Read Microsoft Word - VoIP extensions for analog radio Jan11 text version

VoIP Extensions

for Analog Radio

Omnitronics White Paper

North America Office: 8301 Cypress Plaza Drive, Suite 100, Jacksonville, FL 32256 Tel: (904) 425 0336 Fax: (904) 296 8350 [email protected] Head Office: 27 Sarich Court, Osborne Park, WA 6017, Australia Tel: +61 8 9445 2633 Fax: +61 8 9445 1687 [email protected] International Sales Office: 301 Coronation Drive, Milton, QLD 4064, Australia Tel: +61 7 3369 5733 Fax: +61 7 3369 5799 [email protected]

Introduction In the early eighties, a communications protocol was created that allowed the research community to send data anywhere in the world using packet switching networks. This protocol became known as TCP/IP and ultimately resulted in the creation of the revolutionary Internet. TCP/IP actually refers to a suite of different protocols but, at its core, there exists the fundamental protocol commonly referred to as IP. Up until a few years ago, the majority of applications for "IP" were targeted at nonvoice type traffic. This included email and the transfer of files. However, more recently, the ability to use IP for the transmission of digitized voice has become so dominant that many industry observers are now calling this the "killer" application. Voice over IP, or VoIP as it is known, has revolutionized the telephony world and, now, many in the radio communications industry are realizing that this technology can power traditional twoway radio networks and breathe new life into existing systems. The adaptation of VoIP for radio communications has been referred to as "Radio over IP", although there is no actual standard, as such. Voice over IP or Radio over IP, whichever way you look at it, is driving the convergence of IT and communications. It can deliver several key benefits to fleet mobile operators, including public safety organizations. These include: lower costs, improved reliability and increased interoperability. All of these are derived from the ability of the technology to utilize existing IP infrastructure the IP backbones that make up both local and wide area networks. To help organizations reap the benefits of VoIP, Omnitronics have developed a range of VoIP adapters that enable twoway analog transceivers to be interfaced with IP networks. The purpose of this paper is to explain how Radio over IP works and to describe the typical features and benefits of these adapters. Radio VoIP versus Telephony VoIP Radio and telephony use the same mechanisms to transport voice through packet switched data networks. Voice is converted into digital data using a device called a CODEC; assembled into UDP packets; and transmitted at intervals of around 25ms. At the receiving end, the CODEC also performs the function of converting the digitized samples back into an analog signal. Various digitization standards are available. The most basic standard (G.711) delivers the highest quality audio at 64Kbps. However, other standards, such as G.723.1 and G.729A, can deliver good quality audio at rates as low as 5.3Kbps, thereby minimizing the traffic impact on an existing network. However, radio and telephony differ when it comes to signaling and control. Telephony is concerned with call setup, call monitoring and call control. For example, VoIP needs to be able to initiate a connection, pass dial tones, DTMF strings and call progress tones. It also needs to be able to perform echo cancellation. Radio, on the other hand, does not require these telephony features. But traditional radio functions still need to be controlled and monitored. This includes the PTT function which must be transported transparently through IP and in sync with the audio. Other functions include the COS from the radio which can be used to generate a busy signal or keyup another transceiver at the remote end. Channel change is also a function that may need to be transported through IP. When it comes to radio signaling, some even more interesting problems need to be addressed. Firstly, selective calling tones, such as CCIR SELCAL and ANI, cannot be reliably transported using VoIP when digitization rates below 32Kbps are used. This means they cannot be reasonably compressed. And since one of the goals of VoIP is to reduce IP bandwidth through high compression, VoIP and radio signaling are not compatible. Hence, Radio over IP must transport signaling tones as data messages and not as audio. Similarly,

