DATA COMMUNICATIONS

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DATA COMMUNICATIONS Data Communications and
Networking, Behrouz A Forouzan, 4th edition,
2006, TMH
Mrs P Lavanya Asst. Prof. E. C. E. Dept.
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• Data refers to information presented in
  whatever form is
• agreed upon by the parties creating and
  using the
• data.
• Communication process of exchanging information
• Data Communications are the exchange of data
  between two devices via some form of transmission
  medium.
• For data communications to occur, the
  communicating devices must be part of a
  communication system made up of a combination of
  hardware (physical equipment) and software
  (programs).

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• Effectiveness of data communications system
  depends on four fundamental characteristics
• Delivery The system must deliver data to the
  correct destination
• Accuracy The system must deliver the data
  accurately.
• Timeliness the system must deliver data in a
  timely manner.
• Jitter refers to the variation in the packet
  arrival time. It should be
• zero.

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UNIT - I
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Contents

• Introduction
• - Components
• - Data Representation
• - Data Flow
• Networks
• - Network Criteria
• - Physical Structures
• - Categories of Networks
• The Internet
• Protocols and Standards
• Network Models
• - Layered Tasks
• - The OSI Model
• - Layers in the OSI Model
• - TCP/IP Protocol Suite
• - Addressing

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Introduction(1)

• Components
• - A data communications system has five
  components.
• 1. Message it is the information to be
  communicated.
• 2. Sender It is the device that sends the
  data message.
• 3. Receiver It is the device that receives
  the message.
• 4. Transmission medium It is the physical
  path by which a
• message travels from sender to
  receiver.
• 5. Protocol It is a set of rules that govern
  data communications.

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Introduction(2)
Fig. 1.1 Five components of data communication
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Introduction(3)

• Data Representation
• - Information comes in different forms such as
  text, numbers, images,
• audio, and video.
• Text ASCII(American Standard Code for
  Information Interchange)
• Unicode
• Numbers represented by bit patterns.
• number is directly converted to a binary
  number
• Images represented by bit patterns.
• color images RGB, YCM
• Audio refers to the recording or broadcasting
  of sound or music.
• It is different from
  text, numbers, or images.
• It is continuous, not discrete.
• Video refers to the recording or broadcasting
  of a picture or movie.

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Introduction(4)

• Data Flow
• - Communication between two devices can be
  simplex, half-duplex, or
• full-duplex
• Simplex Communication is unidirectional
• - entire capacity of the channel
  is used
• - Ex Keyboards, Traditional Monitors

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Introduction(5)

• Half-Duplex each station can both transmit and
  receive, but not
• at the same time.
• - entire capacity of the channel is taken
  over by whichever of the two devices is
  transmitting at the time
• - Ex Walkie-talkies and CB radio

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Introduction(6)

• Full-Duplex both stations can transmit and
  receive simultaneously
• - capacity of the link is shared
• - Ex Telephone

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Networks(1)

• A network is a set of devices (often referred to
  as nodes) connected by communication links.
• A node can be a computer, printer, or any other
  device capable of sending and/or receiving data
  generated by other nodes on the network.
• Distributed Processing
• Network Criteria
• A network must be able to meet a certain number
  of criteria. The most important of these are
  performance, reliability, and security.

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Networks(2)

• Performance performance of a network depends
  on a number of factors, including the
  number of users, the type of transmission
  medium, the capabilities of the connected
  hardwares, and the efficiency of the
  software.
• It is often evaluated by two networking metrics
  throughput and delay
• We need more throughput and less delay.
• Reliability It is measured by frequency of
  failure in addition to accuracy of
  delivery
• Security include protecting data from
  unauthorized access, protecting
  data from damage and development, and
  implementing policies and procedures for recovery
  from breaches and data losses.

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Networks(3)

• Physical Structures
• Type of Connection
• - A network is two or more devices connected
  through links.
• - A link is a communications pathway that
  transfers data from one
• device to another.
• - For visualization purposes, it is simplest to
  imagine any link drawn
• between two points.
• - For communication to occur, two devices must
  be connected in
• some way to the same link at the same time.

