ABSTRACT
This chapter looks at how carrier networks structured and organized. Most of carriers are predominantly voice-centric, with a technology stack supporting circuit-switched voice. Nonvoice services such as Frame Relay, ATM, and IP-based services are provided by extra networks, known as overlay networks. In carrier networks to date, the major division has been between circuit switching and transmission. The switching/transmission divide is not just technological, but also a structural feature of organizations and even engineering careers. There are many telecoms engineers around who will proudly state they are in switching or transmission, and each will have a less-than-detailed view of what the other discipline is all about. The traditional problem of switching is essentially one of connection: how to identify end-points, how to request a connection between end-points and how to physically set-up and tear-down the required voice connection.
