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Chapter 14 Connection-Oriented Networking and ATM

Chapter 14 Connection-Oriented Networking and ATM. ATM PVC SVC QOS AAL5. Connection-Oriented Packet Switching in ATM. Connection request by one computer Connection acceptance by other computer End-to-end connection established via a virtual circuit

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Chapter 14 Connection-Oriented Networking and ATM

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  1. Chapter 14 Connection-Oriented Networking and ATM • ATM • PVC • SVC • QOS • AAL5

  2. Connection-Oriented Packet Switching in ATM • Connection request by one computer • Connection acceptance by other computer • End-to-end connection established via a virtual circuit • Connection identifiers assigned to both computers • Data exchange using VPI and VCI identifiers associated with VC • Connection teardown

  3. Asynchronous Transfer Mode (ATM) cell format • 48 bytes of data • 5 bytes of header (figure 14.1) • 4 bits flow control • 1 byte Virtual Path Identifier(VPI) • 2 bytes Virtual Channel Identifier (VCI) • 3 bits payload type • 1 bit priority • 1 byte CRC

  4. Label Switching in ATM • Aka label rewriting • VPI/VCI of cell changed by ATM switch during forwarding using a forwarding table (figure 14.3) • Incoming cell’s VPI/VCI used as index into table containing output interface number and new VPI/VCI for outgoing cell header • Two computers using a given virtual circuit usually have different VPI/VCI values • Computer is aware of its own VPI/VCI, not that of the other computer

  5. Permanent Virtual Circuits(PVC) • Created by network manager • forwarding tables on the ATM switches manually configured (provisioning) • Survives power failure • Requested by customer to ATM network provider

  6. Switched Virtual Circuits(SVC) • Virtual circuit created dynamically (on demand) • Creation of SVC • Computer sends a connection request to switch • As request propagates towards destination, each pair of ATM switches chooses a VPI/VCI to use for the VC and initialize their forwarding tables. • Once all switches along path and the destination computer agree to provide the SVC, a message is sent back to the originating computer to indicate connection request accepted. • If any switch along the path does not agree to provide the VC, an error message is sent back with request denied.

  7. Quality of Service (QOS) • bandwidth(bps) and delay(ms) requirements • constant bit rate (CBR) for uncompressed audio and video • variable bit rate (VBR) for compressed audio and video • Available bit rate (ABR) for bursty data • If QOS requests cannot be satisfied, connection request is denied.

  8. ATM Adaptation Layer 5 (AAL5) • The only one of five adaptation protocols that is used to send data • Computer can send variable-size blocks (up to 64k bytes) to AAL5 on the switch • each block segmented into cells for transmission through ATM network. • AAL5 reassembles cells at destination

  9. Connection Unicast QOS WAN/LAN Fixed size cell Expensive Connection setup latency 10% header overhead Connectionless Broadcast RSVP LAN Variable sized frames No connection setup latency 1% header overhead ATM vs. Ethernet

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