The Network Layer

• The role of the Network Layer
  • in an end system
  • as an intermediate system
• Addressing
  • Name
    • Internet names: the domain name system
  • Location
    • Internet IP addresses identify a connection, not a machine
    • IP address format
    • The OSI address format
    • OSI address authoritiesand naming identifiers
    • Examples
      • A phone number
      • Some additional examples
      • US GOSIP NSAP(Ref: Tang and Scoggins, Open Networking with OSI, Prentice Hall 1992)
  • Route
    • The network must receive enough information from the name and/or address of a destination to allow routing.
• Routing
  • Routing can be done by the originator, in which case a detailed routing is carried in the packet heading
  • More commonly, routing is done by the network
    • Distance Vector Routing
      • Each node builds a table based on information about the distance to adjacent nodes
      • The table is augmented by exchanging information with adjacent nodes
      • The resulting table contains the first step on the least cost path to each reachable node in the network
    • Link State Routing
      • Every node obtains a list of adjacent nodes and their costs for every other node in the network
      • Using this information, the node builds a routing table that provides the first step on the shortest path from itself to any possible destination.
      • This method provides the same kind of result as Distance Vector Routing, but has some advantages in performance.
• Connection Oriented vs. Connectionless Network