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2019/20/21 updated version of 'running osmocom gsm'

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Harald Welte 2021-09-29 00:34:22 +02:00
parent e04fbfa698
commit 68b4a1cb8c
12 changed files with 26228 additions and 0 deletions
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graph G {
rankdir=LR;
MS0 [label="MS",shape=box]
MS1 [label="MS",shape=box]
MS2 [label="MS",shape=box]
MS0--PHY [label="Um"]
MS1--PHY [label="Um"]
MS2--PHY [label="Um"]
subgraph cluster_0 {
label = "sysmoBTS (all-in-one)"
OsmoBTS
OsmoPCU [style="dashed"]
PHY -- OsmoBTS [label="shmem msgq"]
PHY -- OsmoPCU [label="shmem msgq"]
OsmoPCU -- OsmoBTS [label="pcu_sock"]
{ rank=same; OsmoBTS OsmoPCU }
OsmoBSC
OsmoMSC
OsmoHLR
OsmoSGSN [style="dashed"]
OsmoGGSN [style="dashed"]
OsmoBTS -- OsmoBSC [label="Abis/IP\n(lo)"]
OsmoPCU -- OsmoSGSN [label="Gb/IP\n(lo)"]
OsmoSGSN -- OsmoGGSN [label="Gn/IP\n(lo)"]
OsmoBSC -- OsmoMSC [label="A/IP\n(lo)"]
OsmoMSC -- OsmoHLR [label="GSUP/IP\n(lo)"]
{ rank=same; OsmoMSC OsmoSGSN }
}
}

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graph G {
rankdir=LR;
MS0 [label="MS",shape=box]
MS1 [label="MS",shape=box]
MS2 [label="MS",shape=box]
MS0--PHY [label="Um"]
MS1--PHY [label="Um"]
MS2--PHY [label="Um"]
subgraph cluster_0 {
label = "sysmoBTS"
OsmoBTS
OsmoPCU [style="dashed"]
PHY -- OsmoBTS [label="shmem msgq"]
PHY -- OsmoPCU [label="shmem msgq"]
OsmoPCU -- OsmoBTS [label="pcu_sock"]
{ rank=same; OsmoBTS OsmoPCU }
}
subgraph cluster_1 {
label = "Linux PC"
OsmoBSC
OsmoMSC
OsmoHLR
OsmoSGSN [style="dashed"]
OsmoGGSN [style="dashed"]
OsmoBTS -- OsmoBSC [label="Abis/IP"]
OsmoBSC -- OsmoMSC [label="A/IP"]
OsmoMSC -- OsmoHLR [label="GSUP/IP"]
OsmoPCU -- OsmoSGSN [label="Gb/IP"]
OsmoSGSN -- OsmoGGSN [label="Gn/IP"]
{ rank=same; OsmoMSC OsmoSGSN }
}
}

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graph G {
rankdir=LR;
MS0 [label="MS",shape=box]
MS1 [label="MS",shape=box]
MS2 [label="MS",shape=box]
USRP [label="USRP Bxxx",shape=box]
USRP -- OsmoTRX [label="USB"]
MS0--USRP [label="Um"]
MS1--USRP [label="Um"]
MS2--USRP [label="Um"]
subgraph cluster_0 {
label = "Linux PC (all-in-one)"
OsmoTRX
OsmoBTS
OsmoPCU [style="dashed"]
OsmoPCU -- OsmoBTS [label="pcu_sock"]
OsmoTRX -- OsmoBTS [label="UDP"]
{ rank=same; OsmoBTS OsmoPCU }
OsmoBSC
OsmoMSC
OsmoHLR
OsmoSGSN [style="dashed"]
OsmoGGSN [style="dashed"]
OsmoBTS -- OsmoBSC [label="Abis/IP\n(lo)"]
OsmoBSC -- OsmoMSC [label="A/IP\n(lo)"]
OsmoMSC -- OsmoHLR [label="GSUP/IP\n(lo)"]
OsmoPCU -- OsmoSGSN [label="Gb/IP\n(lo)"]
OsmoSGSN -- OsmoGGSN [label="Gn/IP\n(lo)"]
{ rank=same; OsmoMSC OsmoSGSN }
}
}

