From 68b4a1cb8c58a1584b26ccc405c8320f1df00acf Mon Sep 17 00:00:00 2001 From: Harald Welte Date: Wed, 29 Sep 2021 00:34:22 +0200 Subject: 2019/20/21 updated version of 'running osmocom gsm' --- 2021/running_osmo_gsm-2021/running-osmo-gsm.html | 4923 ++++++++++++++++++++++ 1 file changed, 4923 insertions(+) create mode 100644 2021/running_osmo_gsm-2021/running-osmo-gsm.html (limited to '2021/running_osmo_gsm-2021/running-osmo-gsm.html') diff --git a/2021/running_osmo_gsm-2021/running-osmo-gsm.html b/2021/running_osmo_gsm-2021/running-osmo-gsm.html new file mode 100644 index 0000000..31dd73e --- /dev/null +++ b/2021/running_osmo_gsm-2021/running-osmo-gsm.html @@ -0,0 +1,4923 @@ + + + + +Running a basic Osmocom GSM network + + + + + + + + +
+

What this talk is about

+
+
    +
  • + +Implementing GSM/GPRS network elements as FOSS + +
    • +
  • + +Applied Protocol Archaeology + +
    • +
  • + +Doing all of that on top of Linux (in userspace) + +
    • +
+
+
+
+

Running your own Internet-style network

+
+
    +
  • + +use off-the-shelf hardware (x86, Ethernet card) + +
    • +
  • + +use any random Linux distribution + +
    • +
  • + +configure Linux kernel TCP/IP network stack + +
      +
    • + +enjoy fancy features like netfilter/iproute2/tc + +
      • +
    +
    • +
  • + +use apache/lighttpd/nginx on the server + +
    • +
  • + +use Firefox/chromium/konqueor/lynx on the client + +
    • +
  • + +do whatever modification/optimization on any part of the stack + +
    • +
+
+
+
+

Running your own GSM network

+
+

Until 2009 the situation looked like this:

+
    +
  • + +go to Ericsson/Huawei/ZTE/Nokia/Alcatel/… + +
    • +
  • + +spend lots of time convincing them that you’re an eligible customer + +
    • +
  • + +spend a six-digit figure for even the most basic full network + +
    • +
  • + +end up with black boxes you can neither study nor improve + +
      +
    • + +WTF? + +
      • +
    • + +I’ve grown up with FOSS and the Internet. I know a better world. + +
      • +
    +
    • +
+
+
+
+

Why no cellular FOSS?

+
+
    +
  • + +both cellular (2G/3G/4G) and TCP/IP/HTTP protocol specs are publicly + available for decades. Can you believe it? + +
    • +
  • + +Internet protocol stacks have lots of FOSS implementations + +
    • +
  • + +cellular protocol stacks have no FOSS implementations for the + first almost 20 years of their existence? + +
    • +
  • + +it’s the classic conflict + +
      +
    • + +classic circuit-switched telco vs. the BBS community + +
      • +
    • + +ITU-T/OSI/ISO vs. Arpanet and TCP/IP + +
      • +
    +
    • +
+
+
+
+

Enter Osmocom

+
+

In 2008, some people (most present in this room) started to write FOSS +for GSM

+
    +
  • + +to boldly go where no FOSS hacker has gone before + +
      +
    • + +where protocol stacks are deep + +
      • +
    • + +and acronyms are plentiful + +
      • +
    • + +we went from bs11-abis to bsc_hack to OpenBSC + +
      • +
    • + +many other related projects were created + +
      • +
    • + +finally leading to the Osmocom umbrella project + +
      • +
    +
    • +
+
+
+
+

Classic GSM network architecture

+
+
+
+Gsm_structures.svg +
+
+
+
+
+

GSM Acronyms, Radio Access Network

+
+
+
+MS +
+
+

+ Mobile Station (your phone) +

+
+
+BTS +
+
+

+ Base Transceiver Station, consists of 1..n TRX +

+
+
+TRX +
+
+

+ Transceiver for one radio channel, serves 8 TS +

+
+
+TS +
+
+

+ Timeslots in the GSM radio interface; each runs a specific combination of logical channels +

+
+
+BSC +
+
+

+ Base Station Controller +

+
+
+
+
+
+

GSM Acronyms, Core Network

+
+
+
+MSC +
+
+

+ Mobile Switching Center; Terminates MM + CC Sub-layers +

+
+
+HLR +
+
+

+ Home Location Register; Subscriber Database +

+
+
+SMSC +
+
+

+ SMS Service Center +

+
+
+
+
+
+

GSM Acronyms, Layer 2 + 3

+
+
+
+LAPDm +
+
+

+ Link Access Protocol, D-Channel. Like LAPD in ISDN +

+
+
+RR +
+
+

+ Radio Resource (establish/release dedicated channels) +

+
+
+MM +
+
+

+ Mobility Management (registration, location, authentication) +

+
+
+CC +
+
+

+ Call Control (voice, circuit switched data, fax) +

+
+
+CM +
+
+

+ Connection Management +

+
+
+
+
+
+

Osmocom GSM components

+
+
+
+osmocom-cni.png +
+
+
+
+
+

Classic GSM network as digraph

+
+
+
+running-osmo-gsm__1.png +
+
+
+
+
+

Osmocom GSM network

+
+
+
+running-osmo-gsm__2.png +
+
+
+
+
+

Which BTS to use?

