TETRA and the Inter System Interface

Transcription

1 1 TETRA and the Inter System Interface A White Paper produced by the TETRA Association August 2010

2 i Contents Introduction... 1 TETRA Standardisation... 1 The Inter System Interface (The ISI) expectations... 2 Cross Border Communications Country Pilot... 3 Progress to date... 4 The standard... 4 Technical... 4 Operator's investment... 5 Industry investment... 6 Government investment... 6 Council of Ministers Initiative... 7 IoP certificates... 7 Further Development Options... 8 Solving an operational need... 8 Conclusion... 8 Notice The information provided in this White Paper is the best information available to the TETRA MoU Association Ltd at the time of writing. The information is provided by the TETRA MoU Association Ltd and, while we endeavour to ensure that the information is correct, we make no representations or warranties of any kind, express or implied, about the completeness, accuracy, reliability, suitability or availability with respect to the information contained herein for any purpose. Any reliance placed information is therefore strictly at the reader s own risk. In no event will The TETRA MoU Association Ltd be liable for any loss or damage including without limitation, indirect or consequential loss or damage, or any loss or damage whatsoever arising from loss of data or profits arising out of, or in connection with, the use of the information contained in this White Paper.

3 1 Introduction In today s world of high accessibility mobile communications it is perhaps inevitable that expectations are very high when it comes to any form of mobile communications. GSM, 3G and other cellular technologies have led to an expectation that mobile communications should be ubiquitously available wherever you are and whenever you want. Roaming, handover and internetwork calling are so commonplace that no one even considers how these communication techniques are implemented. Indeed, very few users of mobile networks would have any understanding of the complexity of providing these taken for granted services. What then of the land mobile networks such as TETRA, Project 25, Tetrapol and others? TETRA, in particular, has become established as the primary technology for mission critical networks. It is a mature and feature rich technology that has been implemented in well over a hundred countries of the world. One might reasonably expect that TETRA would also have comprehensive internetworking capabilities with such a highly developed technology. As part of the TETRA standard an interface has been specified that is designed to provide comprehensive inter-network connectivity. That interface is called the Inter System Interface; more commonly known as the ISI. It is apparent that some confusion exists in the LMR market about when the ISI is expected to be fully available and what level of functionality it will provide. This paper has been written by the TETRA Association to bring users and potential users up to speed with the status of the ISI and whether or not a fully functional interface will become available from the infrastructure manufacturers. TETRA Standardisation The TETRA standard is actually a suite of standards that together includes all of the features and functionality that makes TETRA such a valuable tool for users of professional radio communications. The core of the standard is the Air Interface protocol that handles all of the signalling between a base station and a subscriber unit. The Air Interface ensures that only legitimate subscribers can access the infrastructure and handles all of the signalling necessary to set up group calls, individual calls, telephone calls, and the various data services that TETRA provides. Direct Mode Operation (DMO) is the standard that does the same for subscribers that need to communicate with each other without access to the base station infrastructure. There are several other standards including the Peripheral Equipment Interface (PEI), and, of course the ISI. Some have argued that additional interfaces should have been defined as part of the standard. However, standardisation of a complex technology such as TETRA requires a huge amount of engineering time in order to define and agree the detailed protocols that are inherent in such technology. A balance therefore has to be struck between the time and cost of developing a standard and the benefit derived from it.

