In the market for… PTT over Cellular platforms
Written by: James Atkinson | Published:
I take the view that a commercial PoC provider seeking full access to the 3GPP Mission Critical ...

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PoC provides two-way radio style services over cellular networks, but there are some key factors that potential customers need to check out before committing, as James Atkinson reports

4G LTE networks are now capable of providing the data speeds and low latency to make Push-to-Talk over Cellular (PoC) services a very attractive proposition. A number of PoC platforms are now established in the UK and elsewhere to provide customers with a reasonable choice.

The first thing to ask is what can the PoC platform guarantee in terms of Quality of Service (QoS), reliability, availability and security? PoC providers are obviously reliant on the performance of the Mobile Network Operators’ (MNOs’) networks, but they can offer higher QoS than consumers get as Tim Allerton, CEO of UK-based Push to Talk International (PTTi), explains.

“We wanted to provide some level of QoS, so we only use static IPs and dedicated APNs [Access Point Name - the gateway between the 2G, 3G and 4G networks and PTTi’s servers]. We can negotiate priority access for that APN. We then use the operator’s QCIs (QoS Class Identifiers) and ARPs (Allocation Retention Priority) to provide dedicated data services to our customers for both the uplink and downlink.

“You can then add higher levels of service using Mission Critical PTT (MCPTT) criteria,” asserts Allerton.

Servers
To provide the necessary control and security the PoC provider needs its own servers. PTTi’s data servers are sited in London using the highest level (Tier 3) hosted service with redundant and dual-powered servers, storage, network links and other components in case the primary server fails. PTTi’s servers have dedicated APNs into each of the UK MNOs and each customer has its own slot on the server and SIM numbers with individual IP addresses.

Wireless Logic, the M2M/IoT managed services solution provider, also offers a PoC service via its Push- to-Talk UK division. It also uses fixed IP SIMs and private APN data routing and makes use of its existing NetPro private network servers housed in Tier 3 data centres in London with fully redundant interconnects.

Jon-Paul Clarke, business development director – UK at Wireless Logic, says: “One of our USPs is being able to offer a range of packages and services from a simple PoC device with a fixed IP SIM to a service using dedicated APNs and additional levels of security and device authentication.”

Roaming
Another approach to providing QoS differentiators is to offer multi-network roaming, as Bournemouth-based iPTT does. All its devices are ‘network unlocked’, so customers can insert their own SIM and use whichever network they want. Alternatively, they can insert an iPTT multi-network SIM, which will automatically switch between the four UK networks. This can be extended for an extra fee to both EU and USA SIM cards.

“If you use one of our multi-network SIMs you minimise the amount of coverage blackspots,” points out Hans Becker, director at iPTT. “The device switches between different networks to find the best signal.

“We offer both standard multi-network SIMs and QoS SIMs. For the QoS SIMs we provide software on the device that enables it to cycle faster through the networks to find the least congested one and so connect you faster.

“If we have mission critical customers, like an ambulance service paramedic, you can also get higher priority access by using a Home Office approved MTPA (Mobile Telecommunications Privileged Access) SIM. The MNOs recognise that it is a priority SIM and bump it up the priority chain. MTPA works on a multi-network basis too,” says Becker.

Wireless Logic also offers roaming. “For example, the Dutch operator KPN provides us with a roaming SIM proposition. The PoC device accesses the multiple network of MNO towers across Europe, but it is rooted through the KPN core network into which we have dedicated links, so the user still gets the priority benefits of having a single fixed IP address and dedicated APN,” says Clarke.

In the USA, ESChat (Enterprise Secure Chat) provides an over-the-top (OTT) PoC service accessing all the main US carriers. Large businesses with dispersed operations across the US can select whichever carrier is best for a particular area. ESChat offers various levels of QoS depending on the carriers. Customers can access ‘best effort’ services from T-Mobile, Sprint and Wi-Fi networks, for example. Or they can choose to access the higher QoS services available from Verizon’s Private Traffic Network Management (PTNM) solution and AT&T’s Dynamic Traffic Management (DTM) service. Qualifying public safety related businesses and government agencies can also access even higher levels of QoS for PoC via AT&T’s dedicated first responder FirstNet networks.

Hosting options
Potential PoC customers should also look at the Cloud hosting options available to them. The UK PoC companies PTTi, iPTT and Wireless Logic provide their own hosted servers and Cloud services, which enables them to deliver high levels of service and security.

In the US, ESChat’s business customers use Amazon’s AWS Standard Cloud across 42 ‘Availability Zones’ with 16 geographic regions around the world. ESChat’s US government agency customers are hosted on Amazon’s AWS GovCloud, an isolated AWS Region, designed to meet specific regulatory and compliance requirements for customers with ‘sensitive’ data traffic.

