Most of what can be achieved via
FEEDNET is courtesy of
software. The sheer hard work, altruism and inventiveness of all open source
authors is gratefully acknowledged here.
PTT, VoIP and RoIP. Confused ?
Over the last few weeks we have been asked on more than one occasion about our
use of VoIP, RoIP and PTT technology. We have also been asked about the
misleading advertising by some companies involved in selling these technologies.
Let us try and distil the essence of what
these terms mean, particularly in the context of FEEDNET. We will do it by
providing some broad definitions of the terms and then by reference to specific
products and technologies together with their respective strengths and
Firstly some definitions:
IP = Internet Protocol.
describes the way that computers talk to each other via a network.
Old fashioned, or “regular” analogue telephones use analogue representations
of the audio to pass along a wire pair to the local telephone exchange. Modern
IP telephones use computer protocols such as IP to talk to each other. You don’t
need to know how IP works to use it. If you are looking at this web page it came
to you via the magic of IP !
= Voice over Internet Protocol.
The concept of using computer communication techniques to link telephones
together is such an important one that it has been given it’s own name – VoIP, or Voice
over Internet Protocol. The idea is to make a telephone that converts sounds
into digital representations, send them over a computer network then have a
telephone at the other end convert them back to faithful reproductions of the
Session Initiation Protocol
Anyone who makes use of VoIP for communications will come across the acronym
SIP at some point. SIP is a kind of signaling method that telephones and
computers use to create pathways between them. There are other methods
but SIP is one of the most important. SIP is not really something that users
need to get involved with, but it's useful to know what it actually is since the
term is used so much.
RoIP = Radio over Internet Protocol.
Before talking of RoIP it is worth a small diversion to look at two terms that
are vital to the understanding of it. Full-duplex and half-duplex.
When you make an ordinary home telephone call both parties can talk at the same
time and be heard – they can interrupt each other. This is full-duplex.
On a typical handheld “walkie talkie” or “two way radio” one of the parties has
to press a button and then can speak. The other party must wait for them to
finish before being able to answer. It is not possible to interrupt, and only
one person can speak at a time. This is half-duplex.
Radio over IP is the name given to the general concept of using VoIP techniques
for transferring the sound information from one end to the other, but in
place of using an ordinary two way telephone, a half duplex radio device is used
at one or both ends. i.e. when two or more people are conversing together, only
one person can speak at one time. VoIP usually implies full duplex
communications over IP. RoIP is usually half duplex. Aside from this they are
almost identical and tend to use the same or similar technologies and protocols
PTT = Push to Talk
“Push to talk” often just refers to the button on a two way radio that one
presses in order to be able to speak and be heard. But the term also means
something a little bigger – it is used to describe a particular type of
communications system. This is what we will focus on here.
PTT system is one where a user is able to listen to others but cannot speak
until the channel is free when the user will take control of it by pressing a PTT
button. On pressing a button they can speak and be heard. Sometimes they are
heard by only a single user or it is possible to have hundreds all joined to the
area where PTT is commonly employed is in RoIP. Here a traditional radio link
is used somewhere in the route between persons talking to each other. PTT can
also be used where it is a plain and simple wired data network, as is the case
where VoIP is employed. In the latter case, every part of the route, is
carried over the internet. The PTT is used to give a two way radio “feel” to
the conversation even though no radio is in use.
use PTT ? Well, for those already well versed in the use of radio networks, it’s
a comforting, intuitive and disciplined way of communicating. PTT often
might have hundreds of individuals in the “net” monitoring for long periods of
time. Normal telephones are good for short but intense conversations. PTT is
good for just monitoring for the occasional message. PTT users manage their
communications simply, efficiently and in an ordered fashion.
For over one
hundred years this has been a core means of having a two way
simultaneous conversation between two geographically remote locations.
having local power (powered from the telephone line itself).
Limited in scope
Slow to deploy.
easily be moved.
Now the de-facto
standard for voice telephone communications. Even if we still put
analogue telephones in our homes they get converted to digital at the
businesses will install analogue nowadays – VoIP is used exclusively.
you can take your telephone with you. You just need a data connection to
make it work.
of services – simple conferencing, paging, messaging, etc.
Low cost. Local
calls can cost the same as long distance calls because both just look
the same from a technical perspective – data over the network.
Apple mobile telephones, Ipads, Tablets, and PCs can all be used for
VoIP, often at no additional cost . They make use of the existing data
Calls are usually free
from VoIP to VoIP numbers.
is dependent on local power supply.
It can be a
complex process to configure the equipment.
Used where one
end of the link is highly mobile, or far from regular public
mountain search and rescue team working in a remote area. With ordinary
two way radio the team can talk between themselves and perhaps with a
distant remote base. Being out of the range of mobile telephones their
options are limited.
