Network Architectures

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Network Architectures

• A reference model that describes the layers of
  hardware and software necessary to transmit data
  between two points or for multiple devices /
  applications to interoperate
• Reference models are necessary to increase
  likelihood that different components from
  different manufacturers will converse
• Two models to learn OSI model and TCP/IP
  protocol suite

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Network Architectures

• A network architecture, or communications model,
  places the appropriate network pieces in layers.
• The layers define a model for the functions or
  services that need to be performed.
• Each layer defines what services either the
  hardware or software (or both) provides.
• the layers work together to allow an application
  to send its data over a network of computers.
• The TCP/IP protocol suite is currently used on
  the Internet, while the OSI model is a
  theoretical model.

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Network Architectures

• The OSI models seven layers

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Network Architectures - OSI

• Application layer where the application using
  the network resides. Common network applications
  include web browsing, e-mail, file transfers, and
  remote logins
• Presentation layer performs a series of
  miscellaneous ?????? functions necessary for
  presenting the data package properly to the
  sender or receiver
• Session layer responsible for establishing
  sessions between users. manages a session by
  initiating the opening and closing of sessions
  between end-user application processes.

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Network Architectures - OSI

• Transport layer provides an end-to-end
  error-free network connection. Makes sure the
  data arrives at the destination exactly as it
  left the source.
• includes error control information in case one
  packet from a sequence of packets does not arrive
  at the final destination, and packet sequencing
  information so that all the packets stay in the
  proper order.
• We say that the transport layer performs
  end-to-end error control and end-to-end flow
  control. This means the transport layer is not in
  use while the data packet is hopping from point
  to point within the networkit is used only at
  the two endpoints of the connection
• Network layer responsible for creating,
  maintaining and ending network connections.
  Transfers a data packet from node to node within
  and between networks.

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Network Architectures - OSI

• As Network layer sends the packet from node to
  node, it generates the network addressing
  necessary for the system to recognize the next
  intended receiver.
• Data link layer responsible for taking the data
  and transforming it into a frame with header,
  control and address information, and error
  detection code
• The Data link layer might also perform flow
  control. In a large network where the data hops
  from node to node as it makes its way across the
  network, flow control ensures that one node does
  not overwhelm the next node with too much data.
• operations are quite similar to some of the
  transport layer operations. The primary
  difference is that the transport layer might
  perform its operations only at the endpoints,
  while the network access layer performs its
  operations at every stop (node) along the path.
• Physical layer handles the transmission of bits
  over a communications channel. Includes voltage
  levels, connectors, media choice, modulation
  techniques (digital or analog data is encoded or
  modulated onto a digital or analog signal ).

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THE SEVEN OSI REFERENCE MODEL LAYERS
Each layer defines a family of function distinct
from those of the other layers.
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An Exchange Using the OSI Model
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Physical Layer

• Coordinates the function required to transmit a
  bit stream over a physical medium.
• Defines the procedures and function that physical
  devices and interfaces have to perform for
  transmission to occur.

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Physical Layer
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Physical layer concerns

• Physical characteristics of interface and media.
  The physical layer defines the characteristics of
  the interface between devices and the
  transmission medium. It also defines the type of
  the transmission media such as copper wires or
  fiber optic cables.
• Representation of bit.
• The physical layer defines the type of encoding
  (how 0s and 1s are changed to signals)
• Data rate The number of bits send per second.
• Synchronization of bits The sender and the
  receiver clocks must be synchronized.
• Transmission mode.
• The physical layer also defines the direction of
  transmission between two devices (the direction
  of signal flow). Simplex, Half duplex or Full
  duplex

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Physical layer concerns

• Line configuration.
• The physical layer is concerned with the
  connection of devices to the medium. In a
  point-to-point configuration, two devices are
  connected through a dedicated link. In a
  multipoint configuration, a link is shared among
  several devices.
• Physical topology.
• The physical topology defines how devices are
  connected to make a network. Devices can be
  connected by using
• a mesh topology (every device is connected to
  every other device),
• a star topology (devices are connected through a
  central device),
• a ring topology (each device is connected to the
  next, forming a ring),
• a bus topology (every device is on a common
  link),
• or a hybrid topology (this is a combination of
  two or more topologies).

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Mesh topology
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Data Link Layer

• Transforms the physical layer, a raw
  transmission facility, to a reliable link and it
  responsible for node-to-node delivery.

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Data Link Layer
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Data Link layer responsibilities

• Framing The data link layer divides the stream
  of bits received from the network layer into
  manageable data units called frames.
• Physical addressing The data link layer adds a
  header to the frame to define the physical
  address of the sender (source address) and/or
  receiver (destination address) of the frame.
• Ex A media access control address (MAC address)
  is a unique identifier assigned to network
  interfaces for communications on the physical
  network segment.
• MAC addresses are most often assigned by the
  manufacturer of a network interface
  controller (NIC) and are stored in its hardware
• The standard format for MAC addresses is six
  groups of two hexadecimal digits.
  e.g. 01-23-45-67-89-ab   or   0123456789ab

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Data Link layer responsibilities

• Flow control If the rate at which the data are
  absorbed by the receiver is less than the rate
  produced in the sender, the data link layer
  impose a flow control mechanism to prevent
  overwhelming the receiver.
• Error control The data link layer adds
  reliability to the physical layer by adding
  mechanism to detect and retransmit damage or lost
  frames and prevent duplication of frames.
• Access control When two or more devices are
  connected to the same link, data link layer
  protocols are necessary to determine which device
  has control over the link at any given time.

