Asynchronous Transfer mode (ATM) is a high speed network that support voice and data communications. ATM operates on data link layer (Layer 2 in the OSI model); it runs over fiber or twisted pair copper cable.
ATM differs from more common data link technologies like Ethernet in several ways. ATM does not use routing protocols. Hardware devices known as ATM switches establish point-to-point connections between the sources and destination. ATM does not use variable length packets, it uses fixed sized cells. ATM cells are made up of 48 bytes of data and 5 bytes for the header information totaling 53 bytes.
ATM technology is designed to improve utilization and quality of service (QoS) on high-traffic networks. Without routing and with fixed-size cells, networks can better manage bandwidth under ATM than under Ethernet. Because of the high cost of ATM compared to Ethernet, ATM is used for the backbone and other high performance, specialized networks.
ATM is designed to be easily implemented by hardware and, faster processing and switch speeds are possible. The bit rates are either 155.520 Mbps or 622.080 Mbps. Speeds on ATM networks can reach 10 Gbps. Along with Synchronous Optical Network (SONET) and several other technologies, ATM is a key component of broadband ISDN (BISDN).
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