{"id":12,"date":"2011-11-20T16:26:10","date_gmt":"2011-11-20T16:26:10","guid":{"rendered":"http:\/\/microsoftgeek.com\/?p=12"},"modified":"2011-11-20T16:26:10","modified_gmt":"2011-11-20T16:26:10","slug":"the-tcpip-stack-and-the-osi-model","status":"publish","type":"post","link":"https:\/\/microsoftgeek.com\/?p=12","title":{"rendered":"The TCP\/IP Stack and the OSI Model"},"content":{"rendered":"<p>In the previous section, we  learned that TCP\/IP is a suite of protocols and rules. It allows us to  communicate with other computers and devices over a connection oriented  network. What we didn\u2019t cover was the TCP\/IP and OSI model- which helps  us understand the TCP\/IP suite in a manner of layers and modules.<\/p>\n<h3>The TCP\/IP Model and Modular Design<\/h3>\n<p>TCP\/IP is responsible for a wide range of activity: it  must interface with hardware, route data to appropriate places, provide  error control, and much more. If you are starting to think the TCP\/IP  suite can get confusing, you wouldn\u2019t be the first.<\/p>\n<p>The developers of TCP\/IP thankfully designed what we  call a modular design- meaning that the TCP\/IP system can be divided  into separate components. You may call these layers or modules.  But why  use a modular design? Not only does it aid in the education process,  but it also lets manufacturers easily adapt to specific hardware and  operating system needs.<\/p>\n<p>For example- if we had a token ring network and an  extended star network, we surely wouldn\u2019t want to create entirely  different network software builds for each one. Instead, we can just  edit the network layer, called the Network Access Layer, to allow  compatibility.  Not only does this benefit manufacturers, but it greatly  aids networking students in education. We can dissect the TCP\/IP suite  into different layers, and then learn about each layer\u2019s specifics one  at a time. Below you\u2019ll see the TCP\/IP model divided into four layers.<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/www.learn-networking.com\/wp-content\/oldimages\/tcp-ip-model.jpg\" alt=\"tcp ip model\" \/><\/p>\n<ul>\n<hr \/>\n<li> <strong>Network Access Layer \u2013 <\/strong>The Network Access Layer is  fairly self explanatory- it interfaces with the physical network. It  formats data and addresses data for subnets, based on physical hardware  addresses. More importantly, it provides error control for data  delivered on the physical network.<\/li>\n<li><strong>Internet Layer \u2013 <\/strong>The Internet Layer provides  logical addressing. More specifically, the internet layer relates  physical addresses from the network access layer to logical addresses.  This can be an IP address, for instance. This is vital for passing along  information to subnets that aren\u2019t on the same network as other parts  of the network. This layer also provides routing that may reduce  traffic, and supports delivery across an internetwork. (An internetwork  is simply a greater network of LANs, perhaps a large company or  organization.)<\/li>\n<li><strong>Transport Layer \u2013 <\/strong>The Transport Layer provides flow  control, error control, and serves as an interface for network  applications. An example of the transport layer would be TCP- a protocol  suite that is connection-oriented. We may also use UDP- a  connectionless means of transporting data.<\/li>\n<li><strong>Application Layer \u2013 <\/strong>Lastly, we have the Application  Layer. We use this layer for troubleshooting, file transfer, internet  activities, and a slew of other activities. This layer interacts with  many types of applications, such as a database manager, email program,  or Telnet.<\/li>\n<hr \/>\n<\/ul>\n<p>The above layers are more complex than the general descriptions  provided, but rest assured, we will get into the specifics in later  sections. For now we have another model to learn- the OSI model.<\/p>\n<h3>The Open System Interconnection Model<\/h3>\n<p>The Open System Interconnection Model, more commonly  known as simply OSI, is another model that can help break the TCP\/IP  suite into modules. Technically speaking, it is exactly the same as the  TCP\/IP model, except that it has more layers. This is currently being  pushed by Cisco since it aids in learning the TCP\/IP stack in an easier  manner. Likewise, you will see the OSI model on many Cisco exams.<\/p>\n<p>Instead of four layers, the OSI model has seven. You  can see a direct comparison of the two models below; notice that only  the Application Layer and Network Layer are divided into smaller layers,  and the Internet Layer is renamed to the \u201cNetwork Layer.\u201d<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/www.learn-networking.com\/wp-content\/oldimages\/osi-model.jpg\" alt=\"osi model\" \/><\/p>\n<ul>\n<hr \/>\n<li><strong>Physical Layer \u2013 <\/strong>They Physical Layer converts data  into streams of electric or analog pulses- commonly referred to as \u201c1\u2019s  and 0\u2019s.\u201d Data is broke down into simple electric pulses, and rebuilt at  the receiving end.<\/li>\n<li><strong>Data Link Layer \u2013 <\/strong>The Data Link layer provides an  interface with the network adapter, and can also perform basic error  checking. It also maintains logical links for subnets, so that subnets  can communicate with other parts of the network without problem.