P25 interoperability for public safety agencies

To keep personnel and communities safe now and in the future, public safety agencies must work together to overcome technology barriers. While interoperability is the ultimate goal, there is often confusion about exactly what interoperability means and just how genuine claims relating to it are.

Interoperability refers to a variety of scenarios including: multiple vendors’ radios working together; multiple agencies working together - for example, police, fire and EMS at an incident scene; neighbouring state-wide networks working together.

Failure to interoperate in any of these scenarios can have drastic consequences. This article addresses multivendor interoperability and its implications for public safety agencies.

Public safety interoperability is critical

Interoperability is a powerful tool for public safety agencies and one that must be right. Personnel and communities rely on the ability of agencies to communicate and coordinate with each other at large events and in times of need. Interoperability achieved can result in success - conversely, its absence can turn difficult events into disasters.

Of the many vendors who claim to offer ‘P25 compliant’ radios, the question must be asked - to what extent are they truly compliant? The reality is that not all P25 radios work on all P25 networks as the standards allow room for interpretation. This is a major concern for public safety agencies finding themselves constrained by proprietary functionality and with varying levels of interoperability between agencies and neighbouring state-wide networks.

To give public safety purchasers confidence that their P25 equipment conforms to performance standards for interoperability and conformance, the P25 Compliance Assessment Program (CAP) was established in 2009. While this is a start to ensuring interoperability between vendors, it is not enough to rely on this program in isolation.

Factors that affect interoperability between vendors include the interpretation and implementation of the P25 standards, radio configurability and certification processes for vendors onto regional and state-wide networks.

Public safety agencies now have access to more information than ever before, giving them the confidence to establish solid future-proofed communication plans. Through the open architecture of P25 technology, users will benefit from greater choice, price competition, more funding options and the ability to purchase a solution to fit the needs of an agency.

Understanding the P25 standards

There is a great deal of misunderstanding among public safety agencies as to exactly what the P25 standards and rollouts are and the benefits they provide.

There are three levels of P25 standards:

• Mandatory: features that, to be P25 compliant, radios must meet the stated functionality as specified by the Telecommunications Industry Association (TIA);
• Standard options: features which, if offered by a manufacturer, must be built to the P25 standard;
• Manufacturer’s extensions: features that are manufacturer-specific, normally proprietary and are not required to be P25 compliant.

Public safety agencies may be unaware of the various levels of P25 standards, only to find themselves trapped by vendor-specific proprietary functionality that limits interoperating with equipment from other manufacturers. The expectation that all ‘P25 compliant’ networks and radios will work together is clouded by the fact that the P25 standards do not exclude proprietary features that may prevent interoperability between radios and network equipment from different vendors.

The P25 phases

There are currently two rollouts of the P25 standards: Phase 1, which is complete, and Phase 2, which is waiting to be published.

The public safety market is only now beginning to understand Phase 1 but there is already a push from vendors promoting Phase 2-capable equipment in relation to the FCC narrowbanding compliance mandate.

However, it is not widely recognised that Phase 1 already meets the narrowbanding requirements of most operators simply by achieving 12.5 kHz operation. 12.5 kHz spectral efficiency may be all that an agency requires.

While Phase 2 standards are sufficiently advanced for manufacturers to develop Phase 2 products, only P25 Trunking operation has been defined so far. For trunked network operators, the main benefit of Phase 2 is improved capacity through greater spectral efficiency: that is, being able to receive two communications paths from one channel on the same frequency, where currently there is only one.

If an agency operates a P25 Phase 1 Conventional network, it needs to be cautious about upgrading to Phase 2, since the standards for Phase 2 Conventional operation are still undefined. These are expected within the next few years.

Phase 2 enables more users and more conversations on existing frequencies, so it has great potential benefit for agencies whose current network is heavily loaded. Agencies with sufficient channels for the number of current and future users will see fewer benefits of implementing Phase 2 as they may pay a premium for more functionality than actually needed. In this scenario it would be more economical to add extra channels to the existing network.

