Chapter 14 ConnectionOriented Networking and ATM

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Chapter 14 Connection-Oriented Networking and ATM

• ATM
• PVC
• SVC
• QOS
• AAL5

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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

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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

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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 cells 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

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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

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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.

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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.

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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

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ATM vs. Ethernet

• 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