Performance basics

Performance can be measured through E2E delay, packet loss, throughput

As packets come into a router link, they're put into a buffer/queue

• With a larger buffer, the end to end communication would slow down
• If the buffer is too small, there will be a rapid buffer overflow
  • Data loss

Arrival rate > link capacity -> q delay & drops

E2E delay factors:

• Nodal processing
  • Time device takes to analyze packet (check bit errors, determine output link, etc)
• Queuing delay
  • R = link bandwidth
  • L = packet length
  • a = average packet arrival rate (pkts/sec)
  • LA (BPS) average bits arrival rate
  • Traffic intensity = La/r
  • Time waiting at output for transmission
  • Depends on congestion level of router
• Transmission delay
  • L = packet length
  • R = link transmission rate
  • Transmission delay = L/R
• Propagation delay
  • d: length of physical length
  • s: propagation speed (~2E8 m/sec)
  • Propagation delay: d/s

Throughput

• Rate (bits/time unit) at which bits are transferred
• Can be instantaneous or average (i.e., rate)
• Effective throughput: Useful data (not metadata, headers, etc.) transferred per unit time
• Limited by bottleneck link: the link constraining E2E throughput (link w/ lowest capacity)