Introduction of modern DECT communication

The advantages of wireless over classic wired telephony are obvious. There is no need to lay communication lines, and company employees gain mobility within the office or enterprise, which allows them to stay in touch without being at their workplace. There are several ways to create a wireless telephone network: using Wi-Fi, DECT, and using highly specialized radio devices.

But practice shows that a solution based on DECT technology is more mature for use in business than alternative technologies. WiFi or WiMax phones offer less security, mobility and convenience. For example, a DECT handset can work for a week without recharging, which cannot be said about a WiFi phone, and the encrypted voice transmission in DECT is practically invulnerable compared to Wi-FI and WPA2 and WPA2.

Modern IP-DECT

The question may arise, why in this case IP telephony and Asterisk, when in the absence of wires any DECT PBX will do?

The main answer is that with this approach, each DECT subscriber is represented in the system as a SIP peer, and DECT is used exclusively as the “last mile”, i.e. as a low-level transport. SIP DECT server transparently converts SIP protocol to DECT.

What gives a transparent SIP interface to a DECT subscriber? In this case, such a DECT phone is no different from a desktop SIP phone. This means that telephone and business functions are programmed not at the DECT server level (and not at the DECT PBX administration level if used), but at the IP PBX level, which means complete freedom of choice of IP PBX solution.

Thus, at the hardware level of the DECT server, transparent conversion of the digital (non-analog) voice signal from the SIP protocol to the radio environment is implemented, and all business logic is left for the implementation of IP PBX.

In our article, we chose Asterisk as the IP PBX, due to the following considerations.

• IP PBX Asterisk is free software that provides zero cost acquisition. However, in addition to the price gain, the introduction of Asterisk in the enterprise allows you to create a truly convergent telephone solution, since the system supports almost all existing communication standards and protocols.
• It should also be noted the absence of dependence on the supplier (vendor lock-in), which allows the use of equipment of any manufacturer in accordance with the requirements and financial capabilities of the company.
• Asterisk has powerful support for all kinds of telephone functions and developed integration interfaces with third-party systems, which allows you to implement any telephone business logic.
• Asterisk subscribers with the FreePBX extension installed can access their personal account in which employees work independently with their personal settings and functions, such as call transfer, voicemail, call history, faxes, etc.

Spectralink equipment was chosen as the DECT solution, due to its following characteristics:

• Built-in support for IP telephony based on the SIP protocol, which allows us to say that this is a “pure” IP DECT solution, which means that there is no voice conversion using the DECT scheme <-> analog / digital lines <-> SIP telephony, from which there are no problems with echo, as well as the ability to use broadband HD codecs.
• System management only through the WEB interface. (without SSH or console connection). Advanced diagnostics and monitoring of the deployed network.
• Support for failover configuration of two DECT servers in hot switching and load balancing modes. Linear scalability, no restrictions on the number of subscribers.
• Support for the function of broadcast, group and individual distribution of messages (up to 20 messages per minute) with the possibility of feedback (confirmation of reading, consent / rejection).
• Support for handset sharing when one handset is used by different employees with different extensions.
• XML-RPC interface for direct integration with external systems, for example, a subscriber availability monitoring service.
• Subscriber stations aimed at various business segments: Medicine, Production, Office. Various protection classes (up to IP 64), there is an explosion-proof model, with an antibacterial coating, with accelerometer sensors (for example, detect a person’s fall, running), the functions of the panic button. But there is also compatibility with the tubes of various vendors (uses the DECT-GAP standard).
• A wide range of additional accessories (base stations, DECT repeaters, several server options, external antennas, handsets)
• High-tech IP-DECT base stations, up to 11 simultaneous conversations with the ability to encrypt all channels simultaneously.

Below, in fig. 1, there is a diagram of the location of elements in the DECT network and their interaction with the IP PBX server.

• The Spectralink 6500 DECT server interacts with the Asterisk IP PBX over a local Ethernet network, performing SIP registration of subscribers and coordination of DECT devices.
• The IP DECT base station also connects to the local network, and receives and sends calls and messages. This architecture allows you to create a distributed wireless network, or “islands” of a wireless network located in a single address space, simply connecting the base station anywhere in the IP DECT network. The radius of the territorial coverage of one base station is 50 meters.
• The repeater itself does not create a coverage area (does not create DECT channels), but “lengthens” the coverage area of ​​the base station. Repeaters are usually installed where there is no need for additional DECT channels, and you only need to expand the radio coverage for existing subscribers.
• Tubes - Spectralink range of tubes is shown depending on the conditions of use.

So, having decided on the components used, we will build a network diagram.

In our example, we would use a configuration of two offices, central and regional, with their integration into a single telephone space.



Asterisk IP PBX is located in the central office.

One Spectralink 6500 SIP DECT server and one IP DECT base station are installed in the central office and in the branch according to the number of required DECT channels.

The Spectralink 6500 branch office registers its DECT subscribers to the host IP PBX. In the event of a drop in the Internet link, communication between internal DECT subscribers is not interrupted. There is also the possibility of connecting the Spectralink DECT server to the local telecom operator via SIP protocol, thus preserving the branch telephone network independence from the central office.

Building any wireless network involves going through the following steps:

• Design . The area, number of storeys of the room, the dimensions of the walls, the material of manufacture (heavy reinforced concrete floors or thin plasterboard structures) are considered. At this stage, it is already possible to calculate the estimated cost of implementation and make a list of the necessary equipment.
• Radio survey . The structure of any building is always individual, it is also necessary to take into account the special needs of the Customer (for example, the presence of a DECT signal in elevator shafts, remote switching points, inability to conduct communications, etc.) Therefore, inspection work should be carried out carefully enough to exclude blind spots.
• System setup . Synchronization of radio base stations for seamless roaming, adding accounts and identification data of subscriber stations, setting up system redundancy (configuration files, auto-refreshing, etc.), connection with a telephone exchange.
• Implementation , physical installation of base stations, network switches, if necessary, communications.
• Testing the correct performance.
• Staff training . Modern IP-DECT systems offer a wide range of additional features. Not to mention tight integration through the API and the specific functionality of the system (for example, emergency alarm buttons on handsets, motion sensors, etc.), it is important to show employees at least the simplest operations of holding, transferring a call, creating conferences using a corporate directory, and others important functions for the job.

Conclusion

As a result of the introduction of modern DECT telephony, you get a scalable, flexible and easy to configure system. Moreover, if we consider the project from the point of view of economic efficiency, you will see the cost of about 1500-2000 rubles in terms of one end user, which is even cheaper than one desktop IP phone.
Business cannot do without communications, and Spectralink’s state-of-the-art solutions will provide a unified, converged mobile network with outstanding quality.