The basic premise of VoIP is the packetization* of audio streams for transport over |
Internet Protocol-based networks. The challenges to accomplishing this relate to the manner in which humans communicate. Not only must the signal arrive in essentially the same form that it was transmitted in, but it needs to do so in less than 150 milli- seconds. If packets are lost or delayed, there will be degradation to the quality of the communications experience, meaning that two people will have difficulty in carrying on a conversation. The transport protocols that collectively are called “the Internet” were not originally designed with real-time streaming of media in mind. Endpoints were expected to re- solve missing packets by waiting longer for them to arrive, requesting retransmission, or, in some cases, considering the information to be gone for good and simply carrying on without it. In a typical voice conversation, these mechanisms will not serve. Our conversations do not adapt well to the loss of letters or words, nor to any appreciable delay between transmittal and receipt. The traditional PSTN was designed specifically for the purpose of voice transmission, and it is perfectly suited to the task from a technical standpoint. From a flexibility standpoint, however, its flaws are obvious to even people with a very limited under- standing of the technology. VoIP holds the promise of incorporating voice communi- cations into all of the other protocols we carry on our networks, but due to the special demands of a voice conversation, special skills are needed to design, build, and maintain these networks. The problem with packet-based voice transmission stems from the fact that the way in |
which we speak is totally incompatible with the way in which IP transports data