if CTCSS tones are to be transported over an IP network then they should also be converted into data messages. In both cases, the equipment that provides the interface between the radio and the IP network must be capable of decoding the CTCSS, SELCAL or ANI audio and converting these into data messages. When receiving a data message containing a signaling string, the same equipment must also be capable of encoding this into the appropriate audio tones. The problem of passing signaling schemes can be further compounded by the inherent packet losses within IP networks. When passing voice, a low rate of packet loss is not really an issue. However, losses in packets containing tone signals can be detrimental, especially when using short tone bursts or when passing modulated tones. All of this is due to the fact that the transmission of digitized voice, whether telephony VoIP or Radio over IP, is achieved using a "send and forget" mechanism called UDP. Ultimately, the most reliable way to transmit signaling schemes and tones through IP is to use a messaging protocol that is transparent to the end user equipment. Benefits of Radio Over IP Twoway radio has always been used to provide mission critical communications across a broad spectrum of industries, ranging from emergency services and security, to utilities, resources and transportation. So far, radio is proven to be the most effective, reliable and cost efficient method of communications for daytoday operations. Now, Radio over IP offers a cost effective way to interconnect radio systems and operators together. It is a technology that enhances and adds value to radio communications networks. There are three distinct benefits of using Radio over IP: 1. lower costs 2. improved reliability 3. increased interoperability The biggest benefit that IP brings to the radio community is cost savings. Firstly, new implementations can leverage from existing IP infrastructure. Many corporations and public safety organizations already maintain their own private IP LAN or WAN. Therefore, no extra cabling or communications paths are required for the installation of a new radio or console. Most areas also support public IP networks that can be used, via VPN's, to augment private LANs. Once a system is in place, further upgrades or expansion is easy and inexpensive, since no significant wiring is required. An indirect benefit of using IP networks is the availability and decreasing cost of equipment. Commercial off theshelf hardware can be used, in terms of the routers and switches that make up the networks. These can be sourced from a broad range of third party manufacturers, in an industry where costs are continually decreasing. The biggest cost saving, however, comes from the technology's ability to replace leased lines and expensive wireless links. Savings from the elimination of analog leased lines, alone, should result in capital payback within 6 months ­ at the most! Radio over IP also provides improved reliability. The interconnections between radios and consoles become more reliable, since they form part of a mesh IP network. This provides an inherently resilient infrastructure that is not subject to a single point of failure.

Finally, there is the added benefit of better interoperability. Once it's in the IP domain, radio audio can be routed to virtually any type of radio system. This allows UHF, VHF and HF radios to be easily interconnected. However, the benefits of interoperability aren't just related to the radio systems, they also apply to corporate communications, and this is made possible through the use of SIP technology. Introduction of SIP SIP is an IETF driven protocol that has revolutionized telecommunications. It is a signaling protocol that controls multimedia communications sessions over IP. Its sole purpose is to negotiate, setup and tear down the sessions whilst the actual multimedia communications is carriedout by other protocols such as VoIP. Historically, Twoway radio was considered an adjunct to the corporate communications system and was treated as an independent system, isolated from the broader corporate communications infrastructure. To provide interoperability between users of the radio network and other communications systems (including other radio systems) required the installation of special bridging and patching equipment. Whilst this works to a certain extent, it doesn't make it easy for an organization to streamline the flow of communications throughout its workforce. To enable an organization to achieve maximum levels of collaboration and productivity, it needs to unify its communications mediums, regardless of whether they are digital or analog radio, PBX, mobile phones or PC's. However, just having "IP connected" radios doesn't mean that an organization can achieve unified communications. That's why SIP needs to be an integral part of VoIP gateways and adapters. When used with land mobile radio, SIP compatible devices provide two significant additional benefits. Firstly, Radio over IP gateways/adapters that are SIP compliant enable the connected radio system to interact with a broader range of corporate communications mediums, without worrying about proprietary technology. In such an organization, subscribers on handheld portables or vehicle mounted radios can communicate with people who are not normally connected to the radio network. As an example, calls can be made between radio users and office staff with SIP compliant telephones. More recently, there has been a proliferation of softphones that are also SIP compliant. Omnitronics is starting to see applications where this level of unified communications eliminates the need for office staff to be desk bound and dramatically increases productivity.

