Summary

Packet Delay and Loss

• Packets queue in router buffers, waiting for turn for transmission
  • queue length grows when arrival rate to link exceeds output link capacity
• Packet loss occurs when memory to hold queued packets fills up
  • loss packet may be retransmitted by previous node, by source end system, or not at all

use traceroute to measure delay by probing each router by 3 packets and measures time intervals between transmission and reply

Throughput

• Throughput rate (bits/time) at which bits are being sent from sender to receiver
  • Instantaneous: rate at given point in time
  • Average: rate over long period of time