Summary.

Network-Layer

  • Transport segment from sending to receiving host
    • Sender: encapsulates into datagrams

Functions:

  • Forwarding: move packets from router input link to appropriate router output link
    • Implemented in Data plane
      • Typically in hardware
  • Routing: determine network route taken by packets from source dest
    • Routing algorithms
    • Implemented in control plane
      • Implemented in software

Data plane:

  • Local, per-router function
    • determine how datagram arriving on router input port, is forwarded to router output port

Control plane:

  • Network- wide logic
    • Determines how datagram is routed among router

Forwarding table:

Determines, where packets are routed

Per-Router Control plane

Individual routing algorithm components in each and every router interact in the control plane

Network Service Model

Defines the characteristics of end too end No guarantees just like UDP. Best effort service

router

  • Number of ports supported by a router can range from a small number in enterprise routers to, hundreds of 10 GBps ports in a router at an ISP’s edge
  • Switching fabric
    • Connects the router’s input ports to its output ports
    • Is completely contained within the router
    • Network inside of a network router
  • Routing processor
    • Routing processor performs control-plane functions
  • Router requirements
    • Router’s input ports, output ports, and switching fabric are almost always implemented in hardware rather than software
    • Router’s dataplane operates at the nanosecond time scale
    • Control functions operate at a millisecond or second time scale
  • Destination-Based Forwarding
    • Router uses forwarding table to look up the output port to which an arriving packet will be forwarded via switching fabric
  • Switching fabric
    • 3 types
      • Memory
      • bus
      • Interconnection network