Connecting Smartphones and Radios using RoIP and the JPS VIA app This document explains the basic concepts related to interoperability between radios and Smartphones using the JPS VIA app. These links hold to the JPS philosophy that the users shouldn t need to change how they operate their devices when engaged in interoperability nets. That is, to Smartphone PoC users, radio channels can be included in PoC talkgroups and treated are identically to other PoC users. On the radio side, whenever a radio user begins a transmission on a radio channel that has been configured in a JPS VIA talkgroup, that user s audio is sent not only to the other radios on that channel, but also to any JPS VIA users in that talkgroup. Likewise, all radio users on that radio channel will hear any audio from associated JPS VIA talkgroup members. No changes in radio operation are necessary.
Connecting Smartphones and Radios Using RoIP and the JPS VIA App 2 The Smartphone/RoIP connections can link to individual radios, or to JPS radio interoperability gateways. The gateways allow dynamic connections that can be changed at will by system operators to match the ever-shifting communications requirements of a disaster situation or other major event. Relevant Vocabulary Explained: PoC stands for PTT (Push-To-Talk) over cellular. A PoC app makes a Smartphone act similarly to a radio. The user simply presses a button and can communicate with everyone in the current talkgroup. No dialing and no waiting for someone to pick up the phone and say Hello. Multiple users can be conferenced together with no need to individually dial in to a conference bridge. Just press the PTT button and talk. JPS VIA is powered by ESChat. Initial versions of JPS VIA are identical to the highly-celebrated ESChat application from SLA with one major addition: JPS collaborated with SLA to add the JPS Radio-over-IP protocol (RoIP) to the PoC server. This allows radios to be interfaced via IP, using the JPS RoIP, so they can be treated just like all other PoC users. Therefore JPS VIA connections can be made to any JPS RoIP-capable device. When this screen capture was taken, a quick ad-hoc talkgroup had been created that consists of four users, the phone user and three entities selected from the Contacts List. One user is the radio system (named JPS.RTP.1). When the phone user presses the PTT (Push to Talk) button, that user s speech will be heard by Gary and Iggy, and is also transmitted on the radio channel. Note that the radio channel is treated the same as all other users. NOTE: There are cell phone models optimized for use with PoC applications such as JPS VIA. These phones include a dedicated/integrated pushbutton PTT switch on the side of the handset, which can be easier to use than pressing the large green area on the touchscreen. JPS is also planning to use the ESChat Software Development Kits (SDKs) to even more tightly integrate JPS VIA with JPS Interoperability Gateways, but in the initial rollout, JPS VIA is the ESChat app, rebranded, with the important RoIP protocol included, and sold through JPS. JPS VIA has other types of radio protocols, including ISSI for P25 radio systems and AIS for DMR systems. Those features are not covered in this document. The JPS-proprietary RoIP protocol was created over 15 years ago to serve a single purpose, to link radios over IP networks while solving the challenges that radio communications pose to typical Voice over IP (VoIP) connections. It includes provisions for radio control signals (particularly COR/PTT) and considers the various delays inherent with LMR systems, and includes multiple codecs to allow optimization of the network link; balancing audio fidelity and tone integrity requirements with available bandwidth.
Connecting Smartphones and Radios Using RoIP and the JPS VIA App 3 Important Radio Terminology: COR is a signal from a radio that indicates when it is receiving a valid signal from another radio (it has become "unsquelched"). When COR is active, useable receive audio will be available to a listener, or in our case, to other equipment connected to the radio. PTT is a signal to a radio instructing it to transmit the audio that is being sent to it. RoIP is also important because of the vast numbers of RoIP-capable interface units and radio interoperability gateways currently installed across the USA and elsewhere in the world. All JPS gateways either have inherent RoIP connectivity (ACU-M, ACU-5000) or include modules that can be configured as RoIP links (ACU-1000/2000/T). These gateways and the RoIP capability are key components of a number of statewide radio interoperability systems used daily for Public Safety communications. It's important to note that most LMR radios, unlike most telephones, are half-duplex. This is also true for a JPS VIA system (and most PoC systems). A person can pick up their radio or a JPS VIA Smartphone, press PTT, and begin talking. Other system users on the same radio frequency, or on a JPS VIA talkgroup will hear, but because it s half-duplex they can t respond until the initial transmission has ended. More Important Radio Terminology Duplex -In a duplex communications link (such as a typical phone call), all parties can talk and listen at the same time. Half-Duplex In a half-duplex system, users cannot transmit (talk) and receive (listen) at the same time. They can only do one or the other. Typically, the user who is currently talking/transmitting has the floor and until the transmission ends, other users can only listen. However, some systems, including JPS gateways and JPS VIA, have methods to allow priority users to preempt the current transmission and retake the floor. For the half-duplex systems described in this document, when any system device has active COR, the audio from that device will be retransmitted (PTT activated) to any other devices that it is connected to. This is an essential aspect of an interoperability gateway, whose basic purpose is linking audio between multiple types of voice communications systems. When one system has a valid audio input, that audio becomes the output of all linked systems. That first system asserts Active COR, causing an Active PTT on all linked devices. More details are provided in the explanations that follow.
