When ATM was originally conceived in the 1990s, many people saw it as the 'next best thing' in networking technologies since it could handle both LAN and WAN technologies, allowing users to 'jump' between LAN and WAN without difficulty, in other words, it would have become a single integrated system combining both.
Unfortunately, ATM never became a "magic" end-to-end solution integrating LAN and WAN technologies. ATM adapters for LAN-based desktops were expensive, and the standards for interconnecting networks using the ATM cell system were often confused and delayed. Telephone companies, ISPs and large corporations made use of ATM for their WAN architecture and critical backbones because of the QoS it could assure.
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Key Elements of ATM Technology
One of the major innovations in ATM is the use of 53-byte fixed-length cells, unlike conventional TCP/IP which uses variable-sized packets. This allows ATM users to build very fast circuits, simply because it is easier to process known data packet sizes rather than to have circuits trying to pinpoint the start and end of data packets. The small ATM packet (composed of a five-byte header and a 48-byte data 'container') also guarantees that voice and video can be slotted into the data stream frequently enough for real-time transmission.
Constant Bit Rate, which guarantees sufficient bandwidth for voice and video transmissions in real time, Unspecified Bit Rate, providing 'best effort' service for non-critical data such as file transfers, Available Bit Rate (ABR) which fine-tunes bandwidth according to LAN traffic congestion levels and Realtime variableBit Rate (rt-VBR) can support multimedia applications that require minimal delays
Another innovation in ATM technology is its ability to interconnect LAN and WAN protocols, allowing for a seamless transfer between WAN and LAN. One mode is called MPOA (Multi Protocol Over ATM) can be used to route TCP/IP protocols and IPX while maintaining ATM's quality of service.
LANE (LAN Emulation) modes allows it to interconnect between rival Ethernet and Token Ring, summarizing their frames or data packets in LANE packets and then converting these into ATM 53-byte cells. MPOA or traditional servers can be used to interconnect differing LAN segments, with the ATM communications protocols handling data transfers.
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Constant Bit Rate, which guarantees sufficient bandwidth for voice and video transmissions in real time, Unspecified Bit Rate, providing 'best effort' service for non-critical data such as file transfers, Available Bit Rate (ABR) which fine-tunes bandwidth according to LAN traffic congestion levels and Realtime variableBit Rate (rt-VBR) can support multimedia applications that require minimal delays
Another innovation in ATM technology is its ability to interconnect LAN and WAN protocols, allowing for a seamless transfer between WAN and LAN. One mode is called MPOA (Multi Protocol Over ATM) can be used to route TCP/IP protocols and IPX while maintaining ATM's quality of service.
LANE (LAN Emulation) modes allows it to interconnect between rival Ethernet and Token Ring, summarizing their frames or data packets in LANE packets and then converting these into ATM 53-byte cells. MPOA or traditional servers can be used to interconnect differing LAN segments, with the ATM communications protocols handling data transfers.
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What is ATM
ATM (Asynchronous Transfer Mode) is a technological system developed for both local and wide area networks (LAN and WAN), and designed to handle data as well as video and voice traffic in real time, all at the same time. The system architecture makes use of switches that set up logical circuits at both ends of the data stream, which ensures unprecedented quality of service (QoS).
Unlike conventional telephone switches that sets up dedicated end-to-end circuits, unused bandwidth in Asynchronous Transfer Mode (ATM) can be used for other purposes if needed. For example, idle or unused bandwidth in a video conferencing meeting can be used to transfer data along the same line.
Large carrier networks (telcos) and large enterprises have made use of ATM technology but it has never been picked up for LAN use.
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Unlike conventional telephone switches that sets up dedicated end-to-end circuits, unused bandwidth in Asynchronous Transfer Mode (ATM) can be used for other purposes if needed. For example, idle or unused bandwidth in a video conferencing meeting can be used to transfer data along the same line.
Large carrier networks (telcos) and large enterprises have made use of ATM technology but it has never been picked up for LAN use.
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Understanding EtherCAT
EtherCAT is, in a sense, a synergy of several distinct technologies and developmental efforts, starting with the "fieldbus."
"Fieldbus" is a broad, non-specific term which describes an updated digital communications system in an industrial setting. An industrial system that makes extensive use of automation - for example, a modern automobile assembly line which uses robots for assembly, welding, painting and other repetitive tasks - requires a highly organized, multi-level structure of controllers to function efficiently.
This usually requires a top-level unit called a Human Machine Interface where a human operator monitors and controls the system; followed by a middle-level comprised by a number of Programmable Logic Controllers (PLCs) which are linkedto the upper-level HMIs by a communications system; and finally, the "fieldbus" which links the PLCs to the actual operational components such as motors, actuators, sensors, etc.
In a human organization, one can think of the HMI as the top-level manager (or Chief Operating Officer) who oversees and directs the company's operations; the PLC is the equivalent of the company's 'middle managers' who head up separate divisions dealing with specific areas of company operations; and the 'operators' - or the people working under the middle managers who handle specific, day-to-day operations or activities: field agents, mechanics, drivers, support personnel, etc.
The 'fieldbus' is the communications system which links the field personnel to the middle managers, providing status reports, implementation data, etc. which are processed and forwarded to the COO.
