1 / 10

Prof. Dr. Ing. PUSZTAI Kalman

Learn about the ATM technology, connection-oriented virtual circuits, QoS support, fixed-size packets, VPI/VCI, SAR, AAL protocols, LAN Emulation, and more.

cwiggins
Download Presentation

Prof. Dr. Ing. PUSZTAI Kalman

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Prof. Dr. Ing. PUSZTAI Kalman ATM networks

  2. ATM overview • Promising technology in early 90s (why?) • Connection-oriented (virtual circuits) • Signalling protocol: Q.2931 • Support for QoS (reserve bandwidth and buffer space for each VC at switches) • Fixed-size packets (cells): 53 bytes

  3. Cells and cell size • Pros and cons of variable-sized packets • Bandwidth efficiency (no zero padding) • Hardware complexity • Benefits of fixed-size packets (cells) • Switch processing is same for all cells • Small cells reduce “preemption delay” • Trade-offs in choosing cell size • Bandwidth efficiency & cell processing speed • ATM: 48B, 5B header, 53B total

  4. ATM cell format 4 16 3 1 8 8 384 (48 bytes) • VPI & VCI: identify virtual-circuit • Type bits: • Explicit Forward Congestion Indication • User signalling bit (used by AAL5: shows last cell of a packet) • Cell Loss Priority bit GFC VPI VCI Type CLP HEC (CRC-8) Payload

  5. Segmentation And Reassembly (SAR) AAL AAL • Also referred to as “fragmentation and reassembly” (in the IP context) • SAR is performed by ATM Adaptation Layer (AAL) • AAL attaches an additional header to the packet needed for reassembly at the receiver • Five different AAL protocols were defined; AAL5 was the most popular in data networks … … A TM A TM

  6. AAL5 SAR protocol Padding CS-PDU User data trailer 48 bytes 48 bytes 48 bytes ATM header Cell payload

  7. VPIs and VCIs • ATM connection identifiers: 8b VPI + 16b VCI • Two-level hierarchy: • Virtual paths are used between major network nodes • Virtual circuits are multiplexed in same virtual paths • Objective: backbone switches need smaller VC table

  8. ATM in the LAN environment • A bit of history: ATM vs Ethernet • Major issue: how to implement broadcast and multicast in an ATM LAN?

  9. ATL LAN Emulation (LANE) • Objective: make ATM network look like shared-media LAN (e.g., Ethernet) to higher-layer protocols Higher-layer Higher-layer protocols protocols (IP, ARP, . . .) (IP, ARP, . . .) Ethernet-like interface Signalling Signalling + LANE + LANE AAL5 AAL5 ATM ATM ATM PHY PHY PHY PHY Host Switch Host

  10. LANE servers • LECS: LAN Emulation Configuration Server • Used to first connect an ATM host to a LANE network • LES: LAN Emulation Server • Keeps track of ATM and MAC addresses for each host • BUS: Broadcast & Unknown Server • Maintains point-to-multipoint VC to all registered clients

More Related