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Data Link layer
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Network layer

• Responsible for the source-to-destination
  delivery of a packet possibly across multiple
  networks (links).
• The network layer ensures that each packet gets
  from its point of origin to its final destination.

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Network Layer
Original source
Final destination
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Network layer responsibilities

• Logical addressing
• The network layer adds a header to the packet
  coming from the upper layer, includes the logical
  addresses of the sender and receiver.
• Routing
• When independent networks or link are connected
  together to create an internetwork ( a network of
  networks) the connecting devices (router or
  gateways) route the packet to their final
  destination Using network layer logical addresses
  in each packet

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Network Layer Example
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Network Layer Example
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Transport layer

• Responsible for source-to-destination
  (end-to-end) delivery of the entire message.
• Ensure that the whole message arrives intact and
  in order.
• Transport layer, may create a connection between
  the two end port.

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Transport layer responsibilities

• Service-point addressing gets the entire message
  to the correct process on that computer, not only
  from one computer to the next but also from
  specific process on the other.
• Segmentation and reassembly divides the message
  into segments, each segment containing a sequence
  number, these numbers enable the T.L to
  reassemble the message when it arrived correctly.
• Connection control
• Connectionless each segment is an independent
  packet. data is sent from one end point to
  another without prior connection. No guarantees
  that data will arrive in the proper sequence
• Connection-oriented make a connection with the
  transport layer on the receiving machine before
  delivering the packets. it guarantees that data
  will arrive in the proper sequence.

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Transport layer responsibilities

• Flow control end-to-end flow control
• Error control the sending transport layer makes
  sure that the entire message arrives at the
  receiving transport layer without error (damage,
  loss,)

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Transport Layer
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Transport Layer Example
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Session layer

• Is the next dialog controller, it establishes,
  maintain, and synchronizes the interaction
  between communicating systems.

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Session layer responsibilities

• Dialog control
• The Session layer allows two systems to enter
  into dialog. Allows the communication between
  two processes to take place either in half-duplex
  (one way at a time) or full-duplex ( two ways at
  a time)
• Synchronization
• Session layer allows a process to add
  checkpoints (synchronization points) into a
  stream of data.

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Session Layer
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Presentation layer

• Is concerned with the syntax and semantics of
  the information exchanged between two systems.

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Presentation layer responsibilities

• Translation
• before being transmitted, information in the form
  of characters and numbers should be changed to
  bit streams.
• Presentation layer is responsible for
  interoperability ????????? between different
  encoding methods. As different computers use
  different encoded methods it translate
• Encryption
• A system must be able to assure privacy.
• Encryption means, that the sender transforms the
  original information to another form and sends
  the resulting message out over the network.
• Compression
• Data compression reduce the number of bits to be
  transmitted.

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Presentation Layer
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Application layer

• The application layer enables the user, wither
  human or software, to access the network. It
  provides user interfaces and support for
  services, such as electronic mail, remote file
  access and transfer.

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Application layer services

• Network Virtual Terminal.
• Network virtual terminal is a software version of
  a physical terminal and allows a user to log on a
  remote host.
• File transfer, Access, and management (FTAM)
• This application allows a user to access files in
  a remote computer, to retrieve file files from a
  remote computers.
• Mail Services.
• This application provides the basis for e-mail
  forwarding and storage.
• Directory services
• This application provides distributed database
  sources and access for global information about
  various objects and services.

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Application Layer
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Summary of Layer Functions
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Network Architectures
Chapter One - Introduction to Computer Networks
And Data Communications

• The TCP/IP protocol suite (Internet model)

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Network Architectures TCP/IP
Chapter One - Introduction to Computer Networks
And Data Communications

• Application layer equivalent to OSIs
  application and presentation layers
• Transport layer equivalent to OSIs transport
  layer
• Network (Internet or internetwork) layer
  equivalent to OSIs network layer
• Network access (data link/physical) layer
  equivalent to OSIs data link and physical layers

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Network Architectures
Chapter One - Introduction to Computer Networks
And Data Communications

• Logical and physical connections A logical
  connection is one that exists only in the
  software, while a physical connection is one that
  exists in the hardware
• Note that in a network architecture, only the
  lowest layer contains the physical connection,
  while are higher layers contain logical
  connections

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Logical and physical connections
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The TCP/IP protocol suite in action

• Note the flow of data from user to web browser
  and back
• At each layer, information is either added or
  removed, depending on whether the data is leaving
  or arriving at a workstation
• The adding of information over pre-existing
  information is termed encapsulation

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TCP/IP model in summary
SNMP
HTTP
Network layer
Network access layer
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frequently used applications in application layer

