12 ATM architecture ATM adaptation layer AAL only at edge of ATM network data

12 atm architecture atm adaptation layer aal only at

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12 ATM architecture ATM adaptation layer (AAL): only at edge of ATM network data segmentation/reassembly roughly analogous to Internet transport layer ATM layer: “network” layer cell switching, routing physical layer physical ATM AAL physical ATM AAL physical ATM physical ATM end system end system switch switch
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13 ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL): “adapts” upper layers (IP or native ATM applications) to ATM layer below Handles transmission errors Segmentation and reassembly Handling lost cells Flow control like TCP
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14 ATM Adaptation Layer (AAL) [more] Different versions of AAL layers, depending on ATM service class: AAL1: Connection oriented for CBR services, e.g. voice, video conferencing AAL2: for VBR (Variable Bit Rate) services, e.g., MPEG video,airline reservation, banking transactions… AAL5: for data (eg, IP datagrams), IP over ATM supports both connection oriented and connectionless (TCP and UDP)
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15 ATM Layer Service: transport cells across ATM network analogous to IP network layer very different services than IP network layer Network Architecture Internet ATM ATM ATM ATM Service Model best effort CBR VBR ABR UBR Bandwidth none constant rate guaranteed rate guaranteed minimum none Loss no yes yes no no Order no yes yes yes yes Timing no yes yes no no Congestion feedback no (inferred via loss) no congestion no congestion yes no Guarantees ?
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16 ATM Layer: Virtual Circuits Permanent VCs (PVCs) Direct connectivity b/n sites. (leased line) guarantees availability of a connection does not require call setup procedures Switched VCs (SVC): dynamically set up on per-call basis (telephone call) extra time and overhead required to set up the connection.
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ATM Virtual Connections ATM networks are fundamentally connection- oriented, a virtual channel (VC) must be set up across the ATM network prior to any data transfer. 17
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18 Virtual circuits: signaling protocols used to setup and maintain VC used in ATM not used in today’s Internet Higher L AAL ATM L Physical Layer Higher L AAL ATM L Physical Layer 1. Initiate call 2. incoming call 3. Accept call 4. Call connected 5. Data flow begins 6. Receive data
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19 ATM Layer: ATM cell
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ATM cell header fields Generic Flow Control (GFC) — controls the flow of traffic for different quality of services. Virtual Path Identifier (VPI) and Virtual channel identifier (VCI) identifies the next destination of a cell as it passes through a series of ATM switches on the way to its destination. Payload Type (PT) first bit=0, user data, bit=1 control data. The second bit 0 = no congestion, 1 = congestion Cell Loss Priority (CLP) —If the CLP bit equals 1, the cell should be discarded in preference to cells with the CLP bit equal to 0.
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