Getting Started with 3G » History » Revision 9
Revision 8 (neels, 03/03/2017 12:14 AM) → Revision 9/52 (neels, 03/03/2017 12:15 AM)
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h1. Getting Started with 3G
_This reflects the state of Osmocom 3G development on 2017-02-24_
If you have your 3G femto cell[1], this is how to get started:
The physical setup is:
<pre>
_____________ _____________
| | | |
| femto |<--Ethernet-->| Laptop/PC |
|___________| |___________|
</pre>
On the protocol layer, the femto cell is the hNodeB and talks to various core
network elements over the ethernet cable, typically all located on your
computer, and talks to the phone (UE) over the air:
<pre>
+--------+
,-->| Osmo |
/ | MGCPGW |
| | |<--MGCP
| +--------+ \
/ |
+------------+<--RTP +--------+ `->+----------+
UE <-->| hNodeB | | Osmo | | OsmoMSC | +------+
UE <-->| |<--Iuh---->| HNB-GW |<--IuCS-->| | | Osmo |
| | | | | (VLR)|<-GSUP->| HLR |
| | | | +----------+ GSUP->+------+
+------------+<--GTP-U | | /
\ | | +------+<---' +------+
| | |<--IuPS-->| Osmo |<--GTP-C--->| Open |
| +--------+ | SGSN | GTP-U--->| GGSN |
| +------+ / +------+
\_______________________________/
</pre>
h1. Core Network
To get your 3G core network up and running, you need to manually build specific
branches from various Osmocom projects:
* libosmocore: master
* libosmo-abis: master
* libosmo-netif: sysmocom/sctp
* libosmo-sccp: sysmocom/iu
* libsmpp34: master
* asn1c: aper-prefix-onto-upstream
* libasn1c: master
* osmo-iuh: master
* openggsn: master
* openbsc: sysmocom/iu -- *DISCLAIMER!* This branch is not yet capable of talking to OsmoHLR and thus no true UMTS (3G) Authentication is possible yet; should be coming soon.
* osmo-hlr: master
See [[Build from Source]] on build instructions; the git command to get onto a
branch other than 'master' is:
<pre>
git checkout the_branch_name
</pre>
Once the CN stack is built, set up the configuration and launch the core
network components. Find further below example configuration files and a run
script that may help to get you started. Here are some details explained:
Tell the osmo-hnbgw which local IP address to use to listen for Iuh
connections. This needs to be on an interface reachable by the hNodeB. The IuCS
and IuPS links towards the osmo-msc and osmo-sgsn default to 127.0.0.1 and
127.0.0.2, respectively, i.e. it's easiest to run osmo-msc and osmo-sgsn on
the same machine as the osmo-hnbgw. These will listen on the proper port
(14001) without further configuration.
Also tell the MGCPGW (osmo-bsc_mgcp) which local IP address to bind to, which
has to be reachable both by the hNodeB as well as the osmo-msc process. The
osmo-msc.cfg is then told where to reach the MGCPGW.
A notable detail for 3G data is that the GGSN has to be reachable by the
hNodeB. Since the GTP standard defines fixed port numbers which both SGSN and
GGSN have to to use, the SGSN may not bind on the same IP address as the GGSN!
Typically this requires to add another IP address to your ethernet interface.
On linux this is achieved, for example, by:
<pre>
sudo ip addr add 10.9.1.13/32 dev eth0
</pre>
The above adds the address 10.9.1.13 to eth0, which works e.g. when your
machine is in a 10.9.1.0/24 net and the address 10.9.1.13 is not yet taken by
anyone else. (You probably want to use something like 192.168.0.222 instead.)
Also, IP forwarding and masquerading must be enabled for your GGSN to be able
to connect to your mobile phones to the internet uplink. On linux, that can be
done for eth0 by:
<pre>
sudo sh -c "echo 1 > /proc/sys/net/ipv4/ip_forward"
sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
</pre>
You may need a different interface, possibly a wildcard like 'eth*'.
The GGSN needs permissions to create a @tun@ device, which @sudo@ will allow.
It may be safer though to allow your user to create tunnels instead of running
the GGSN as root.
If programs complain about missing library @.so@ files, you will probably need
to @export LD_LIBRARY_PATH=/usr/local/lib@. With sudo that would be @sudo
LD_LIBRARY_PATH=/usr/local/lib ggsn ...@, and you may need to add "SETENV" to
your sudoers config -- see the sudo documentation.
