Introduction of modern DECT communication

The advantages of wireless compared to classic wired telephony are obvious. There is no need to build communication lines, and employees of the company gain mobility within the office or enterprise, which allows them to stay connected without being in 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 business use than alternative technologies. WiFi or WiMax phones provide less protection, mobility and convenience. For example, a DECT handset can work for a week without recharging, which is not the case with a WiFi phone, and the encrypted voice transmission in DECT is almost invulnerable compared to WPA and WPA2 for Wi-FI.

Modern IP DECT

A question may arise: why, in this case, IP telephony and Asterisk, when, in the absence of wires, any DECT PBX will work?
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The main answer is that with this approach each DECT subscriber is represented in the system as SIP peer, and DECT is used exclusively as the “last mile”, i.e. as a low-level transport. SIP DECT server performs transparent conversion of 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 to choose an IP PBX solution.

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

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

• IP PBX Asterisk is free software that provides zero acquisition cost. 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 lack of dependence on the supplier (vendor lock-in), which allows you to use the equipment of any manufacturer in accordance with the requirements and financial capabilities of the company.
• Asterisk has a powerful support for various phone functions and advanced integration interfaces with third-party systems, which allows you to implement any telephone business logic.
• Asterisk subscribers with a FreePBX extension installed have access to a user's personal account in which employees work independently with their personal settings and functions, such as call transfer, voice mail, 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 SIP, which suggests that this is a “pure” IP DECT solution, which means no voice conversion using the DECT <-> analog / digital lines <-> SIP telephony, hence the absence of problems with echo, as well as the possibility of using 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 fault-tolerant configuration of two DECT servers in hot switching and load balancing modes. Linear scalability, no restrictions on the number of subscribers.
• Support for broadcast, group and unicast messages (up to 20 messages per minute) with the possibility of feedback (read confirmation, consent / rejection).
• Support the ability to share a handset when one handset is used by different employees with different internal numbers.
• XML-RPC interface for direct integration with external systems, for example, the subscriber accessibility monitoring service.
• Subscriber stations aimed at different business segments: Medicine, Production, Office. Different protection classes (up to IP 64), there is an explosion-proof model, with antibacterial coating, with accelerometer sensors (for example, detecting a person’s fall, running), alarm button functions. But there is also compatibility with handsets from various vendors (uses the DECT-GAP standard).
• A wide range of additional accessories (base stations, DECT repeaters, several server options, external antennas, tubes)
• High-tech IP-DECT base stations, up to 11 simultaneous conversations with the ability to encrypt all channels simultaneously.

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

• The Spectralink 6500 DECT server over a local Ethernet network communicates with the Asterisk IP PBX, performing SIP registration of subscribers and coordination of DECT devices.
• IP DECT base station also connects to the local network, and carries out and receive / send 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 by connecting a base station anywhere in the IP DECT network. The radius of territorial coverage of one base station is 50 meters.
• The repeater itself does not create a coverage area (does not create DECT channels), but “extends” the coverage area of ​​the base station. Repeaters are usually placed where there is no need for additional DECT channels, and all that is required is to expand the radio coverage area for existing subscribers.
• Tubes - the Spectralink line is shown depending on the conditions of use.

So, having decided on the components used, we will construct 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.



IP PBX Asterisk is located in the central office.

At the central office and at the branch, one Spectralink 6500 SIP DECT server is installed, as well as IP DECT base stations according to the number of DECT channels required.

The branch Spectralink 6500 registers its DECT subscribers in the head IP PBX. In the event of a drop in the Internet link, the connection between internal DECT subscribers is not interrupted. It is also possible to connect the Spectralink DECT server to a local SIP protocol operator, thus preserving the independence of the branch's telephone network from the central office.

The construction of any wireless network involves the following steps:

• Design . The area, the height 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, survey work should be carried out carefully enough to exclude blind areas.
• 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-supervision, etc.), a bundle with a telephone station.
• Implementation , physical installation of base stations, network switches, if necessary, communication.
• 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 specific system functionality (for example, emergency alarm buttons on handsets, motion sensors, etc.), it is important to show employees at least the simplest operations to hold, transfer a call, create conferences using the corporate directory, and others important functions to work.

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 per one end user, which is even cheaper than a single desktop IP phone.
Business can not do without the means of communication, and modern solutions Spectralink provide a single, converged mobile network with amazing quality.