GFP Client-dependent Functions THE GENERIC FRAMING PROCEDURE GFP

3 ATM Networks The Asynchronous transfer mode ATM architecture was standardized by ITU-T in 1987 as the preferred architecture for the broadband integrated services data network B-ISDN. The broadband integrated services data network was conceived as a future high-speed network that would have replaced the telephone network and other data networks. It would have provided a single network for the transport of voice, video, and data. The term asynchronous transfer mode was chosen in contrast to synchronous transfer mode STM , which was proposed prior to the standardization of ATM and which was based on the SONETSDH hierarchy. The term transfer mode means a telecommunication technique for transferring information. Despite the enormous technological advancements in networking, the integration of voice, video, and data on to the same network is still elusive. Currently, ATM is a mature technology that is primarily used in the backbone. For instance, it is widely used in the backbone of Internet service providers ISPs and it has been deployed to provide point- to-point and point-to-multipoint video connections. It is also used in cellular telephony to carry multiple voice connections using the ATM adaptation layer 2 AAL 2. ATM is used for circuit emulation, which is a service that emulates a point-to-point T1E1 circuit over an ATM network. ATM is also used in access networks such as ADSL-based residential access networks and ATM passive optical networks APON. ATM is not visible to the networking users, as is, for instance, the ubiquitous TCPIP protocol. In view of this, it is often mistaken as a network that it is no longer in use – which is absolutely not the case ATM constituted a novel departure from previous networking architectures, and it has built-in mechanisms that permit it to transport different types of traffic with different QoS. Until the advent of multi-protocol label switching MPLS architecture in the late 1990s, ATM was the only networking technology that provided QoS on a per connection basis. The reader is encouraged to develop a good understanding of ATM and its congestion control schemes, before proceeding to Chapter 6 on MPLS. This chapter is organized as follows. We first present the main features of the ATM architecture, such as the structure of the header of the ATM cell, the ATM protocol stack, and the physical layer. Then, we briefly describe the ATM shared memory switch architecture which is the dominant switch architecture, and various scheduling algorithms used to determine the order in which ATM cells are transmitted out. Subsequently, we describe the three ATM adaptation layers AAL: AAL 1, AAL 2, and AAL 5. We conclude the chapter with a description of classical IP and ARP over ATM, a technique standardized by IETF designed for the transport of IP over ATM. Connection-oriented Networks Harry Perros  2005 John Wiley Sons, Ltd ISBN: 0-470-02163-2