Once you have configured the IP addresses, start up your core network: launch
osmo-msc, osmo-bsc_mgcp, osmo-sgsn, ggsn and osmo-hnbgw. You should see log
messages indicating established IuCS and IuPS links (HNBGW, MSC and SGSN).
h2. Core Network Configuration Example
Here is a specific 3G core network configuration example, including a highly
specialized launcher script that configures the network (on a linux system) and
runs all the programs needed for a 3G core network -- but be aware:
*config:*
* This was run in a 192.168.0.1/24 subnet, yours may vary.
* Your femto cell will get itself an IP address from your DHCP server, which
will almost certainly differ from this example. You (so far still) need to
set this address in the mgcp.cfg.
* The ggsn.conf 'listen' address here is the additional interface (ala 'ip addr
add' above) and needs to match whichever address you picked there.
* Make sure all the other IP addresses in the config files match yours.
* Make sure the MCC and MNC match the ones configured in the femto cell.
*run.sh*:
* It assumes the Osmocom libs and programs to be installed in /usr/local/*.
* It launches each component in a separate X terminal.
* It uses rxvt-unicode, you may want to change the @urxvt@ call to your favorite xterm instead.
* Make sure the ethernet interface makes sense.
* Make sure the IP address makes sense.
* Run it in a directory where it will find the various configuration files.
* It runs most of the processes in a gdb for easier debugging.
* Once you hit Enter in the original terminal where you started, all the other
terminals will be torn down in one fell swoop (hopefully).
* *TODO* it doesn't launch osmo-hlr *TODO* (add once the 3G branch is rebased onto the VLR branch)
Now that you've taken notice of the points above, here are the config and
script: attachment:3G-config-example.tar
h1. Femto Config
With your CN up and running, configure the hNodeB to contact osmo-hnbgw via
Iuh. Also make sure the PLMN ID matches the MCC and MNC in the osmo-msc.cfg --
otherwise the hNodeB may reject all attach requests.
Depending on your femto cell, the steps to configure it will be radically
different:
* [[Configuring the ip.access nano3G]]
* ...
h1. Subscriber Configuration
For your phone loaded with your USIM to be able to subscribe to your network,
the IMSI needs to be authorized to enter and the authentication keys need to be
added to the HLR.
*TODO* currently, the sysmocom/iu branch has a hardcoded Ki of
000102030405060708090a0b0c0d0e0f, and you need a SIM card that offers only
non-UMTS pre-R99 authentication. We need to rebase the sysmocom/iu branch onto
the VLR development (neels/vlr) in order to enable full UMTS authentication and
so that sysmoUSIMs added to our OsmoHLR work with our 3G stack.
See [[Accelerate3G5 -- neels]] to read the latest progress.
h1. APN for Data Service
For the 3G data service to work, phones generally need an APN added to their
configuration, or they will not even attempt to establish a data connection.
For the Osmocom 3G CN, any arbitrary APN name will do.
The APN configuration steps are usually similar to:
* Navigate to APN settings:
** 'Settings'
** 'Wireless & Networks'
** 'Mobile networks'
** 'Access Point Names'
* You should see the list of APNs (possibly empty)
* Press the Menu button
* Choose 'New APN'
* Enter values for 'Name' as well as 'APN'
** For both, any nonempty value is sufficient, e.g. "test".
* Again press the Menu button
* Choose 'Save'
* The APN should now appear in the list of APNs.
* Possibly tap the bullet icon to select the APN as default.
h1. Further Links
The "3G Voice Works" blog post from 2016 has some explanations:
https://osmocom.org/news/59
With almost any question, you can go back to the 3GPP specs. Here is a list of which is for what:
* [[GSMStandards]]
* and [[Interesting3GPPSpecsForDevelopers]]
h1. Tips and Facts
h3. Analyzing RTP streams in wireshark
IuCS actually uses UP over RTP. See 3GPP TS 25.414, and 25.415 6.6.2.
(an interesting insight is https://www.ietf.org/mail-archive/web/avt/current/msg05907.html )
In the wireshark preferences, go to protocol IuUP, enable it and enter the dynamic protocol
number that you see in the RTP frames (e.g. 96).
h3. 3GPP Specs
With almost any question, you can go back to the 3GPP specs. Here is a list of which is for what:
* [[GSMStandards]]
* and [[Interesting3GPPSpecsForDevelopers]]
h1. Help
If you experience problems you may ask for assistance on our
"mailing list":https://lists.osmocom.org/mailman/listinfo/openbsc.
------
fn1. For details on obtaining suitable 3G hardware, you can ask at info@sysmocom.de
or on our "mailing list":https://lists.osmocom.org/mailman/listinfo/openbsc.
