How the CCC Camp 2019 LTE network works
=======================================
:author:	Harald Welte <laforge@gnumonks.org>
:copyright:	2019 by Harald Welte (License: CC-BY-SA)
:backend:	slidy
:max-width:	45em

== Intro

* we had GSM networks at CCC events since 2008
** Initially using proprietary, E1-attached Siemens BTS and OpenBSC (later OsmoBSC)
* we had GSM networks at European Hacker Camps since 2009 (HAR)
* we had UMTS (3G) for a few years now, too
** using Osmocom stack with OsmoHNBGW / OsmoMSC / OsmoSGSN

== LTE

* new network elements with new acronyms

[graphviz]
----
digraph {
  rankdir = LR;
  eNB -> MME [label="S1AP"];
  MME -> HSS [label="DIAMETER"];
  MME -> SGW [label="GTPv2C"];
  SGW -> PGW [label="GTPv2C"];
  PGW -> PCRF [label="DIAMETER"];
  eNB -> SGW [label="GTP-U"];
  SGW -> PGW [label="GTP-U"];

  { rank = same; HSS; PCRF; }
}
----

== LTE

* new protocols on all layers of all interfaces
** S1AP between eNodeB and MME
** GTPv2C between MME and SGW and SGW and PGW
** DIAMETER between everyone and HSS

== FOSS LTE software

* srsLTE for eNodeB and UE
** main focus on UE; eNodeB features somewhat limited
** super simplistic srsEPC suitable for only the scarcest of use cases
* OpenAirInterface
** obscure code base; difficult to build; "
** very research oriented
** RAN part under non-free, non-opensource but 'source available' license
* nextepc

== nextepc

* Implements all key LTE network (EPC) elements
** MME
** SGW
** PGW
** HSS
** PCRF

== interfacing with Osmocom 2G/3G core

* shared subscriber (and key) database
** LTE: HSS, speaking DIAMETER
** 2G/3G: HLR, speaking MAP (Osmocom:GSUP)
* We need a so-called 'inter-working function (IWF)
** translate from DIAMETER to GSUP and vice-versa

== osmo_dia2gsup

* Best FOSS DIAMETER support contained in Erlang/OTP
* Fairwaves contributed GSUP protocol codec in Erlang
* I wrote a translator for the two minimal procedures
** AuthInfo (Obtain authentication tuples)
** UpdateLocation (registration)

== Network layout

[graphviz]
----
digraph G {
  rankdir = LR;

  { rank = same; eNB0; eNB1; eNB2; eNB3; eNB4; eNB5 };

  eNB0 -> eNB1 [label="X2"];
  eNB1 -> eNB2 [label="X2"];
  eNB2 -> eNB3 [label="X2"];
  eNB3 -> eNB4 [label="X2"];
  eNB4 -> eNB5 [label="X2"];

 eNB0 [label="eNB (RBS6402)"];
 eNB1 [label="eNB (RBS6402)"];
 eNB2 [label="eNB (RBS6402)"];
 eNB3 [label="eNB (RBS6402)"];
 eNB4 [label="eNB (RBS6402)"];
 eNB5 [label="eNB (RBS6402)"];

 { rank = same; MME; SGW; };

 MME [label="MME (nextepc)"];
 SGW [label="SGW (nextepc)"];

 eNB0 -> MME [label="S1AP"];
 eNB1 -> MME [label="S1AP"];
 eNB2 -> MME [label="S1AP"];
 eNB3 -> MME [label="S1AP"];
 eNB4 -> MME [label="S1AP"];
 eNB5 -> MME [label="S1AP"];

 MME -> dia2gsup [label="DIAMETER"];

 eNB0 -> SGW [label="GTP1U"];
 eNB1 -> SGW [label="GTP1U"];
 eNB2 -> SGW [label="GTP1U"];
 eNB3 -> SGW [label="GTP1U"];
 eNB4 -> SGW [label="GTP1U"];
 eNB5 -> SGW [label="GTP1U"];

 SGW -> PGW [label="GTP1U"];
 SGW -> PGW [label="GTPv2C"];

 dia2gsup -> OsmoHLR [label="GSUP"];
}
----

== EOF

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