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Networks(4)

• There are two types of connections
  point-to-point and multipoint.
• Point-to-point
• - there is a dedicated link between two
  devices.
• - entire capacity of the link is reserved for
  transmission between
• those two devices.
• - connection can be a physical wire or cable or
  a microwave or a
• satellite link

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Networks(5)

• Multipoint
• - also called multidrop
• - more than two specific devices share a single
  link
• - capacity of the channel is shared, either
  spatially or temporally.
• - if several devices can use the link
  simultaneously
• spatially shared connection
• - if users must take turns time shared
  connection

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Networks(6)

• Physical Topology
• Refers to the way in which a network is laid out
  physically.
• Two or more devices connect to t link
• Two or more links form a topology.
• Topology of a network is the geometric
  representation of the relationship of all the
  links and linking devices to one another.

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Networks(7)

• Mesh
• - every device has a dedicated point-to-point
  link to every other device.
• - to have a mesh network with n nodes, n(n-1)/2
  physical links are
• needed.
• - to accommodate that many links, every device
  on the network must
• have n-1 input/output (I/O) ports
• - Advantages
• 1. use of dedicated links eliminate traffic
  problems
• 2. robust
• 3. there is the advantage of privacy or
  security.
• 4. fault identification and fault isolation
  easy
• - Disadvantages
• 1. installation and reconnection are difficult.
• 2. the sheer bulk of the wiring can be greater
  than the available space
• 3. hardware required to connect each link is
  prohibitively expensive
• - limitedly used

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Fig. A fully connected mesh topology
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Networks(8)

• Star
• - every device has a dedicated point-to-point
  link only to a central
• controller, usually called a hub.
• - devices are not directly linked to one
  another.
• - does not allow direct traffic between devices.
• - the controller acts as an exchange If one
  device wants to send data to
• another, it sends data to the controller,
  which then relays the data to the
• other connected device.
• - Advantages
• 1. less expensive than mesh, each device needs
  only one link and one I/O port to connect it
  to any number of others.
• 2. easy to install and reconfigure
• 3. Far less cabling is needed to mesh
• 4. robustness
• 5. easy fault identification and fault
  isolation

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Networks(9)

• Star
• - Disadvantages
• 1. dependency of the whole topology on one
  single point, the hub.
• 2. more cabling is required than in some other
  topologies
• - used in LANs

Fig. A star topology
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Networks(10)

• Bus
• - It is multipoint
• - one long cable acts as a backbone to link all
  the devices in a network
• - Nodes are connected to the bus cable by drop
  lines and taps.
• - a drop line is a connection running between
  the device and the main cable
• - a tap is a connector that splices into the
  main cable
• - as a signal travels along the backbone, some
  of its energy is transformed
• into heat.
• - therefore, the signal becomes weaker and
  weaker as it travels farther and
• farther.
• - for this reason there is a limit on the number
  of taps a bus can support and
• on the distance between those taps.
• - Advantages
• 1. ease of installation
• 2. uses less cabling than mesh or star

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Networks(11)

• Bus
• - Disadvantages
• 1. difficult reconnection and fault isolation
• 2. difficult to add new devices.
• 3. signal reflection at the taps can cause
  degradation in quality.
• 4. a fault or break in the bus cable stops all
  transmission
• - used in the early LANs.

Fig. A bus topology
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Networks(12)

• Ring
• - each device has a dedicated point-to-point
  connection with only the two
• devices on either side of it (each device is
  linked to only its immediate
• neighbors either physically or logically).
• - a signal is passed along the ring in one
  direction, from device to device,
• until it reaches its destination.
• - each device in the ring incorporates a
  repeater.
• - when a device receives a signal intended for
  another device, its repeater
• regenerates the bits and passes them along

Fig. A ring topology
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Networks(12)

• Ring
• - Advantages
• 1. relatively easy to install and reconfigure
• 2. fault isolation is simplified
• - Disadvantages
• 1. unidirectional traffic
• 2. a break in the ring can disable the entire
  network
• - used in Token ring LANs

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Networks(13)

• Hybrid Topology
• - a network can be hybrid.

