CCITT defines broadband service as “A service requiring transmission channels capable of supporting rates greater than 1.5 Mbps or primary rate of ISDN or T1 or DS1 in digital terminology.”
As shown in figure BISDN is not a technology but a platform supported by different technologies, including ATM, SONET, and IN (intelligent network).
The Need for Broadband
One of the most important factors driving the need for broadband communications is changing user needs and demands. The prior to late 1970s and early 1980s, public network needs were almost entirely driven by telephony (voice communication). Data traffic has been growing slowly until recently, indicating the changing of user needs and demands. Many conditions led to this sudden drastic change.
Together, lower cost and increased processing power of computers enabled a number of users to appear in the public network, but their applications and needs are completely different. To name few needs :
- Video Telephony
- Low-cost video conferencing
- High-Definition Television (HDTV)
- hi-fi audio distribution
- LAN interconnect
- CAD / CAM / CAE
- Super-computing and channel extension
Each of these is a potential application for broadband communications because they all have very high bandwidth requirements.
In addition to these new applications, other factors are also driving the need for broadband around the world. They include following :
- The service demand has changed in nature. Customers want mobility (both terminal and personal), bandwidth on demand, access to management functions, flexibility in establishing connections, end-to-end connectivity, and management.
- A competitive market generally operates more efficiently than a regulated one.
- Equipment and components for the processing and transport of information are becoming increasingly inexpensive.
Overview of Broadband Technologies
The above figure shows a broadband network that can be implemented with technologies. The information (Voice, Data, and Video) that originates at the source node is carried to the destination through a switched network. The origination and destination are typically LAN based. The Fiber Distributed Data Interface (FDDI), Distributed Queue Dual Bus (DQDB), and Asynchronous Transfer Mode (ATM) are three emerging LAN protocols that coordinate information flow at the source and destination node. These protocols replace the current standards of Ethernet and Token ring.
Data that flows from the originating node into the switched network is routed using Frame Relay, SMDS, ATM, etc. All these technologies can be used together, and each can use any physical transmission medium, such as fibre, co-axial cable, wireless, etc. Each physical medium has its own standard for implementation. For fibre Synchronous Optical NETwork (SONET) is used in the United States and Canada, and Synchronous Digital Hierarchy (SDH) is used in Europe and Asian Countries. ATM is also widely used global standard. When ATM is combined with SONET / SDH, it is called as BISDN.
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