8.1. The Need for VoIP Protocols
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 300 milliseconds. If packets are lost or delayed, there will
be degradation in the quality of the communications experience.
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 resolve
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 understanding of the technology. VoIP holds the
promise of incorporating voice communications into all 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. Speaking and
listening consist of the relaying of a stream of audio, whereas the
Internet protocols are designed to
chop everything up, encapsulate the bits of information into
thousands of packages, and then deliver each package in whatever
way possible to the far end. Clearly, some sort of bridge was
required. |