The second key benefit happens at even the simplest level of SIP. Radio over IP devices that are SIP enabled provide greater flexibility within radio networks because SIP makes it possible to structure these networks so that they can be reconfigured dynamically. This applies to both user calls and intersite links. For example, radio calls can be made to specific destinations, on demand. This brings efficiency to a network from both the IP and radio traffic viewpoints. SIP also allows links between radio sites to be managed such that link paths can be reconfigured to meet specific operating needs. IP Remote Range Omnitronics have developed and evolved a range of Radio over IP products since 2005. The IP Remote range of products provides Voice over IP extensions for analog radio equipment complete with SIP functionality. Omnitronics provides three devices within this family: · IPR100 Single Channel VoIP Adapter · IPR110Plus SIP Gateway · IPR400 Four Channel VoIP Interconnect The IPR100 was the first of the family and carries the core features and capabilities found in the IPR110Plus and the IPR400. The IPR110Plus is designed to integrate with SIP telephony and the IPR400 provides additional audio bridging capabilities for multiradio sites. The IPR100 uses standardized VoIP RTP technology but with extensions to support radio over IP. Each device enables an analog twoway radio to be remotely controlled over an IP link, either in a LAN or WAN environment. Working in pairs, two IPR100 units can be used to create a backtoback IP link between two radios. Alternatively, a number of IPR100 units may be connected in a group to provide pointtomultipoint communications (or bridging). A pair of units can also be used to provide remote control and monitoring of a single radio from an operator's handset or console. The IP Remote family has been specifically designed to transport signaling schemes including SELCAL, ANI, EIA, MDC1200, CTCSS and DTMF over highly compressed data networks. It achieves this by directly decoding the analog signaling tones and encoding them into data messages. Similarly, the reverse operation (analog encoding) is performed at the opposite end. The devices use standard RTP and RTCP protocols for the transmission of audio and data. In addition, SIP is supported to the extent that the device can accept incoming requests. This means that consoles and other VoIP devices can make connections to an IPR100, transmit and receive audio, then break the connection when it is no longer required. The IPR110Plus supports full SIP functionality allowing it to act as a gateway to the telephony world. Not only will this device accept SIP connections but it can also generate SIP connections to destination devices including SIP PBX systems and VoIP service providers. These requests can be initiated from the radio network using predefined speed dial lists. Voice Activity Detection (VAD) and silence suppression are also standard features across the product range. Together, these enable the product to make optimal use of the available IP bandwidth. With VAD and silence suppression, audio packets are generated only whilst a person is actually talking. VAD is also useful when connecting to end equipment that does not provide a COS (or Mute) output. It performs a VOX function.

Another major feature of the IP Remote family is its builtin security. The devices support AES 128bit encryption which can be enabled for all voice and data transmissions. This is similar to the security level used by banks on the Internet. It provides peace of mind to operators, especially those in the public safety area. Hardware The devices in the IP Remote family interface to a radio through a fourwire E&M port with an RJ45 connector. The port is balanced with 600Ohm transformer coupling, providing isolation between the device and the radio and virtually eliminating ground noise and induced signals. The E&M facilities also provide isolation and can be configured for relay control or optoisolated (voltage) input/output. Links, accessible from the rear panel, also allow the PTT and COS signals to be configured to source or sink power. The IPR100 and IPR110Plus also have a handset port that provides a balanced, halfduplex, connection to a standard Omnitronics 960 Handset or Console. Multiple peripherals can be attached to the handset port allowing a number of operators to share a single radio. Multicasting The audio from both the radio and handset ports is digitized using a Codec using G.711 compression. However, an onboard DSP allows further compression down to 13kbps, using a GSMcompliant algorithm. The audio is then transported over IP using a technique using one of two techniques. Traditional techniques for sending IP packets include unicasting and broadcasting. Unicast transmissions are pointtopoint only. If you want to send a packet to ten different destination devices then you must transmit ten copies of the same packet. This floods the network with unnecessary traffic. Broadcast transmissions overcome this problem by sending just one copy of a packet (i.e. point to multipoint). However, broadcast transmissions cannot easily traverse a WAN and they end up being processed by all devices on a network, regardless of whether the device needs the packetized data or not. Multicasting overcomes these problems. Using multicasting, the IPR device sends one copy of a packet to a group of receivers that want to receive it. In this way, IPR applications make efficient use of available bandwidth and are not limited by domain boundaries but can be used throughout the entire corporate network. Conferencing There are situations however where multicasting will not work completely. Typically, this is due to network infrastructure limitations and most commonly occurs with the Internet. In these scenarios, The Omnitronics IPR100 provides a simulated multicast mode called Remote Conferencing for the Internet (RCI). RCI enables the IPR100 can be set up to transmit digitized audio to multiple destinations. This allows two or more radios (or consoles) to be connected together in a conference (or party line) mode. Whilst this technique was designed for Internet use, it can be utilized to advantage in LANs. Configuration Each IPR device incorporates its own web server. This means that the device can be configured through a standard web browser such as Internet Explorer. The web interface serves up a series of pages which typically presents the following: · Version information · Status information ­ current addresses · Configuration ­ IP addresses; RTP parameters including Codecs, VAD and jitter buffers; audio levels, device operation


Diagnostics ­ loop back test, local test tone generation; remote playing of a Wave file; firmware upgrades

