More on WANs Fiber Optic Cables Used in Internet backbone Speeds over 100 Gbps Team at the University of Southampton achieved a throughput of ~70 Tbps, with the signal traveling at 99.7% the speed of light (New Scientist)

Network Tools Available on site like http://ping.eu/ Tools ping (try millersville.edu) DNS lookup Visit site using IP address Reverse lookup traceroute whois (authoritative name servers)

Ethernet Uses a wire or fiber, called the channel Engineers “tap” into the channel to connect a computer Can then send/recv signals All computers, including the sender, can detect the signal

Ethernet Network Protocol Rough analogy: conversation at a cocktail party One person talks, everyone listens When talker stops, it is briefly quiet, and someone else starts If two persons start talking, they hear the conflict and pause briefly, until one begins talking again Decentralized scheme (no plan or schedule control) Each computer listens to the channel, and if it's quiet, it's free. A computer starts to transmit; if another starts at the same time, they hear garbled message; both stop for a random time and then try again. Shortest random wait gets the channel

Ethernet vs. Internet Internet Ethernet Uses point-to-point network to implement point-to-point communications Allows multiple communications taking place concurrently along its different paths Ethernet Uses broadcast network to implement point-to-point communications Allows only one communication at a time

Connecting to the Internet Two basic methods Connect via an Internet service provider (ISP) Connect through a campus or enterprise network

1. Connections by ISP Most home users use ISPs Modems convert digital output to carrier format

1. Connections by ISP Signals are sent to carrier Carrier modem receives signals, sends to server Server connects to the Internet via a gateway Smart phones also have modems

2. Enterprise Network Connections Connect via organization’s network Organization connects to the Internet by a gateway

Wireless Networks Variation of a LAN connection Protocol name is 802.11 g@54 Mbps, n@150 Mbps, ac@867 Mbps Uses access point/router Physically connected to an ISP’s modem Capable of broadcasting and receiving signals, usually radio frequency (rf ) signals

The World Wide Web Some computers connected to the Internet are Web servers Supply files to browsers Web servers and their files comprise the World Wide Web (WWW)

The World Wide Web Web pages are files Text Images Video Audio Programs

Requesting a Web Page Web requests use client/server interaction Browser is client Web server is server File specified using URL (Universal Resource Locator) Web browsers and servers use HTTP protocol

Requesting a Web Page The URL has three main parts: http://cs.millersville.edu/~zoppetti/101/index.html The URL has three main parts: Protocol tells the computers how to handle the file Server computer’s name or the name given by the domain hierarchy Page’s pathname tells the server which file (page) is requested and where to find it

Describing a Web Page Servers do not store Web pages as images Pages are stored in source files as a description of how they should appear on the screen Browser receives the description and renders image

Describing a Web Page Two advantages to storing and sending the source file Less space Browser can adapt image for your machine

The Internet and the Web Some Web servers Have www as part of their domain name Add www if you leave it out Work either way When is the www required and when is it optional?

The Internet and the Web Web addresses consist of host names And host names have an IP address DNS server requires name to match exactly

The Internet and the Web Incorrect name results in Accessing wrong IP address google.com vs google.gov DNS lookup fails (“Server Not Found”) Web administrators may register similar forms of a URL yahoo.com

File Structure Directory Hierarchy Think of any hierarchy as a tree Folders can contain folders as well as files Think of any hierarchy as a tree folders are the branch points files are the leaves

File Structure Directory Hierarchy All hierarchies have branch points and leaves Hierarchy trees are often drawn sideways or upside down Two terms are standard, however: Down in the hierarchy means into subfolders (towards the leaves) Up in the hierarchy means into folders (toward the root)

File Structure Part of the directory hierarchy is shown in the pathnames of URLs: airandspace.si.edu/exhibitions/gal100/pioneer.html Page is specified by a pathname that specifies file With each slash (/) we move into a subfolder or to the file

Organizing the Folder Last item in pathname is file Unless URL ends in /, then server looks for “index.html” Course page example

Summary Point-to-point, multicast, broadcast, synchronous, and asynchronous communications IP addresses, domains, IP packets, IP protocol, WANS and LANS, Ethernet protocol, ISPs, enterprise networks, and wireless networks

Summary Difference between the Internet and the Web File hierarchies

Quiz How many bytes are in an IPv6 address? The ______ translates from host names to IP addresses. TCP/IP is a key ______ used on the Internet.