interoperation
Right: a ‘tactical patch’ scenario for cross-border co-operation. It enables unrelated talk groups from neighbouring countries to communicate as a single team. SwMI denotes the switching and management infrastructure of a TETRA network
Individual call Group call
Site" A2
MS A1
Site" A1
MS B1
Site" A3
MS A3
Site" B2
Site" B4
MS A2 MS B3
Site" B1
MS B2
Site" B3
SwMI A
IP network
based on middleware could solve the problem in a network- independent fashion. As I have mentioned, vendor lock-in is another challenge
experienced by end-users. Proprietary architectures do not allow interoperation with base stations and dispatcher workstations from other vendors. Although this particular problem is almost impossible to address, it is certainly possible to interconnect networks based on available system Application Programming Interfaces (APIs) in order to expand the coverage of existing networks. Another practical problem faced by users is the
infl exibility of existing infrastructure solutions to perform software upgrades step-by-step, to adapt a region-specifi c confi guration, or to fi nd solutions for redundancy in order to achieve high availability.
MS B1 MS A2
Site" A2
MS A1
Site" A1
MS A3
Site" A3
Site" A6
Group call
Site" B1
Site" A4
SwMI B MS B2
Site" A15
SwMI B
Limitations of ISI T e top-tier TETRA infrastructure suppliers promised to solve a number of these problems using the TETRA Inter System Interface (ISI), and after almost ten years of delays this interface is now completed as a TETRA Interoperability Profi le (TIP). T e fi rst phase of interoperability testing has been
successful, but the ISI has some signifi cant limitations. T ese include high cost, reliance on almost obsolete technologies (E1, Primary Rate ISDN), and the fact that it supports roaming, individual voice calls and SDS transfer only. Group calls, relied upon by more than 80 per cent of users
within the public safety user groups, will not be supported by ISI until a further phase of testing has been undertaken. No time-scale for testing of group calls has been announced.
Scenarios for interoperability Identifi ed below are three diff erent scenarios for system interconnections. Not all of these scenarios may be applicable to all end-users. Whether or not they are relevant depends on the user organization and existing networks. Generally speaking, the earlier the user is in the process of planning and deploying a TETRA network, the more scenarios may be applicable.
Scenario 1: tactical patch T is scenario can be interesting for two applications. T e fi rst, illustrated in the accompanying diagram, supports co-operation between public safety offi cers across a national border, or between neighbouring regions in a large country. One use of cross-border co-operation would to co-ordinate a
SwMI A
IP network A tactical patch for inter-agency co-operation 30
raid on a criminal organization operating in diff erent countries. Instead of using GSM and fi xed-line phones, it would be more eff ective to allow police offi cers in diff erent countries to use TETRA terminals to communicate as one team. T e 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
TE TRA TODAY Issue 2 February - April 2011
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