The International Telecommunications Union (ITU) has defined broadband as any rate higher than primary rate (T1 or 1.544 Mbps). Bandwidth demands of advanced multimedia applications built on the WWW, as well as the Internet, telephony, videoconferencing, and similar networking applications are at last being matched by advances in transmission technology and their application to networks.
Different characteristics of applications drive the need for broadband network support. They include the following:
• High traffic volumes necessitated by increasing use of traditional applications. Increasing use of e-mails that contain documents, graphics, and even moving pictures. Client-server architecture-based applications and large file transfers result in large volumes of traffic, which benefit from broadband networks. Increasing capacity-access networks, especially different forms of digital subscriber line (DSL) circuits, are providing low-cost, high-bandwidth access to single users to their homes, vastly increasing the traffic volumes the supporting
transport networks need to carry.
• Special client-server applications, such as those supported by the WWW, are interactive in nature. Increased bandwidth is needed to provide acceptable latency for increasingly complex graphicintensive contents or to support the increasing use of Web-initiated downloads of large files (such as executables or large audio-video
files).
• Applications that are inherently broadband, such as moving digital images, digital photography, music, and VOD, necessitate a broadband infrastructure.
• Convergence of telephony and data networks, at the core transport level transmitting transparently circuit-switched data, or in the use of voice-over-packet technologies in packet-switching networks, will result in the need to transfer large volumes of voice/data necessitating increasing deployment of broadband networks.
Audio bit-rates range from CD-quality sound, which yields a 1.411 Mbps at 44.1 KHz sampling with 16-bit quantization, to 64 Kbps for digital telephony. With compression algorithms, MPEG layer 3 produces CDquality voice stream of 128 Kbps with 12:1 compression rates, and typical vocoders produce 8-Kbps compressed speech rates in telephone networks.
Video streams produced by MPEG-1 to support 720 pixels sample density per line, 576 lines per frame, and 30 frames per second TV sizes have variable rate bit streams ranging from 1.86 Mbps to a maximum of 15 Mbps.
The mix of different services, in addition to having different bit rates, have different traffic characteristics and real-time needs that require the network to guarantee a defined QoS generally defined in terms of sustained bit rate, excess bit rate, and burst size.
To handle such traffic volumes and QoS guarantees, emerging networks have used latest transmission, switching, and protocol technologies.
While narrowband transmissions generally operate over copper wires or coaxial cables, broadband transmission technologies use the large bandwidth provided by optical fibers. Currently, the wireless transmission technologies have also been developed to carry DS3 rates (45 Mbps) and above to form important segments of access networks in a broadband architecture.
Broadband rates are described in optical carrier (OC) rates:
OC-1 51.84 Mbps
OC-3 155.52 Mbps
OC-12 622.08 Mbps
OC-24 1244.16 Mbps
OC-48 2488.32 Mbps
OC-192 9953.28 Mbps
Advances in optical transmission technologies have recently produced dense wavelength division multiplexing (DWDM) technology. DWDM allows splitting of light into multiple wavelengths (colors), each of which can carry data at 10 Gbps and enables a single fiber to carry up to 100 different wavelengths giving an aggregate bandwidth of more than 1 Tbps per fiber.
Similar to T1 and T3 framing in traditional data/voice networks, the Synchronous Optical Network (SONET) standard, as part of a larger telephony standard called Synchronous Digital Hierarchy (SDH) by the Comite Consulatif Internationale de Telegraphie et Telephonie (CCITT), defines the framing for transmission of digital data over fiber. The basic building block in SONET is a synchronous transport signal Level 1 (STS-1) frame, which is organized as a 9-row by 90-column byte array, transmitted row first.
The basic frame timing used in T1 circuits (i.e., 8,000 frames per second) gives an STS-1 rate of 51.84 Mbps (90 × 9 × 8 × 8,000). SONET framing allows multiplexing of low-speed digital signals such as DS1 or DS3 and is able to integrate services such as ATM, which is made up of fixed length cells of 53 bytes in length.
ATM is a technology linked to the development of broadband Integrated Services Digital Network (ISDN) in the 1980s. As a packet-switched high-performance technology, ATM can support multiservice applications, including multimedia. Established standards for network and user interface, signaling, and traffic management have facilitated ATM’s rapid growth and adaptation to different networking needs. ATM architecture provides switched and permanent categories of virtual circuit connections [i.e., permanent virtual circuits (PVCs) and switched virtual circuits (SVCs)] between end systems and promotes optimized utilization of bandwidth by defining different classes of services.
The explosive growth in the broadband needs of emerging applications dictate the need for fiber-based infrastructure development. The ATM networking technology and fiber synergy has encouraged network service providers to increasingly deploy ATM-based transport networks.