4 2 The Inter System Interface was included as part of the standards suite right from the early days of the standardisation process. However, the pressures of completing the voice services to satisfy urgent users needs resulted in prioritising the core elements of the standard in order to make them available to the market place in a timely manner. Although important, the ISI was considered less urgent at the time and work on that interface standard was therefore completed later. Was this a good decision? Well, the working groups clearly felt the need to prioritise their efforts in order to achieve acceptable timescales for the availability of TETRA systems and equipment. The core elements of the TETRA standard were defined as the Air Interface and the DMO standards. These provided immediate benefits to users wanting to replace their ageing analogue systems. Other standards such as the Peripheral Equipment Interface and the ISI were to be completed later in the process. It also has to be recognised that the need for the ISI only becomes significant once a substantial number of adjacent networks are operational. The Inter System Interface (The ISI) expectations In the early days of TETRA s development there were two primary expectations from the ISI. The first was the ability to handle cross border communications for the European Public Safety Agencies and the second was to provide the ability to create large networks from different manufacturer s infrastructure. The cross border requirement is being addressed and some effort has already been put into providing this functionality. The second objective was, perhaps, an ambitious target bearing in mind the complexity of TETRA networks and the wide variety of different infrastructures. The ISI may be a suitable mechanism to provide interconnectivity between regional networks. Indeed there are many large countries outside of Europe such as Brazil, China, Russia etc. for whom there is a need to interconnect many such regional systems but, at this time, it is unlikely that large homogeneous networks created from a multi-vendor supply will become a viable proposition. The ISI may be considered to be too complex an interface when connecting smaller networks together especially if there is no need for fully independent fleet maps or advanced security features. Many of the smaller systems are based on packet switched technologies whereas the full ISI requires QSIG and ROSE circuit based protocols. In such situations bespoke interfaces may be more cost effective than the standardised ISI. Cross Border Communications During the late 1980s and the early 1990s Europe was undergoing a transition to a borderless society following, what has become known as, the Schengen Agreement. This was a European decision to remove borders between countries and allow a free flow of citizens between them. This resulted in a number of issues for the Public Safety and Security agencies. Firstly it meant that each of the member countries had to take responsibility for the immigration of non EU citizens into Europe as, once past Schengen s outer border, they would be free to roam into any of the Schengen countries. Secondly, the freedom to cross borders also meant that those with criminal intent would also be able to freely cross borders. As a result it became apparent that there was a need to ensure good communications between the Public Safety and Security agencies of each of the Schengen countries and enable Public Safety officers to travel across borders without losing communications.

5 3 A group was created, which became known as Schengen Telecom, which was tasked with recommending solutions to ensure that radio communications were harmonised within Europe. First an agreement was reached with NATO to release 2x5MHz within the MHz band across Europe so that all users would be able to use common equipment for radio communications. Second it was necessary to select a single technology for use in this band and enable users to communicate with each other regardless of their location. After much work by the Public Safety organisations from Belgium, UK, Finland and the Netherlands, assisted by the ETSI technical committees, the emerging ETSI standard TETRA was chosen as the open European standard for Schengen. This was not universally adopted because certain countries were already committed to other technologies. In particular, France was rolling out a nationwide network based on the French designed proprietary technology known as Tetrapol. However, most EU and many non EU countries did decide in favour of TETRA technology and, as a result, TETRA has now become widely adopted throughout Europe. Following on from this success TETRA has been adopted across the globe and is now present in at least 117 countries of the world. Harmonisation of technology and spectrum is not the complete answer to cross border working and it was apparent that a means of interconnecting the infrastructures from each of the countries was required. This is necessary to ensure that subscribers roaming into another network can be checked and authorised for access to the visited network and also to ensure that a roaming subscriber could still communicate with his own organisation. This resulted in a need for an Inter System Interface. The Public Safety Cross Border requirements were therefore fed into ETSI s standardisation working groups. Over the last few years the number of operational Public Safety TETRA networks has increased. It therefore follows that the number of borders where cross border communication is required is increasing. This, along with an increasing number of both natural and man-made disasters affecting members of the European Union, is resulting in an increased demand for a solution to the Inter System Interface. 3 Country Pilot In 1996 the public safety administrations of three countries decided to run a trial in order to understand more about how cross border co-operation might work and how the radio communication system could be used. The three countries were Germany, the Netherlands and Belgium. The trials were supported by two infrastructure manufacturers Motorola who were supplying a national infrastructure for the Netherlands and a pilot system for Germany and Nokia 1 who were supplying a national infrastructure for Belgium. The trials did not take place until the necessary infrastructure was in place and this occurred during The German town of Aachen was chosen for the trials due to its close proximity with the borders of The Netherlands and Belgium. The trials were primarily intended to address the operational issues relating to cross border operations for which a relatively simple physical internetwork interface was required between the networks. 1 Nokia s TETRA business has since been acquired by EADS Defence and Security

