The Inter-System Interface (ISI) is the standard way to connect TETRA networks together.
Some radio users regularly operate in an area that is at the border of two radio networks – either regional ones, or different country networks. It’s likely that they work together and communicate with people who use the other network.
Therefore, it would be best for them if they could easily use their own radio in both networks. To communicate with their own organizations, but also with people in the other network.
In other words, they need to roam to another TETRA network. They also need cooperation talk groups that have members from both networks.
ISI makes this possible.
The public safety organizations of different countries often have to communicate together. A pioneering TETRA project between Sweden and Norway aimed to make it as easy as using their own public safety radio networks.
The ISI project for Norway and Sweden aimed to ensure that emergency services can use their TETRA radios in both countries and communicate with those from another nation, as well as with their own team and home control room.
Get the inside information on the project from this free article.
More than 200 people from health care, emergency services and police from both Sweden and Norway participated in the ISI exercise in November 2016.
This video shows how the two countries' national radio communication was connected and used in a scenario of a bus accident.
Copyright © 2016 MSB, the Swedish Civil Contingencies Agency
The first trial of cross-border interconnected TETRA networks at sea took place on 23 November 2010. In the trial, German and Swedish officers communicated using Sweden’s Rakel network and successfully handled the communications around an imaginary incident near Ystad, Sweden.
Is ISI available?
Yes. TETRA System Releases 6 and above from Airbus DS include ISI functionality.
Is ISI interoperable?
Yes. Multivendor implementations are possible.
Does ISI support data?
Yes. In addition to group calls and one-to-one calls, the ISI standard includes covers status and text messages.
What is the physical connection between networks?
The physical connection is via fractional E1. A call occupies a 64 kbit/s E1 slot.
Since software Release 6, the TETRA systems from Airbus DS have included ISI functionality that meets the following standard specifications:
As long as the two networks support ISI functionality that adheres to the current ETSI standard, communication across network borders is possible even when the two networks have a different vendor.
Smooth communication across network borders is possible when the vendors providing TETRA interconnectivity have similar commitment to ISI.