Fig. A hybrid topology a star backbone with
three different networks
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Networks(14)

• Categories of Networks
• - a network is a group of connected
  communicating devices such as
• computers or printers etc.
• - the category into which a network falls is
  determined by its size.
• - a LAN normally covers an area less than 2 mi.
• - a WAN can be worldwide.
• - networks of size in between are referred to as
  MANs and span tens of
• miles

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Networks(15)

• LAN
• - usually privately owned
• - links the devices in a single office,
  building, or campus
• - a LAN can be as simple as two
• PCs and a printer connected
• together in someones home
• office or it can extend
• throughout a company and
• include audio and video
• peripherals.
• - designed to allow resources to
• be shared between PCs or WSs.

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Networks(16)

• LAN
• - resources to be shared can be hardware,
  software, or data.
• - in addition to size, LANs are distinguished
  from other types of networks
• by their transmission media and topology.
• - a given LAN uses only one type of transmission
  medium.
• - most common LAN topologies are bus, ring, and
  star
• - today, LANs data rates are normally 100 or
  1000 Mbps
• - Wireless LANs are the newest evolution in LAN
  technology

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Networks(17)

• WAN
• - provides long-distance transmission of data,
  image, audio and video
• information over large geographic areas
  that may comprise a country, a
• continent, or even the whole world.
• - a WAN can be as complex as the backbones that
  connect the Internet
• or as simple as a dial-up line that connects a
  home computer to the
• Internet
• - normally refer to the first as a switched WAN
  and to the second as a
• point-to-point WAN

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(No Transcript)
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Networks(18)

• WAN
• - swithced WAN connects the end systems, through
  a router to another
• LAN or WAN.
• - point-to-point WAN is normally a line leased
  from a telephone or cable
• TV provider that connects a home computer or a
  small LAN to an Internet
• Service Provider (ISP).
• - Wireless WAN is becoming more and more popular
  today.

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Networks(19)

• MAN
• - covers the area
• inside a town or
• a city.
• - designed for
• customers who
• need a high-
• speed
• connectivity,
• and have end-
• points spread
• over a city or
• part of city.

Fig. a MAN
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internet

• Interconnection of Networks internetwork
• - when two or more networks are connected, they
  become an
• internetwork, or internet.

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Internet(1)

• The Internet
• - the Internet is a communication system that
  has brought a wealth of
• information to our fingertips and organized it
  for our use.
• - the Internet is a structured, oraganized
  system
• - the most notable internet is called the
  Internet, a collaboration of more
• than hundreds of thousands of interconnected
  networks
• - private individuals, government agencies,
  schools, research
• facilities, corporations, and libraries in
  more than 100 countries use the
• Internet.

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Internet(2)

• - millions of people are users.
• History
• - this extraordinary communication system came
  into being in 1969.
• - the Advanced Research Projects Agency (ARPA)
  in the Department
• of Defense (DoD)
• - Network Control Protocol (NCP)
• - Transmission Control Protocol (TCP)
• - Transmission Control Protocol (TCP) and
  Internetworking Protocol
• (IP)

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Internet(3)

• The Internet Today
• - today, Internet is not a simple hierarchical
  structure
• - It is made up of many wide- and local-area
  networks joined by
• connecting devices and switching stations.
• - It is difficult to give an accurate
  representation of the Internet because it
• is continually changing
• - today most end users who want Internet
  connection use the services of
• Internet Service Providers (ISPs).
• - there are international service providers,
  national service providers,
• regional service providers, and local service
  providers.
• - The Internet today is run by private
  companies, not the government.

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Internet Today

• ISP (Internet service providers)
• NISP (national ISP)
• NAP (network access point)

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Internet(4)

• International Internet Service Providers
• - at the top of the hierarchy are the
  international service providers that
• connect nations together.
• National Internet Service Providers
• - these are backbone networks created and
  maintained by specialized
• companies.
• - these networks are connected by complex
  switching stations called
• network access points (NAPs).
• - some national ISP networks are also connected
  to one another by private
• switching stations called peering points
  (normally operate at a high data
• rate upto 600Mbps.

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Internet(5)

• Regional Internet Service Providers
• - these are smaller ISPs that are connected to
  one or more national ISPs.
• - they are at the third level of the hierarchy
  with a smaller data rate.
• Local Internet Service Providers
• - provide direct service to the end users.
• - local ISPs can be connected to regional ISPs
  or directly to national ISPs.
• - a local ISP can be a company that provides
  Internet services, a
• corporation with a network that supplies
  services to its own employees, or
• a nonprofit organization, such as a college or
  a university, that runs its
• own network.

