Networks and the Internet

1. Topic 3 Networks and the Internet

2. Three Important Networking Technologies Networks, Internet, WWW

3. A Modem M M 0 0 1 1 1 0 1 0 0 1 1 1 0 1 Networks, Internet, WWW

4. Data communications Sending messages/information between two or more computers.

5. Data communications media

6. Example Connections & Service Notes: TP=Twisted Pair, C=Coaxial Cable, F=Fiber, S=Satellite, MT=Microwave Towers/cellular T1, T2, T3 are dedicated lines from Org to ISP or ISP to Internet OC Internet backbone lines

7. http://mindprod.com/jgloss/transmissionspeed.html http://indianblogger.com/understanding-the-generations-1g-2g-3g-and-4g/

8. Data Communication • Network: two or more computers or devices linked by communication lines. • Each computer/device is a node • Transmitter and receiver are nodes • The network is the medium • Communication rules are defined by a protocol

9. Data Communication • Communication protocol • An agreed-upon format or procedure for transmitting data. • Implemented in hardware and/or software • Key issues • Deliver message efficiently • Detect errors • Correct errors Networks, Internet, WWW – 5 of 22

10. Messages and Packets Message A Trailer Body Header Packet A1 Packet A2 Packet A3

11. Version (4 bits) Diff-Serv (8 bits) Flow Label (20 bits) Marks a packet as part of a specific flow Payload Length (16 bits) Next Header (8 bits) Name of next header Hop Limit (8 bits) Source IP Address (128 bits) Destination IP Address (128 bits) Next Header or Payload (Data Field) A Packet

12. Router 1 Router 2 Internet Routers Router 4 Router 4

13. Routers Router 1 Router 6 Router 8 Router 3 Router 5 Router 5 Router 5 Router 4 Router 4 Router 2 Router 7 Router 9

14. Sending Messages Across a Network

15. U.S. Internet Backbone Networks, Internet, WWW – 1 of 20

16. LANs and WANs • LAN (local area network) • A network that connects systems within a limited physical area (department, dorm). • WAN (wide area network) • A network that connects systems throughout a large geographic area (entire business, university/branches).

17. A LAN

18. A WAN

19. Internetworking • Process of linking two or more networks. A bridge links similar networks A gateway links dissimilar networks

20. Router and a Switch

21. Internet Addressing

22. Internet Addressing • Physical transmission requires IP address • Domain name system converts domain name to equivalent IP address

23. Internet Addressing http://www.visualware.com/ http://www.whatismyip.com/

24. Internet Addressing

25. TCP/IP • Summary: TCP and IP were developed by a Department of Defense (DOD) research project to connect a number different networks designed by different vendors into a network of networks (the "Internet"). It was initially successful because it delivered a few basic services that everyone needs (file transfer, electronic mail, remote logon) across a very large number of client and server systems. Several computers in a small department can use TCP/IP (along with other protocols) on a single LAN. The IP component provides routing from the department to the enterprise network, then to regional networks, and finally to the global Internet. On the battlefield a communications network will sustain damage, so the DOD designed TCP/IP to be robust and automatically recover from any node or phone line failure. This design allows the construction of very large networks with less central management. However, because of the automatic recovery, network problems can go undiagnosed and uncorrected for long periods of time. • As with all other communications protocol, TCP/IP is composed of layers: • IP - is responsible for moving packet of data from node to node. IP forwards each packet based on a four byte destination address (the IP number). The Internet authorities assign ranges of numbers to different organizations. The organizations assign groups of their numbers to departments. IP operates on gateway machines that move data from department to organization to region and then around the world. • TCP - is responsible for verifying the correct delivery of data from client to server. Data can be lost in the intermediate network. TCP adds support to detect errors or lost data and to trigger retransmission until the data is correctly and completely received. • Sockets - is a name given to the package of subroutines that provide access to TCP/IP on most systems.

26. TCP/IP TCP is a connection-oriented transport protocol that sends data as an unstructured stream of bytes. By using sequence numbers and acknowledgment messages, TCP can provide a sending node with delivery information about packets transmitted to a destination node. Where data has been lost in transit from source to destination, TCP can retransmit the data until either a timeout condition is reached or until successful delivery has been achieved. TCP can also recognize duplicate messages and will discard them appropriately. If the sending computer is transmitting too fast for the receiving computer, TCP can employ flow control mechanisms to slow data transfer. TCP can also communicate delivery information to the upper-layer protocols and applications it supports.