<\/li>\n<li><strong>Network Layer \u2013 <\/strong>Much like the Transport Layer of  the TCP\/IP model, the Network Layer simply supports logical addressing  and routing. The IP protocol operates on the Network Layer.<\/li>\n<li><strong>Transport Layer \u2013 <\/strong>Since we left out the error and  flow control in the Network Layer, we introduce it into the Transport  Layer. The Transport Layer is responsible for keeping a reliable  end-to-end connection for the network.<\/li>\n<li><strong>Session Layer \u2013 <\/strong>The Session Layer establishes  sessions between applications on a network. This may be useful for  network monitoring, using a login system, and reporting. The Session  Layer is actually not used a great deal over networks, although it does  still serve good use in streaming video and audio, or web conferencing.<\/li>\n<li><strong>Presentation Layer \u2013 <\/strong>The Presentation Layer  translates data into a standard format, while also being able to provide  encryption and data compression. Encryption or data compression does  not have to be done at the Presentation Layer, although it is commonly  performed in this layer.<\/li>\n<li><strong>Application Layer \u2013 <\/strong>The Application Layer provides a  network interface for applications and supports network applications.  This is where many protocols such as FTP, SMTP, POP3, and many others  operate. Telnet can be used at this layer to send a ping request- if it  is successful, it means that each layer of the OSI model should be  functioning properly.<\/li>\n<hr \/>\n<\/ul>\n<h3>Now, the Bad News<\/h3>\n<p>Now that we\u2019ve reviewed each layer, you have to commit  each layer and its function to memory. Most networking exams require  that knowledge of each layer be present. We realize that remembering  seven different layers is tough- so we use a mnemonic.  A mnemonic is  simply a tool we can use to remember all seven layers. Look at each  beginning letter of each layer- it\u2019s PDNTSPA, starting with the Physical  Layer. You could come up with a phrase such as \u201cPlease Do Not Throw  Sausage Pizza Away,\u201d to help you remember each layer name.<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/www.learn-networking.com\/wp-content\/oldimages\/osi-pnemonic.jpg\" alt=\"osi pnemonic\" \/><\/p>\n<p>It is important to remember that each layer is a standard- not an  implementation. This means that not all network communication will  necessarily use each layer. We partly covered this with the Session  Layer, which isn\u2019t always necessarily used. Some devices such as routers  only operate at the third layer and below. Some devices are even more  limited- repeaters only work at the physical layer of the OSI model.<\/p>\n<h3>Closing Comments<\/h3>\n<p>The OSI and TCP\/IP model are fairly prevalent in networking- don\u2019t be  surprised if you see them more than you\u2019d like. If you take anything  from this section, remember to use a pneumonic to memorize each layer  name in order. You can get as crazy as you\u2019d like with the phrase you  use, but \u201cPlease Do Not Throw Sausage Pizza Away\u201d is generally the  easiest to remember.<\/p>\n<p>In the next article, we will be specifically looking at how data  moves from one computer to another- and how it moves through the OSI  model. Don\u2019t worry if this seems new to you and you don\u2019t quite take all  of it in, simply review it some more and move on to the next section.  And, as always, you can review the previous section if you didn\u2019t quite  grasp all the concepts in this one.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>In the previous section, we learned that TCP\/IP is a suite of protocols and rules. It allows us to communicate with other computers and devices over a connection oriented network. What we didn\u2019t cover was the TCP\/IP and OSI model- which helps us understand the TCP\/IP suite in a manner of layers and modules. The [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-12","post","type-post","status-publish","format-standard","hentry","category-networking-stuff"],"_links":{"self":[{"href":"https:\/\/microsoftgeek.com\/index.php?rest_route=\/wp\/v2\/posts\/12","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/microsoftgeek.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/microsoftgeek.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/microsoftgeek.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/microsoftgeek.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=12"}],"version-history":[{"count":2,"href":"https:\/\/microsoftgeek.com\/index.php?rest_route=\/wp\/v2\/posts\/12\/revisions"}],"predecessor-version":[{"id":14,"href":"https:\/\/microsoftgeek.com\/index.php?rest_route=\/wp\/v2\/posts\/12\/revisions\/14"}],"wp:attachment":[{"href":"https:\/\/microsoftgeek.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=12"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/microsoftgeek.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=12"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/microsoftgeek.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=12"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}