OpenBSC GPRS » History » Revision 30
Revision 29 (laforge, 02/20/2017 04:46 PM) → Revision 30/37 (neels, 02/24/2017 03:39 PM)
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h1. [[OpenBSC:]] GPRS/EDGE Setup page
h2. Pre-requisites
* BTS hardware: [[openbsc:sysmoBTS]], USRP, [[UmTRX:]], [[openbsc:nanoBTS]] with GPRS or EDGE support. [[openbsc:BS11]] are not supported.
* A compiled GGSN from [[OpenGGSN:]]
* A working and up-to-date [[OpenBSC:]] (see [[openbsc: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 (recommended)
*** Depending on your authorization policy (see [[OsmoSGSN:]] user manual), it may refuse inbound roaming. It is easiest if you have a SIM that matches your custom MCC/MNC network
h2. Setup
First a little picture to illustrate the different elements and their interactions :
!gprs.2.png!
h3. 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:
<pre>
apt install libdbi0-dev libdbd-sqlite3 libtool autoconf git-core pkg-config make libortp-dev
</pre>
Please follow instructions provided at [[Build from source]] in order to install these projects:
* openggsn
* libosmocore
* libosmo-abis
* libosmo-netif
* openbsc
* osmo-pcu
h3. [[OpenBSC:]] configuration
The first step is to configure [[OpenBSC:]] for gprs support. Add this to the @network/bts@ node in @openbsc.cfg@:
<pre>
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
</pre>
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 configuration 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 :
<pre>
phys_chan_config PDCH
</pre>
h3. [[OsmoSGSN:]] configuration
Here's a sample SGSN configuration file @osmo-sgsn.cfg@ with some explanations :
<pre>
!
! 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
!
</pre>
* 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@
h3. [[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@)
<pre>
# TAG: listen
# Specifies the local IP address to listen to
listen 192.168.1.129
</pre>
* The configuration given to phones, IP pool & DNS.
<pre>
# 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
</pre>
h3. [[OsmoPCU:]] configuration
<pre>
pcu
flow-control-interval 10
cs 2
alloc-algorithm dynamic
alpha 0
gamma 0
</pre>
h3. Network configuration
You will also need to configure some networking rules to allow connectivity from @tun0@. Look up linux networking/nat howtos on google.
h4. Modern systems
Add following setting to /etc/systemd/network:
wired.network:
<pre>
[Match]
Name=enp2s0
[Network]
DHCP=ipv4
IPMasquerade=yes
</pre>
tun.network:
<pre>
[Match]
Name=tun0
[Network]
Address=192.168.0.1
IPMasquerade=yes
</pre>
The setup above assume that you're using interface *enp2s0* to access the internet from the machine which runs openggsn. Notice the *IPMasquerade* option on both interfaces. This also assume the default 192.168.0.1/24 ip address range used by openggsn. If your situation differs - adjust accordingly using https://www.freedesktop.org/software/systemd/man/systemd.network.html as a reference.
h4. Legacy systems
The basic setup for testing only in a safe environment would be :
<pre>
sh# echo 1 > /proc/sys/net/ipv4/ip_forward
sh# iptables -A POSTROUTING -s 192.168.254.0/24 -t nat -o eth0 -j MASQUERADE
</pre>
(replace @eth0@ by the interface providing your machine connectivity)
h4. DNS issues
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:
<pre>
sh# iptables -t nat -I PREROUTING -i tun0 -p udp --dport 53 -j DNAT --to-dest 1.2.3.4
</pre>
(replace @1.2.3.4@ with the ip-address of your DNS-Server)
You can put this into .sh file and reference it from openggsn config using
<pre>
ipup /full/path/to/your.sh
</pre>
h2. Running
Sample startup sequence (adjust logging and configuration files location as you see fit):
<pre>
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
</pre>
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.
h2. Authorization Policy
Authorization determines whether a particular subscriber can access
your network or not.
The following 4 authorization policy options are available:
** @accept-all@: All IMSIs will be accepted.
** @acl-only@: Accept only IMSIs, which are explicitly white-listed by the Access Control List (ACL), and the rest will be rejected.
** @closed@: Accept only home network subscribers. The combination of MCC and MNC fully identifies subscriber's Home network. The ACL is also heeded.
** @remote@: GSUP protocol is uesed to remotely access a HLR. Only remote subscription data will be used.
Example: Assign or change authorization policy:
<pre>
OsmoSGSN> enable
OsmoSGSN# configure terminal
OsmoSGSN(config)# sgsn
OsmoSGSN(config-sgsn)# auth-policy acl-only
OsmoSGSN(config-sgsn)# write
Configuration saved to sgsn.cfg
OsmoSGSN(config-sgsn)# exit
OsmoSGSN(config)# exit
OsmoSGSN# disable
OsmoSGSN>
</pre>
In the example acl-only is selected as authorization policy.
After this we are saving current changes to configuration file using command @write@ to make this policy persistent.
h2. 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.
You can access vty from
* [[OsmoNITB:]] on port 4242 See [[osmonitb:osmo-nitb_VTY]]
* [[OsmoSGSN:]] on port 4245. See [[osmosgsn:osmo-sgsn_VTY]]
h3. wireshark dissector for GPRS / GMM messages
In wireshark's default configuration, GMM messages show merely as UDP packets without being decoded.
(port 23000 going between the SGSN and PCU, see [[cellular infrastructure:Port Numbers]])
* Right-click on such a packet to open the context menu,
* _Decode as..._
* _GPRS-NS_
