ATM - Asynchronous Transfer Mode (ATM) Dr. Sanjay P. Ahuja,...

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Asynchronous Transfer Mode (ATM) Dr. Sanjay P. Ahuja, Ph.D. Professor School of Computing, UNF
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2 Goals of ATM 1. ATM, also known as cell relay, involves the transfer of data in discrete chunks called cells . Multiple logical connections can be multiplexed over a single path. This is similar to packet switching except that the packets are variable sized and cells are of a fixed size. 2. ATM is used in the WANs and is not constrained to a particular physical medium or data rate (155 Mbps, 622 Mbps, and 2.5 Gbps). 3. ATM has minimal error and flow control capabilities to reduce the overhead of cells the overhead of protocol processing, enabling ATM to operate at high data rates.
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3 ATM Protocol Architecture
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4 ATM Protocol Architecture … Physical Layer Concerned with specifications of the transmission medium and signal encoding . Data rates specified include 155 and 622 Mbps with other data rates possible. ATM Layer Defines transmission of data in fixed size cells and also defines the logical connections (Virtual circuits and virtual paths). ATM Adaptation Layer (AAL) Supports transfer protocols not based on ATM. It maps higher layer information into ATM cells to be transported over an ATM network, then collects information from ATM cells for delivery to higher layers (e.g. a IP packet can be mapped to ATM cells). (There are 3 planes in the protocol architecture: the User plane is for user traffic including flow and error control; the Control plane is for connection control; the Management plane manages the system as a whole and coordinates the planes and layers).
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5 ATM Protocol Layers …
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6 Virtual Paths (VPs) and Virtual Circuits (VCs)
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7 Virtual Paths (VPs) and Virtual Circuits (VCs) … ATM Logical Connections are referred to as Virtual Circuit Connections (VCCs). A VCC is set up between two end users and a variable-rate, full-duplex flow of cells is exchanged over the connection. A Virtual Path Connection (VPC) is a bundle of VCCs that have the same endpoint. So all cells flowing within all the VCCs in a VPC are switched together. VPC helps control cost by grouping connections sharing common paths through the network into a single unit. Network management can then be applied to a small number of groups of connections instead of a large number of individual connections. Advantages of VPCs: 1. Simplified network architecture (network functions can be separated into those related to a VCC and those related to a group of connections (VPC)). 2. Increased network performance and reliability since the network deals with fewer entities. 3. Reduced processing and short connection set-up time (most of the work is done when a VPC is set-up. By reserving capacity on a VPC in anticipation of later calls, new VCCs can be set-up be executing simple control functions at end-points of the VPC; no call processing is required at transit nodes. So addition of new VCCs to an existing VPC involves minimal processing). 4.
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This note was uploaded on 07/29/2011 for the course CNT 6707 taught by Professor Ahuja during the Spring '11 term at UNF.

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ATM - Asynchronous Transfer Mode (ATM) Dr. Sanjay P. Ahuja,...

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