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Information |
The Promise of Voice over IP.
For over a decade now the prospect of using
the internet to carry voice calls has been
‘next years technology’. Although
there has not yet been any revolution in the
way we route our phone calls, a number of
enabling technologies, services and providers
are now in place which can finally deliver
a reliable, high-quality solution at very
low cost. Most businesses and individuals
who are serious internet users now have un-timed
and effectively un-limited connection to the
internet. Users can spend all day downloading
data from the other side of the world at no
added cost. And yet, when those same users
make a phone call they are charged by the
minute, whether the call is local, national
or international. In practice the data may
well travel over exactly the same route, on
the same wires, owned by the same people.
Only the billing mechanism and price is different.
Wouldn’t it be better for the end user
if the telephone call went with the internet
traffic with the attendant price saving? Another
attractive application for many businesses
would be to connect home workers and sub-offices.
The only on-going cost at each site would
be the charge for an always-on internet connection.
The remote sites could use the internet connection
to log-in to the main office network and also
run their telephones as extensions to the
main office phone system. A third use of Voice-over-IP
technology is to replace the expensive telephone
system that most companies require. The idea
is to use existing computer hardware such
as servers and Ethernet cabling to handle
telephone traffic. Telephone system functions
such as call-transfer and hold could be handled
by software and telephone devices could just
be plugged into a network point instead of
dedicated wiring.
The three applications outlined above can
be summarised as:
• Long-distance call routing.
• Point-to-point connections.
• In-house PBX systems.
We’ll consider each of these applications
in greater detail in a moment, but first let’s
have a look at the hardware.
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VoIP Hardware.
From the very beginning of the internet
the idea of being able to call Auntie Gladys
in Australia for just the cost of a local
connection to the internet has had users scrambling
for their headsets and microphones and running
voice applications on their PCs. And it worked,
though the need for a pre-emptive phone call
to get Aunty Gladys ready rather spoilt the
effect. In the real world, reliance on Microsoft
work-station platform stability for telephone
services is not practicable and actually,
most people want a hard plastic telephone
to hold to their ear. Headsets and microphones
are just not acceptable.
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VoIP
Phones
Now, assuming that there is some sort of
Ethernet connection nearby, an ideal solution
would be a hard plastic telephone with an
Ethernet connection on it. Such a device is
called a VoIP phone. At the simplest level
a couple of VoIP phones on a network lets
you make calls between them. The network can
be just the wires running around your office.
Or it could be two internet connections at
opposite sides of the planet, as long as there
is a route between them.
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VoIP Gateways
But what if you already have a telephone
system (called a PBX) in your office and you want
to set it up so that the existing extensions on
your desks can access your VoIP/internet connection
as well as the standard phone lines? To do this
you will need a device which connects between
your telephone system and your Ethernet network.
It’s called a VoIP Gateway. VoIP Gateways
have telephone ports which come in two flavours.
One flavour has a connection to plug a phone into,
called an FXS port. The other flavour has a connection
for a phone line, called an FXO port. So you can
see that VoIP gateways can connect to either the
trunk line side of your PBX or to the extension
side of your PBX. For all this to work your PBX
should be able to support connections to ordinary
phones or ordinary phone lines. This standard
is called POTS, which stands for Plain Old Telephone
System. If your phone system uses only special
digital phones or has only ISDN trunk lines, then
you will need to contact your PBX supplier and
ask them if POTS type ports can be provided as
well. You will find VoIP gateways available with
one or more ports in various mixes of FXO and
FXS flavours. You just select a device to handle
the connections you require. To summarise then,
a VoIP gateway has an Ethernet port and one or
more telephone ports. FXO ports behave as if they
were a telephone and FXS ports pretend to be a
telephone line.
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Routing
the Traffic
Now we have some hardware to provide
the telephone interface we need to arrange to
pass telephone traffic between the two ends.
Actually, this is the hard part of VoIP. There
is usually some way to achieve any desired application
though some care may be required in specifying
the routing hardware and software.
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Point
to Point Connections
To call one VoIP device from another you can just
‘dial’ its IP address. The situation
can get more complicated if the devices are on
sub-nets working behind routers, but the principle
is just the same. The path between the VoIP devices
is more complicated, especially if NAT routing
is being used, but with careful selection of routers
the path can be made effectively transparent.
One way to set up the path across the internet
is to use a virtual-private-network, VPN. This
approach is especially suitable for connecting
various branches of a company. Once the VPN paths
are configured, each of the devices at the sub-offices
appears as if they were on the same local network.
No more need to think about routing at all. The
easiest way to set up VPN is with a router which
handles the VPN termination itself. Of course,
in practice, it would be inconvenient to dial
the full IP address for every call. To get around
this, VoIP phones and gateways have ‘Speed-Dial’
memories. These memories give access to the correct
path by just dialling two or three digits. VoIP
phones and gateways can even be configured to
‘hot-dial’ a given address, that is,
dial the number as soon as the handset is lifted
(or when a call comes in for an FXO device). This
function is especially useful for routing calls
to your extension at the office through to your
home. Speed dial memories can also be used to
store domain addresses, such as ‘my-voip.co.uk’.
This function means you can have access to VoIP
services even when your ISP provides you with
a dynamic IP (one in which your IP address may
change from day to day). It also means you have
control of your VoIP telephone ‘number’,
even if you change service provider.
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Long
Distance call routing
To minimize call costs to ordinary phone lines
in a foreign country: First you need to get your
call traffic onto the internet using a voice-gateway
in conjunction with your internet connection.
Second, you need to get the traffic delivered
to an internet address in the foreign country.
Third, you need to get your call off the internet
and back into the phone system of the destination
country. That way all you will be paying for is
the call within the destination country. This
third phase can be achieved in two ways. If all
your calls are to (or from) one or two target
countries then you could buy an FXO port gateway
and just plug it into some local phone lines there.
Obviously this will entail having an office in
the destination countries. Think of this as a
DIY solution. It is likely to be a contender if
you operate a foreign sub-office or similar. A
more common solution for the ‘off-ramp’
phase is to use a third-party service. These services
are becoming increasingly common, very practicable
and very economical. Although you will pay by
the minute for connection through the service
providers system, this is usually more than offset
by the better rates they get on call delivery
in the destination country. Such service providers
are usually registered telco’s in the destination
country and thus pay only for the ‘last-mile’
delivery of calls. The resultant end user rates
are usually much lower than the cost of a standard
national call within the UK, or wherever you are.
These IP-Telephony services use software called
a Gate-Keeper. This software keeps track of users
billing and routes calls in the most appropriate
way.
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In-House
PBX Systems
By putting VoIP telephones at each desk and
running some GateKeeper software you can use
your computer network as a telephone system.
This route is excellent if you need unified
messaging where faxes, voice messages and emails
are all stored in individual users own boxes.
Unfortunately there is only one significant
manufacturer of this type of system, Avaya (formerly
Network Alchemy), a division of Lucent. The
lack of competition results in a rather higher
price than one might expect to pay for an equivalent
conventional PBX and you may find the feature
set excludes some features you would expect
to find. No doubt new brands will appear shortly
and we at ITSOS will definitely be monitoring
this developing field.
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