As many agencies are feeling driven to buy P25 Phase 2 now to narrowband their communications solutions, it is important to understand two options: purchase Phase 2-capable equipment now and hope that it complies with the interoperability standards when they are finalised or purchase P25 Phase 1 equipment to achieve narrowbanding compliance now and upgrade to Phase 2 when the interoperability is defined, if greater spectral efficiency is needed when budget allows.

To avoid purchasing new hardware, users should consider only those radios that offer either hardware or software upgradability so they will only have to pay for the upgrade cost to obtain Phase 2 features. If an upgrade is not supported, they should negotiate a commitment with the vendors. A commercial upgrade policy for P25 Phase 1 radios to Phase 2, such as Tait offers, allows users to plan now for a staged migration to fit with their timing and budget.

When planning a migration, it is important to consider the network in its entirety, including coverage, antennas and backhaul (linking between sites), and not to consider it in parts. Consultation with network design experts can design and deliver a comprehensive migration plan.

Public safety agencies are already seeing equipment marketed as ‘Phase 2-ready’, but it is not clear when the upgrades will be available. There is presently no P25 Compliance Assessment Program (CAP) testing for the Phase 2; consequently, no manufacturer has undergone Phase 2 CAP testing and interoperability cannot, therefore, be guaranteed.

P25 compliance

CAP is a government initiative to define ‘P25 compliant’ by creating a framework of standardised conformance tests for manufacturers’ equipment.

P25 CAP testing provides public safety agencies with objective evidence that their equipment meets P25 standards for interoperability and conformance. The CAP suite of tests currently encompasses P25 Phase 1 and will include testing for Phase 2 to demonstrate interoperability between vendors’ equipment.

The outputs of P25 CAP testing include Supplier’s Declaration of Compliance (SDoCs) and Summary Test Reports (STRs) which vendors publish to the Responder Knowledge Base website: www.rkb.us, and gives vendors the ability to state that version x of Tait’s radios work on version y of Motorola’s infrastructure equipment for example.

• SDoCs state that a particular radio meets CAP requirements;
• STRs show the actual test results from the CAP laboratory and are typically of one radio’s performance on another vendor’s network. They show which tests were passed or failed.

Publication of these documents on the RKB website is proof of interoperability based on the CAP tests. This is often a requirement for some funding grants which mandate P25 CAP-tested equipment, providing an incentive for vendors to participate in P25 CAP testing to achieve interoperability with other vendors. Agencies looking to purchase can ask vendors for these documents to make informed purchasing and funding decisions.

It is important to note that a failure in a P25 CAP test can still result in compliance as it might be a failure on an ‘optional’ item. Test failures should be seen as positive outcomes since they demonstrate that the testing is working and they encourage vendors to collaborate to ensure that errors are caught and exposed in a controlled environment, allowing them to be fixed prior to deployment in the real world. A ‘failure’ identifies an area of functionality that is likely to be corrected by any given vendor.

P25 CAP testing does have some limitations:

• It guarantees a minimal level of interoperability. The CAP, just as the P25 standards themselves, is growing and evolving as new requirements are added.
• Proprietary extensions are not covered in the testing - only mandatory standards and some standard options are included. There is a risk of problems being found at deployment; however, most vendors are experienced enough to resolve these issues as they arise.
• P25 CAP performance can’t give coverage and performance guarantees as coverage and performance depends on many aspects including the specifications of the radio itself.

Nevertheless, the P25 CAP represents a detailed and vendor-neutral yardstick of interoperability that has been embraced by manufacturers who have willingly invested time and effort to test each other’s equipment.

The pitfalls affecting interoperability

It is a reasonable expectation when purchasing P25 equipment that all P25 radios should work on P25 networks if they have passed the necessary CAP tests. However, individual radio idiosyncrasies, confusion about the P25 standards and programming and configuration are just some factors that affect the level of interoperability.

