ALL YOU NEED TO KNOW ABOUT...
TELEPHONY & LINUX
Off the hook
Charlie Stross takes a look at the brave new world of Linux and open source
telephony: what s all the fuss about, and where it is heading?
he history of computing has been intimately
entangled with telephony ever since Post Office
telephone engineer Tommy Flowers was drafted
Tin to help Alan Turing design the first British
computers.
Linux is no exception. Descended from UNIX, a system
developed by a telephone company s research arm,
these days Linux is being used to control tele-
phone switchboards and to act as a gate-
keeper between telephone systems
and the Internet. It s also taking its
first steps as a link in the new
technologies of voice-over-IP,
also known as internet tele-
phony. What s going on?
Meet Greg Herlein.
Greg is one of the lead-
ing lights of the
OpenPhone project.
Every computer should
be able to act as a phone -
hopefully a very smart and
programmable phone, Greg
explains. And that s just for starters;
the goal of the OpenPhone project is an
application framework that provides mod-
ules for all the various jobs phone equipment
needs to do, including teleconferencing, signalling,
and routing calls. Such a system absolutely has to be open:
like fax machines, the usefulness of internet phones
depends upon how many other devices are out there that
they can interoperate with, says Herlein. If a Linux-based
OpenPhone can only call other Linux computers, it s of
limited value. However, if an OpenPhone can call any
other computer regardless of operating system, or any
other phone anywhere in the world that s powerful!
There are two ways of using a computer as a phone:
voice over IP (VoIP), in which data streams connect two
computers over the internet, and conventional telephony,
in which the computer talks the same networking proto-
cols as the telephone exchanges and uses software to han-
dle calls intelligently (for example, as part of an integrated
messaging system that combines phone, email, SMS, fax,
and other media in a single framework).
P-P-Pick up a
phoneguin
Voice over IP/Internet telephony
Quicknet Linux guru, Ed Okerson, AKA
Before you can use a computer as a phone, it needs hard-
Super Phoneguin. His drivers for
ware that lets it do the job. Quicknet Technologies, a
Quicknet s telephony cards are in the Linux
kernel. Equivalence, a Quicknet subsidiary,
Californian company, makes hardware telephony cards:
develops an open source implementation of
these boards aren t full-scale telephone switches, but they
the H.323 conferencing protocol
42LinuxUser/June 2001
provide audio processing and data compression in hard- also have a lots of Internet connectivity, Linux and tele-
ware, along with an analogue phone line interface (in the phony will become, we believe, more prominent as a por-
case of the PhoneJACK card). Quicknet is serious about tion of the typical ISP s product offerings and business.
Linux and IP telephony. Linux offers developers an excep-
tionally flexible and robust environment for developing Frameworks and call management
reliable dedicated telephony applications, comments Numerous groups are working on open source communi-
Stacey Reineccius, the company s CEO. cations software that can go into a framework, gluing VoIP
The idea of a telephony card is that you plug your desk telephony and conventional telephony into a common
telephone into it; thereafter, you can use the telephone as a infrastructure. At present a lot of the work is going into fill-
terminal. Drivers that come with the card can also forward ing in gaps: telephony is a hidebound field, and there are
your calls via TCP/IP to a similarly equipped PC, or the no open source implementations for many of the com-
public switched telephone network (PSTN). Quicknet s mon protocols. This is changing, though: take Vovida.org
PhoneJACK lets you plug a phone into your PC and use it as an example. Vovida Networks, a manufacturer of
to make Voice-over-IP calls; its related LineJACK card lets switches, was acquired by Cisco in 2000; a large chunk of
you switch between PSTN and IP calls. their codebase has been open-sourced, and Cisco contin-
Quicknet s IP telephony cards help provide support for ues to support a community website that is hosting the
Voice over IP traffic by allowing you to turn a PC into a development of the OpenH323 protocol stack, and numer-
gateway; but to get the most out of an office full of these ous other bits and pieces, notably a SIP (session initiation
systems you need a switchboard or PBX (private branch protocol) stack. Vovida s protocol suites cover MGCP, RTP,
exchange) so you can hook up your voice-over-IP phone SIP, COPS, RADIUS, and TRIP (telephony routing over IP); a
system to the public switched telephone network (PSTN). range of protocols that have established themselves in the
The first example of this to appear on Linux is Asterisk (see voice-over-IP field.
