The OSI Model

1
The OSI Model

• From Application to Physical

2
Application Layer

• The Application Layer may be thought of as the
  protocol layer. The Application layer is called
  the Application Layer because it involves the
  use of digital applications (think internet
  browser) paired with protocols.

3
For example
EXE File
Hyper Text
Hyper Text Transfer Protocol
RTF File
File Opens in Firefox

• If you were to use Firefox (an application) to
  acess a website (a .html file (data)), you must
  acess it through the HTTP protocol (hyper-text
  transport protocol).

4
The Three Aspects of the Presentation Layer

• Data formats here are examples, Postscript,
  ASCII, or binary formats
• Compatibility with the host operating system
• Encapsulation of data into message "envelopes"
  for transmission through the network

5
Session LayerPort Layer"

• Keene McCully

6
Session Layer

• The Session Layer is the fifth out of seven.
• Responds to service requests from the
  presentation layer and issues service requests to
  the transport layer.
• Provides for either full duplex or half-duplex
  operation and establishes check pointing,
  adjournment, termination, and restart procedures

7
Diagram

• The connection is maintained while the two end
  points are communicating back and forth in a
  conversation or session of some duration.
• Each session is related to a particular port, a
  number that is associated with a particular upper
  layer application

8
Transport Layer

• Responds to requests from Application
• Issues requests to Network
• Connection Oriented
• Ordered Delivery
• Reliable Data
• Flow Control
• Congestion Avoidance

9
Network Layer

• Responds to requests from Transport
• Sends requests to Data Link
• Connected or Connectionless
• Source to Destination Delivery
• Routers
• IP Addresses

10
Data Link Layer

• The data link layer is layer two of the
  seven-layer OSI model as well as of the
  five-layer TCP/IP reference model. It responds to
  service requests from the network layer and
  issues service requests to the physical layer.
• This is the layer which transfers data between
  adjacent network nodes in a wide area network or
  between nodes on the same local area network
  segment. The data link layer provides the
  functional and procedural means to transfer data
  between network entities and might provide the
  means to detect and possibly correct errors that
  may occur in the Physical layer. Examples of data
  link protocols are Ethernet for local area
  networks and PPP, HDLC and ADCCP for
  point-to-point connections.
• Data Link Interfaces
• ODI
• NDIS
• SANA II

11
Data Link (illustration)
12
Physical Layer
13
Physical Layer

• The physical layer is level one in the seven
  level OSI model of computer networking as well as
  in the five layer TCP/IP reference model.
• The physical layer is the most basic network
  layer, providing only the means of transmitting
  raw bits rather than packets over a physical data
  link connecting network nodes. No packet headers
  nor trailers are consequently added to the data
  by the physical layer. The bit stream may be
  grouped into code words or symbols, and converted
  to a physical signal, which is transmitted over a
  physical transmission medium. The physical layer
  provides an electrical, mechanical, and
  procedural interface to the transmission medium.
• Physical Layer Interfaces
• Network adapter
• Repeater
• Ethernet hub
• Modem

14
Physical Layer (illustration)
15
Works Cited

• "Data Link Layer." 02-17-07
• lthttp//en.wikipedia.org/wiki/Data_link_layergt.
• "Physical Layer image." 02-17-07
  lthttp//joule.bu.edu/hazen/DataSheets/Ethernet/et
  hernet_files/ct840714.gifgt.
• "Physical Layer." 02-17-07
  lthttp//en.wikipedia.org/wiki/Physical_layer
  gt.
• "Data Link Layer image." 02-17-07
• lthttp//www.rhyshaden.com/images/osi_a.gifgt.

16
Works Cited

• http//en.wikipedia.org/wiki/Session_layer
• http//homepages.uel.ac.uk/u0419171/image/pic2.gif
  
• http//www.ie.u-ryukyu.ac.jp/kono/cisco/2002/netw
  ork-basic/stills/still2-10f.gif
• http//searchnetworking.techtarget.com/sDefinition
  /0,290660,sid7_gci212967,00.html
• http//www.answers.com/topic/presentation-layer

17
Citations

• "Contact TorchBearer Sauces." TorchBearer Sauces.
  15 Feb. 2007 lthttp//www.torchbearersauces.com/lib
  /img/post-office.gifgt.
• "Mail Man." Magic Mud. 15 Feb. 2007
  lthttp//www.magicmud.com/P20Mail20Man.jpggt.
• "Wikipedia." Wikipedia. 15 Feb. 2007
  ltwww.wikipedia.orggt.