Performance Metrics Neil Tang 9/10/2008 CS440 Computer Networks

Outline Bandwidth (Throughput) Latency (Delay) Delay  Bandwidth Jitter CS440 Computer Networks

Bandwidth (Throughput) Bandwidth: the number of bits that can be transmitted from one end to another in a certain period of time. Link Bandwidth VS. End-to-End Bandwidth Why “Width”: Each bit can be looked as a pulse of some “width”. Another Meaning of Bandwidth: the width of a frequency (spectrum) band. CS440 Computer Networks

Latency (Delay) Latency: how long it takes for a message to travel from one end to another. Link Latency VS. End-to-End Latency Latency: Latency = Propagation delay + Transmit delay + Queuing delay Propagation delay = Distance / Speed-of-Light Transmit delay = PacketSize / Bandwidth Round Trip Time (RTT) (only includes propagation delay) CS440 Computer Networks

Effective Throughput TransferTime = one-way latency + setup time Effective Throughput = TransferSize/TransferTime TransferSize only includes DATA bits CS440 Computer Networks

Delay  Bandwidth Delay  Bandwidth : The number of bits the channel can hold (the volume of the pipe). CS440 Computer Networks

Jitter The bandwidth needs may vary. Jitter: It is the variation in packet latency and caused by queuing delay. Solution: Buffering at the receiver Network Interpacket gap Packet source sink 1 2 3 4 CS440 Computer Networks