behind computing xxxvi Introduction and communications. You need to understand the impact these forces have on net- work traffic and therefore on network infrastructure. The telecommunications revolution has spawned great growth in the amount and types of traffic, and we'll see even more types of traffic as we begin to incorpo- rate human senses as part of the network. The coming chapters talk in detail about what a network needs in order to handle the various traffic types. Traffic Types Given today's digital scenario, the traditional distinctions between traffic types are no longer relevant; in the end, everything is a series of ones and zeros. Nonetheless, there are still specific requirements in terms of bandwidth needed, latency consider- ations, and loss tolerance, and it therefore still makes sense to differentiate between the traffic types. In today's environment, telecommunications embodies four main traffic types, each of which has different requirements in terms of network capacity, tolerance for delays-and particularly variations in the delay-in the network, and tolerance for potential congestion and therefore losses in the network: voice, data, image, and video. The following sections describe these traffic types. Voice Traffic Voice traffic has been strong in the developed world for years, and more subscriber lines are being deployed all the time. However, some 3 billion people in the world have never used even a basic telephone, SO there is yet a huge market to serve. Voice communications are typically referred to as being narrowband, meaning that they don't require a large amount of network capacity. But it is important to note that the days of voice as a distinct category are numbered. In the digital era, voice bits are no different from data or video bits: They are all ones and zeros being exchanged over a network. However, for voice services to be intelligible and easy to use, delays must be kept to a minimum, so the delay factors in moving informa- tion from Point A to Point B have to be tight