Eng/Abdulrahman M. Abutaleb
P T E R
Asynchronous Transfer Mode (ATM) is a technology that was defined by the ITU-T (formerly known as the CCITT) in the early 1990s. The related standards describe a transport technology in which information is carried in small, fixed-length data units called cells. ATM is a project invented by the telephone industry because after Ethernet was widely installed, the computer industry never rallied around any higher-speed network technology to as it standard. The telephone companies filled this vacuum with ATM, although in October 1991,many computer vendors joined with the telephone companies to setup the ATM forum, an industry group that will guide the future of ATM. ATM is designed to replace the entire circuit-switched telephone system with cell switching and be able to handle data and television as well.
ATM networks are connection-oriented. This Course provides summaries of ATM protocols, services, and operation. Figure 1 illustrates a private ATM network and a public ATM network carrying voice, video, and data traffic. [pic]
In particular, this course focuses on how ATM devices efficiently process and transmit user traffic as discrete, fixed-length ATM cells at very high speeds.
ATM technology can be used in the following types of networking environments: • Private workgroup or enterprise networks
• Large public networks
• Hybrid combinations of both private and public networks
ATM technology is rapidly being implemented in these networking environments to enable the seamless interconnection of local area networks (LANs) and wide area networks (WANs). Furthermore, ATM technology enables the switching and transport of multiple traffic types at comparatively high speeds in a single switching fabric.
2- ATM Benefits:
ATM technology offers the following primary benefits:
• Bandwidth efficiency—ATM efficiently supports the aggregate transmission requirements of a network by allocating bandwidth on demand, based on actual user needs. Bandwidth allocation is accomplished without administrative intervention. Furthermore, network bandwidth is scalable to meet future user needs for higher transmission rates. • Scalability —ATM is highly flexible, accommodating a wide range of traffic types, traffic rates, and communications applications. ATM interface standards exist for data rates as low as 1.544 Mbps (DS1) and as high as 2.4 Gbps (SONET).
• Application transparency—The fixed-length size of an ATM cell is an effective compromise between the typically lengthy packets of data communications repetitive frames of telecommunications (voice) applications. The asynchronous nature of ATM data transmission allows a wide range of ATM devices to support traffic at rates and degrees of burstiness compatible with the user’s applications, rather than at rates and degrees of burstiness convenient to the network. In other words, ATM allows the network to be tailored to the user’s needs, rather than forcing the user’s applications to fit the network’s characteristics. ATM affords the following user benefits:
— Provides timely access to network resources
— Supports message traffic of variable length
— Provides higher transmission speeds
— Provides self-routing capabilities for multiple traffic types — Supports new data communications and telecommunications applications — Offers guaranteed network access for voice and video applications — Enables users to request a desired level and quality of service — Provides protection mechanisms against network congestion conditions
• Networking advantages—ATM is a simple, fast, cell-switching technology that derives its cell routing capabilities from information carried within each cell. Thus, no data processing occurs above the cell level in an ATM network; this...
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