Outline: Internet and ATM

• Internet
  • Routing
  • TCP (Transmission Control Protocol)
• ATM (Asynchronous Transfer Mode)
  • Routing
  • QoS (Quality of Service)

The Internet

• Designed to survive nuclear attack
• Popularized by WWW
• Best-Effort Service
• No guarantees, no security
• Self-organizing
• No central point of control/failure

Example

Characteristics

• Defined by Internet Protocol (IP)
• Each network interface has a unique Network address (IP address)
• DNS converts node names to IP addresses (global distributed redundant database)
• Building the routing tables

Routing Overview

• Manual
• Full Maps
• Hierarchical Routing
• BGP (Boundary Gateway Protocol)

Manual Routing

Only works for small internets.

Full Maps

Each router independently uses received information to build a map of the entire network, and from that its routing table.

Problems: does not scale (too much information being broadcast), maps may be out of date resulting in routing loops.

Hierarchical Routing

Group computers into networks, and only store paths to networks in the routing tables.

Group networks into autonomous systems (ASs), and only store paths to ASs in the routers outside the AS.

BGP

• Boundary Gateway Protocol
• Each AS advertises the other ASs it can reach, together with the path to reach them and some measure of the "distance".
• Inconsistent distance information is detected by looking at the paths.

TCP

• Transmission Control Protocol
• Adds reliability to IP
• Adds congestion control (throttling) to IP
• Only runs on the end-systems (IP has to run on all the routers)
• Adds demultiplexing ("ports") to IP
• Adds connections to IP

How TCP works

• sequentially number all data sent in each direction
• acknowledge data as it's received
• if there is no ack within a certain time, retransmit
• if there are W (W = window) outstanding (unacked) packets, stop and wait.
  • receiver can make W smaller if it is getting data too fast
  • sender can make W smaller if there are indications of congestion:
    • increased round-trip time
    • packet loss

ATM

• Asynchronous Transfer Mode -- as opposed to SONET (Synchronous Optical Network)
• originally telephone technology
• virtual circuits
• 53-byte fixed-size cells with 5-byte header
• resource reservation:
  • video
  • audio
  • best-effort

ATM Switching

• 5-byte header has a two-part identifier
• identifier is only meaningful in one direction along a single link
• when cell is received, switch:
  • uses port number and identifier as index into table containing:
    • outgoing identifier
    • outgoing port number
    • QoS indication
  • places outgoing identifier into cell header
  • routes cell to outgoing port
• table is set up at "virtual circuit setup time"

Example

ATM QoS

• Leaky bucket
• Example: 100 sources, each sending at rate r <= (0.1 + 1.5t)Mb/t
  • if t >> 1, r =~ 1.5 Mb/s
  • if t << 1, burst <= 0.1 Mb
  • therefore, traffic can be carried with no loss by a 155Mb/s link with a 10Mb buffer.
  • Maximum delay is (10Mb / 155Mb/s) =~ 0.065 s = 65ms.
• Leaky bucket and QoS reservations can be used to bound delay and eliminate or bound data loss.