IT 210: Web-based IT Winter 2012 Measuring Speed on the Internet and WWW

Sources of Delay  Latency Delay: Length of pipe (time to traverse)  Bandwidth: Size of pipe (how much it holds)  Packet Loss/Error rates: Friction in pipe  Content: Amount of data being transferred Bandwidth Delay

Delay x Bandwidth Product (volume)  Amount of data “in flight” or “in the pipe” (i.e., how much the pipe holds)  Example: 100ms x 45Mbps = 576KB Bandwidth Delay

Bandwidth (bit rate, maximum throughput, channel capacity)  Bandwidth: amount of data that can theoretically “fit” on the network in a single unit of time (e.g., 10 Mbps)  Measured in Mbps (or some other bits/time)  Throughput is the actual (not theoretical maximum) bandwidth

Bandwidth/Throughput Calculator

Latency (total delay)  Time to get a message from point A to point B  Often measured in round-trip time (RTT)  Composed of: Propagation delay: distance/propagation speed Transmission delay: message size/bandwidth Queue delay: time spent waiting in line at routers etc. Processing time: time to process a packet (e.g., check for errors, decide where to route)

Latency Calculator

BYU vs NSU (in russia)

Packet Loss  Queue overflow: when data arrives at the queue faster than it can be transmitted new packets are discarded  Noise: distortions in the underlying transmission medium (e.g., electrical circuit) change a packet’s data causing it to fail an error check

Delays Based on Content  Images (resize/compress offline, not via )  Remove unnecessary CSS & Javascript  Move Javascript to end (unless needed in )  Limit ads and analytics tools being used  Compress javascript, CSS, & HTML (e.g., use gzip)  Use caching when possible (e.g., use cach-control appropriately, use Content Delivery Networks – CDNs)  Minimize HTTP Requests (e.g., combine all scripts into single file, combine images into a single one)

Navigation Timing Javascript API

Online Speed Optimization Tools

BitTorrent  Peer-to-peer service for sharing large files  Each file separated into parts  Parts distributed among many devices that use BitTorrent service  When file is downloaded pieces come from different sources in any order and are reassembled

Questions…  What is responsible for a “slow” speed if: A text message is sent via satellite link to someone in China? A movie file is downloaded via a DSL modem?

Questions…  What is the transmission delay of a 20MB file sent over a link with a 10Mbps throughput?