Understanding the Internet’s Underlying Architecture. Transmission Control Protocol (TCP). The language that computers use to communicate over the internet Breaks information into packets Packets are then sent throughout the network to their destination
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Transmission Control Protocol (TCP) • The language that computers use to communicate over the internet • Breaks information into packets • Packets are then sent throughout the network to their destination • At the destination, packets are assembled back to their original form
Internet Protocol (IP) • Ensures that packets are sent to the right destination • Each packet is put in a separate IP envelope that has the destination address on it • All packets go to the same destination • Routers determine most efficient path (they could be different for different packets)
Networking Hardware • Hubs: Link groups of computers together • Bridges: Link Local Area Networks (LAN) • Gateways: Similar to bridges but translate data from one type to another • Repeaters: Amplify data signals for long distance transmission • Routers: Transmit data packets between two different networks
Caching • To make browsing faster, different computers will save web pages — called caching • Cache can be: • On your computer • On your ISP’s computer • On the web server
DNS Server Types • Domain Name Service • special Host servers dotted around the Internet • They help translate computer identifiers that humans can use into the IP addresses computers need to route information • three different types of these (DNS) servers • Root name servers • Primary name servers • Local name servers
Root Name Servers • Only thirteen of them throughout the world • Control a database that contains the location of DNS primary name servers for every top-level domain (TLD) • .com, .edu, .gov, .us, … • There over one hundred of top-level domains, counting country codes • Local name servers send them the top-level portion of a domain name • they look-up and return the IP Address of the primary name server for that particular top-level domain
Primary & Local Name Servers • A primary name server controls the DNS database for a given top-level domain • The edu primary name server knows where to find the local server for uwm.edu • A local name server keep track of the sub-domains and computers for that organization • The uwm.edu local name server knows which computers match alphar.csd.uwm.edu or miller.cs.uwm.edu
Local Name Servers • The name servers transform the domain name that humans can remember into an IP address the computers can work with • But what is an IP address?
IP Addresses • Needed a way to identify individual computers on the internet • Each computer has a unique address • For one computer to send a message to another, it must know the IP address of the destination • IP stands for Internet Protocol
IP Addresses • Format: • x.x.x.x • Where each x is a number from 0 to 255 • Do the math: • 256*256*256*256 = 4,294,967,296 addresses • Despite this, we are running out of IP addresses • Static vs Dynamic
Packet Switching • A telephone line connection is fixed from start point to end point • This is called a circuit-switched network • In internet, the connection line is not fixed • There can be more than one path between source and destination • This is called a packet-switched network
Source file Destination file Application data packet packet TCP layer IP layer Other layers Internet TCP/IP
TCP/IP — Benefits • Each packet individually addressed • Allows for packets to travel any route to destination • Net is decentralized, so not all packets will follow same route • Allows for overall faster transfer • Better error correction • If a packet is damaged, only need to get that one back rather than whole file
To Learn More… • Check out the animated explanation athttp://www.learnthenet.com/english/animate/webworks.html • Here are several pages on web componentshttp://www.learnthenet.com/english/section/www.html • Here is a more detailed treatment of the webhttp://www.cio.com/WebMaster/sem2_home.html