+
+
    +
  • + +Proprietary BTS of classic vendor + +
      +
    • + +Siemens BS-11 is what we started with + +
      • +
    • + +Nokia, Ericsson, and others available 2nd hand + +
      • +
    +
    • +
  • + +OsmoBTS software implementation, running with + +
      +
    • + +Proprietary HW + PHY (DSP): sysmoBTS, or + +
      • +
    • + +General purpose SDR (like USRP) + OsmoTRX + +
      • +
    +
    • +
+

We assume a sysmoBTS in the following tutorial

+
+
+
+

OsmoBTS Overview

+
+
+
+osmo-bts.svg +
+
+
    +
  • + +Implementation of GSM BTS + +
    • +
  • + +supports variety of hardware/PHY options + +
      +
    • + +osmo-bts-sysmo: BTS family by sysmocom + +
      • +
    • + +osmo-bts-trx: Used with OsmoTRX + general-purpose SDR + +
      • +
    • + +osmo-bts-octphy: Octasic OCTBTS hardware / OCTSDR-2G PHY + +
      • +
    • + +osmo-bts-litecell15: Nutaq Litecell 1.5 hardware/PHY + +
      • +
    +
    • +
+

See separate talk about BTS hardware options later today.

+
+
+
+

BTS Hardware vs. BTS software

+
+
    +
  • + +A classic GSM BTS is hardware + software + +
    • +
  • + +It has two interfaces + +
      +
    • + +Um to the radio side, towards phones + +
      • +
    • + +Abis to the wired back-haul side, towards BSC + +
      • +
    +
    • +
  • + +with today’s flexible architecture, this is not always true + +
      +
    • + +the hardware might just be a network-connected SDR and BTS software +runs o a different CPU/computer, or + +
      • +
    • + +the BTS and BSC, or even the NITB may run on the same board + +
      • +
    +
    • +
+
+
+
+

Physical vs. Logical Arch (sysmoBTS)

+
+
+
+running-osmo-gsm__3.png +
+
+
+
+running-osmo-gsm__4.png +
+
+
+
+
+

Physical vs. Logical Arch (SDR e.g. USRP B2xx)

+
+
+
+running-osmo-gsm__5.png +
+
+
+
+running-osmo-gsm__6.png +
+
+
+
+
+

IP layer traffic

+
+
    +
  • + +Abis/IP signaling runs inside IPA multiplex inside TCP + +
      +
    • + +Port 3002 and 3003 betewen BTS and BSC + +
      • +
    • + +Connections initiated from BTS to BSC + +
      • +
    +
    • +
  • + +Voice data is carried in RTP/UDP on dynamic ports + +
    • +
+

⇒ Make sure you permit the above communication in your +network/firewall config

+
+
+
+

Configuring Osmocom software

+
+
    +
  • + +all native Osmo* GSM infrastructure programs share common architecture, as + defined by various libraries libosmo{core,gsm,vty,abis,netif,…} + +
    • +
  • + +part of this is configuration handling + +
      +
    • + +interactive configuration via command line interface (vty), similar + to Cisco routers + +
      • +
    • + +based on a fork of the VTY code from Zebra/Quagga, now libosmovty + +
      • +
    +
    • +
  • + +you can manually edit the config file, + +
    • +
  • + +or use configure terminal and interactively change it + +
    • +
+
+
+
+

Configuring OsmoBTS

+
+
    +
  • + +OsmoBTS in our example scenario runs on the embedded ARM/Linux system + inside the sysmoBTS + +
    • +
  • + +we access the sysmoBTS via serial console or ssh + +
    • +
  • + +we then edit the configuration file /etc/osmocom/osmo-bts.cfg as + described in the following slide + +
    • +
+
+
+
+

Configuring OsmoBTS

+
+
+
+
bts 0
+ band DCS1800 <1>
+ ipa unit-id 1801 0 <2>
+ oml remote-ip 192.168.100.11 <3>
+
+
    +
  1. +

    +the GSM frequency band in which the BTS operates +

    +
    2. +
  2. +

    +the unit-id by which this BTS identifies itself to the BSC +

    +
    3. +
  3. +

    +the IP address of the BSC (to establish the OML connection towards it) +

    +
    4. +
+
+ + + +
+
Note
+		All other configuration is downloaded by the BSC via OML. So most +BTS settings are configured in the BSC/NITB configuration file.
+
+
+
+
+

Purpose of Unit ID

+
+
    +
  • + +Unit IDs consist of three parts: + +
      +
    • + +Site Number, BTS Number, TRX Number + +
      • +
    +
    • +
+
+
+running-osmo-gsm__7.png +
+
+
    +
  • + +source IP of all BTSs would be identical + +
    • +
+

⇒ BSC identifies BTS on Unit ID, not on Source IP!

