Network Concepts

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Network Concepts

• Rong Wang
• CGS3285
• School of Computer Science
• University of Central Florida
• Spring2004

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RECOMMENDED READING

• From textbooks
• Chapter 7 of Data Communications From Basics to
  Broadband, 3rd Edition by William J. Beyda (ISBN
  0-13-096139-6)
• Page 813 and Chapter 2 of Data Communications
  and Networking, 3rd Edition, Behrouz A. Forouzan
  (ISBN 0-07-251584-8)

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NETWORKS

• Network
• A set of devices (often referred to as nodes)
  connected by communication links.
• Node
• A device that is capable of sending and/or
  receiving data generated by other nodes o the
  network (e.g., a computer, printer)
• Distributed processing
• A task is divided among multiple computers
• Network criteria
• Performance
• Reliability
• Security

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TYPE OF CONNECTION

• Point to point
• A dedicated link is provided between two devices
• Multipoint
• More than two specific devices share a single link

Point to point connection
Multipoint connection
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TYPE OF CONNECTING TOPOLOGY
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MESH TOPOLOGY

• Every device has a dedicated point-to-point link
  to every other devices
• Dedicated
• Link carries traffic only between the two devices
  it connects
• A fully connected mesh network has n(n-1)/2
  physical channels to link n devices
• Every device on the network must have n-1
  input/output (I/O) ports
• Advantage
• Less traffic, robust, secure, easy to maintain
• Disadvantage
• Need more resource (cable and ports), expensive

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STAR TOPOLOGY

• Each device has a dedicated point-to-point link
  only to a central controller, usually called a
  hub.
• No direct traffic and link between devices
• Advantage
• Less expensive
• Easy to install and reconfigure
• Robustness
• Disadvantage
• Single point of failure

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BUS TOPOLOGY

• A multipoint topology
• All devices are linked through a backbone cable
• Nodes are connected to the bus cable by drop
  lines and taps.
• Drop line
• A connection running between the device and the
  main cable
• Tap
• A connector that either splices into the main
  cable or punctures the sheathing of a cable to
  create a contact with the metallic core
• Advantage
• Ease of installation
• Disadvantages
• Difficult reconnection and fault isolation
• Broken or fault of the bus cable stops all
  transmission

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RING TOPOLOGY

• Each device is dedicated point-to-point
  connection only with the two devices on either
  side of it
• A signal is passed along the ring in the
  direction, from device to device, until it
  reaches its destination
• Each device in the ring incorporates a repeater
• Advantage
• Relatively easy to install and reconfigure
• Fault isolation is simplified
• Disadvantage
• Unidirectional traffic

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NETWORK MODEL

• A network model is a layered architecture
• Task broken into subtasks
• Implemented separately in layers in stack
• Functions need in both systems
• Peer layers communicate
• Protocol
• A set of rules that governs data communication
• It represents an agreement between the
  communicating devices

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INTERNET LAYERS
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PEER TO PEER PROCESS

• Communication must move down through the layers
  on the sending device, over to receiving device
• Are the receiving device, communication must move
  up through the layers
• 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 the receiving device, the message is unwrapped
  layer by layer, with each process receiving and
  removing the data meant for it

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PEER-TO-PEER PROCESS

• The passing of the data and network information
  down through the layers of the sending device and
  backup through the layers of the receiving device
  is made possible by interface between each pair
  of adjacent layers
• Interface defines what information and services a
  layer must provide for the layer above it.

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AN EXCHANGE USING INTERNET MODEL
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PHYSICAL LAYER

• Responsible for transmitting individual bits from
  one node to the next
• Function
• Physical characteristics of interfaces and media
• Representation of bits
• Data rate
• Synchronization of bits
• e.g., RC-232-c interface

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DATA LINK LAYER

• Responsible for transmitting frames from one node
  to the next
• Function
• Framing
• Physical addressing
• Flow control
• Error control
• Access control

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NODE-TO-NODE DELIVERY
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Example 1
In following Figure a node with physical address
10 sends a frame to a node with physical address
87. The two nodes are connected by a link. At the
data link level this frame contains physical
addresses in the header. These are the only
addresses needed. The rest of the header contains
other information needed at this level. The
trailer usually contains extra bits needed for
error detection
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NETWORK LAYER

• Source-to-destination delivery,
• Responsible from the delivery of packets from the
  original source to the final destination
• Functions
• Logical addressing
• routing

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SOURCE TO DESTINATION DELIVERY
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Example 2
In the Figure we want to send data from a node
with network address A and physical address 10,
located on one LAN, to a node with a network
address P and physical address 95, located on
another LAN. Because the two devices are located
on different networks, we cannot use physical
addresses only the physical addresses only have
local jurisdiction. What we need here are
universal addresses that can pass through the LAN
boundaries. The network (logical) addresses have
this characteristic.
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TRANSPORT LAYER

• Process-to- process delivery
• Responsible for delivery of a message from one
  process to another
• Functions
• 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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Example 3
Following Figure shows an example of transport
layer communication. Data coming from the upper
layers have port addresses j and k (j is the
address of the sending process, and k is the
address of the receiving process). Since the data
size is larger than the network layer can handle,
the data are split into two packets, each packet
retaining the port addresses (j and k). Then in
the network layer, network addresses (A and P)
are added to each packet.
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APPLICATION LAYER

• Responsible for providing services to the user
• Functions
• Mail services
• File transfer and access
• Remote log-in
• Accessing the World Wide Web

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SUMMARY OF DUTIES
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A UNIVERSAL ARCHITECTURE?

• Each manufacturer has its own architecture
• Need for a single architecture to connect
  equipment from different manufacturers
• International Standards Organization (ISO)
  developed a general architecture model known as
  the Open Systems Interconnection or OSI Model
• Seven layers
• TCP/IP is the de facto standard
• Provides a common method for describing
  communication architectures, tasks and functions.
• Meant to help connect equipment from multiple
  manufacturers
• Supported in principle but not in fact
• Often referred to as a Reference Model

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OSI - THE MODEL

• A layered model
• Each layer performs a subset of the required
  communication functions
• Each layer relies on the next lower layer to
  perform more primitive functions
• Each layer provides services to the next higher
  layer
• Changes in one layer should not require changes
  in other layers

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OSI LAYERS
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OSI MODEL

• First four layers
• Almost the same as first four layers of Internet
  model
• Session layer
• The network dialog controller,
• It establishes, maintains and synchronize the
  interaction between communicating system
• Function
• Dialog control
• Synchronization
• Presentation layer
• Concerned with the syntax and semantics of the
  information exchanged between two system
• Functions
• Translation
• Encryption
• Compression
• Application layer
• Enables the user to access the network
• Functions
• Network virtual terminal
• File transfer, access and management

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FITTING THE PIECES TOGETHER

• Physical Layer
• Analog and Digital signals
• Data rates
• Transmission impairments
• Line coding
• Transmission mode
• Parallel vs. serial
• Synchronous vs. asynchronous
• Direction of transmission
• Modulation and demodulation
• Multiplexing
• Guided and Unguided transmission media
• Data link layer
• Error detection, correction and error control