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How to Build an Embedded Asterisk IP-PBX Contents. Free Telephony Project Why Embedded Asterisk Motivation Open Hardware Open Hardware Hacking Credits Products Demo. Free Telephony Project 1. many people working in open software we are working in open hardware

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  • Free Telephony Project

  • Why Embedded Asterisk

  • Motivation

  • Open Hardware

  • Open Hardware Hacking

  • Credits

  • Products

  • Demo

Free telephony project 1
Free Telephony Project 1

  • many people working in open software

  • we are working in open hardware

  • professional telephony hardware designs

  • that we give away

  • to improve the world a little

Free telephony project 2
Free Telephony Project 2

  • designs can be copied modified, re-used without restriction

  • we encourage cloning of our products

  • trend: functionality shifting from hardware to (free) software

  • trend: total system costs constantly dropping

Free telephony project 3
Free Telephony Project 3

  • falling hardware costs are a good thing (especially for the developing world)

  • so rather than protecting IP we leverage these trends

  • by giving away free hardware designs

  • and encouraging cloning!

Why free telephony project
Why Free Telephony Project?

  • Hardware designs are free as in speech

  • Use FOSS and Open Hardware to drive system costs to $0

  • Lower the cost of telephony for everyone on the planet

  • A phone call should be a human right, not a privilege

Why embedded asterisk
Why Embedded Asterisk

  • Small size (DSL router)

  • Low power 3W (battery, solar)!

  • No moving parts (fans or disks)

  • Quiet

  • Reliability (parts count, connectors)

  • Low cost (few hundred $)

  • Just plain cool!

Ip pbx and asterisk
IP-PBX and Asterisk

  • A open source PABX (PBX) that can route calls between the PSTN and VOIP

  • Usual FOSS advantages – low cost and open

  • VOIP experiencing massive growth

  • Primary sponsor Digium but many contributors

  • Hence alternatives such as FreeSwitch, CallWeaver, etc, etc


  • Typical installation x86 PC plus PCI card to connect to the telephone lines/telephones.

  • Paradigm shift away from x86/PCI cards

  • History: Embedded = IP-only and no DSP (Echo cancellation and codecs not possible)

  • Analog Devices Blackfin Processor has challenged this paradigm!

Blackfin processor
Blackfin Processor

  • A powerful DSP (1 GMAC)

  • AND runs uClinux

  • Breaks the two processor (host/DSP) paradigm

  • Low cost ($5 - $15 each)

  • Well supported by vendor and community

  • Open hardware and software

Ip pbx hardware 101
IP-PBX Hardware 101

Host PC

PCI Card


Device Driver

PCI Bridge

FXO Port

x86 CPU

Ethernet Card

DSP hardware

FXS Port

Ip pbx hardware 1011
IP-PBX Hardware 101

Embedded PBX


Blackfin CPU

FXO Port

DSP software

Device Driver

FXS Port

Ip pbx hardware 1012
IP-PBX Hardware 101

  • Many redundant parts removed

    • Lower cost

    • Smaller size

    • Lower power

    • Enhanced reliability

  • Don’t need “hardware” DSP – Blackfin CPU is a DSP


  • Complex development environment

    • Cross compiler & tool-chain

    • Customized kernel and apps

  • Learning Curve

  • Low memory ~64MB

  • uClinux (offset by partial MMU)

  • Care and feeding of the cache

Motivation 1
Motivation 1

  • Various motivations across the people and companies involved in the project.

  • Obvious business potential in a $200 IP-PBX with multiple ports.

  • Enabler for service models.

  • My motivation is Social & Geeky rather than Business.

Motivation 2
Motivation 2

  • I like building stuff

  • Would like to use my hardware/DSP skills to improve the world a little

  • Open software like Linux and Asterisk has been a great thing for the World.

  • Craig Newmark (Craigslist) : Nerd values “Get yourself comfortable, then do something fun to change the world a little”

Open hardware 1
Open Hardware 1

  • reference designs that anyone is free to copy, re-use, modify

  • CAD files, prototypes

  • differences from open software

  • atoms cost more than bits

  • you need a factory

Open hardware 2
Open Hardware 2

  • many advantages over closed development

  • similar to open software

  • many eyes

  • low bug count

  • dramatic reduction in R&D cost and time

Open hardware 3
Open Hardware 3

  • CVS/SVN for version control of designs

  • re-using hardware building blocks

  • helping each other get strange parts

  • blog instead of log book – share experience

  • chat to help debug hardware

Open hardware 4
Open Hardware 4

  • normal hardware costs include 70% overhead

  • exciting new business models, e.g. OLPC

  • dramatic price reductions

  • local manufacture

  • customisation, localisation, e.g. solar, wireless

How to hack telephony hardware in linux
How to Hack Telephony Hardware in Linux

  • Schematic Entry (gschem)

  • PCB Design (PCB)

  • Verilog HDL (Icarus)

Design process flow
Design Process Flow

Design Schematics (gschem)

Write Verilog Code (Icarus)

Design PCBs (PCB)

Assemble Prototype Hardware

Debug and Test Hardware

Port Asterisk to Blackfin (gcc)

Integrate and Test system

Hardware hacking is getting easier
Hardware Hacking is Getting Easier!!

  • Build sophisticated surface mount circuits.

  • Order strange parts on-line e.g. Digikey

  • Prototype PCB costs dropping

  • Stereo Microscope + soldering tools < $500

  • Open hardware designs

  • Free CAD tools

  • Help from on-line communities

Open hardware ip pbx products
Open Hardware IP-PBX Products

  • IP04 4-port Analog IP-PBX (production)

  • IP08 8-port Analog IP-PBX (prototype)

  • E1/T1 PRI-Appliance (prototype)

  • BRI-Appliance (prototype)

Case study ip04
Case Study - IP04

  • Switches analog and VoIP calls

  • fanless, low power (5W), rugged, compact

  • open hardware and software

  • easy to customise, e.g. simple UI

  • potential for very low cost ($100), compared to $2,000 retail for similar products

  • stable but not feature complete (CID, GUI)

Free phone call
'Free” Phone Call

  • between Adelaide and Beijing using two IP04's

  • open hardware design

  • designed with open CAD software

  • running uClinux and Asterisk

  • using VOIP ($0 call cost)

  • Freest phone call ever?

How to build an embedded asterisk ip pbx rowetel ucasterisk

  • Boots from a Battery

  • phone call

  • telnet, asterisk CLI

  • GUI


In no particular order:

  • Atcom (China) for putting the IP04 into mass production

  • Astfin team for developing build system, PRI and BRI-ISDN hardware

  • Analog Devices for Blackfin and great uClinux support

  • Linux and Asterisk communities

  • Many others who contributed (e.g. drivers, software fixes)


For more information