Data Communication

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Data Communication

• Stream Bcom
• Practical Session
• May 24th 2008 M7
• Session Leader FM Obegi

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OSI/ISO TCP/IP Model

• A protocol for communication between computers,
  used as a standard for transmitting data over
  networks and as the basis for standard Internet
  protocols.

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• Transmission Control Protocol/Internet Protocol)
  A communications protocol developed under
  contract from the U.S. Department of Defense to
  internetwork dissimilar systems. Invented by
  Vinton Cerf and Bob Kahn, this de facto Unix
  standard is the protocol of the Internet and the
  global standard for communications.

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Reliable and Unreliable

• The TCP/IP suite provides two transport methods.
  TCP ensures that data arrive intact and complete,
  while UDP just sends out packets. TCP is used for
  everything that must arrive in perfect form, and
  UDP is used for streaming media, VoIP and
  videoconferencing, where there is no time to
  retransmit erroneous or dropped packets in
  realtime.

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IP Makes It Routable

• TCP/IP is a routable protocol, and the IP
  "network" layer in TCP/IP provides this
  capability. The header prefixed to an IP packet
  contains not only source and destination
  addresses of the hosts, but source and
  destination addresses of the networks they reside
  in. Data transmitted using TCP/IP can be sent to
  multiple networks within an organization or
  around the globe via the Internet, the world's
  largest TCP/IP network. The terms "TCP/IP
  network" and "IP network" are synonymous.

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The IP Identifies Everything

• Every node in a TCP/IP network requires an IP
  address (an "IP") which is either permanently
  assigned or dynamically assigned at startup using
  DHCP (Dynamic Host Configuration Protocol)

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• Upper LayersLayers 7 through 4 comprise the
  upper layers of the OSI protocol stack. They are
  more geared to the type of application than the
  lower layers, which are designed to move packets,
  no matter what they contain, from one place to
  another.
• Lower LayersLayers 3 through 1 are responsible
  for moving packets from the sending station to
  the receiving station.

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Remembering The OSI LayersVarious mnemonics can
to help remember the order, such as

• All People Should Try New Diet Pepsi
• Angry Protestors Strive To Numb Dirty Politics
• All People Seem To Need Data Processing
• Please Do Not Tease Stupid Party Animals
• Please Do Not Throw Sausage Pizza Away
• Please Do Not Take Sales-People's Advice

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1 Physical

• Deals with the physical (i.e., electrical and
  mechanical) aspects of transmitting data (e.g.,
  voltage levels, pin-connector design, cable
  lengths, and grounding arrangements).

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2 Data-Link

• Deals with the transmission of data frames (e.g.,
  packets) over a physical link between network
  entities, including the incorporation of
  error-correction coding into the data frames.  
• It establishes an error free connection
• Splits data into data frames
• CDR

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Network

• Deals with establishing logical paths for data
  between a pair of computers (source and
  Destination) and handling any switching among
  alternative routes between the computers, as well
  as with definitions of how to break files (or
  messages) up into individual packets of data, in
  such a way that the packets can be transmitted
  and then reassembled.  

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4 Transport

• Deals with data transfer between end systems
  flow control for two computers (e.g., how
  Netscape on your PC talks with the UT Libraries
  Online Webpage)
• Uses TCP and UDP Protocols
•  

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5 Session

• Deals with establishing , maintaining, a session
  btn computers and managing sessions when one
  application process requests access to another
  applications process (e.g., Microsoft Word
  importing a chart from Excel)
•  

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  6 Presentations

• Deals with syntactic representation of data and
  how to be presented on the VDU or printer

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7 Applications

• Deals with the interface between a user and the
  host computer For example, a program in a client
  workstation uses commands to request data from a
  program in the server. Common functions at this
  layer are opening, closing, reading and writing
  files, transferring files and e-mail messages,
  executing remote jobs and obtaining directory
  information about network resources.

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• IP Address Network Host ID Hosts
• Class A 1-126 1 16M
• 10. 1.1.1
• Class B 128-191 2 65,000
• 172.16 .1.2
• Class C 192-223 2 254
• 192.168.2 .1

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• 127.0.0.0 Loopback testing

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Advantages of Networks

• Speed
• Security
• Centralized S/W mgt
• Recourse sharing
• Email
• Flexible
• Workgroup Computing

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Internetworking

• The process of interconnecting two or more
  individual networks to facilitate communications
  among their respective nodes. Note The
  interconnected networks may be different types.
  Each network is distinct, with its own addresses,
  internal protocols, access methods, and
  administration.

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Network Hardware

• File servers
• Workstation
• NIC
• Concentrators
• Repeater/Hub/Switch
• Bridges
• Routers

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Security

• Protecting a network from unwanted intruders

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Firewall

• A "firewall" is an over-arching term to describe
  a specialized defense system for a computer
  network. The term comes from construction, where
  specialized fire-prevention systems involve
  fire-resistant walls being placed strategically
  in buildings and cars to slow the spread of a
  fire. In the case of computers, the term
  describes hardware or software that slows the
  invasion of a computer system by blocking viruses
  and hackers.

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• A computer firewall itself can take hundreds of
  different forms. It can be a specialized software
  program, or a specialized physical hardware
  device, or often a combination of both. Its
  ultimate job is to block unauthorized and
  unwanted traffic from getting into a computer
  system.

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