www.asteriskpbx.com), a PBX application running initially Then there s
If an OpenPhone can call any
on Tormenta or Adtran Atlas T1 and T3 frame relay cards also Voxilla, an
(with Quicknet PhoneJACK cards for Voice over IP). open source pro-
other computer regardless of
Asterisk lets you set up call routing logic, provides features ject that aims to
such as call bridging, transfer, and parking, voice mail, and build a complete
operating system, or any other
intercom facilities. Other features of software PBXs mirror suite of telecom-
those of real small office exchanges: the ability to route munications mod- phone anywhere in the world -
calls via different internet telephone carriers (or standard ules for use with
that s powerful!
PSTN carrier), track calling histories, automatically re-route Linux. The broad
Greg Herlein
IP calls via a new carrier in event that a network connec- requirement is to
tion becomes unavailable, and route faxes via the Internet. be able to switch
Quicknet s committment to Linux includes sponsor- multimedia streams (which, after all, is what telephony is
ship of the OpenH323 effort. OpenH323 is an open source about). The Voxilla team broke the requirements down
project to develop an open source implementation of into four categories: applications, converts, protocols, and
H.323, the standard for teleconferencing over TCP/IP. The device drivers. The intersection of Linux and telephony
company also produces a number of boards intended for gives rise to a bewildering alphabet soup: for example, dif-
use with Linux, notably the LinuxJack board, which they ferent protocols are required to talk to switches, paging
support with open sourced drivers. towers, conferencing applications, messaging tools, and so
We have found that Linux is not only a fantastic prov- on. Meanwhile, the GNUcomm project, run by the Free
ing environment for developing technologies but it makes Software Foundation, is busy trying to build a multimedia
for an extremely cost effective server side system when streaming/switching suite; the goal is to allow switching of
needed for call control and billing, but as a client or low multimedia streams and calls over IP.
density installation it makes terrific sense for small-scale All these protocol projects are components in the big
servers, says Reineccius. Telephony and Linux are a nat- Lego jar of Linux telephony. Two key items are coming
ural fit. They will continue to run into, over and through together: the first is a complete set of telephony protocols
each other for some time to come. Telephony demands in the form of a framework that lets applications call high-
reliability and low costs. Voice over IP requires that plus level functions (for example, to establish a voice call from
good Internet access. As most ISPs use Linux as the primary your computer to a telephone number via an IP/PSTN gate-
operating system under the systems and technologies and way); this is the goal of the OpenPhone project. The sec-
phone systems used human opera- Post Office monopoly in 1982, a services and transport for calls.
tors sitting in front of a plug board: new entity effectively came into Telcos are in the business of
Talking about
they d physically connect the lines existence: the public switched tele- selling network bandwidth. Rather
to two households by running a phone network (or PSTN). The than using discrete wires for each
telephony and
wire from the line the call came in PSTN is regulated by Oftel, the circuit through their network, calls
on to the outgoing line. Later, Office of Telecommunications: are converted into data streams at
computers...
electromechanical switches came equipment which meets their stan- the exchange and the packets
into use: a committee within the dards (which mostly boil down to routed to their destination. This
If you want more than two people
ITU called the CCITT (Comité compatability with CCITT stan- allows the telcos to multiplex calls
to be able to talk to each other by
Consultatif International dards and some basic safety speci- between two exchanges, making
telephone, you need a network: a
Téléphonique et Télégraphique) fications) can be connected to the better use of their network. Unlike
set of lines with phones on the end
was established to develop stan- PSTN, and a number of telcos Internet traffic, telco traffic is
of each one, and a mechanism in
the centre that connects the tele- dards for telephone switching and (telecommunications companies mostly encapsulated using ATM, a
phone making a call with the tele- data communications. such as British Telecom or Cable technology that transfers data in
phone receiving it. The first tele- With the dissolution of the old and Wireless) provide switching
CONTINUED ON PAGE 45 >
LinuxUser/June 2001 43
ALL YOU NEED TO KNOW ABOUT...
