wiki:OpenBSC_GPRS

OpenBSC GPRS/EDGE Setup page

Pre-requisites

  • SDR transceiver: SysmoBTS, USRP, UmTRX, nano BTS with GPRS or EDGE support. BS-11 are not supported.
  • A compiled GGSN from OpenGGSN (make sure to use the osmocom version. git://git.osmocom.org/openggsn.git )
  • 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 osmo-sgsn refuses all roaming, so you need a SIM that matches your custom MCC/MNC network

Setup

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

Next, download the OpenGGSN source code:

git clone git://git.osmocom.org/openggsn.git

Compile OpenGGSN:

cd openggsn
dpkg-buildpackage -tc -uc -us
sudo dpkg -i ../*.deb

Now download everything else:

git clone git://git.osmocom.org/libosmocore; git clone git://git.osmocom.org/libosmo-abis; git clone git://git.osmocom.org/libosmo-netif; git clone git://git.osmocom.org/openbsc

Compile the rest:

cd libosmocore; dpkg-buildpackage -tc -uc -us; sudo dpkg -i ../*.deb
cd libosmo-abis; dpkg-buildpackage -tc -uc -us; sudo dpkg -i ../*.deb
cd libosmo-netif; dpkg-buildpackage -tc -uc -us; sudo dpkg -i ../*.deb
cd openbsc/openbsc; dpkg-buildpackage -tc -uc -us; sudo dpkg -i ../*.deb

You should now have a working copy of ggsn, osmo-sgsn and osmo-nitb on your machine. You will also need OsmoPCU:

git clone git://git.osmocom.org/osmo-pcu 
autoreconf -if
./configure
make

It can be executed in-place - no installation necessary.

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 192.168.0.128

The gprs nsvc 0 remote entries 192.168.0.128:23000 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

Osmocom SGSN configuration

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

!
! Osmocom SGSN configuration
!
!
line vty
 no login
!
sgsn
 gtp local-ip 192.168.1.128
 ggsn 0 remote-ip 192.168.1.129
 ggsn 0 gtp-version 1
!
ns
 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 192.168.0.128
 encapsulation udp local-port 23000
 encapsulation framerelay-gre enabled 0
!
bssgp
!
  • 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
listen 192.168.1.129
  • 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 192.168.254.0/24

# TAG: pcodns1/pcodns2
# Protocol configuration option domain name system server 1 & 2.
pcodns1 208.67.222.222
pcodns2 208.67.220.220

OsmoPCU configuration

pcu
 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 192.168.254.0/24 -t nat -o eth0 -j MASQUERADE

(replace eth0 by the interface providing your machine connectivity)

Running

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 224.0.0.1 -d DRLL:DCC:DMM:DRR:DNM:DMSC:DHO:DGPRS:DNS:DLLC:DCTRL

osmo-pcu/src
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.

Troubleshooting

  • 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:
[Match]
Name=tun*

[Network]
Description=Expose GGSN's connected mobiles to Internet
IPForward=ipv4
IPMasquerade=yes
Address=192.168.0.1

might be necessary for systemd-networkd.

You can access vty from

Last modified 8 weeks ago Last modified on Dec 13, 2015, 11:18:30 PM

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