With an RoIP
link as part of their two way radio network, they can make a phone call
from a two way radio handset – to anywhere in the world.. Or perhaps
they can temporarily link to another team working in another part of
the mountain range.
usually makes use
of PTT although VOX is a possibility too.
RoIP can add
effective two way radio coverage to a telephone system
RoIP can link
together disparate parts of a two way radio network via the internet. Or
see it as linking different two way radio networks to make one larger
When we use the term
"radio" we don't mean wifi or 3G cellular. Although these technically
use radio waves of course, we tend to think of them differently.
On the one hand
it is a strength that RoIP generally only allows half duplex operation
but compared with full duplex this can be seen as a restriction.
telephones when one end of the link is half duplex can be a little
frustrating as one of the parties may not be trained in the more
disciplined type of operation that half-duplex requires.
RoIP can be
expensive (but need not be). RoIP systems are often known as Dispatch
systems. This is because a typical Dispatch Controller will talk to
radio users (taxis, ambulances etc) but will not use a normal hand held
radio to do so. Instead they will use dispatch software on a PC that
keeps records of who is where for example.
RoIP (see above)
makes use of PTT, but here we refer to PTT being used over an
exclusively fixed or 3G data network.
familiar with conference calls, PTT is like having a lot of folk in one
big conference call and all of them have their microphones on mute.
When someone speaks, they release their Mute button, speak and then
operate it again. Everyone in the conference hears what they said.
In the PTT
world instead of a Mute button there is a PTT button which actually does
the opposite. Press to speak, release to go back to listening.
groups of people to share a “channel” when they are all connected to the
internet has nothing to do with RoIP and is totally dependent on the
users own data connection.. Examples are the products from Zello,
Broadnet Systems etc.
standard two way radio look and feel to what is essentially telephone
understand, simple to use.
Can operate from
Apple phones, Android Phones, tables, PCs etc at no additional cost
although there are usually charges made by the service provider for
access to the server.
Depends on good
quality data connection to a service provider who operates a computer
server which provides the service.
Can be slow –
with delays before messages are heard. Not too much of a problem with a
home or business broadband connection, but often very poor using mobile
work at all well in 2G mobile areas. Normally inoperable under these
PoC (PTT over
This is very similar to the many PTT offerings made by Zello, Broadnet etc
but the difference is that PoC is an integral part of a mobile telephone
company infrastructure and it works much better for that reason.
PoC works well over 2G /3G/4G mobile links and is usually advertised as
being of carrier grade quality.
PoC is part of a mobile telephone company's offering, it is not a bolt
on by third party providers.
PoC was always much bigger in the USA. There have been offerings from O2
and Orange in the UK and they were of very high quality with a true
reach identical to that of the regular mobile phones.
Expensive and not taken up in large numbers. There are no current
providers in the UK.
Watch out for misleading
careful of extravagant claims concerning PTT products both in relation to
network provision and in comparisons with Tetra/Airwave.
Tetra/Airwave is a PTT radio network that employs over 5,000 dedicated base stations
providing a RoIP service.
A PTT handset
designed for use only on 3G/WiFi may look like a Tetra/Airwave handset but it
will not operate on a
network comparable to Tetra/Airwave and is dependent on your 3G or broadband
Everyone is, of course, free to compare anything with anything - a Boeing 737 can be
compared with a child's scooter - they're both means of transport after all. But
for practical purposes we would normally say that there is no comparison
between them and likewise we would say there is no comparison between
Tetra/Airwave and an internet accessible PTT computer server such as provided by
Broadnet advertises that it “Operates
the UK's largest push to talk & dispatch network covering 99% of the UK."
which it compares to Tetra/Airwave. Very misleading. We can't
find one UK provider of PTT handsets that actually operates a country-wide network**.
Broadnet and ITC utilise computers which you access by means of the internet.
Tetra/Airwave claims to cover 99% of the UK so we would advise you to be
very wary of a small business selling handsets that claim this kind of coverage.
clarify, if you are happy with your internet access (3G or Broadband) then you can indeed
use one of the many PTT Internet servers provided by companies like Zello,
Intouch, Radphone, PushtoTalk Phones Ltd., Phonetrader, Broadnet, ITC Global Communications etc. All of these can be useful services in
their own right but be clear that you understand their limitations. In
Scotland there are many large areas not covered by 3G telephones and most SIMs
work with only with one operator, be it O2, Vodafone or others. This might
leave you without 3G coverage. Resilience planners will also be very
sensitive to the dangers of relying on mobile telephone technology during incidents.
We stress these points
because questions about claimed coverage come up very frequently in
conversations with user services.
point, we've been asked if it is true that you can make a phone call to the
public networks from one of
these PTT Handsets.
Yes, a PTT handset
is nothing more than a mobile telephone running an internet based app. So if you put a SIM
in it then you of course can make a phone call!
