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– 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

TCP/IP

packet

Source file

Application data

Other layers

IP layer

TCP layer

packet

Destination file

Internet

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