OpenBTS: UMTS

Introduction

OpenBTS-UMTS is a Linux-based application that uses a software radio to present a UMTS network to any standard 3G UMTS handset or modem. It builds upon the OpenBTS framework, where the MS or UE is treated as an IP endpoint at the edge of the network.

Release Features/Capabilities

• supports original UMTS Release 99 (or Release 3)
• supports packet-switched services only (i.e. data)
• supports a single U-ARFCN
• supports one or two high-speed active data sessions
• spreading factors of 4-256
• rate-1/2 convolutional coding
• rate-1/3 turbo coding
• maximum downlink data speed of 106 Kbytes/s
• maximum uplink data speed of 52 Kbytes/s
• Integrity Protection of GSM SIMs
• Features not supported in this release:
  • circuit-switched services (e.g. voice, text)
  • handover
  • Inter-RAT mobility (moving b/w a 2G and 3G network)
  • paging
  • ciphering
  • USIM-based authentication

Supported Hardware

Software Radios

Initial integration of the OpenBTS-UMTS public release was accomplished with the Range Networks SDR1 (a.k.a. RAD1). Integration with other software-defined radios is ongoing, see Radio Integration for more information about connecting OpenBTS and OpenBTS-UMTS to different radio interfaces.

The Range Networks SDR1 was designed primarily for 2G and 2.5G operation. Thus, operation with the OpenBTS-UMTS release can not be guaranteed with all SDR1 radios, since the USB2.0 interface is highly stressed to maintain the required data rates for 3G. Moreover, it requires a reprogramming of the SDR1's clock chip from 52Mhz to 61.44Mhz, which is described later on this page.

CPU requirements

OpenBTS-UMTS is a more computationally intensive application than OpenBTS, since the UMTS channel bandwidth is roughly 13x larger than a GSM channel. Generally, a multi-core high performance CPU is required, such as Intel Core i3, i5, or i7 running at more than 1.6Ghz. Intel Atom processors are too weak to support the current implementation

Range Networks Development Kits

There's good news and bad news for users or Range Networks development kits. The good news is that you already have an SDR1 that may work. The bad news is that it is connected to an Atom-based CPU board, which is not suitable for UMTS. You will need to connect your SDR1 to a more powerful CPU board.

Phones/Modems tested

• Works
  • iPhones (3, 4, and 5)
  • HTC Velocity
  • Samsung Galaxy
  • Palm Pre
  • a variety of Multitech modems
• Doesn't work
  • None so far. Please update at will.

SIMS and Authentication

UMTS mandates mutual authentication between the UE and the NodeB. This is a major change from 2G/2.5G authentication, where only the BTS authenticates the MS.

A good presentation of UMTS security is available at http://www.netlab.tkk.fi/opetus/s38153/k2003/Lectures/g42UMTS_security.pdf

Another detailed description is available at http://www.3g4g.co.uk/Tutorial/ZG/zg_security.html

So what does this mean? The subscriber registry will need to know the SIM's K_i value to

• perform authentication and
• enable integrity protection.

Without proper authentication and integrity protection, the UE will not attach (or register) with OpenBTS-UMTS. For most users, this means you must provide the SIMs for the UEs on the network. The only way to use SIMs from another provider is to obtain the K_i through a roaming interface to the provider's HLR/HSS.

This also means that some of the features the circumvented authentication in OpenBTS, like open registration, are not possible with OpenBTS-UMTS.

