Sometimes the number of subscribers is small, and the territory is measured by long distances (truck drivers, logistics) and it is not economically feasible to build your own radio communication system. In this case, you have to think of using of group communication over public cellular networks with PTT over Cellular (POC) technology.
In true professional radio systems one Group requires 1 talk channel. The same goes for data transfer. Thus, you can create a group call for thousands of users while using a limited network resource – only 1 channel.
In POC systems, to organize one group call, each specific subscriber needs an individual data channel. It is necessary to public operator to reserve capacity equal to the number of subscribers. That is why it does not seem reasonable for an operator to prioritize POC traffic.
There is also the problem of allocating a timeslot to multiple users within one base station. In the case of group call, the delay in providing voice traffic to different users can be up to 2 seconds. You may predict a disaster in operational procedure with that delays.
POC can be really interesting for truck drivers and services similar in use – logistics. However, the condition of the operator’s 3G / 4G coverage on the roads makes the task of organizing communications unpredictable.
Some of the disadvantages of using smartphones for technological purposes can be avoided if the POC software if it supports industry-designed voice codecs – such as ACELP as in the TETRA standard.
Our company proposes to use POC technology not as an independent architecture, but as an extension of the existing DAMM TetraFlex professional radio communication system in areas where the installation of a base station is not cost-effective or impossible, but at the same time there is WiFi or LTE, 3G, GSM / EDGE coverage.
Functionality of DAMM POC Node
– individual terminal-to-terminal calls;
– group calls terminal-group of terminals;
– dispatch calls to a terminal or a group of terminals;
– localization (positioning) of subscribers with the help of a dispatcher console;
– work via Wi-Fi or cellular networks;
– multi-level user authentication and data protection;
– transfer of video files and video streams from the terminals to the dispatcher;
– emergency call;
– keeping of up to 14 levels of priorities for users;
– use of terminals with assigned push-to-talk button;
– recording of conversations and export to external media (on a dedicated closed resource of the Customer);
– connection to the telephone network of the company;
– call forwarding within the POC network;
– low-speed industrial codec TETRA ACELP (12 kbps) on client devices;
Key parameters of Infrastructure DAMM POC Node.
The infrastructure is built on the MESH principle – without a single point of failure, and the number of connected terminals is determined by the ground infrastructure hardware.
Conditional limits are defined by licensed features that allow you to define the following parameters of the POC network:
– up to 999 independent POC nodes, each of which can have an independent connection to the ground infrastructure, a set of licenses, external interfaces;
– up to 255 active subscribers for each program unit/interface, taking into account the available communication channel;
– licensed number of network users (subscribers):
a) up to 50 subscribers;
b) up to 100 subscribers;
c) up to 250 subscribers;
d) up to 500 subscribers;
e) up to 1000 subscribers;
f) up to 10,000 subscribers;
g) up to a maximum of 150,000 subscribers;
– up to 25 independent segments (servers) for recording conversations;
– up to 1000 independent organizations / subdivisions within the network, connected by rules and profiles;
– up to 20 dispatch consoles per Segment/Node;
Data protection
Protection of client’s data from interception and substitution is carried out through:
– personal Authentication Key,
– PIN code,
And the protection of voice streams and conversations is carried out through a VPN tunnel based on Cisco AnyConnect with content encryption with the required depth.
As a firewall, you must use Cisco ASA 55xx, which allows you to create an individual client password to form a VPN tunnel.
Where to begin?
The required minimum set of equipment to build up Group Dispatch Cellular Communication System should include:
1. Server with redundant power supply, two SSD drives and RAID;
2. Cisco AnyConnect VPN platform consisting of:
– ASA 55xx firewall of the required performance and with a license for remote connection of the required number of users;
– AnyConnect VPN clients for client devices (to be installed);
– a dedicated domain name and an SSL certificate issued for it;
– a dedicated IP address for the server and a stable connection to the Internet at a speed proportional to the predicted traffic.
3. Personal smartphones with PTT button.
The recommended smartphone is the RugGear RG725 to which you can connect external professional radio accessories like RSM.