Connecting Smartphones and Radios Using RoIP and the JPS VIA App 4 Step by Step Explanation of Interoperability Using RoIP and JPS VIA The NXU-2A interfaces one radio to an IP network via RoIP The NXU-2A interfaces a single radio to an IP network via RoIP and provides the ability to remotely connect radios to dispatch stations, interoperability gateways, or to other radios. In the figure below a pair of NXU-2A devices are connected back-to-back via IP, linking a pair of radios. The devices may be located a continent away from each other. Each of the radios cabled directly to an NXU-2A is referred to as a donor radio their purpose is to serve as the conduit for the radio systems on either side of the diagram that will be connected via IP. Note that when the radio on the far left transmits, that signal is picked up by the donor radio at the local NXU-2A. This donor radio then has active COR. The received audio, along with the active COR signal, is transferred via RoIP from its local NXU-2A to the NXU-2A on the right side of the diagram. When the latter NXU-2A detects COR, it sends a PTT signal, along with the received audio, to its own donor radio. This donor radio retransmits the audio to the local radios on its channel or talkgroup (far right of diagram). Each donor radio/nxu-2a pair is connected by a custom radio interface cable. This custom functionality is needed both to match the type of connector used on the donor device and to properly present the required audio levels, impedance levels, and control signals to that device. JPS has a library of cables customized for hundreds of different makes and models of radios.
Connecting Smartphones and Radios Using RoIP and the JPS VIA App 5 Real World LMR with Repeater The initial diagram showed the donor radios each communicating directly with handheld radios in the field; the field radios could also be mobiles in a delivery vehicle or patrol car. In the real world, LMR systems typically rely on the use of a repeater. In a repeater system, each user transmits on one frequency and receives on another. We'll use F1 as the end user device transmit frequency and F2 as its receive frequency. The repeater uses the opposite, transmitting on F2 and receiving on F1. It retransmits whatever it receives, and at a higher power level. There is no noticeable delay between what comes out of the talker's mouth and what is heard by the listener's ear however, for trunked radio systems there can be a significant initial call set up delay while the trunking controller assigns a frequency to the transmission. More on this below. Note This delay is one of the radio system interface issues that the DSP algorithms contained within the JPS Radio Interoperability devices are designed to deal with. JPS VIA Connected to Trunked LMR System There are two types of radio repeater systems: conventional (not trunked) and trunked. A trunking system chooses available frequencies for its users, automatically switching radios on an active talkgroup to a common available channel. When a radio user in a trunked LMR system wants to communicate, that user selects the desired talkgroup and presses the PTT button on their handheld radio. However, the user s radio is not immediately ready to communicate with the selected talkgroup. Instead, it first communicates with the trunked repeater system, which sets up the call by putting users (both the call initiator and the radios that person wants to talk with) on an available open frequency. The radio call initiator then hears a beep (typically called a go-ahead tone or acknowledgement tone) that lets the user know that the call is set up and it s okay to begin speaking. In the figure above, two radio channels are connected over an IP network using NXU-2A Radio-to-IP interfaces and being retransmitted by repeaters. Note that the two radio systems don t have to be of a similar frequency or type. One could be VHF and the other 800 MHz.
