it 210: web-based it winter 2012 measuring speed on the internet and www
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IT 210:Web-based IT
Winter 2012Measuring 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 <img>) Remove unnecessary CSS & Javascript Move Javascript to end (unless needed in <head>) 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?