TELEPHONY & LINUX
Just putting phone-based system administration tools.
Bayonne isn t a graphical application: it s a server. To do
you through
something useful with Bayonne you need to write scripts
Right: The music-on-hold
in the ccscript language. Ccscript is a state-based language
setup screen for Andrews
and Arnold s Penguin
that is driven by events, such as a user punching a DTMF
Communications Server,
the single-box turnkey digit in a voice menu, receiving a call disconnect signal,
small business communi-
and so on. It can play sound samples from stored files on
cations server which
enables easy control of
disk, collect caller ID information, record from the phone
the popular Alchemy PBX
to an audio file on disk, and so on. In fact, using Bayonne
as well as doubling as a
network appliance provid-
you can rapidly write a script that implements a company-
ing all the standard
wide voicemail system, with password protection, the abil-
Internet-related services
ity to replay received messages on demand, ability to email
Below: A preview release
of the new user interface received audio files to a user s email box, and so on. As of
for the Penguin. Features
the Milestone Six release, Bayonne provides XML services,
include integration with
BT s billing information,
allowing you to add voice services to XML-based applica-
enabling call costs to be
tion servers.
trace to individual exten-
sions. Matt Bishop, R&D
Bayonne s driver support is currently relatively limited,
team leader, says: It s
but it is designed to take plugins that let it interface to
possible to get these fea-
tures on applications writ-
other systems: in particular it is capable of driving multiple
ten for Windows, but the
price is higher and we Quicknet LineJACK cards (for example, to provide a multi-
believe that LInux gives
line voicemail system). Drivers for Voicetronix s analogue
our customers a more sta-
ble platform.
DSP cards, Pika MonteCarlo telephone cards, Dialogic and
Aculab cards are also supplied. The list of supported cards is
expanding slowly, as vendors wake up to the sales poten-
tial of open source software.
Don t expect installing a Bayonne system in your com-
pany to be easy: the total absence of easy-to-use adminis-
tration tools, and the requirement to dink around with
VoIP cards and drivers, make it a job for specialists.
However, if you want to build a cheap, efficient voicemail
system that can cope with several simultaneous callers, or
if you want to build your own system for forwarding voice
calls over the Internet between distant offices, Bayonne
may reward a week s work with a system that is tailored to
your requirements. In particular, the ability to build a
v-commerce system that mimics the structure of your e-
commerce website may be well worth the trouble.
ond item is the integration of telephony into unified mes-
saging frameworks, systems that allow all communications Computer-telephony integration
systems (phone, pager, fax, email, and others as yet Just about every company has a PBX, the local switch that
undreamed of) to be integrated into allows multiple telephone extensions to talk to each other,
a single system. or route external calls out to the PSTN via the cheapest
A lot of customers,
provider. Linux can help here, too.
Messaging frameworks Andrews and Arnold, a British telephony equipment
especially in Europe,
The higher level packages are exem- supplier, has found Linux works well as a system for con-
plified by Bayonne, the GNU inte- trolling PBX s. It has written drivers that allow a Linux sys-
are telling us that they
grated voice response server. tem to talk to a Lucent Technology Network Alchemy
Bayonne provides a service daemon switch. The Network Alchemy range are popular cheap
want Linux implemen-
that can automatically process tele- PBX s aimed at small to medium enterprises; they provide
phone calls it s scripted, so you can up to 180 telephone extensions on up to 60 trunks. These
tations, not NT
control call flow, and is intended for telecoms routers are also TCP/IP aware: they can provide
Alan Pound, Aculab
building voice mail systems and tele- access to ISDN and leased line connections, and support
< CONTINUED FROM PAGE 43
tion switched through to the PAD these are in turn converted back a short-range high bandwidth data
small, fixed-size packets. (ATM is (packet assembler/disassembler, into digital form by the exchange, protocol that can run over existing
designed to support switched traf- X.25 equivalent of a router). then transmitted to the ISP, where twisted-pair wires. Some switches
fic, between two points.) The arrival of the Internet was a they re turned back into analogue are now designed to route TCP/IP
However, prior to the arrival of rude shock to the telcos, who had form by the ISP s modems or packets directly over ATM net-
the Internet the telcos provided previously milked the lucrative routers before being re-digitised. It works, blurring the boundary
data transport via their own pack- business data communications all seems a lot simpler to keep the between a telco and an ISP.