Connecting Smartphones and Radios Using RoIP and the JPS VIA App 6 A trunked LMR system is somewhat analogous to a JPS VIA system. When JPS VIA users press PTT on their cellular handsets, the JPS VIA system has a momentary delay while it sets up the call with other users in the chosen talkgroup, and then gives the call initiator a beep to indicate that the system is ready and they can begin talking. Because of this similarity, we can swap out a repeated radio system on one side of the diagram and replace with a JPS VIA system, see below. The JPS VIA server interfaces the radio system to the JPS VIA talkgroup via an RoIP to link the NXU-2A on the radio side. Interoperability devices are designed to deal with. When the JPS VIA conversation begins, the JPS VIA server will use RoIP to send an Active COR signal, to the NXU-2A, along with the JPS VIA conversation audio. The NXU-2A will then initiate a PTT output to its donor radio. For a conventional (non-trunked) system, the radio will immediately begin transmitting the incoming audio to the repeater, to be picked up by the other system radios on the same channel. For a trunked radio system, the channel acquisition delay mentioned previously occurs before the radio system is ready to transmit the audio. One of the NXU- 2A s radio interface algorithms is a delay buffer to hold up the audio while the trunked system acquires a channel. This process is transparent to the user. For calls initiated on the radio side, the NXU-2A sends receive audio from the donor radio plus an Active COR indication to the JPS VIA server via the RoIP link. The JPS VIA server handles any necessary audio delays. It s important to note that there is no direct connection between a radio and a Smartphone. The radio system behaves exactly as if there were no Smartphones involved, as the Smartphone interface is through a donor radio that is identical to any other radio in the system. Similarly, the JPS VIA Smartphone system behaves the same as it always has. The server handles the RoIP interface so that, to the rest of the JPS VIA system, the radio channel acts no differently than any other JPS VIA user. Smartphone users interact through the JPS VIA server, while radio users interact through the repeater. This is the same with or without radio to Smartphone conversations, so users on either end need not worry about modifying their standard methods of operating their devices. JPS VIA System connected to Repeated LMR System via Cellular JPS VIA Server and NXU-2A
Connecting Smartphones and Radios Using RoIP and the JPS VIA App 7 There is no practical limitation on the number of radio channels or talkgroups that can be included in a JPS VIA talkgroup, though each will need its own dedicated NXU-2A/donor radio combination (or other JPS radio interface) While the radios shown above are in the same LMR Repeater system, they could be in entirely other systems in widely spaced locations. A benefit of JPS RoIP technology is that system radios can be located anywhere there is a network connection. Use of JPS ACU Radio Interoperability Gateways as Multiple Radio to RoIP Interfaces JPS Interoperability Solutions also offers a variety of Radio Interoperability Gateways. Their main purpose is to capably link any voice communications format to any other. However, they are also capable of functioning as multiple-channel versions of the NXU-2A in JPS VIA+LMR applications. JPS VIA to LMR integration using the JPS ACU-2000 Modular Radio Interoperability Gateway The ACU-2000 can link voice communications systems locally or over an IP network. A typical local setup includes the following: local cross-connections within the chassis controlled by the CPM module, an HSP module providing an audio interface and local control capability, and up to 12 interface modules installed as needed to link devices such as radios, cell phones, telephones, SIP phones, iden phones, or satellite phones to the system. This Local Interoperability System can be interfaced via an IP network with software control programs, remote radios, SIP devices, and other Local Interoperability Systems. The ACU-2000 can also perform a simpler function without any of these dynamic module-to-module crosspatches, and provide up to twelve JPS VIA+LMR channels. In this mode, each DSP-2 module is capable of a single RoIP-to-Radio link, and functions just like a single NXU-2A device.
Connecting Smartphones and Radios Using RoIP and the JPS VIA App 8 The image is an ACU-2000 with a complement of different types of modules, capable of dynamic patching. The DSP-2 modules can also be configured to function like NXU-2A units plugged into a chassis. In this mode they don t interact with other modules in the chassis. Therefore, if all that is needed is a set of independent Radio to IP interfaces, JPS can supply a stripped-down version, minus the CPM and HSP modules, plus up to 12 DSP-2 modules in standalone Radio Interface mode. Cellular JPS VIA Server Interfacing to Multiple Donor Radios via an ACU-2000 This application is most useful for cases in which there are numerous donor radio resources at the same location, as illustrated above. Many additional features available with JPS VIA This document explains how radios are interfaced with the JPS VIA Smartphone App and does not attempt to describe all of its other great features and capabilities. Please contact JPS for further information.