History of VoWLANs
The two primary technologies of VoWLANs are wireless LANs and VoIP. Both have been evolving over the past decade and are now stable enough to support wireless voice communications.
The earliest indication of VoIP systems was in the mid-1990s, when Vocaltec, Inc. released Internet Phone Software. This software ran on PCs and translated voice signals into digital packets that could be sent over the Internet. Both the sending and receiving callers must use the same software. Sound quality was not as good as traditional telephones, but long distance calls could be made for free.
Throughout the late 1990s, entrepreneurs began establishing gateways and switches to allow people to make free phone calls over the Internet using standard telephones. The users had to utilize a PC to set up the call, but then they were free to talk from standard wired telephones connected to a PC. With these systems, the VoIP market began evolving. Many companies, including Cisco, began selling VoIP equipment about the year 2000 to enterprises to converge voice and data and provide mobility.
In the early 1990s, the first wireless LAN products, NCR WaveLAN and Motorola Altair, appeared on the market. At this time, there were no applicable standards and prices were relatively high, at around $1,500 per wireless adapter. As a result, only companies having applications with significant benefits from wireless connectivity, such as inventory management and price marking, could afford to deploy wireless LAN solutions.
Figure 1-2 summarizes the evolution of the 802.11 standard. In 1997, the Institute of Electrical and Electronics Engineers (IEEE) ratified the first version of the 802.11 wireless LAN standard. 802.11 at this point provided up to 1Mbps and 2Mbps data rate operation in the 2.4GHz frequency band using direct sequence and frequency hopping, which are both spread spectrum technologies. The capacity of these first 802.11 solutions was not good enough to effectively support voice applications.
Figure 1-2 Evolution of the 802.11 Standard
To enhance the performance of wireless LANs, the IEEE ratified the 802.11a and 802.11b standards in 1999. 802.11a provides up to 54Mbps data rates in the 5GHz band using orthogonal frequency division multiplexing (OFDM). 802.11b extends the maximum data rates of the initial 2.4GHz direct sequence 802.11 standard to 11Mbps. Later, in 2004, IEEE released 802.11g, which further extends data rates in the 2.4GHz band to 54Mbps using OFDM. The higher data rate 802.11 standards, 802.11a, 802.11b, and 802.11g, offer adequate capacity for supporting VoWLAN applications. 802.11a, however, provides the highest capacity, mainly because the Radio Frequency (RF) channels in the 5GHz band do not overlap with each other as they do in the 2.4GHz band. 802.11n, which will offer 100Mbp or more performance, is nearing ratification.
Other recent improvements to the 802.11 standard include security (802.11i), which includes much stronger encryption and authentication mechanisms than the initial standard. The use of Temporal Key Internet Protocol (TKIP) and Advanced Encryption Standard (AES), along with 802.1i protocols, makes wireless LANs very secure. Also, the ratification of the 802.11e standard in 2006 offers quality of service important for VoWLAN applications.
Within the past couple of years, the prices for wireless LAN adapters have decreased to well under $100 each. This dramatic drop in prices has fueled the proliferation of wireless LANs for a variety of applications in all markets. The Wi-Fi Alliance has also been actively promoting wireless LANs through the Wi-Fi brand and mandating interoperability testing.
Because of the proliferation of wireless LANs, VoWLAN solutions are also proliferating. Companies offering VoIP equipment, such as Cisco, have been marketing VoWLAN phones that interface with their digital telephony systems. Even service providers, such as Vonage, now offer Wi-Fi phones that interface with their Internet Protocol (IP) telephony service.