From cec90c77924e749911ccba6abdd0e4a32b9904e1 Mon Sep 17 00:00:00 2001
From: Harald Welte <laforge@gnumonks.org>
Date: Tue, 25 Apr 2017 15:06:40 +0200
Subject: osmocon slides update

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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-gsm.svg[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
+}
+----
+
+== Simplified OsmoNITB GSM network
+
+[graphviz]
+----
+digraph G {
+	rankdir=LR;
+	MS0 [label="MS"]
+	MS1 [label="MS"]
+	MS2 [label="MS"]
+	MS3 [label="MS"]
+	BTS0 [label="BTS"]
+	BTS1 [label="BTS"]
+	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_nitb {
+		label = "OsmoNITB";
+		BSC
+		MSC [label="MSC/VLR"]
+		HLR [label="HLR/AUC"]
+		BSC->MSC [label="A"]
+		MSC->HLR [label="C"]
+		MSC->EIR [label="F"]
+		MSC->SMSC;
+	}
+}
+----
+
+which further reduces to the following minimal setup:
+
+[graphviz]
+----
+digraph G {
+	rankdir=LR;
+	MS0 [label="MS"]
+	BTS0 [label="BTS"]
+	MS0->BTS0 [label="Um"]
+	BTS0->BSC [label="Abis"]
+	BSC [label="OsmoNITB"];
+}
+----
+
+So our minimal setup is a 'Phone', a 'BTS' and 'OsmoNITB'.
+
+== 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 OsmoNITB
+
+* 'OsmoNITB' is the `osmo-nitb` executable built from the `openbsc`
+  source tree / git repository
+** just your usual `git clone && autoreconf -fi && ./configure && make install`
+** (in reality, the `libosmo*` dependencies are required first...)
+** nightly packages for Debian 8, Ubuntu 16.04 and 16.10 available
+* 'OsmoNITB' 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 OsmoNITB
+
+----
+network
+ network country code 1 <1>
+ mobile network code 1 <2>
+ short name Osmocom <3>
+ long name Osmocom
+ auth policy closed <4>
+ encryption a5 0 <5>
+----
+<1> MCC (Country Code) e.g. 262 for Germany; 1 == Test
+<2> MNC (Network Code) e.g. mcc=262, mnc=02 == Vodafone; 1 == Test
+<3> Operator name to be sent to the phone *after* registration
+<4> Only accept subscribers (SIM cards) explicitly authorized in HLR
+<5> Use A5/0 (== no encryption)
+
+
+== Configuring BTS in OsmoNITB (BTS)
+
+----
+network
+ bts 0
+  type sysmobts <1>
+  band DCS1800 <2>
+  ms max power 33 <3>
+  periodic location update 6 <4>
+  ip.access unit_id 1801 0 <5>
+  codec-support fr hr efr amr <6>
+----
+<1> type of the BTS that we use (must match BTS)
+<2> frequency band of the BTS (must match BTS)
+<3> maximum transmit power phones are permitted (33 dBm == 2W)
+<4> interval at which phones should send periodic location update (6 minutes)
+<5> Unit ID of the BTS (must match BTS)
+<6> Voice codecs supported by the BTS
+
+
+== Configuring BTS in OsmoNITB (TRX)
+
+----
+network
+ bts 0
+  trx 0
+   arfcn 871 <1>
+   max_power_red 0 <2>
+   timeslot 0
+    phys_chan_config CCCH+SDCCH4 <3>
+   timeslot 1
+    phys_chan_config TCH/F <4>
+    ...
+   timeslot 7
+    phys_chan_config PDCH <5>
+----
+<1> The RF channel number used by this TRX
+<2> The maximum power *reduction* in dBm. 0 = no reduction
+<3> Every BTS needs need one timeslot with a CCCH
+<4> We configure TS1 to TS6 as TCH/F for voice
+<5> We configure TS6 as PDCH for GPRS
+
+
+== 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 stderr of 'OsmoBTS' and 'OsmoNITB'
+** '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
+|OsmoPCU|4240
+|OsmoBTS|4241
+|OsmoNITB|4242
+|OsmoSGSN|4245
+|===
+* ports are bound to 127.0.0.1 by default
+* try tab-completion, `?` and `list` commands
+
+== Using the VTY (continued)
+
+* e.g. `show subsciber` to display data about subscriber:
+----
+OpenBSC> show subscriber imsi 901700000003804
+    ID: 12, Authorized: 1
+    Extension: 3804
+    LAC: 0/0x0
+    IMSI: 901700000003804
+    TMSI: F2D4FA0A
+    Expiration Time: Mon, 07 Dec 2015 09:45:16 +0100
+    Paging: not paging Requests: 0
+    Use count: 1
+----
+
+* try `show bts`, `show trx`, `show lchan`, `show statistics`, ...
+
+== Further Reading
+
+User Manuals::
+See http://ftp.osmocom.org/docs/latest/
+Wiki::
+See http://osmocom.org/projects/openbsc
+
+== 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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