Alternatively, ESChat customers can host their PoC services in their own premises to provide enhanced security and off-network operations on an isolated PoC system completely ‘air-gapped from the Internet’.

Applications
All PoC platforms offer the key Land Mobile Radio (LMR) features of group calling and messaging. The service allows you to create as many call groups as you want, as unlike LMR systems where channels are finite, PoC allows any number of virtual channels.

They also allow you to create dynamic call groups on the hoof using the dispatcher. Most will enable late entry into a group calls, device over the air programming and the ability to stun and unstun terminals remotely.

Most PoC companies will also provide dispatching software allowing you to support GPS-based services to locate and track users and devices in real time and often to provide historical snail-trail location data. You can add Lone Worker monitoring, alarm features, and full call recording, logging, and playback.

LMR Integration
Integrating PoC services with existing LMR systems is also something to ask about. LMR manufacturers have invested in this kind of service including Motorola Solutions’ WAVE over-the-top PoC platform and its Kodiak Networks’ carrier-integrated PoC solution. Tait Communications offers its UnifyVoice and UnifyVehicle solutions, while Hytera has just unveiled a complete PoC solution including the management platform, dispatch platform, server, PoC apps and terminals.

PTTi had developed a TETRA gateway, while iPTT is set to unveil its LMR interoperability solutions in the autumn. ESChat provides both basic RoIP (Radio over Internet Protocol) and advanced radio interoperability using the ISSI (Inter-RF Subsystem Interface) gateway to integrate with P25 networks and the AIS (application interface specification) protocol for DMR networks.

Security
Ensuring secure communications is vital to many businesses and organisations, so it is worth checking what your potential PoC provider offers. Wireless Logic’s Clarke says: “We already offer customers a range of VPN services, which allow users to create secure tunnels from the device to the network core/hosted server to ensure full encryption and security.

“But we are working with Icom UK to take this further by inserting the SIM into the device and a password is sent to the RADIUS account in the core network/hosted server, so the SIM is authenticated only to that device.”

OMA-PoC and MCPTT
Most PoC platforms currently comply with the Open Mobile Alliance OMA-PoC standard, but this may well be replaced by the 3GPP-based MCPTT standard when the specifications are eventually deployed by MNOs. 4G LTE-based MCPTT specifications are still being developed by 3GPP in Release 15 (due for completion in September) with more enhancements to follow in Release 16 (due for completion at the end of 2019).

It is not yet clear when mobile operator integrated MCPTT controlling servers will be commercially deployed, or what sort of price users can expect to pay for MCPTT services. However, it is something that mission critical PoC users should keep an eye on. For the most part, the services available on current 4G LTE networks are more than adequate for most business PoC users.

For those wanting access to mission critical levels of service as they exist now in the UK, PoC platforms would need to provide a dedicated path into the MNO’s PCRF (Policy and Charging Rules Function) server. The PCRF authenticates and authorises the MC user, while the MNO’s QCIs and ARPs will decide the level of priority of the user and the level of priority and pre-emption of the call/data session.

Pricing and contracts
Pricing is pretty straightforward. PTTI’s Allerton says: “All you have to do is buy a PTT device, one of our SIM cards with x amount of data usage and get an account. You pay a fixed fee per annum. We offer 150 hours of talktime and 500Mb of data per month as standard.”

Becker says iPTT offers a four hours of talk time a day as standard. “But we provide tailor made packages and ensure the SIMs are preloaded with the required data capacity.”

Clarke says: “Packages are tailored to what device you want, the amount of talktime and data you require, the choice of networks and the level of security and authentication you want.”

Becker warns: “The single biggest thing to watch out for is making sure the talk time you buy is right for your needs. Even if you get it wrong, we are very flexible and will upgrade the package whenever necessary if you need more talk time. But whatever package you buy it makes for predictable invoicing, which keeps finance directors happy.”


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Comments
I take the view that a commercial PoC provider seeking full access to the 3GPP Mission Critical level of QCIs and priorities via a link to an operator PCRF, as mentioned in the article, is an aspirational vision except in the case of being partnered with a Public Safety organisation. A senior technical member of staff at EE has described the ESN as an early LTE-based implementation of the network slicing concept being formally developed in 5G with the addition of the external partner interface into the PCRF. He stated that the limitations of the LTE/EPC architecture made implementing such a slice more than once very challenging. So, a current LTE cellular network that is supplying Public Safety services could be loath to extend the full offer to a commercial PoC operator without a compelling business case (especially as they would need to prioritise and pre-empt Public Safety use over commercial PoC). One might hope that you could get a standard radio bearer using normal QCIs but with an ARP higher than for normal users, but lower than that of Public Safety users. This is independent from the challenge of getting a cellular handset which is capable of supporting the 3GPP Mission Critical QCIs.
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