The following sections provide a broad overview of the technologies and protocols that provide the framework for the detailed coverage on ATM interworking.
Different characteristics of applications drive the need for broadband network support. They include the following:
• High traffic volumes necessitated by increasing use of traditional applications. Increasing use of e-mails that contain documents, graphics, and even moving pictures. Client-server architecture-based applications and large file transfers result in large volumes of traffic, which benefit from broadband networks. Increasing capacity-access networks, especially different forms of digital subscriber line (DSL) circuits, are providing low-cost, high-bandwidth access to single users to their homes, vastly increasing the traffic volumes the supporting
transport networks need to carry.
• Special client-server applications, such as those supported by the WWW, are interactive in nature. Increased bandwidth is needed to provide acceptable latency for increasingly complex graphicintensive contents or to support the increasing use of Web-initiated downloads of large files (such as executables or large audio-video
files).
• Applications that are inherently broadband, such as moving digital images, digital photography, music, and VOD, necessitate a broadband infrastructure.
• Convergence of telephony and data networks, at the core transport level transmitting transparently circuit-switched data, or in the use of voice-over-packet technologies in packet-switching networks, will result in the need to transfer large volumes of voice/data necessitating increasing deployment of broadband networks.
Audio bit-rates range from CD-quality sound, which yields a 1.411 Mbps at 44.1 KHz sampling with 16-bit quantization, to 64 Kbps for digital telephony. With compression algorithms, MPEG layer 3 produces CDquality voice stream of 128 Kbps with 12:1 compression rates, and typical vocoders produce 8-Kbps compressed speech rates in telephone networks.
Video streams produced by MPEG-1 to support 720 pixels sample density per line, 576 lines per frame, and 30 frames per second TV sizes have variable rate bit streams ranging from 1.86 Mbps to a maximum of 15 Mbps.
The mix of different services, in addition to having different bit rates, have different traffic characteristics and real-time needs that require the network to guarantee a defined QoS generally defined in terms of sustained bit rate, excess bit rate, and burst size.
To handle such traffic volumes and QoS guarantees, emerging networks have used latest transmission, switching, and protocol technologies.
While narrowband transmissions generally operate over copper wires or coaxial cables, broadband transmission technologies use the large bandwidth provided by optical fibers. Currently, the wireless transmission technologies have also been developed to carry DS3 rates (45 Mbps) and above to form important segments of access networks in a broadband architecture.
Broadband rates are described in optical carrier (OC) rates:
OC-1 51.84 Mbps
OC-3 155.52 Mbps
OC-12 622.08 Mbps
OC-24 1244.16 Mbps
OC-48 2488.32 Mbps
OC-192 9953.28 Mbps
Advances in optical transmission technologies have recently produced dense wavelength division multiplexing (DWDM) technology. DWDM allows splitting of light into multiple wavelengths (colors), each of which can carry data at 10 Gbps and enables a single fiber to carry up to 100 different wavelengths giving an aggregate bandwidth of more than 1 Tbps per fiber.
Similar to T1 and T3 framing in traditional data/voice networks, the Synchronous Optical Network (SONET) standard, as part of a larger telephony standard called Synchronous Digital Hierarchy (SDH) by the Comite Consulatif Internationale de Telegraphie et Telephonie (CCITT), defines the framing for transmission of digital data over fiber. The basic building block in SONET is a synchronous transport signal Level 1 (STS-1) frame, which is organized as a 9-row by 90-column byte array, transmitted row first.
The basic frame timing used in T1 circuits (i.e., 8,000 frames per second) gives an STS-1 rate of 51.84 Mbps (90 × 9 × 8 × 8,000). SONET framing allows multiplexing of low-speed digital signals such as DS1 or DS3 and is able to integrate services such as ATM, which is made up of fixed length cells of 53 bytes in length.
ATM is a technology linked to the development of broadband Integrated Services Digital Network (ISDN) in the 1980s. As a packet-switched high-performance technology, ATM can support multiservice applications, including multimedia. Established standards for network and user interface, signaling, and traffic management have facilitated ATM’s rapid growth and adaptation to different networking needs. ATM architecture provides switched and permanent categories of virtual circuit connections [i.e., permanent virtual circuits (PVCs) and switched virtual circuits (SVCs)] between end systems and promotes optimized utilization of bandwidth by defining different classes of services.
The explosive growth in the broadband needs of emerging applications dictate the need for fiber-based infrastructure development. The ATM networking technology and fiber synergy has encouraged network service providers to increasingly deploy ATM-based transport networks.
The following sections provide a broad overview of the technologies and protocols that provide the framework for the detailed coverage on ATM interworking.
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