Networks

Ethernet

Invented by Dr. Robert Metcalfe in 1970 at Xerox Palo Alto Research Center

Allows group of computers to communicate in a Local Area Network (LAN)

A drawing of the first Ethernet system by Bob Metcalfe

Ethernet protocol

Ethernet uses a system where each computer listens to the cable before sending anything through the network

Information or data is broken into packets If network is clear computer will transmit or send the data until it

arrives at the destination without colliding with any other packet Carrier Sense Multiple Access/Collision Detection (CSMA/CD)

if any device attached to a network, such as file servers, printers, or workstations (called nodes) is sending data on the cable computer will wait and try again when the line is clear

Ethernet networkCollision

Packets

Packets include the following information

Packets are ordered and reassembled at destination

sender's IP address receiver's IP address

total number of packets number in packet sequence

Switched Ethernet

Replace shared Ethernet with dedicated segment for each node

Segments connect to a switch that can connect many single station segments switches allow different nodes of a network to

communicate directly with one another efficiently Only devices on segments are the switch and end node

switch picks up transmission before it reaches another node

forwards transmission over the appropriate segment since any segment contains only a single node, the frame

only reaches the intended recipient allows many conversations to occur simultaneously

Switched Ethernet network

Packet switching

Used to optimize the use of bandwidth available in a network and to minimize latency bandwidth: difference between the highest and lowest

frequencies of a transmission channel latency: time it takes for packet to cross a network connection

Packets individually routed between nodes with no previously established communication path travel to destination by the router depending on the amount of

traffic on any given channel at the time of transmission Not all packets traveling between the same two hosts will

necessarily follow the same route even those from a single message

Destination computer reassembles the packets into their appropriate sequence

internet/Internet

An internet is a collection of interconnected networks Wide Area Network (WAN) Gateways, routers, backbones, switching

The Internet is the largest example of an internet

The Internet

“Information Superhighway” Transports vast amounts of information traffic from point to point

at high speeds along telephone lines, cables, satellites and microwave links

Web browser: “Window to the Internet” Internet Service Provider (ISP)

companies that allow you to connect to their computers which in turn are connected to the Internet

Routers computer on network that directs information to destination

Internet Backbone Phone lines and cables Network Service Providers (NSPs) Network Access Points (NAPs) allow data to move from one

network to another

How the Internet works

Protocol allows computers and networks to communicate in order to

exchange information TCP/IP

Transmission Control Protocol/ Internet Protocol set of protocols that allows the Internet to operate

TCP is responsible for breaking information into packets and recombining packets into original form

IP ensures that the information gets to destination computer IP address: numerical address of destination computer

152.3.233.7 Domain names: text equivalent of IP address

www.duke.edu Domain Name Service (DNS): translates domain name into IP

address