6 4 A number of issues became apparent including: The need to co-ordinate fleet maps Agreement on a common language for interworking between agencies The need for common procedures The need for consistent terminology A detailed report from the 3 country pilot is available from the TETRA Association web site 2. A recent initiative has been proposed for extending the 3 Country Pilot. In 2008, three organisations (C 2000, ASTRID and BDBOS) agreed that the ISI should be implemented in a couple of years. They agreed on a common "list of requirements" in 2008, which was based on the paper of TETRA Association/ OUA TIP-phasing for ISI (TF , 17 Jan. 2008). The aim was to offer a basis for further standardisation of the ISI. Based on this list of requirements, the industry (EADS and Motorola) submitted a road map for the development of the ISI." Further details can be obtained from the TETRA Association. Progress to date The standard The ISI standard comprises multiple parts and the relevant documents are EN through to EN and TS These documents are available from ETSI. The ISI standard as a whole was completed by December 2003 (i.e. was ready for implementations) and updated and corrected by October It is a fact that some of the TETRA infrastructure manufacturers have been working on the development of the ISI but progress has been limited. This may seem strange bearing in mind that the need for the ISI as stated by the European Public Safety agencies is increasing. At least one manufacturer is continuing with their development and in May 2010 a Memorandum of Understanding was announced for a solution on cross-border communication to be implemented between Sweden s Rakel network and the German BDBOS network in order that cross border trials could take place. At this stage, only some of the features of the ISI according to the ISI standard are implemented, especially group call functionality is not included. Both systems have been supplied by the same manufacturer. ISI implementation between multiple manufacturers systems however remains a challenge. The reasons for the lack of progress are many and complex: Technical With the success of inter-network roaming in the cellular phone industry it may seem strange that progress in the TETRA industry has not been similarly effective. However, it should be recognised that the roaming capability in a cellular environment is significantly easier to achieve than it is with TETRA. If a GSM user roams to another country then a message is sent to the home network asking for confirmation that this is a valid and credit worthy user and that roaming is allowed. 2 This report can be found in the Reports area of the Library under the Resources section of the TETRA Association website. see

7 5 If the response from the home network is positive then all further calls to that handset are forwarded through the visited network. All outgoing calls are billed back to the home network. With the possible exception of call diversion and availability information there is little else that needs to be tracked across interface. TETRA networks, on the other hand, do not just provide person to person calling. A TETRA subscriber will be part of one or more talk groups in its home network. When the subscriber migrates or roams to another network, not only is it necessary to authenticate him on to that network, but decisions will need to be made about what kind of traffic is forwarded to the user and what is not. If the user has been sent to assist with a major incident in a foreign country then he may not need to continue his membership of his home talk group. It will be necessary to assign him temporarily to a new talk group which may have been set up as a temporary group or may be a normal group in that country. Despite being re-assigned, the user will need to be able to call his home dispatch centre for authority to perform certain actions, but also needs to be able to receive calls from the visited dispatch centre who will be issuing instructions to deal with the incident. Questions arise with regard to telephone calls made by a visiting user. Will they be allowed? Should they be billed back to the originating network or the cost covered locally? Encryption complicates roaming subscribers significantly as national police forces may be unwilling to release encryption keys to visiting users. Although European Public Safety agencies have standardised on the TEA2 encryption algorithm it is possible that different encryption algorithms may be in use in the different countries outside of European Public Safety systems. End to End encryption too may be difficult to coordinate especially if different algorithms are used. The issues described above are far from an exhaustive list of the technical and operational considerations that need to be addressed when users roam from one country to another. However, they serve to illustrate the complexities involved in specifying and developing the Inter System Interface. Indeed a key issue to be addressed is that the existing systems do not have coordinated fleet maps and this, in itself, is a major hurdle in solving the ISI issue. Additional detail describing this issue can be found in the 3 country pilot report 3. Operator's investment Many networks, including public safety networks, are run on a commercial or pseudo commercial basis. Cross border cooperation incidents are likely to represent only a very small fraction of the total traffic within the national public safety network, even if the need to support those is clearly identified. Thus it is not likely that the network operator could cover the ISI investment cost with the possible income accumulated from roaming fees or cross-border calls; the end users may not even pay any additional fee for the use of the ISI. Operators may therefore be tempted to use their available investment budgets to deploy first some other new functionality in their network rather than to set aside funding for the ISI. Alternative and dedicated funding for the ISI could encourage the network operators to proceed more quickly. 3 This report can be found in the Reports area of the Library under the Resources section of the TETRA Association website. see

