1. Networks

2. 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

3. 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 network Collision

4. 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

5. 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

6. Switched Ethernet network

7. 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

8. 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

9. 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

10. 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