et-switched network: running on market. While huge amounts of signals digital from one end to the The blurred boundaries go both
protocols such as X.25, these net- money could be made by supplying other: but the original technology ways. Voice calls require bidirec-
works (such as British Telecom s TCP/IP connectivity, there were for doing this, ISDN, is now dated tional data transfers: why not carry
Packet Switchstream service) were inefficiencies in the system. and sluggish. voice calls over TCP/IP? The tech-
expensive, slow, and not universal- Making a call to your ISP via The current approach is to nologies of Voice-over-IP, or IP
ly accessible. The commonest way modem entails turning digital data transmit packets between Telephony, got started by compa-
of accessing the service was via a (leaving your computer) into audio exchanges using ATM, then relay nies who wanted to merge their
leased line, a permanent connec- frequency tones (via the modem); data to the consumer using ADSL,
CONTINUED ON PAGE 46 >
LinuxUser/June 2001 45
ALL YOU NEED TO KNOW ABOUT...
TELEPHONY & LINUX
Key links virtual private network applications. In fact, these switches OC3 cards, able to handle data rates up to 155Mbits/sec), is
OpenPhone
blur the boundary between internetworking hardware and developing the Whirlwind computer telephony platform:
www.openphone.org
telephony, acting as LAN hubs and routers as well as tele- essentially an operating system for voice applications.
Voxilla
phone switchboards. Whirlwind is a cross-platform development: We had a lot
www.voxilla.org
Andrews and Arnold s Linux tools allow a Linux server of customers, especially in Europe, telling us that they
Asterisk soft PBX
to drive a Network Alchemy router. Configuration of the want Linux implementations, not NT, says Alan Pound,
www.asteriskpbx.com
router from Linux is possible: more to the point, the Linux Aculab s managing director.
Quicknet
www.linuxjack.com
server can provide full call logging (into a MySQL database, Whirlwind runs on NT, Linux, and Solaris, and provides
GNUcomm
if desired), a comprehensive voicemail system that goes an implementation of the ECTF s S.100 and S.300 APIs,
www.fsf.org/software/
beyond the one built into the Network Alchemy systems, which specify how computer telephony applications
gnucomm/
and APIs to allow integration of Linux-based applications. should interface to standard CT Bus boards. (CT Bus
gnucomm.html
With the Alchemy system we use, almost any Linux defines a single communications bus that can be installed
Bayonne
http://bayonne. box will do even a 486. We normally recommend some- in various popular personal computer card slots (ISA/EISA,
sourceforge.net
thing bigger, and it depends on the number of channels, PCI, and the emerging compact PCI).
