ATM: (continued)

• ATM Addresses
• QoS
• Connection Routing
• IP over ATM:
  • CLIP
  • LANE
• ATM Switches

ATM Addressing

• 20-byte (160-bit) addresses
• Only used during connection setup
• Structured (components can be used for connection routing)
• Must ultimately identify a link (i.e. a switch and a port on that switch)

ATM QoS

• Quality of Service: what the network provides to the connection
• Traffic Descriptor: what the host provides to the network (traffic contract)
• Service classes:
  • Constant bit-rate (CBR)
  • Variable bit-rate (VBR): Real-Time (RT), Non-Real-Time(NRT)
  • Available bit-rate (ABR)
  • Unspecified bit-rate (UBR)

Quality of Service Parameters

• Minimum Cell Rate, e.g. MCR >= 1,000 cells/s = 424,000 b/s
• Cell Loss Ratio (CLR), e.g. CLR <= 10^{-12}
• Mean Cell Transfer Delay (mean CTD), e.g. mean CTD <= 90ms
• Maximum Cell Transfer Delay (max CTD), e.g. max CTD <= 100ms
• Cell Delay Variation (CDV), e.g. CDV <= 40ms

Traffic Descriptors

• Dual Leaky Bucket, in parallel (neither is allowed to overflow)
• Each Leaky Bucket has:
  • maximum rate R (cells/s)
  • capacity C (cells)
• Peak rate leaky bucket: PCR (Peak Cell Rate), CDVT (Cell Delay Variation Tolerance)
• Mean rate leaky bucket: SCR (Sustained Cell Rate), BT (Burst Tolerance)

Traffic examples

• CBR: defined by PCR and CDVT specified loss rate and delays
• VBR: SCR < PCR, size of burst (sequence of cells arriving with rate R, SCR < R <= PCR), bounded by BT
  • RT: specified loss rate and delays
  • NRT: specified loss rate
• ABR: at least minimum rate (requires feedback from network to increase rate)
• UBR: best-effort

Connection Routing

• General Routing problem: in a distributed system, find a route between a specified source and a specified destination
• Two general solutions:
  1. Look at your neighbors' routing tables ("distance vector")
  2. Keep a map of the entire network ("link state")
• In ATM, route must be able to satisfy QoS, so simple connectivity is not enough
• Distance vector only works well when there is a single metric ("cost", "distance", or "delay")
• Therefore, ATM uses link state

IP over ATM

• LANE:
  • LAN (logically shared medium) Emulation
  • Host keeps translation table from Ethernet address to ATM address
  • LANE server(s) provide new translation table entries
  • Packet can be forwarded from ATM to Ethernet by a router
• CLIP
  • Classical IP over ATM
  • ATM is the "data-link layer" technology
  • "ARP" resolves IP to ATM addresses
  • SVC used to carry IP packets, must be closed after a period of inactivity.

ATM Switches

• N * N (input * output ports) switch
• Bus or Crossbar (Switching Fabric) to carry packets from input port to output port(s)
• Easy multicast
• Controller to do signaling, set up forwarding tables

ATM Switch Buffering

• Without buffers, can only handle exact permutations
• Input Buffering:
  • Buffer is between input port and crossbar
  • Head-of-line blocking: packets for a free port blocked by packets at the "head of the line" for a congested port
• Output Buffering:
  • No head-of-line blocking
  • Buffer must be able to accept N cells for each cell sent
• Priority Buffers (low priority cells can't block high priority cells)

ATM Questions

• What does QoS give us that a few priorities wouldn't?
• Is connection-oriented the right model?
• How expensive is non-reordering of cells, and is it worth it?
• Why is ATM more expensive than Ethernet?
• ATM Scalability: (155Mb/s, 622Mb/s, 2.4Gb/s, 10Gb/s....) how far can it go?