Voice over IP (VoIP) is a proven and cost-effective way of delivering voice across the enterprise, however, some employees who rely on voice contact to exchange important information — healthcare workers or workers in a manufacturing plant, for example — can’t easily reach a landline or rely on cell phones. For these users, Voice over Wireless (VoWLAN) is an alternative solution.
Wireless — or more accurately, cordless — phones have been around for a long time: Digital Enhanced Cordless Telecommunications (DECT) connects portable handsets to a base station and is commonly used by consumers and small business, but it can’t compete with modern products or enterprise-grade requirements.
Besides improved coverage, VoWLAN is attractive to business users because:
- many companies provide in-building Wi-Fi for mobile data use and this, along with their investment in a VoIP network, can be extended to incorporate a VoWLAN service;
- cellular phones are expensive and unreliable because of poor signal coverage;
- any phone that supports IEEE 802.11 Wi-Fi should be able to connect to a VoWLAN network, meaning employee smartphones can be re-purposed; and
- VoWLAN services offer more features than a cellular network.
Network design considerations
VoWLAN is vulnerable to the same Quality of Service problems that affect VoIP but has additional problems introduced by wireless connection. Since users are likely to expect the same quality from their VoWLAN service as they get from a fixed line, QoS is a key design consideration.
A site survey should be used to identify best access point placement, power levels, user characteristics and call volumes, and repeated when there are significant changes to the user population or building / campus layout.
While data users generally stay in one place, or perhaps move between a desk and office on a single floor, the same can’t be said of users whose job requires they move around during a call. Consequently, access points need to be purposefully placed to provide coverage in dead spots such as stairwells, passageways or elevators. Moreover, products like the Cisco Aironet 4800 should be used to automatically re-assign the call to the next best access point as the caller moves, to prevent calls dropping.
Some areas are more likely to be used for calls than others, so, call density should also be factored into design. As a rough rule-of-thumb, 15-20 voice devices per access point is a reasonable average to aim for, and a two-minute call could use up to 1.5MB of data, so that needs to be factored into bandwidth calculations at the same time. Using 5GHz is often a better choice since channels are less congested and provide faster throughput.
Take advantage of vendor design guides such as that offered by Cisco to dig deeper into these and other design considerations.
VoWLAN equipment comprises a Wireless IP phone or smart/cell phone, wireless access points, wired network to connect the access points to a controller that routes calls and provides feature such as call forwarding and voicemail.
It’s wise to buy the access points and controller from the same vendor to ensure interoperability since they are the heart of the system, but you can be more selective when considering handsets.
The other option is enabling smartphones, whether company or user-owned, for VoWLAN use. Most smartphones can connect to a Wi-Fi network, primarily for data, but the same connection can be used for voice with an appropriate app and configuration changes.
The Digium softphone is an android or IoS app that allows a smartphone to use the VoWLAN to connect to and use the enterprise VOIP network in much the same way as desk phone, allowing the user access to enterprise VOIP features such as call transfer, vmail or address book.
Alternatively, users can utilize Wi-Fi calling services provided by an increasing number of carriers, using the enterprise IP network for the ‘last hundred meters’.
Another option is to use Closed User Group SIMs on smartphones. This will reduce charges for calls made within the building or campus, but there is still a charge to pay to the carrier and they don’t solve the problem of poor signal or dead spots.