• The TCP/IP application layer includes several
  frequently used applications
• Hypertext Transfer Protocol (HTTP) to allow Web
  browsers and servers to send and receive World
  Wide Web pages
• Simple Mail Transfer Protocol (SMTP) to allow
  users to send and receive electronic mail
• File Transfer Protocol (FTP) to transfer files
  from one computer system to another
• Telnet to allow a remote user to log in to
  another computer system
• Simple Network Management Protocol (SNMP) to
  allow the numerous elements within a computer
  network to be managed from a single point

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Protocol LayeringThe Internet is build this way

• Internet Protocol (IP) provides a way to deliver
  packets to a destination

SSH, FTP, HTTP, SMTP
DNS, VoIP
TCP
UDP
Internet Protocol
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Internet (IP) addresses

• mmhh_at_dmu.ac.uk (email)
• http//www.apoptygma.eu.org (www)
• ftp//ftp.uk.debian.org (file transfer)
• telnet//towel.blinkenlights.nl (telnet)
• 144.32.100.24
• 148.122.211.110
• 195.224.53.39
• 62.250.7.101

These are the IP addresses of the above sites.
IP addresses are 32 bits grouped into 4
octets. (Octet 8 bits a number from 0-255)
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Three different kinds of addresses

• Host names (e.g., www.cnn.com)
• IP addresses (e.g., 64.236.16.20)
• MAC addresses (e.g., 00-15-C5-49-04-A9)
• Ports Each process that wants to communicate
  with another process identifies itself to the
  TCP/IP protocol suite by one or more ports. A
  port is a 16-bit number, used by the host-to-host
  protocol to identify to which higher level
  protocol or application program (process) it
  must deliver incoming messages

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MAC Address vs. IP Address

• MAC addresses
• Hard-coded in read-only memory when adaptor is
  built
• Like a social security number
• Flat name space of 48 bits (e.g.,
  00-0E-9B-6E-49-76)
• Portable, and can stay the same as the host moves
• Used to get packet between interfaces on same
  network
• IP addresses
• Configured, or learned dynamically
• Like a postal mailing address
• Hierarchical name space of 32 bits (e.g.,
  12.178.66.9)
• Not portable, and depends on where the host is
  attached
• Used to get a packet to destination IP subnet

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Protocol LayeringThe Internet is build this way

• TCPTransmission Control Protocol, reliable
  connect-oriented transfer of a byte stream.
• TCP uses packets to maintain connections across
  a network, and thus is layered above IP.

SSH, FTP, HTTP, SMTP
DNS, VoIP
TCP
UDP
Internet Protocol
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Transmission Control Protocol

• TCP is connection-oriented.
• HTTP is an application layer protocol which uses
  TCP as its transport.
• Each host has a very formal way of ensuring the
  accuracy of the message it receives in a
  connection-oriented transport.
• Being connection-oriented introduces a guarantee
  of reliability in the connection.
• Reliability every byte of data is guaranteed to
  be received at the other end.
• 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.

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Protocol LayeringThe Internet is build this way

• UDPUser Datagram Protocol, best-effort
  connectionless transfer of individual messages.
• UDP just sends or receives raw packets with a
  best-effort approach, also layered above IP
• It adds no reliability, flow-control, or error
  recovery to IP. It simply serves as a
  multiplexer/demultiplexer for sending and
  receiving datagrams, using ports to direct the
  datagrams

SSH, FTP, HTTP, SMTP
DNS, VoIP
TCP
UDP
Internet Protocol
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Protocol LayeringThe Internet is build this way

• SSH, FTP, HTTP, SMTP and many more applications
  use TCP connections to communicate data back and
  forth

SSH, FTP, HTTP, SMTP
DNS, VoIP
TCP
UDP
Internet Protocol
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Protocol LayeringThe Internet is build this way

• DNS, VoIP, and many more applications use UDP
  packets to communicate data
• DNS A domain name system server translates a
  human readable domain name (such as example.com)
  into a numerical IP address

SSH, FTP, HTTP, SMTP
DNS, VoIP
TCP
UDP
Internet Protocol
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Layers in the Example
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Layers in the Example
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Layers and Services

• Service provided by TCP to HTTP
• reliable transmission of data over a logical
  connection
• Service provided by IP to TCP
• unreliable transmission of IP datagrams across an
  IP network
• Service provided by Ethernet to IP
• transmission of a frame across an Ethernet
  segment
• Other services
• DNS translation between domain names and IP
  addresses
• ARP Translation between IP addresses and MAC
  addresses

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Sending a packet from Argon to Neon
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Sending a packet from Argon to Neon
128.143.71.21 is not on my local
network. Therefore, I need to send the packet to
my default gateway with address 128.143.137.1
128.143.71.21 is on my local network. Therefore,
I can send the packet directly.
frame
frame
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• DNS Domain Name System
• DNS is the application that turns our web site
  addresses into Internet Protocol addresses.
• Like an operator, given a name it will return a
  phone number.

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Chapter One - Introduction to Computer Networks
And Data Communications
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