Along with workplaces such as factories, warehouses, schools and hospitals, there are a growing number of traditionally office-based working environments that require flexible, mobile IT and telecommunications networks. It is currently estimated that as many as 80% of workers across all industries are potentially mobile around their workplace and may require access to wireless voice communications.

The standard DECT- (Digital Enhanced Cordless Telecommunications) commonly used for domestic or corporate purposes for digital portable (cordless) phones is an ETSI (European Telecommunications Standards Institute). DECT (like GSM) is a cellular system and the major difference between GSM and DECT systems is that the cell radius on DECT is 25 to 100 meters, while in GSM is 2 to 10 km. *

The implementation of wireless Local Area Networks (WLANs) using IP-enabled wireless data handsets began from several years ago and was considered simple, inexpensive and a reliable method of delivering VoWLAN. The main attraction of a WiFi system is that it offers a single infrastructure for supporting wireless telephony and data, potentially providing a substantial return on investment by reducing hardware costs as well as longer-term operational, maintenance and support costs. But in the other hand, WLAN data applications are typically confined to the areas of a workplace where workstations and PCs are located, as well as meeting rooms and individual offices. WLAN generally does not extend to halls, staircases or outdoor areas.

To provide blanket coverage is complicated due to the co-channel interference inherent in the 802.11 standards. Access points too close together interfere with each other and if placed too far apart, holes are created in the coverage and the user can experience handover problems hence, providing the necessary amount of simultaneous coverage while avoiding interference is much more difficult than it should be. To upgrade a WLAN system to a full VoWLAN network there is necessary to increase the number of existing access points and this means significant additional cost, not only associated with the hardware itself, but with the high level of specialist expertise required for voice deployment, which demands careful channel allocation for each access point.

The DECT versus WLAN (WiFi) debate focuses mainly on arguments centre around whether the wireless telephony system (DECT) is more acceptable for voice applications than the Voice over Wireless LAN. DECT is a mature technology that has gone through the complete standardization process addressing issues such as availability and quality of service, and this is why it is supported by traditional vendors whose main business comes from traditional circuit-switched carriers, where voice network engineers work on the basis of 99.999% availability.

In contrast, the 802.11 networks were designed to carry data, not voice, 802.11b and 802.11g have no built-in mechanisms which tells the network to prioritize voice packets over data, a surge in network traffic may therefore disrupt voice calls, which in many cases, is not only an inconvenience, but a serious threat to customer service and business operations. In industries such as hospitality and retail, lost or interrupted calls mean lost revenue. Typically, 99% availability is considered acceptable by LAN designers for data packets. The difference may not seem significant, but while a half second network dropout every minute will go largely un-noticed by PC users such a delay will be obvious on the phone.

Another key quality challenge facing WLANs is the ability to roam between access points. While DECT telephony networks support seamless handover for voice calls being made on the move, the 802.11 standard currently only supports break-before-make handover. Again, when we consider that the 802.11 standard was originally designed for data, this does not prove a problem as data is transmitted in discrete packets, but for voice, handover between the access points needs to be very fast in order to have a voice call free of interruptions. Rather than addressing this critical issue, the 802.11i security standard, makes the situation worse by extending handover to over 70 milliseconds (ms), a break considered by many to be unacceptable for voice calls. When a user moves from one access point to another while making a voice call, an encrypted tunnel must be broken down through one access point and reformed through the new one. If this process takes more than 50 ms, the user will hear a break in the conversation.

Additionally, the security schemes commonly used for Wi-Fi handsets, Wireless Equivalent Privacy (WEP) and Media Access Control (MAC) are widely regarded as insufficient. While the 802.11i standard addresses the security issue, as mentioned previously, it is likely to have a negative impact on call handover delays forcing Wi-Fi users to choose between enhanced security and better voice quality two factors that most businesses regard as equally critical. In comparison, the DECT standard incorporates built-in security protocols that eliminate eavesdropping, impersonation and other security breaches like:
- 128-bit authentication and identification access security.
- Encryption system based on derived or static 64-bit cipher keys transmission security.

While WLAN systems can be configured to provide up to seven active handsets operating per access point on a voice-only 802.11b WLAN, the more realistic limit is four or five connections before quality suffers. And, if voice is being added to a WLAN which is also carrying data, this drops to around three simultaneous voice conversations per access point. Comparatively, the capacity of DECT, which was specifically designed to handle a high density of users, typically supports eight simultaneous conversations. In complete contrast to WLAN, DECT base stations can simply be co-located in traffic hot spots to provide the required number of additional voice channels, without the problem of co-channel interference.

Even when DECT is more appropriate for voice, there will be several implementation where WiFi is the selection for making phone calls. Standards are evolving and there will be a lot of improvements on the next years. For sure, both technologies will continue being used on the mid future, becoming a solution for wireless developers.

Always feel free to call ABP's pre-sales support to discuss you application and get the pros and cons of different solutions.

The ABP Team

*Premium products in the DECT space are Aastra's DECT solution or snom M3 DECT phones. More on products on abptech.com under product section or product specific BLOGS)

** Commercial grade Wi-Fi phones selected by ABP Technology are Hitachi-Cable Wireless IP3000/IP5000 and Pirelli Broadband DP-L10

Read more on WiFi versus DECT and wireless VoIP.