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graph G {
rankdir=LR;
MS0 [label="MS",shape=box]
MS1 [label="MS",shape=box]
MS2 [label="MS",shape=box]
USRP [label="USRP Bxxx",shape=box]
USRP --OsmoTRX [label="USB"]
MS0--USRP [label="Um"]
MS1--USRP [label="Um"]
MS2--USRP [label="Um"]
subgraph cluster_0 {
label = "Linux PC (BTS)"
OsmoTRX
OsmoBTS
OsmoPCU [style="dashed"]
OsmoPCU -- OsmoBTS [label="pcu_sock"]
OsmoTRX -- OsmoBTS
{ rank=same; OsmoBTS OsmoPCU }
}
subgraph cluster_1 {
label = "Linux PC (Core)"
OsmoBSC
OsmoMSC
OsmoHLR
OsmoSGSN [style="dashed"]
OsmoGGSN [style="dashed"]
OsmoBTS -- OsmoBSC [label="Abis/IP"]
OsmoBSC -- OsmoMSC [label="A/IP"]
OsmoMSC -- OsmoHLR [label="GSUP/IP"]
OsmoPCU -- OsmoSGSN [label="Gb/IP"]
OsmoSGSN -- OsmoGGSN [label="Gn/IP"]
{ rank=same; OsmoMSC OsmoSGSN }
}
}

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Running a basic Osmocom GSM network
===================================
:author: Harald Welte <laforge@gnumonks.org>
:copyright: sysmocom - s.f.m.c. GmbH (License: CC-BY-SA)
:backend: slidy
:max-width: 45em
//:data-uri:
//:icons:
== What this talk is about
[role="incremental"]
* 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
[role="incremental"]
- 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?
[role="incremental"]
- 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
[role="incremental"]
** 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
image::Gsm_structures.svg[width=850]
== 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
image::osmocom-cni.png[width=850]
== Classic GSM network as digraph
[graphviz]
----
digraph G {
rankdir=LR;
MS0 [label="MS"]
MS1 [label="MS"]
MS2 [label="MS"]
MS3 [label="MS"]
BTS0 [label="BTS"]
BTS1 [label="BTS"]
MSC [label="MSC/VLR"]
HLR [label="HLR/AUC"]
MS0->BTS0 [label="Um"]
MS1->BTS0 [label="Um"]
MS2->BTS1 [label="Um"]
MS3->BTS1 [label="Um"]
BTS0->BSC [label="Abis"]
BTS1->BSC [label="Abis"]
BSC->MSC [label="A"]
MSC->HLR [label="C"]
MSC->EIR [label="F"]
MSC->SMSC
}
----
== Osmocom GSM network
[graphviz]
----
digraph G {
rankdir=LR;
MS0 [label="MS"]
MS1 [label="MS"]
MS2 [label="MS"]
MS3 [label="MS"]
BTS0 [label="OsmoBTS"]
BTS1 [label="OsmoBTS"]
MS0->BTS0 [label="Um"]
MS1->BTS0 [label="Um"]
MS2->BTS1 [label="Um"]
MS3->BTS1 [label="Um"]
BTS0->BSC [label="Abis"]
BTS1->BSC [label="Abis"]
subgraph cluster_cni {
label = "Osmocom CNI";
BSC [label="OsmoBSC"]
MSC [label="OsmoMSC (SMSC inside)"]
HLR [label="OsmoHLR"]
BSC->MSC [label="AoIP"]
MSC->HLR [label="GSUP"]
}
}
----
== 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
image::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)
[graphviz]
----
include::arch-sysmobts.dot[]
----
[graphviz]
----
include::arch-sysmobts-allinone.dot[]
----
== Physical vs. Logical Arch (SDR e.g. USRP B2xx)
[graphviz]
----
include::arch-usrp.dot[]
----
[graphviz]
----
include::arch-usrp-allinone.dot[]
----
== 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> the unit-id by which this BTS identifies itself to the BSC
<3> the IP address of the BSC (to establish the OML connection towards it)
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
[graphviz]
----
graph G {
rankdir=LR;
BTS0 [label="BTS\nUnit 5/0[/0]"]
BTS1 [label="BTS\nUnit 23/0[/0]"]
BTS2 [label="BTS\nUnit 42/0[/0]"]
NAT
BSC [label="BSC/NITB"]
BTS0 -- NAT [label="10.9.23.5"]
BTS1 -- NAT [label="10.9.23.23"]
BTS2 -- NAT [label="10.9.23.42"]
NAT -- BSC [label="172.16.23.42"]
}
----
* 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
** asciidoc is part of the source
** PDF renderings at https://downloads.osmocom.org/docs/latest/
== 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
|===
* https://osmocom.org/projects/cellular-infrastructure/wiki/Port_Numbers
* ports are bound to 127.0.0.1 by default
** can be bound to other IPs or ANY via config file
* try tab-completion, `?` and `list` commands
== 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!
[role="incremental"]
* 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

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