Although the communication linkages between the different levels may appear to be simple, this can become increasingly complex if one considers the multitude of actions and activities that take place at the 'field' level - many of which have to be coordinated with each other, requiring an exchange of information at that level and going upwards to 'middle managers' which, in turn, have to interact and communicate with each other, and so on.
Posted by: Wasim Javed
"Fieldbus" is a broad, non-specific term which describes an updated digital communications system in an industrial setting. An industrial system that makes extensive use of automation - for example, a modern automobile assembly line which uses robots for assembly, welding, painting and other repetitive tasks - requires a highly organized, multi-level structure of controllers to function efficiently.
This usually requires a top-level unit called a Human Machine Interface where a human operator monitors and controls the system; followed by a middle-level comprised by a number of Programmable Logic Controllers (PLCs) which are linkedto the upper-level HMIs by a communications system; and finally, the "fieldbus" which links the PLCs to the actual operational components such as motors, actuators, sensors, etc.
In a human organization, one can think of the HMI as the top-level manager (or Chief Operating Officer) who oversees and directs the company's operations; the PLC is the equivalent of the company's 'middle managers' who head up separate divisions dealing with specific areas of company operations; and the 'operators' - or the people working under the middle managers who handle specific, day-to-day operations or activities: field agents, mechanics, drivers, support personnel, etc.
The 'fieldbus' is the communications system which links the field personnel to the middle managers, providing status reports, implementation data, etc. which are processed and forwarded to the COO.
Although the communication linkages between the different levels may appear to be simple, this can become increasingly complex if one considers the multitude of actions and activities that take place at the 'field' level - many of which have to be coordinated with each other, requiring an exchange of information at that level and going upwards to 'middle managers' which, in turn, have to interact and communicate with each other, and so on.
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Ethernet
Ethernet is the established (and favored) communications standard for local area networks, originally designed to connect different computers to each other for sharing information and data. Ethernet technologies have gone through several phases of development and these have all been for the purposes of simplifying the connections between computers and users as well as increasing the size of the pipeline (through which information will flow) to establish maximum efficiency in resource allocation.
One of the major contributions of Ethernet development are the concepts of information 'packets' - bundles of information or instructions which are then streamed to every computer in the network - and traffic control systems - this mechanism ensures that information packets are sent to the correct recipients. There are also procedures in place to ensure that recipients can still receive the packets even if the computers are 'busy'.
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One of the major contributions of Ethernet development are the concepts of information 'packets' - bundles of information or instructions which are then streamed to every computer in the network - and traffic control systems - this mechanism ensures that information packets are sent to the correct recipients. There are also procedures in place to ensure that recipients can still receive the packets even if the computers are 'busy'.
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What is EtherCAT
EtherCAT stands for "Ethernet for Control Automation Technology." It is an open-source, high performance system that aims to use Ethernet protocols (the favored system for Local Area Networks) in an industrial environment, especially for factories and other manufacturing concerns which make use of robots and other assembly-line technologies.
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How Collisions Occur under CSMA/CD
Imagine a very simple Ethernet network with only two nodes.
Each node, independently, decides to send an Ethernet frame to the other node.
Both nodes listen to the Ethernet wire and sense that no carrier is present.
Both nodes transmit simultaneously, causing a collision.
Both nodes detect the collision and each node waits a random amount of time before transmitting again.
Collisions are normal on an Ethernet network. A small amount of collisions are expected in the protocol design.
If too many nodes are transmitting on an Ethernet network the number of collisions can rise to an unacceptable level. This can reduce the amount of available bandwidth on an Ethernet network because so much bandwidth is lost in retransmission.
Ethernet switches greatly reduce the already minor difficulties experienced with the CSMA/CD protocol.
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Each node, independently, decides to send an Ethernet frame to the other node.
Both nodes listen to the Ethernet wire and sense that no carrier is present.
Both nodes transmit simultaneously, causing a collision.
Both nodes detect the collision and each node waits a random amount of time before transmitting again.
Collisions are normal on an Ethernet network. A small amount of collisions are expected in the protocol design.
If too many nodes are transmitting on an Ethernet network the number of collisions can rise to an unacceptable level. This can reduce the amount of available bandwidth on an Ethernet network because so much bandwidth is lost in retransmission.
Ethernet switches greatly reduce the already minor difficulties experienced with the CSMA/CD protocol.
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What is CSMA/CD
CSMA/CD (Carrier Sense Multiple Access / Collision Detection) is the protocol used in Ethernet networks to ensure that only one network node is transmitting on the network wire at any one time.
Carrier Sense means that every Ethernet device listens to the Ethernet wire before it attempts to transmit. If the Ethernet device senses that another device is transmitting, it will wait to transmit.
Multiple Access means that more than one Ethernet device can be sensing (listening and waiting to transmit) at a time.
Collision Detection means that when multiple Ethernet devices accidentally transmit at the same time, they are able to detect this error.
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Carrier Sense means that every Ethernet device listens to the Ethernet wire before it attempts to transmit. If the Ethernet device senses that another device is transmitting, it will wait to transmit.
Multiple Access means that more than one Ethernet device can be sensing (listening and waiting to transmit) at a time.
Collision Detection means that when multiple Ethernet devices accidentally transmit at the same time, they are able to detect this error.
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