P25 definition is still work-in-progress by the TIA, which leaves room for uncertainty in features such as data communications or AVL/location services. The standards themselves have variations on standardised functions based on a network-to-network scenario. Some P25-defined functions, such as Failsoft operation, require as yet undefined supporting features to make them work. If each vendor implements the supporting features differently, the standard Failsoft functionality becomes non-standard since it depends on proprietary design of the supporting function.

Radio operation is often configured at the user or vendor level and if it doesn’t match the network configuration problems can arise. Vendors should be able to offer strong support staff to resolve these issues.

Usability is vendor specific, it is not related to the P25 standards and is one of the major obstacles to having multiple vendors on a state-wide network as the network certification tests are based on existing radio functionality and not on the P25 standards themselves. It is recommended that users create some usability standards if they are looking to get multiple vendors on their network and it is a good practice that not every feature of the radio is defined as it may end up reducing the ability for other radios to come onto the network. Users need to make sure that the testing criteria matches the requirements and that this criteria won’t become a limitation later if multiple vendors need to work on the network.

Multivendor procurement enables greater options to find a solution that best fits users’ needs and budgets, and a highly prescribed testing criterion for agencies can limit options. The core feature sets are defined through the mandatory standards.

The standard options and manufacturer’s extensions, however, are largely defined by individual vendors or when programming, therefore no ‘uniform’ operation necessarily exists.

Vendors may choose not to implement a particular standard option and ‘standard’ P25 radios may well have ‘non-standard’ features on them, so it is important that purchasers understand these features early in the buying cycle to avoid being locked in to a particular vendor.

Vendors cannot guarantee radios will be interoperable if they use non-standard functionality. This can become a roadblock to multiple vendors supplying radios for networks. It is important that users make wise decisions when accepting non-standard functionality as they can end up limiting the choice of radio paying more as a result. For example, a user may purchase some affordable encryption only to later discover that it is a proprietary encryption. This encryption package will now restrict them from purchasing any other type of radio unless it also has the licence for that proprietary encryption. These licences also have their caveats: vendors may be charged a royalty fee per radio making it impossible to compete against it or the licence may not be for the full function of the feature. Don’t get trapped into proprietary features that will restrict future options.

Each network owner specifies different rules for radios to operate on their network, which can result in a lack of interoperability if proprietary functionality is specified as a prerequisite to get on the network. Benefits of being on a state-wide network include greater coverage, vendor choice and improved interoperability with neighbouring agencies.

Greater understanding can ensure interoperable future

A challenge all public safety agencies face is that of genuine interoperability with other agencies and it could be when it is needed the most that it is not available. The open standard architecture of P25 aims to define this for network operators; however, in reality, the standards allow for variation and, as a result, genuine interoperability may be compromised. Those tasked with purchasing equipment for their agency face the daunting task of selecting the best solution for their needs now and into the future. There are actions that need to be taken which address these and will help protect personnel and communities.

While some vendors are promoting Phase 2 as driven by the FCC mandate, it is important to understand that Phase 1 can meet immediate, and potentially only, narrowbanding needs. The only 6.25 kHz mandate is in the 700 MHz band. If users are purchasing now, ask vendors for proof that the equipment meets P25 performance standards for interoperability and conformance.

P25 CAP is one way network operators can purchase from a new vendor. In addition, they can ask to see which vendors’ radios have been tested on their proposed network and which, if any, features are proprietary. Vendors concerned with interoperability will actively participate in the P25 CAP.

Claiming interoperability does not guarantee interoperability. Vendor interpretation and misunderstanding of standards, usability and differing certification processes all lead to a confusing and frustrating lack of interoperability when they are led to believe that P25 equals interoperability. To make certain they are designing an interoperable future, they have to understand the P25 standards and phases, and what requirements they have from a user and network perspective.

Match testing criteria for network certification to agency needs and use the resources available, such as CAP, to research options thoroughly before committing to one vendor. Thorough research can present options offering greater value for budget requirements and will ensure communications go where and to whom they are needed.