PTToC allows users to replicate radio features like group
communication or instant duplex communication with
a simple button push. This smartphone application
presents an opportunity for staff without radios to access
commmunication features that radio provides, from their
WiFi networks are pervasive now, and offer excellent
broadband coverage in many places. As long as a PTT user
is connected to the internet – through a cellular network,
WiFi or another bearer – they can communicate through the
PTT app on their smartphone.
Is PTToC Mission Critical?
Mission critical systems must guarantee a certain level of
service, which cannot be guaranteed on cellular networks
today. In particular, availability and latency cause problems
for mission critical users.
• Public carriers are more prone to failure during large
emergencies. Large events can clog public networks,
even take them down. However, mission critical networks
are built for availability, and even if the network fails,
users can still communicate through simplex mode. You
simply don’t have that type of redundancy with PTToC.
• On LMR, the time between pressing the button and
when a call is received is typically 200 milliseconds.
On a public cellular network that services millions of
consumers, mission critical users simply don’t have
control of that timing. When there are too many people
active on the network, there can be unacceptable delays.
But while PTToC cannot be mission critical today, it can still
offer benefits for mission critical organizations.
Expand the user network
Even mission critical organizations have a percentage of
staff who do not require critical communications. Ideally
you would connect them to the network, but often, the
additional cost can’t be justified.
Let’s look at public transport for example. Many staff on
a train don’t have push-to-talk device radios today, but
they do carry mobile devices for mobile ticketing or other
data tasks. If there is a safety issue, a security incident
or emergency, a push-to-talk application on that device
means a ticketing agent can alert dispatch or the conductor
through the group communication network.
Available anytime and anywhere
Another big advantage of PTToC is the IP connection. As
long as your smartphone is connected to the internet, you
can connect to your critical network from anywhere in the
world. Imagine you’re a police chief who’s off-duty on a golf
course in Hawaii, and you learn about a major event in your
home town. Through the IP connection, you can instantly
join your organization’s communication, ask the right
questions and talk to your people, or just listen in to make
sure the situation is under control.
Cellular and WiFi signals will work where private radio
data LMR system signals may not. In large buildings like
malls or hospitals, and underground locations like utilities
substations, WiFi gives your people an extra layer of
coverage that helps fill black spots.
Integrating PTToC into your network
Integrating mission critical radio with PTToC can create a
“network of networks” for the best of both worlds. Several
techniques are already in use.
Increasingly, simple analog gateway devices are integrating
a PTToC domain into a land mobile radio domain, so that
audio can pass between push-to-talk app users and users
on the radio system.
That audio gateway can also be transformed with protocols
such as ISSI for P25 and AIS for DMR. These intelligent IP-based software gateways pass both audio and information
like the subscriber unit ID or emergency call-out signaling
from unit to unit.
The next step – currently under development – will truly
unify the push-to-talk and the land mobile radio for the
end user. If a user pushes the PTT button on the radio or
speaker mic, the device will select whether the signal will
transmit over LMR or broadband. This decision is automatic,
depending on the strongest available signal. This will be the
ultimate integration technique because the user doesn’t
need to decide between devices. They can use a traditional
device and gain access to the “network of networks” for the
best coverage possible.
The road ahead for PTToC
The standards body that manages the mission critical
PTToC is the 3rd Generation Partnership (3GPP). Their
primary goal is to replicate LMR features in the cellular
world. Through the standards, we can safely predict a
number of enhancements in the future of PTT. These