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Protocols and Standards(1)

• Protocols
• - a protocol is a set of rules that govern data
  communcations.
• - a protocol defines what is communicated, how
  it is communicated, and
• when it is communicated.
• - key elements of a protocol are syntax,
  semantics, and timing.
• Syntax
• - refers to the structure or format of the data,
  meaning the order in which
• they are presented.
• Semantics
• - refers to the meaning of each section of bits.

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Protocols and Standards(2)

• - How is a particular pattern to the
  interpreted, and what action is to be
• taken based on that interpretation?
• Timing
• - refers to two characteristics when data
  should be sent and how fast
• they can be sent.

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Protocols and Standards(3)

• Standards are essential in
• - creating and maintaining an open and
  competitive markets for equipment
• manufacturers
• - guaranteeing national and international
  interoperability of data and
• telecommunications technology and
  processes.
• - provide guidelines to manufacturers, vendors,
  government agencies, and
• other service providers to ensure the kind of
  interconnectivity necessary in
• todays marketplace and in international
  communications.
• - they are fall into two categories de facto
  and de jure.

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Protocols and Standards(4)

• De facto
• - meaning by fact or by convention
• - these are the standards that have not been
  approved by an organized
• body but have been adopted as standards
  through widespread use.
• De jure
• - meaning by law or by regulation
• - standards that have been legislated by an
  officially recognized body

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Standards Organizations

• Standards are developed by
• Standards creation committees
• Forums
• Regulatory agencies
• Standards committees forums
• Standards committees are slow moving
• Forums are made up of interested corporations
• Forum are able to speed acceptance of a
  particular technology

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Standards Committees

• ISO
• Voluntary international organization
• ITU-T
• Formerly, CCITT formed by UN
• ANSI
• Private non-profit corporation in the US
• IEEE
• The largest engineering society in the world
• EIA
• Non-profit organization in the US

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Internet Standards

• IETF (Internet Engineering Task Force)
• Internet Draft
• working document with no official status
• with a 6-month lifetime
• RFC (Request for Comment)
• Edited, assigned a number, and made available to
  all interested parties

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UNIT I(B)
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Contents

• Introduction
• - Components
• - Data Representation
• - Data Flow
• Networks
• - Network Criteria
• - Physical Structures
• - Categories of Networks
• The Internet
• Protocols and Standards
• Network Models
• - Layered Tasks
• - The OSI Model
• - Layers in the OSI Model
• - TCP/IP Protocol Suite
• - Addressing

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Network Models

• A network is a combination of hardware and
  software that sends data from one location to
  another.
• Hardware consists of the physical equipment that
  carries signals from one point of the network to
  another.
• Software consists of instruction sets that make
  possible the services that we expect from a
  network.
• Computer networks are created by different
  entities.
• Standards are needed so that these heterogeneous
  networks can communicate with one another.

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Network Models Layered Tasks(1)
Fig.Tasks involved in sending a letter
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Network Models Layered Tasks(2)

• - the tasks involved in data exchange are
  grouped as hierarchical
• layers.
• - each layer uses the services of the layer
  immediately below it.
• - the two layered models that dominated data
  communications and
• networking are Open Systems Interconnection
  (OSI) model and
• TCP/IP protocol suite.

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Network Models OSI Model(1)

• - An ISO standard that covers all aspects of
  network communications is
• Open Systems Interconnection (OSI) model
• - First introduced in late 1970s.
• - It is a set of protocols that allows any two
  different systems to
• communicate regardless of their underlying
  architecture.
• - It is a model for understanding and designing
  a network architecture that
• is flexible, robust, and interoperable.
• - It consists of seven ordered, separate but
  related layers, each of which
• defines a part of the process of moving
  information across a network.

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OSI Model

• ISO is the organization. OSI is the model

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Network Models OSI Model(2)

• - Each layer defines a family of functions
  distinct from those of the other
• layers.
• - Within a single machine, Layer 3 uses the
  services provided by layer 2
• and provides services for layer 4.
• - Between machines, layer x on one machine
  communicates with layer x on
• another machine.
• - This communication is governed by an
  agreed-upon series of rules and
• conventions called protocols.
• - The processes on each machine that communicate
  at a given layer are
• called peer-to-peer processes.