Andrews and
but an 800MHz PIII machine with SCSI disks was hard Essentially Whirlwind is an operating system for com-
Arnold
pushed to register one per cent usage with 30 channels of puter telephony applications, providing access to voice
www.aa.nu
voicemail including DTMF decode, says Adrian Kennard, channels and allowing applications written using the
OpenH323
technical director of Andrews and Arnold. The tools we S.100 APIs to talk to the boards; this is a proprietary system,
www.openh323.org
have written do multi-Alchemy voicemail and voice-based but other vendors are also implementing S.100 and S.300
applications, as well as phone control and call billing sys- compliant systems, and applications written to these open
tems. standards are portable between comput-
In this system Linux isn t acting as a er telephony systems. The ECTF stan-
telephone switch or voice-over-IP gate- dards show that the telephony industry
One day, your
way; it s acting as a control centre for in general is moving in the direction
existing PBX s. It s possible to write com- that the computer industry moved in
plex applications for automating call the 1980s, first towards open standards,
telephone
centre operations or providing on-line and then towards open source. Linux is
technical support screening relatively seen as a strategic platform by some of
will run Linux
easily, because of the availability of the largest computer telephony hard-
open programming interfaces. The per- ware vendors; as it advances in the serv-
formance of the voicemail server is also noteworthy: a er sector, more and more CT systems like Whirlwind will
machine costing two or three thousand pounds can pro- appear on it.
vide voice mail for hundreds of users.
In addition to selling straightforward PBX control sys- The future s bright the future s open
tems (with integrated voicemail and fax services), Andrews Telephony is just another kind of networking, albeit one
and Arnold have some specialised telephony applications with a wide variety of bewilderingly complicated (and pro-
already available, notably hotel and legal billing systems prietary) protocols. The telephony industry is discovering
that, in conjunction with an appropriate office exchange, Linux, just as Linux is discovering telephony.
can automate the telephony operations of those business- On one hand, Linux telephony enthusiasts like Greg
es: the low cost, reliability, and ease of integration of Linux Herlein are working to make Linux a platform for handling
are all assets in these markets. telephone calls. On the other hand, traditional telephone
Controlling the external PBX is not the ultimate in hardware companies like Aculab (which builds kit for
Linux telephony integration: for that, the Linux box needs switching calls) are discovering the lure of an open plat-
to be the PBX as in the case of the Asterisk soft PBX men- form and common standards.
tioned earlier or indeed to be the platform it runs on. As the telephone industry adopts standards such as
The holy grail of the high-level computer telephony those of the ECTF (which allow CORBA-compliant pro-
market is integrated messaging, in which every type of grams to talk to telephone switches), and as Linux learns to
communication, fax, pager, SMS, phone, email, goes handle voice-over-IP, the fields are converging: and one
through a common framework. Aculab, the UK-based ven- day, your telephone will run Linux.
dor of high-end telephony boards (up to and including
< CONTINUED FROM PAGE 45
message on a voicemail system ing, and T.120 for real time data Nortel, Lucent and many others,
local area network and telephone and email it to the recipient, or to conferencing protocol. These pro- and is interoperable with a plethora
extension systems. The initial take email and automatically fax it tocols have been implemented as of H.323 devices including Cisco
incentive was to reduce the num- out to a destination that doesn t open source: the core code is avail- VoIP gateways, gatekeepers and
ber of routers or switches a busi- have email access. The core stan- able from www.openh323.org, and phones, says Quicknet.
ness needed: then there was the dards that made this possible were builds on Linux for x86. The goal of H.323 is a complex protocol; for
opportunity of using spare band- established by the H.323 commit- the OpenH323 project is to create controlling calls, two simpler proto-
width on expensive leased lines to tee of the International Multimedia a full-scale implementation of the cols, SIP (Session Initiation
connect voice calls between Telecommunications Consortium H.323 teleconferencing protocol: Protocol) and MGCP (Media
remote sites. Once the basics of and supported by the ITU. it s supported by an Australian Gateway Control Protocol), are
connecting calls via TCP/IP were H.323 defines standards for company, Equivalence, a subsidiary building momentum. An open
available, other options opened up: real-time packet-based communi- of Quicknet Technologies. source version of MGCP has been
the ability to connect calls from the cations: related standards include OpenH323 has now been com- released by Vovida; no open SIP
PSTN over TCP/IP meant that, for H.225 for call control protocol, mercially tested and/or deployed implementation is available yet.
example, it s possible to record a Q.931 for digital subscriber signal- not just by Quicknet but also by
46LinuxUser/June 2001
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