8 6 Industry investment It is clear that different infrastructure manufacturers have developed their systems from different starting points and that this has influenced the design of the core components of each infrastructure. For example, some manufacturers based their designs on existing telecoms platforms where as others used existing analogue LMR systems and a few started with a clean sheet of paper. In many case the development and integration of the ISI into existing platforms is a complex, resource intensive and costly exercise. In order to maintain a competitive edge, manufacturers also need to develop new functionality and next generation systems. Diverting engineering resources to the development of the ISI is therefore not an easy decision to make in today s highly competitive world; unless of course a substantial market exists for the ISI. Government investment Whilst many countries, especially in Europe, have indicated their desire and/or need for the ISI, few have been prepared to commit substantial budget allocation to purchase the capability once it becomes available. This results in a chicken and egg situation, where industry will not invest in the technology without commitment from users, and users will not commit to a technology without a clear timescale and cost or, in some cases, against unproven functionality. In order to alleviate this difficulty an initiative is underway to seek central funding from the European Commission that would unblock the current impasse. (See Council of Ministers Initiative below) In addition to the physical implementation costs of an ISI it has to be recognised that there are substantial ongoing costs of maintaining the interface between different national systems. Currently the ISI is specified to utilise multiple 64kbit/s E1 connections between switches. As the interface is based on circuit switched connections this implies that permanent nailed-up connections may need to be made between one national infrastructure and every other infrastructure where roaming is required. Assuming that the operational requirement is for cross border working only and for those with only a small number of neighbouring countries this may be an acceptable, if costly, operational cost. However, there may be a need for support teams to move from one European country to another even if they do not have adjacent borders. Where major incidents occur and roaming is required throughout the EU, then the cost of providing nailed-up circuits to each and every other EU country would clearly be prohibitive. For such requirements an alternative solution would need to be found. Whilst the comments above relate to the European Union, similar situations will exist where regional networks need to be connected within a larger, possible national network.

9 7 Council of Ministers Initiative Within Europe the Police Cooperation Working Group (PCWG) operates under the Committee of Permanent Representatives in the European Union. The PCWG has set up an ISI subgroup to make recommendations to the European Commission for funding that would facilitate progress of the ISI. The ISI group is made up from a number of public safety agencies including those from the original 3 country pilot nations and is supported by several manufacturers. Although initially the focus will be on finding a solution in the form of a prototype for the TETRA TETRA interface it is also recognised that a need exists for a feasibility study on a Tetrapol Tetrapol interface and a TETRA Tetrapol interface. The Public Safety organisation PSC-E may become involved in the initiative and the TETRA Association has also offered its support. Whilst the PCWG initiative has to be welcomed, and may ultimately be the catalyst to unblocking the current impasse, it must be recognised that this will not provide a speedy solution. The ISI group will be required to develop recommendations for the PCWG to submit to the European Commission. The Commission will then need to debate the issue and, assuming a positive outcome, allocate funding from a future budget. In the current economic climate within Europe there is no certainty of such a positive outcome. If a research grant was approved, and with the testing and validation that would be required, it seems that any fully operational ISI between all main suppliers of European Public Safety TETRA systems is unlikely to be available before 2015 at the earliest. IoP certificates Readers of this paper may be forgiven for being confused by the publication of IoP certificates for the ISI. 4 These certificates were issued against a limited subset of the functionality of the ISI specification and are not necessarily available from production equipment. Group calling functionality was a significant omission from the IoP testing undertaken and is a fundamental requirement of mission critical users. It was, however, a positive result that two manufacturers were able to demonstrate the necessary cooperation to achieve a successful testing process and that a basic set of functions could be shown. However, unless all of the manufacturers developing ISI are prepared to implement the feature set developed by the participants in the 3 Country pilot then real user requirements will not be satisfied. 4 The IoP certification process has been developed by the TETRA Association in order to ensure demonstrable compatibility between different manufacturers equipment. See

