One use of cross-border co-operation would to co-ordinate a raid on a criminal organization operating in different countries. Instead of using GSM and fixed-line phones, it would be more effective to allow police officers in different countries to use TETRA terminals to communicate as one team.

The tactical patch allows transparent communications between two (or more) normally unrelated talk groups within two separate networks.

Obviously, group calls are most important in this scenario. Individual calls may be possible as well, but should be regarded as special calls because it is necessary to know the terminal number in the foreign network. A kind of prefix may be needed in order to dial direct.

A second tactical patch scenario is to interconnect overlapping networks from different organizations (see diagram at the foot of the preceding page). In this case, users working in different radio networks may need to communicate with each other during an incident or event. Authorization for co-operation is typically granted by the officer in charge within the control room of the regional or nationwide network.

Some examples are:

• collaboration between public and private fire brigades during a large-scale incident or disaster. Private fire brigades are typically deployed by airports, tunnel operators and large industrial plants.
• communication between security personnel and public safety officers during incidents in sports stadiums, airports, shopping malls.
• communication between armed forces and police officers. Military personnel operating on a private system at a military base or compound can interoperate with public safety officers during events or incidents.
• communication between fire brigades, police and medical services during a large-scale incident or disaster, where these agencies operate their own independent networks.
• connecting a rapid-deployment radio system to the regional or countrywide network to scale up capacity during a large-scale incident or disaster. Here, both networks are supervised by the same user group.

In these scenarios, group calls are basically the only means of communication. The tactical patch connects two (or more) normally unrelated talk groups within two separate networks.

Scenario 2: expand coverage To expand coverage of an existing radio network by deploying additional networks requires multiple radio networks to act as one single radio network. This is challenging, because all current radio networks are based on proprietary architectures and thus cannot be integrated easily.

The need for this scenario (see diagram below) is obvious. It provides choice for the end user when there is a need to expand coverage or capacity. The user need no longer rely on the original supplier only and can thus avoid vendor lock-in.
With TETRA, the terminals should be able to work in both networks without reprogramming. This means that the Mobile Country Code (MCC) and Mobile Network Code (MNC) must match, and the same subscriber database must be shared by both networks. In practice, this is possible only if the networks are operated by the same agency.

Support of a rich set of functionalities will also be expected. These may include group calls, individual calls, text and status messaging, roaming, efficient cell handover, packet data gateways, encryption, authentication, and supplementary services such as calling line identification, talking party identification, pre-emptive priority etc.

Scenario 3: migration to another network This scenario is very similar to mobile phone roaming to a foreign cellular network.

When the radio is moved beyond the coverage area of its home network, it starts searching for other radio networks. If the foreign network indicates that it supports migration, the radio terminal will attempt to register on it as a visitor. Using an authentication-based handshake mechanism, authorized radio terminals will be granted access as visitors to the foreign network. In TETRA, this scenario is referred to as migration.

The objective of this scenario is identical to that of the TETRA Inter System Interface (ISI). But because the ISI is currently limited to supporting individual calls and SDS and status messaging only, the aim of ODINI is to support all functionalities which are important to end-users of mission-critical radio networks.

A real-life example of this scenario is cross-border operation by public safety officers. When an offender crosses the border during a car chase, the police can continue communicating whilst driving into the foreign country. Obviously, national policy should allow this type of scenario, but with the focus on international collaboration to combat crime, there is certainly a trend to permit such operations.

Solution based on IP

ODINI aims at supporting these scenarios by means of an open solution. Although some interoperability solutions currently exist, they are often too limited in their functional scope, are based on proprietary solutions, or are based on obsolescent technologies.
(中国集群通信网 | 责任编辑：陈晓亮)