Build, Install, Setup, and Run Instructions

The following instructions support the Range Networks SDR1 radio. To build and run the software, you will want to use the following steps:

Prerequisites

Several prerequisites are required to successfully build and run OpenBTS-UMTS, including:

• Ensure you have a Ubuntu 12.04 i386 (32-bit) server system with a connection to the Internet.
• You may also need available packages such as build-essentials and g++, several other packages are setup when building OpenBTS, see the BuildInstallRun page for more information.
• You will need the ASN1C compiler setup and installed. Version 0.9.23 of ASN1C is required.
• OpenBTS-UMTS needs sipauthserve to register and process handsets coming onto the network. See Building and Installing the Subscriber Registry and sipauthserve for more information.
  • Don't forget to add a subscriber, use a SIM with a known IMSI and Ki value.
  • Ensure you have launched sipauthserve:

  cd /OpenBTS
  sudo ./sipauthserve &

Obtaining the OpenBTS-UMTS Source Code

OpenBTS-UMTS is available on GitHub, ensure that you have Git version 1.8.2+ installed on your system, and then:

  git clone https://github.com/RangeNetworks/OpenBTS-UMTS

Building and Setting Up OpenBTS-UMTS

You are now ready to build OpenBTS-UMTS, from your checked-out OpenBTS-UMTS directory:

  ./autogen.sh
  ./configure
  make
  sudo make install

The OpenBTS-UMTS application will be placed into the /OpenBTS-UMTS directory. Before running it, there are several other support steps necessary. The first is to instantiate some run-time artifacts needed by OpenBTS-UMTS, including the initial database:

  sudo mkdir /var/log/OpenBTS-UMTS

Create the configuration database with this command:

  sudo sqlite3 /etc/OpenBTS-UMTS/OpenBTS-UMTS.db ".read OpenBTS-UMTS.example.sql"

Copy sipauthserve's comp128 to run-time directory of OpenBTS-UMTS

  sudo cp /OpenBTS-UMTS/comp128 /OpenBTS-UMTS/

You will need to go into the TransceiverRAD1 directory and run the following script right before running the OpenBTS-UMTS binary in the apps directory (OpenBTS-UMTS/apps/):

  sudo ./clkit_61_44mhz.sh

You will need to setup forwarding in iptables to properly forward data between your devices, your host machine, and the Internet. Create a file called /etc/OpenBTS-UMTS/iptables.rules and insert the following:

  *nat
  :PREROUTING ACCEPT [0:0]
  :POSTROUTING ACCEPT [0:0]
  :OUTPUT  ACCEPT [0:0]
  -A POSTROUTING -o eth0 -j MASQUERADE
  COMMIT
  *filter
  :INPUT ACCEPT [0:0]
  :FORWARD ACCEPT [0:0]
  :OUTPUT ACCEPT [0:0]
  COMMIT

Then, edit your Ubuntu network settings to include the rules script:

  sudo edit text/plain:/etc/network/interfaces

Insert into your Internet-facing network interface:

  pre-up iptables-restore < /etc/OpenBTS-UMTS/iptables.rules

Running OpenBTS-UMTS

After successfully building and configuring, you are ready to launch OpenBTS-UMTS:

  cd /OpenBTS-UMTS
  sudo ./OpenBTS-UMTS

Several useful commands are available for debugging the packet-switched OpenBTS-UMTS application. Launch the OpenBTS-UMTS CLI to manipulate and configure your UMTS installation.

  sudo /OpenBTS-UMTS/OpenBTS-UMTSCLI

In the CLI, type 'help' and press ENTER for a list of available commands. 'help command' gives you a detailed info on a particular command. Type 'quit' to exit the CLI. THis does not stop the OpenBTS-UMTS.

FAQ

Regarding troubleshoot SDR1, YMMV

My data stream is always dropping, what can I do?

Try increasing the transceiver buffer size. The default is 1e6, but this can be increased depending on your available hardware.

  config UMTS.RLC.TransceiverBufferSize 5000000
  rawconfig UMTS.RLC.TransceiverBufferSize 100000000

Referensi

• http://openbts.org/w/index.php/OpenBTS-UMTS
• http://openbts.org/w/index.php/BuildInstallRun#Build_and_Install_the_Subscriber_Registry_and_Sipauthserve
• https://github.com/RangeNetworks/OpenBTS-UMTS (source code)