10 8 Further Development Options The original specification of the ISI was based upon an E1 link between infrastructures. However, since that specification was developed, some infrastructure manufacturers have adopted an IP based network architecture. As a result of this, a work item has been initiated within ETSI to add a specification for an IP based interconnection between infrastructures as an additional option. Once complete, users will be able to evaluate the most cost effective interconnection architecture between systems for their particular situation. The requirements of mobility management, authentication and inter-nation fleet mapping still remain the most significant technical issues that need to be solved regardless of the type of interconnection used. Solving an operational need The TETRA Association has always sought to ensure that it represents the interests of the User organisations as well as Manufacturing Industry. Indeed the variety of member types has been one of the Association s key strengths. It is therefore unfortunate that, with regard to the ISI, industry and its customers have been unable to reach an agreement on a mutually acceptable way forward. Without doubt, the citizens of Europe should be served by Public Safety agencies that are equipped with the best possible tools to undertake their sometimes difficult and hazardous tasks. The need of those agencies to have the ability to operate across national borders, particularly in times of crisis or disaster, has been voiced for more than a decade. The Association urges industry to step up to the plate and find a solution to the ISI requirement. With genuine cooperation between industry members the best possible communications capabilities could be provided with a minimum of delay. However, one must recognise that there are two sides to every coin and one cannot expect industry to invest in new technology without a demonstrable market. The Association therefore believes that the User Community should share the responsibility of finding that solution by jointly committing to purchase ISI capability in order that industry can move forward with the development. Whilst EC research funding may help towards a long term solution, it is clear that the ability of the emergency services to respond to cross border incidents will be sub-optimal until ISI capabilities are in place. Conclusion It is unfortunate that the Public Safety agencies of Europe and elsewhere in the world are currently unable to communicate effectively across borders and between networks. With the threat of natural and manmade disasters increasing steadily the citizens of this world will expect to see the collaborative efforts of agencies from different countries in dealing with such events. The ISI will provide benefits for routine operations across borders too and a solution for interconnecting networks is needed if those agencies are to operate effectively.

11 9 It is a positive step forward that operational trials are underway between two users (Germany and Sweden) albeit with limited functionality. It can be expected that this will be a stimulus for further progress in the future. Whilst the initiative to seek funding from the European Commission for a European solution has to be welcomed, the success of this is far from certain and the timescales for a more comprehensive solution are distant to say the least. There can be no doubt that the costs of development for this complex interface are high and, at this time, the market for the capability is unclear. Whilst criticism has been laid at the door of the manufacturers for the lack of progress, perhaps with some justification, the users too must recognise that the laws of supply and demand are as relevant to the ISI as to any other communications technology. For industry to make the investment, a demonstrable market needs to exist. Without a firm commitment to purchase the ISI, industry will make its own decisions as to where they will get the best return from their development budgets. Whilst the ISI is undoubtedly a complex technical requirement there is no doubt that a solution can be found. For that solution to be available in the near future, industry and the user community needs to come together to agree an operationally acceptable user requirement and an economically viable means of delivering it. In the meantime users will need to make do with other, less effective, processes for dealing with cross border cooperation. The TETRA Association - August 2010