CSC 600 Internetworking with TCP/IP

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CSC 600Internetworking withTCP/IP

• Unit 2 Client-Server Model and Sockets(Ch.2, 3,
  21, 22)
• Dr. Cheer-Sun Yang
• Fall 2000

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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.

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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.

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Sample Data Representation

• Bits can be sent as a voltage or current through
  a wire
• For example
• zero 1 volts
• one -1 volts
• (Later well see some problems with this
  representation)

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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.

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Chapter 2 Transmission Media

• Copper Wires
• Glass Fibers
• Radio
• Satellites
• Geosynchronous Satellites
• Low Orbit Satellites
• Low Orbit Satellite Arrays
• Microwaves
• Infrared
• Laser Lights

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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)

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COAXIAL CABLE
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More about Coaxial Cable

• Coaxial cable typically transmits information in
  one of two modes baseband or broadband mode.
• Baseband mode - the cables bandwidth is devoted
  to a single stream of data.
• Broadband mode - the bandwidth is divided into
  ranges. Each range typically carries separate
  coded information.

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Ethernet

• Transceiver used to connect an Ethernet and a
  host.

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

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Router
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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.

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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
  routers point-of-view. Thus, IP datagrams can be
  passed from Internet to Token Ring without going
  through application level gateway.
• See Fig. 3.3

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A Virtual Network
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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)

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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.

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Client-Server Model(contd)

• 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.

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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.

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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.

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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_zero8

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Internal Socket Structure

• struct
• int family
• int type
• int protocol,
• struct sockaddr_in local_socket_addr
• struct sockaddr remote_socket_addr

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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

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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()