Alternatively, critical settings may also be configured through the RS232 port on each device. All IP devices must be assigned an IP address. This can be either a static address or a dynamic address. Static addresses are fairly easy to work with. As the name implies, the static address doesn't change. It can be associated with a name and that name can be used for all communications. Dynamic addresses, on the other hand, are issued to IP devices by a DHCP server and the address can change regularly. However, they are more commonly used because of cost and efficiency. The differences between the two methods become more apparent when using the Internet. This is where dynamic addressing becomes problematic. However, the IPR range employs a feature called Dynamic DNS to overcome this problem. Dynamic DNS allows the device to track changes in its public IP address and to update relevant hosts accordingly. In addition it periodically checks on any configured remote domains and performs required adjustments when any remote end experiences a change in its public IP address. Overall, this feature works to make the problem of dynamic addressing transparent to the user. Applications The IP Remote family can be used under three general scenarios: · Remote radio access · Pointtopoint radio interconnection · Radio bridging via IP Remote Radio Access An operator can control and monitor a remote transceiver across a LAN or a WAN. The Transmit and Receive audio, along with the PTT and Busy/COS signals, are transported over the link transparently. SELCAL, ANI and DTMF are also transported reliably, regardless of the level of compression that is employed. Multiple Omnitronics handsets and consoles can be multidropped to provide shared access to the transceiver by a number of operators. 960 Console IP Network 960 Handset Operator End Radio End SELCAL/DTMF More sophisticated applications can be supported using Omnitronics SIP compatible consoles. These consoles enable operators to select multiple remote channels for communications.

The IPR110Plus provides connection to a private SIP PBX or to a public VoIP service provider. In the example below, the radio connected to the IPR110Plus becomes an extension on the SIP server's database. It is given a phone number that enables calls to be routed between it and the PBX or the PSTN. Operators using the radio network are able to make PSTN calls by keying predefined DTMF or SELCALL strings.

The above example demonstrates how organisations can extend radio network access to an office environment through a SIP PBX or even to users at home using thirdparty VoIP providers. Compliance with the industry standard protocol of SIP is what makes this radiotelephony application possible. Pointtopoint radio interconnection In this scenario, a pair of IPR100 units can be used to replace a leased line or a UHF/VHF link. Two radios can be connected backtoback over an IP link. This can typically be used to interconnect two repeater sites over a Wide Area Network. The PTT and COS signals are transported over the link as data messages. The IPR100 will provide a configurable PTT output to the radio. It will also accept a configurable COS input from the radio. An active COS signal from the radio will enable the transmission of voice packets over the IP network and generate a PTT output at the opposite end. IP Network PTT/COS PTT/COS

Where the communications equipment is not able to provide a COS output, the VOX function of the IPR100 can be used. When a voice signal is detected at the radio port of the IPR100, an internal COS signal is generated and transmitted to the destination IPR100. This will also enable the transmission of voice packets over the IP network. A configurable hang period is automatically applied to the VOX function. This application in this example could also be achieved using other devices in the IP Remote family. Radio bridging across IP The third application scenario makes best use of the multicasting technique. The IPR100 allows a number of transceivers to be interconnected over a LAN or WAN. Each IPR100 unit is linked to a common multicast group address. When one transceiver receives audio, voice packets are transmitted to the multicast address. Any other IPR100 unit that is linked to that address will accept those VoIP packets and retransmit the audio to its respective radio. IP Network Multicast IP Conclusion Voice over IP has become the dominant technology for interfacing to and interconnecting twoway radio systems. There are many benefits to be gained from the application of this technology. These are drawn from the ability to leverage off existing private and public IP networks to provide cost savings and increased operational flexibility. Omnitronics provide a cost effective way of integrating new and existing analog equipment into the IP domain. The IP Remote range of products has evolved in response to our customer's needs. The devices facilitate the easy interfacing of twoway radio transceivers into the digital domain and provide support for legacy signaling schemes such as EIA, ANI and MDC1200. Going a step further, Omnitronics have now added SIP technology to the range of VoIP adapters and gateways. This will enable users to reap greater benefits from better system flexibility. More importantly, it has made the goal of true unified communications that includes tworadio traffic, a practical reality.


Microsoft Word - VoIP extensions for analog radio Jan11

9 pages

Report File (DMCA)

Our content is added by our users. We aim to remove reported files within 1 working day. Please use this link to notify us:

Report this file as copyright or inappropriate


You might also be interested in

77-2148 EBI system architecture
Microsoft Word - VoIP extensions for analog radio Jan11