test your 3GPP core network without the need to invest in a 3G radio access network. An important application of sgsnemu is the testing of roaming connectivity through a GPRS roaming exchange. sgsnemu will first attempt to use GTPv1. If unsuccessful it will fallback to GTPv0.

Required software

Tun

Both osmo-ggsn and sgsnemu uses the tun package. You need at least tun version 1.1. With Linux tun is normally included from kernel version 2.4.7. To configure automatic loading:

  1. Add the following line to /etc/modules.conf: alias char-major-10-200 tun
  2. depmod -a

Alternatively you can execute "modprobe tun" on the commandline.

Gengetopt

Gengetopt is required if you want to change the options defined in the cmdline.ggo source file. You need at least gengetopt version 2.8. If you are just going to compile the programs you don't need gengetopt.

To use gengetopt for the sgsnemu do the following: cd sgsnemu gengetopt < cmdline.ggo --conf-parser

For more information about gengetopt see http://www.gnu.org/software/gengetopt/gengetopt.html

Compilation and Installation

Please refer to the project homepage

Running osmo-ggsn

Use osmo-ggsn -h for a list of available options. All options available on the command line can also be given in a configuration file. See examples/osmo-ggsn.cfg for the format of this file.

Start osmo-ggsn as root using the command:

osmo-ggsn -c examples/osmo-ggsn.cfg

First a tun network interface will be created. In the above example the network interface address is 192.168.0.0 and the mask is 255.255.255.0. You can check that this interface is up by using ifconfig.

After tun has been successfully established the ggsn will wait for GTP create PDP context requests on the local interface 10.0.0.40. Currently all requests are accepted, and no password, username or APN validation is performed.

When receiving a create PDP context request a dynamic IP address will be allocated from the address pool determined by --dynip. In the above example the first allocated address will be 192.168.0.1, followed by 192.168.0.2 and so on. The request is confirmed by sending a create PDP context response message to the peer (SGSN).

Now IP packets will be forwarded between the tun network interface and the established GTP tunnel. In order to allow users to access the external network routing needs to be set up. If private addresses are used you need to configure network address translation. See the Linux Networking HOWTO for details.

Remember to enable routing:

echo 1 > /proc/sys/net/ipv4/ip_forward

If you installed using a binary RPM package it is possible to start osmo-ggsn by using the Sys 5 script:

/etc/init.d/osmo-ggsn start

Running sgsnemu

Use sgsnemu -h for a list of available options. All options available on the command line can also be given in a configuration file. See examples/sgsnemu.conf for the format of this file.

If you want to test a GRX roaming connection you will need to do the following:

  1. Install sgsnemu on a Linux Box. See under installation above.
  2. Connect your Linux box with sgsnemu installed to the GPRS core network. You also need a free IP address that can be used by sgsnemu.
  3. You need to configure networking in terms of interface address, subnet mask and default route. See the Linux Networking HOWTO for details.
  4. Launch sgsnemu with something like:

sgsnemu --listen 10.0.0.50 --remote 10.0.0.40 --dns 10.20.38.51 --timelimit 10 --contexts 0

sgsnemu will print something like the following on the screen:

Using DNS server: 10.20.38.51 (10.20.38.51) Local IP address is: 10.0.0.50 (10.0.0.50) Remote IP address is: 10.0.0.40 (10.0.0.40) IMSI is: 240011234567890 (0x98765432110042) Using APN: internet Using MSISDN: 46702123456

Initialising GTP library OsmoGGSN[1823]: GTP: gtp_newgsn() started Done initialising GTP library

Sending off echo request Waiting for response from ggsn........

Received echo response. Cause value: 0

This is quite good. It means that you managed to send off an echo request to a remote GGSN, and it was friendly enough to answer you. If you did not get an echo response it means that something is wrong either with your setup OR with the GRX connection OR with your roaming partners connection.

If the above went well you might want to try to establish a PDP context to the remote GGSN. Note that you should be careful when establishing PDP contexts using sgsnemu as each established PDP context will result in a Charge Detail Record (CDR) being generated by the GGSN. You should use real IMSI and MSISDN from a valid test SIM card. Otherwise some poor customer might get charged for your testing. Also note that you are establishing a connection to the Gi network, so please be carefull not to route internet traffic onto the GPRS core network! Assuming you know what you are doing:

sgsnemu --listen 10.0.0.50 --remote 10.0.0.40 --dns 10.20.38.51 --timelimit 10 --contexts 1 --apn internet --imsi 240011234567890 --msisdn 46702123456 --createif --defaultroute

sgsnemu will print something like the following on the screen:

Using DNS server: 10.20.38.51 (10.20.38.51) Local IP address is: 10.0.0.50 (10.0.0.50) Remote IP address is: 10.0.0.40 (10.0.0.40) IMSI is: 240011234567890 (0x98765432110042) Using APN: internet Using MSISDN: 46702123456

Initialising GTP library OsmoGGSN[1838]: GTP: gtp_newgsn() started Done initialising GTP library

Sending off echo request Setting up PDP context #0 Waiting for response from ggsn........

Received echo response. Cause value: 0 Received create PDP context response. Cause value: 128 Setting up interface and routing /sbin/ifconfig tun0 192.168.0.1 /sbin/route add -net 192.168.0.0 netmask 255.255.255.0 gw 192.168.0.1

Now a context is established to the remote GGSN. The IP address of the context is 192.168.0.1. You should be able to ping a known address on the Gi network of the roaming partner. You should even be able to do web browsing through the PDP context.

Note however that you probably need to adjust your routing tables, so that you make sure that all GRX traffic is routed to the GPRS core network and everything else through the PDP context. The proper way to do this is to use policy routing. Also note that you are effectively connecting the same computer to both the Gn and Gi network, so please be carefull not to route internet traffic onto the GPRS core network and please protect yourself against hackers! For this reason it is advised to always use --contexts 0 when testing a live network.

After --timelimit seconds the PDP context is disconnected with the following messages from sgsnemu:

Disconnecting PDP context #0 Received delete PDP context response. Cause value: 128 Deleting tun interface