OpenBSC GPRS/EDGE Setup page


  • BTS hardware: sysmoBTS, USRP, UmTRX, nanoBTS with GPRS or EDGE support. BS11 are not supported.
  • A compiled GGSN from OpenGGSN
  • A working and up-to-date OpenBSC (see Building_OpenBSC)
    • You will need to (re-)build it after having installed OpenGGSN so that the libgtp is detected and the SGSN binary osmo-sgsn built.
  • A custom SIM for your network
    • Currently OsmoSGSN refuses all roaming, so you need a SIM that matches your custom MCC/MNC network


First a little picture to illustrate the different elements and their interactions :

Compiling OpenBSC with [E]GPRS

The guide below was tested on Ubuntu 15.10 but should work on Debian as well.

First you need to download all dependencies:

apt install libdbi0-dev libdbd-sqlite3 libtool autoconf git-core pkg-config make libortp-dev

Please follow instructions provided at Build from source in order to install these projects:

  • openggsn
  • libosmocore
  • libosmo-abis
  • libosmo-netif
  • openbsc
  • osmo-pcu

OpenBSC configuration

The first step is to configure OpenBSC for gprs support. Add this to the network/bts node in openbsc.cfg:

gprs mode gprs
gprs routing area 0
gprs cell bvci 2
gprs nsei 101
gprs nsvc 0 nsvci 101
gprs nsvc 0 local udp port 23000
gprs nsvc 0 remote udp port 23000
gprs nsvc 0 remote ip

The gprs nsvc 0 remote entries is the IP/port of the machine running the SGSN as seen from the BTS. It will be sent by OpenBSC to the BTS in the configration phase and the BTS will connect back to the SGSN.

The second step is to allocate some timeslots to packet data. For this, just change the 1 or more network/bts/trx/timeslot nodes using :

phys_chan_config PDCH

OsmoSGSN configuration

Here's a sample SGSN configuration file osmo-sgsn.cfg with some explanations :

! Osmocom SGSN configuration
line vty
 no login
 gtp local-ip
 ggsn 0 remote-ip
 ggsn 0 gtp-version 1
 timer tns-block 3
 timer tns-block-retries 3
 timer tns-reset 3
 timer tns-reset-retries 3
 timer tns-test 30
 timer tns-alive 3
 timer tns-alive-retries 10
 encapsulation udp local-ip
 encapsulation udp local-port 23000
 encapsulation framerelay-gre enabled 0
  • The gtp local-ip entry is the local IP the SGSN will bind to.
  • The ggsn 0 remote-ip entry if the remote IP of the GGSN. The SGSN will connect to it.
  • Those two IPs must be different even if you're running both processes on the same machine. A solution for that is to put several IP aliases on the same network interface or use the loopback interface.
  • The encapsulation settings must be the same IP/port than you've setup in openbsc.cfg

OpenGGSN configuration

The ggsn.conf file is pretty well documented. What is mostly of interest here is :

  • The configuration of the GTP link. (Must match the ggsn 0 remote-ip entry in osmo-sgsn.cfg)
# TAG: listen
# Specifies the local IP address to listen to
  • The configuration given to phones, IP pool & DNS.
# TAG: dynip
# Dynamic IP address pool.
# Used for allocation of dynamic IP address when address is not given
# by HLR.
# If this option is not given then the net option is used as a substitute.
# dynip

# TAG: pcodns1/pcodns2
# Protocol configuration option domain name system server 1 & 2.

OsmoPCU configuration

 flow-control-interval 10
 cs 2
 alloc-algorithm dynamic
 alpha 0
 gamma 0

Network configuration

You will also need to configure some networking rules to allow connectivity from tun0. Look up linux networking/nat howtos on google.
The basic setup for testing only in a safe environment would be :

bash# echo 1 > /proc/sys/net/ipv4/ip_forward
bash# iptables -A POSTROUTING -s -t nat -o eth0 -j MASQUERADE

(replace eth0 by the interface providing your machine connectivity)

In some cases the DNS server might be hardcoded in the phones APN settings. To work around this problem one might choose to enforce the usage of a specific DNS server by redirecting all DNS traffic via iptables:

bash# iptables -t nat -I PREROUTING -i tun0 -p udp --dport 53 -j DNAT --to-dest

(replace with the ip-address of your DNS-Server)


Sample startup sequence (adjust logging and configuration files location as you see fit):

osmo-nitb -s -c ~/.config/osmocom/open-bsc.cfg -l ~/.config/osmocom/hlr.sqlite3 -P -m -C -T --debug=DSQL:DLSMS:DRLL:DCC:DMM:DRR:DMSC:DHO:DGPRS:DNS:DLLC:DCTRL 2>&1 | tee /tmp/openbsc.log
sudo ggsn -c ~/.config/osmocom/ggsn.conf -f -d
osmo-sgsn -c ~/.config/osmocom/osmo-sgsn.cfg -d DRLL:DCC:DMM:DRR:DNM:DMSC:DHO:DGPRS:DNS:DLLC:DCTRL

cd osmo-trx/Transceiver52M
sudo chrt 20 ./osmo-trx
cd osmo-bts/src/osmo-bts-trx
sudo chrt 15 ./osmobts-trx -c ~/.config/osmocom/osmo-bts.cfg -i -d DRLL:DCC:DMM:DRR:DNM:DMSC:DHO:DGPRS:DNS:DLLC:DCTRL

sudo ./osmo-pcu -c ~/.config/osmocom/osmo-pcu.cfg

Note: OsmoTRX is only necessary with USRP/UmTRX transceivers (At the time of writing 201509-fairwaves-rebase branch of OsmoBTS is necessary as well for compatibility).

Once you're done with experimenting and ready for production setup it might be convenient to create systemd units so all the parts are started automatically.


  • double-check that your phones have APN set to something. "Internet" will do for example. The value of APN is not checked but if it's unset the phones' baseband might not even try to initiate GPRS connection.
  • check that NAT and packet forwarding works properly. Something like this:

Description=Expose GGSN's connected mobiles to Internet

might be necessary for systemd-networkd. You can access vty from

gprs.png - General GPRS setup (26 KB) tnt, 06/10/2010 01:35 PM

gprs.2.png (26.1 KB) sylvain, 01/12/2012 10:47 AM

gprs_example_config.tar - complete set of config files including README for working GPRS data service (20 KB) neels, 10/06/2016 07:50 PM