Networks and the Internet Topic 3 Three Important Networking Technologies Networks, Internet, WWW A Modem Networks, Internet, WWW MM Data communications Sending messages/information between two or more computers. Data communications media ImplementationExample Speed MultiplierMedia Dial Up Modem56 kbps1 Wireless S500 kbps10XS Wireless 3G MT1,500 kbps30XMT DSL1+ Mbps20XTP Cable Modem2+ Mbps40XC Ethernet LAN Mbps200X 2,000XTP, C, F T1, T2, T3TP, C, F OC-19210,000 Mpbs200,000XF 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 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 Data Communication Networks, Internet, WWW 5 of 22 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 Messages and Packets Packet A1Packet A2Packet A3 Message A Trailer Body Header A Packet 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 Source IP Address (128 bits) Diff-Serv (8 bits) Version (4 bits) Hop Limit (8 bits) Destination IP Address (128 bits) Next Header or Payload (Data Field) Routers Router 4 Router 2 Router 1 Router 4 Internet Routers Router 3 Router 4 Router 6 Router 7Router 9 Router 8Router 1 Router 2 Router 4 Router 5 Sending Messages Across a Network U.S. Internet Backbone Networks, Internet, WWW 1 of 20 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). A LAN A WAN Internetworking Process of linking two or more networks. A bridge links similar networks A gateway links dissimilar networks Router and a Switch Internet Addressing Physical transmission requires IP address Domain name system converts domain name to equivalent IP address Internet Addressing Internet Addressing 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. 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.