If you already
own a mobile telephone you will already have a telephone number for it. When you
buy or rent a SIM for your PTT handset you will be carrying a second
mobile telephone with another mobile number.
install our Teamspeak PTT solution onto our existing mobile telephones. These
telephones are also used
for our FEEDNET Voip Network running one of the many VoIP apps, but in our case
we rather like Zoiper.
Some Examples of VoIP/RoIP/PTT Services:
Sipgate provide access to thepublic
local geographic and non-geographic telephone numbers. Residential andbusinessVoIP
and mobile phone services are provided on a prepaid,bring
Your Own Devicebasis.
To use Sipgate
you need to sign up (you can use some facilities free - go to their
website and try them)
When you sign up
you get a telephone number and a password. Program your VoIP phone with
their details and your passwords. Now you can make and receive calls
using your internet connection. Everything passes over the internet in a
digital format using the SIP VoIP protocol.
use of Sipgate to provide an outside dialing facility for FEEDNET VoIP
obviously cannot be depended on as a means of communication independent
of public services so we do not rely on it,
preferring to build extensive repeater networks to cover our region.
Not a service, but a piece of software. It is such an amazing one that
it is well worth mentioning here !
Asterisk is a complete VoIP/RoIP server that is open source and in use
in thousands of locations across the world.
Easy to set up by those who are IT literatem Asterisk can be configured
via GUIs supplied by third parties. We prefer not to use them since we
do some unusual things with our FEEDNET installation. Interfacing
Asterisk to a repeater system cannot be done with GUIs, you will need to
modify config files directly to do this.
Asterisk is a
core component of FEEDNET’s systems.
We use it for
general telephony, and we use it for conference calling, voicemail,
messaging and paging
repeaters and radio access points that connect wirelessly to FEEDNET and
can provide links from handhelds to outside callers
servers are located at different points on the network and they pass
calls between them.
cope with almost all codecs and we prefer G729 for its low bandwidth and
We often use
Cisco phones which are available for £15 second hand and that have G729
Broadnet provides a PTT app for Android and it operates servers to
provide a PTT VoIP service.
Computer aided dispatch also available.
A mobile telephone handset is available with a separate PTT button.
Saves you tapping the screen PTT button.
this is an internet based system. If there is no internet access, then
it doesn’t work.
could technically make use of Broadnet through the FEEDNET Internet Gateway but we
do not want to rely on public services during an incident. We also
prefer to be wary of giving credence to some of the claims we have seen
about network coverage.
Teamspeak as an alternative. See below.
Zello sell a PTT Android APP and a hosted server. Actually you can try
it as a free service. It is just like Broadnet but based in the US .
UK users have noticed bad latency problems. i.e. long delays from
speaking to being heard.
this is an internet based system. If no internet access, then it
We do not see any real
gain from connecting FEEDNET to Zello even though it is technically
Teamspeak is a long established proprietary VoIP system. The Apps and
the server are available to non-profit organizations freely.
Teamspeak provides PTT functionality and is noted for being a well
designed and effective system with widespread usage in business and in
the gaming community where low latency, high speed communications are of
Teamspeak has been around since 2001 and it does not make unrealistic
claims about its service.
Teamspeak is the
current FEEDNET choice for a PTT application. We believe Teamspeak to
be ideal for FEEDNET because a free licence is available and the server
can be operated in-house at FEEDNET node locations. The team can make
use of all the PTT functionality of Broadnet and Zello, but
unlike with those systems, we can use Teamspeak when the main public
services are unavailable.
Also there are
many more facilities than the other PTT apps. We can use file transfers
and other workgroup applications.
Many of our
operators and users prefer to carry Apple devices rather than Android.
The Teamspeak mobile apps for both Android and Apple are second to none.
Echo cancellation on full duplex, and noise reduction all work very well
in Teamspeak. You can program one of your telephone's physical buttons
to be the PTT or you can use the soft-button on the screen.
Mumble is an open source VoIP application that makes use of PTT like
more or less like Teamspeak.
Mumble is popular amongst home users and was first released in 2005.
Mumble is not as slick as the commercial offerings but many say it has
the lowest latency (delay) of any of the PTT VoIP systems.
Android Apps are available but many believe they are unreliable and many
do not recommend it for that reason.
FEENET can make
use of Mumble and it works well with PC softphones.
found the Android softare to be reliable enough for us so we don't use
it for FEEEDNET at this time.
** To clarify: A network is an
interconnected collection of nodes whose purpose is to provide communication
between them. A company that operates a network will either own the nodes
themselves or they will lease them, maybe on a shared basis. FEEDNET
for example has a very small network comprising some tens of nodes. It does have
an internet gateway so is accessible from any one of billions of internet access
points across the globe. It can't claim to operate a network with billions
of nodes though - this would be very faulty and misleading logic !!