Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Lecture 4 Networking Part 2 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 3-5 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 3-6 Ethernet vs. Internet • Internet – Uses point-to-point network to implement pointto-point communications – Allows multiple communications taking place concurrently along its different paths • Ethernet – Uses broadcast network to implement point-topoint communications – Allows only one communication at a time 3-7 Connecting to the Internet • Two basic methods 1. Connect via an Internet service provider (ISP) 2. 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 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 1. Less space 2. 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 – 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: 1. Down in the hierarchy means into subfolders (towards the leaves) 2. 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.