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CSC 600 Internetworking with TCP/IP

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  1. CSC 600Internetworking withTCP/IP Unit 2: Client-Server Model and Sockets(Ch.2, 3, 21, 22) Dr. Cheer-Sun Yang Fall 2000

  2. Theoretical Basis for Data Transmission • Information can be transmitted through a medium by varying some physical property. • The physics of the universe (noise, distortion, attenuation) places some limits on what can be sent over a channel. • Purpose of physical layer – to transport a raw bit stream from one machine to another.

  3. How do we transmit these waves? • Feed an electrical signal to the antenna of a transmitter • The signal makes the atoms of the antenna vibrate (changing energy levels). • This change causes the antenna to emit electromagnetic waves.

  4. voltage +1 0 -1 1 0 1 0 0 1 Sample Data Representation • Bits can be sent as a voltage or current through a wire • For example: • zero = +1 volts • one = -1 volts • (Later we’ll see some problems with this representation…)

  5. Bandwidth A given transmission medium can accommodate signals within a given frequency range. The bandwidth is equal to the difference between the highest and the lowest frequencies that may be transmitted. For example, a telephone signal can handle frequencies between 300 Hz and 3300 Hz, giving it a bandwidth of 3000 Hz. This means, very high- or low-pitched sound cannot pass through the telephone system. Sometimes, bandwidth is used to denote the number of bits that can be transmitted.

  6. Chapter 2 Transmission Media • Copper Wires • Glass Fibers • Radio • Satellites • Geosynchronous Satellites • Low Orbit Satellites • Low Orbit Satellite Arrays • Microwaves • Infrared • Laser Lights

  7. Twisted Pair • Insulated Copper wires, about 1mm thickTwisted, to avoid forming an antenna: reduces interference • Two major kinds • Cat 3 (1988 and earlier) • four pairs: (allows four telephone lines) • Cat 5: (new installations) • more twists per centimeter, and Teflon insulation • more suitable for high speed networks. • Shielded vs. Unshielded: • shielded twisted pair (STP) • (shield serves as ground, some applications in business use this, but becoming more rare) • unshielded twisted pair (telco local loop to home is usually UTP)


  9. More about Coaxial Cable Coaxial cable typically transmits information in one of two modes: baseband or broadbandmode. • Baseband mode - the cable’s bandwidth is devoted to a single stream of data. • Broadband mode - the bandwidth is divided into ranges. Each range typically carries separate coded information.

  10. Ethernet • Transceiver: used to connect an Ethernet and a host. transceiver host

  11. Ethernet

  12. 10/100 Ethernet 10 BASE T 10Mbps baseband Twisted-pair

  13. Chapter 3Internet Architecture • Repeater – extending a cable (UTP, STP, Optical Fiber). • Bridge – interconnecting two LANs which operate in the data link layer. Example: 2 TCP/IP LANs. • Router – interconnecting two WANs. e.g., the Internet, which operate on the network layer. Example: an Ethernet LAN and a Token Ring. • Gateway – interconnecting different networks in the application layer. For example, one network implements OSI and another implements TCP/IP.

  14. Router

  15. Interconnect Through IP Routers • In a TCP/IP internet, special computers called IP routers or IP gateways provide Interconnections among physical network. • Routers use the destination network, not the destination computer, when forwarding a packet.

  16. What is a Network? • In a TCP/IP internet, TCP/IP can be built over various media-access sublayer. • If TCP/IP over Ethernet, it is the Internet architecture. • If TCP/IP over ring connection, it is the IBM Token Ring. • But, all are called TCP/IP networks from the router’s point-of-view. Thus, IP datagrams can be passed from Internet to Token Ring without going through application level gateway. • See Fig. 3.3

  17. A Virtual Network

  18. Unanswered Questions • How does a router identify a computer? • Chapters 4, 5, 6 cover this. • How does an IP datagram look like? • Chapter 7 introduce this. • How does a TCP segment look like? • Chapter 13 talks about this. • How does an application use the services provided by TCP or UDP? • next topic. (Ch. 22)

  19. Chapter 21Client-Server Model • A host will execute the server program which will always wait for requests for connection. • Another host will execute a client program. • The client and the server will use 3-way handshaking to initiate the communication. • After the connection is established, the client and the sender can send/receive messages. • This model is called a connection-oriented model.

  20. Client-Server Model(cont’d) • The previous model uses TCP/IP. • If UDP/IP is used, after the connection is called, the client only receives the remote endpoint information. • A client then uses the information to identify the destination address for a socket. • This model is called a connectionless model.

  21. Chapter 22. Socket Interface • Services provided by TCP and UDP to the application layer, called an Application Program Interface (API). • There are many versions on various machines: BSD UNIX, Windows, Linux. • TCP provides a connection-oriented service; • UDP provides a connectionless service.

  22. Socket Interface • The network interface is similar to other I/O system calls: OPEN, READ, WRITE, CLOSE. • In addition, it also provides the following: • Create a socket • Bind – specifying a local address • Connect – connecting sockets to a destination • Listen – a server waits for a connect request • Accept – a server accepts the request • Many others.

  23. Socket Address Structure struct sockaddr_in { u_char sin_len; u_short sin_family; u_short sin_port; struct in_addr sin_addr; char sin_zero[8]; };

  24. Internal Socket Structure struct { int family; int type; int protocol, struct sockaddr_in local_socket_addr; struct sockaddr remote_socket_addr; };

  25. Socket System Calls Int socket (int Family, int Type, int Protocol); Family – defines the protocol group: IPv4, IPv6, UNIX domain Type – stream socket, datagram socket, or raw socket Protocol – usually is set to zero for TCP and UDP

  26. Connection-Oriented socket() client server bind() listen() socket() connectrequest accept() connect() Blocks until server receives a connect request from client write() data read() read() data write close() close()