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Interaction between layers in the OSI model

• Layer and interface

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Network Models OSI Model(3)

• - At the physical layer, communication is
  direct.
• - Each layer in the sending device adds its own
  information to the
• message it receives from the layer just above
  it and passes the whole
• package to the layer just below it.
• - At layer 1 the entire package is converted to
  a form that can be
• transmitted to the receiving device.
• - At the receiving machine, the message is
  unwrapped layer by layer, with
• each process receiving and removing the data
  meant for it.
• - Each interface defines the information and
  services a layer must provide
• for the layer above it.

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Network Models OSI Model)

• - physical, data link and physica layers
  network support layers.
• - session, presentation and application layers
  user support layers.
• - At layer 1 the entire package is converted to
  a form that can be
• transmitted to the receiving device.
• - At the receiving machine, the message is
  unwrapped layer by layer, with
• each process receiving and removing the data
  meant for it.
• - Each interface defines the information and
  services a layer must provide
• for the layer above it.

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An exchange using the OSI model

• Encapsulation with header and possibly trailer

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Physical Layer

• The physical layer is responsible for movements
  of individual bits from one hop (node) to the
  next
• Mechanical and electrical specification, the
  procedures and functions

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Physical Layer Duties

• Physical characteristics of interfaces and media
• Representation of bits
• Data rate
• Synchronization of bits
• Line configuration
• Physical topology
• Transmission mode

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Data Link Layer

• The data link layer is responsible for moving
  frames from one hop (node) to the next
• Transform the physical layer to a reliable
  (error-free) link

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Data Link Layer Duties

• Framing
• Physical addressing
• Flow control
• Error control
• Access control

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Hop-to-Hop Delivery
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Network Layer

• The network layer is responsible for the delivery
  of packets from the source host to the
  destination host

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Network Layer Duties

• Logical addressing and routing

Data Communications, Kwangwoon University
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Transport Layer

• The transport layer is responsible for delivery
  of a message from one process to another

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Transport Layer Duties

• Service-point (port) addressing
• Segmentation and reassembly
• Connection control
• Flow control
• Error control

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Reliable Process-to-Process Delivery of a Message
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Session Layer

• Session layer is responsible for dialog control
  and synchronization

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Presentation Layer

• Presentation layer is responsible for
  translation, compression, and encryption

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Application Layer

• Application layer is responsible for providing
  services to the user

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Application Layer Services

• Network virtual terminal
• Mail services
• File transfer, access, and management
• Directory services

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Summary of Layers
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TCP/IP and OSI Model
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TCP/IP Protocol Suite

• Host-to-network Physical and data link layer
• No specific protocol
• Network layer
• IP(Internet Protocl), ARP(Address Resolution
  Protocol), RARP(Reverse ARP), ICMP(Internet
  Control Message Protocol), IGMO(Internet Group
  Message Protocol)
• Transport layer
• TCP(Transmission Control Protocol), UDP(User
  Datagram Protocl), SCTP(Stream Control
  Transmission Protocol),
• Application Layer
• Combined session, presentation, and application
  layers

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Addressing

• Four levels of addresses in TCP/IP protocols
• Physical (link), logical (IP, network), port, and
  specific addresses

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Relationship of Layers and Addresses
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Physical Address

• A node with physical address 10 sends a frame to
  a node with physical address 87. The two nodes
  are connected by a link (bus topology LAN). As
  the figure shows, the computer with physical
  address 10 is the sender, and the computer with
  physical address 87 is the receiver.

070102012C4BA 6-byte (12 hexadecimal
digits) physical address.
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Logical (IP) Address

• The physical addresses will change from hop to
  hop, but the logical addresses usually remain the
  same

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Port Address

• The physical addresses change from hop to hop,
  but the logical and port addresses usually remain
  the same

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Specific Address

• Some application have user-friendly addresses
  that are designed for that specific address
• Example 1 e-mail address kchung_at_kw.ac.kr
• Defines the recipient of an e-mail
• Example 2 URL (Universal Resource Locator)
  www.kbs.co.kr
• Used to find a document on the WWW

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