+
+
+
+

Configuring Osmocom CNI

+
+
    +
  • + +Osmocom CNI is the collection of all the non-BTS Osmocom projects for 3GPP network operation, of which + the minimally required are osmo-bsc, osmo-msc and osmo-hlr. You also will need osmo-stp for SIGTRAN and osmo-mgw for user plane. + +
      +
    • + +just your usual git clone && autoreconf -fi && ./configure && make install + +
      • +
    • + +(in reality, the libosmo* dependencies are required first…) + +
      • +
    • + +nightly packages for Debian 9-11, buntu 19.x/20.x/21.x available + +
      • +
    +
    • +
  • + +runs on any Linux system, like your speakers' laptop + +
      +
    • + +you can actually also run it on the ARM/Linux of the sysmoBTS itself, + having a literal Network In The Box with power as only external + dependency + +
      • +
    +
    • +
+
+
+
+

Configuring Osmocom CNI

+
+
    +
  • + +each program has a config file + +
    • +
  • + +simple example given in doc/examples/osmo-*.cfg of each git repo + +
    • +
  • + +each program has a user manual and a VTY command reference manual + + +
    • +
+
+
+
+

What a GSM phone does after power-up

+
+
    +
  • + +Check SIM card for last cell before switch-off + +
      +
    • + +if that cell is found again, use that + +
      • +
    • + +if not, perform a network scan + +
        +
      • + +try to find strong carriers, check if they contain BCCH + +
        • +
      • + +create a list of available cells + networks + +
        • +
      • + +if one of the networks MCC+MNC matches first digits of IMSI, this is +the home network, which has preference over others + +
        • +
      +
      • +
    +
    • +
  • + +perform LOCATION UPDATE (TYPE=IMSI ATTACH) procedure to network + +
    • +
  • + +when network sends LOCATION UPDATE ACCEPT, camp on that cell + +
    • +
+

→ let’s check if we can perform LOCATION UPDATE on our own network

+
+
+
+

Verifying our network

+
+
    +
  • + +look at log output of Osmocom programs + +
      +
    • + +OsmoBTS will terminate if Abis cannot be set-up, expected to be re-spawned by init / systemd + +
      • +
    +
    • +
  • + +use MS to search for networks, try manual registration + +
    • +
  • + +observe registration attempts logging level mm info + +
    • +
+

→ should show LOCATION UPDATE request / reject / accept

+
    +
  • + +use the VTY to explore system state (show *) + +
    • +
  • + +use the VTY to change subscriber parameters like extension number + +
    • +
+
+
+
+

Exploring your GSM networks services

+
+
    +
  • + +use *#100# from any registered MS to obtain own number + +
    • +
  • + +voice calls from mobile to mobile + +
    • +
  • + +SMS from mobile to mobile + +
    • +
  • + +SMS to/from external applications (via SMPP) + +
    • +
  • + +voice to/from external PBX (via MNCC) + +
    • +
  • + +explore the VTY interfaces of all network elements + +
      +
    • + +send SMS from the command line + +
      • +
    • + +experiment with silent call feature + +
      • +
    • + +experiment with logging levels + +
      • +
    +
    • +
  • + +use wireshark to investigate GSM protocols + +
    • +
+
+
+
+

Using the VTY

+
+
    +
  • + +The VTY can be used not only to configure, but also to interactively + explore the system status (show commands) + +
    • +
  • + +Every Osmo* program has its own telnet port + +
    • +
+
+ +++ + + + + + + + + + + + + + + + + + + + + + +

Program

Telnet Port

OsmoBTS

4241

OsmoBSC

4242

OsmoMSC

4254

OsmoHLR

4258

+
+ +
+
+
+

Using the VTY (continued)

+
+
    +
  • + +context-sensitive command line interface like Cisco and many others + +
    • +
  • + +show commands to introspect + +
      +
    • + +try show bts, show trx, show lchan, show statistics, … + +
      • +
    +
    • +
  • + +enable + configure terminal for configuration mode + +
    • +
  • + +interactive reference, tab-completion + +
    • +
  • + +logging enable adds log target to VTY session + +
    • +
+
+
+
+

Further Reading

+
+
+
+User Manuals +
+
+

+See http://ftp.osmocom.org/docs/latest/ +

+
+
+Wiki +
+
+

+See https://osmocom.org/projects/cellular-infrastructure/wiki +

+
+
+
+
+
+

The End

+
+
    +
  • + +so long, and thanks for all the fish + +
    • +
  • + +I hope you have questions! + +
    • +
  • + +have fun exploring mobile technologies using Osmocom + +
    • +
  • + +interested in working with more acronyms? Come join the project! + +
    • +
  • + +Check out https://osmocom.org/ and openbsc@lists.osmocom.org + +
    • +
+
+
+ + -- cgit v1.2.3