• Forwarding
  • Move packets from a router's input link to appropriate router output link (i.e., it handles the individual steps)
  • Relies on forwarding table (result of running a routing algorithm)
• Routing:
  • Determine route taken from src to destination
• HOL blocking
  • Reduces throughput, increases latency
  • Possible solutions
    • Virtual Output Queueing
    • Advanced Scheduling Algorithms
  • Multiple layers of OSI model
    • DLL, Net layer, Transport
• Output port queueing: possible delay/loss by output buffer overflow (arrival rate exceeds output line speed)

Scheduling Policies

• Packet scheduling: deciding which packet to send next on link
  • Ex: First come first serve, priority, round robin, weighted, etc.
• Priority schedule:
  • Arriving traffic classified by class (by header fields)
  • Packet from highest priority queue is sent (FCFS within priority class)
• Weighted Fair Queuing
  • Each class, i, has a weight (w)
  • Time is given to each queue according to associated weight

Queuing Theory

• We try to predict performance like queuing delay, buffer size,
  • Avg num of packets in system (Little's Thm)
  • Arrival pkt process (Poisson dist)
  • Queuing (serving) discipline (FIFO, Priority Queuing, WFQ)
  • and more