The greatest test 802.11 will have to face when being compared to the Public Switched Telephone Network (PSTN) is its capability to transmit voice with the clarity of the PSTN. The immediate assumption is that the quality of service (QoS) of an 802.11 network is inadequate for voice transmission. As demonstrated in the previous chapter, QoS on 802.11 networks can be engineered to equal that of wired networks. Its wide acceptance in enterprise networks is testimony to this. This chapter explores how voice becomes data in voice over Internet Protocol (VoIP) and that 802.11 is wireless IP; therefore, VoIP can travel over 802.11, delivering voice with a quality equal to that of the PSTN.

The threat to telephone companies is that it is infinitely cheaper to beam data (and voice) to customers than it is to run a copper wire or coaxial cable to them. In addition, the potential data flow to a subscriber over an 802.11 network is exponentially greater than that of the 56 Kbps delivered via a telco's copper-wire dial-up connection. The emergence of softswitch as a switching alternative to Class 4 and Class 5 switches makes it all the more feasible for 802.11 service providers to offer voice services independent of the telephone company or for subscribers (especially enterprises) to be their own telephone company, effectively bypassing the PSTN entirely.

PSTN Architecture

The PSTN, over which the vast majority of the voice traffic in North America travels, is comprised of three elements. The...