{"id":517,"date":"2012-03-02T19:53:58","date_gmt":"2012-03-02T19:53:58","guid":{"rendered":"http:\/\/microsoftgeek.com\/?p=517"},"modified":"2012-03-02T19:53:58","modified_gmt":"2012-03-02T19:53:58","slug":"how-the-application-layer-works","status":"publish","type":"post","link":"https:\/\/microsoftgeek.com\/?p=517","title":{"rendered":"How the Application Layer Works"},"content":{"rendered":"<p>In the previous section we reviewed several  aspects of the Transport Layer. We learned a great deal of information;  covering sockets, ports, TCP, UDP, segments, and datagrams. Now we will  take a look at the fourth and final layer of the TCP\/IP stack: the  Application Layer.<\/p>\n<h3>What Does The Application Layer Do?<\/h3>\n<p>A lot of newcomers to TCP\/IP wonder why an Application  Layer is needed, since the Transport Layer handles a lot of interfacing  between the network and applications. While this is true, the  Application Layer focuses more on network services, APIs, utilities, and  operating system environments.<\/p>\n<p>If you know the TCP\/IP stack and OSI model well enough, you\u2019ll know  that there are three OSI model layers that correspond to the TCP\/IP  Application Layer.<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/www.learn-networking.com\/wp-content\/oldimages\/osi-tcp-model.jpg\" alt=\"tcp osi model\" \/><\/p>\n<p>By breaking the TCP\/IP Application Layer into three separate layers,  we can better understand what responsibilities the Application Layer  actually has.<\/p>\n<p><strong>The OSI Equivalent of the TCP\/IP Application Layer<\/strong><\/p>\n<ul>\n<hr \/>\n<li> <strong>1. Application Layer &#8211;<\/strong> The seventh OSI model layer  (which shouldn\u2019t be confused with the TCP\/IP stack\u2019s Application  Layer). It supports network access, as well as provides services for  user applications.<\/li>\n<li><strong>2. Presentation Layer &#8211;<\/strong> The Sixth OSI model layer  is the Presentation Layer. It translates data into a format that can be  read by many platforms. With all the different operating systems,  programs, and protocols floating around, this is a good feature to have.  It also has support for security encryption and data compression.<\/li>\n<li><strong>3. Session Layer &#8211;<\/strong> The fifth layer of the OSI model  is the Session Layer. It manages communication between applications on a  network, and is usually used particularly for streaming media or using  web conferencing.<\/li>\n<hr \/>\n<\/ul>\n<p>To better grasp the concepts of the Application Layer, we\u2019ll take a look at a few examples of the Application Layer in action.<\/p>\n<h3>Application Layer APIs<\/h3>\n<p>If you aren\u2019t hip on the nerdy lingo- don\u2019t worry: an  API simply stands for Application Programming Interface. An API is just a  collection of functions that allows programs to access an internal  environment.<\/p>\n<p>A good example of an API is DirectX. If you\u2019ve ever run a multimedia  application and used Windows at the same time, odds are you have come  into contact with DirectX. DirectX is made up of many different  components that allow programmers to create multimedia applications  (such as video games).<\/p>\n<p>There are many types of APIs to delve into. You may have heard of  NetBIOS, Winsock, or WinAPI among others. The world of APIs has also  extended to web services. You may have heard of a Google API, for  instance. In this case Google allows developers to use its internal  functions, yet also keeps Google\u2019s internal code safe from prying eyes.  (Otherwise, there would be a few security concerns on Google\u2019s part.)<\/p>\n<h3>Network Services<\/h3>\n<p>The Application Layer handles network services; most notably file and printing, name resolution, and redirector services.<\/p>\n<p>Name resolution is the process of mapping an IP address to a  human-readable name. You may be familiar with the name Google more so  than the IP address of Google. Without name resolution, we would have to  remember four octets of numbers for each website we wanted to visit-  not very friendly is it?<\/p>\n<p>A redirector, otherwise known as a requester, is a service that is  largely taken for granted. It is a handy little service that looks at  requests a user may make: if it can be fulfilled locally, it is done so.  If the request requires a redirection to another computer, then the  request is forwarded onto another machine. This enables users to access  network resources just like they were an integral part of the local  system. A user could browse files on another computer just like they  were located on the local computer- obviously redirector services are  fairly powerful.<\/p>\n<p>Lastly we have file and print services. If a computer needs to access  a file server or a printer, these services will allow the computer to  do so. It is fairly self-explanatory, but worth reviewing nonetheless.<\/p>\n<h3>Network Utilities<\/h3>\n<p>This is where most people have experience- within the  network utilities section of the Application Layer. Every time you use a  Ping, Arp, or Traceroute command, you are taking full advantage of the  Application Layer.<\/p>\n<p>It\u2019s quite convenient that the Application Layer is located on the  top of the TCP\/IP stack. We can send a Ping and, if successful, can  verify that the TCP\/IP stack is successfully functioning. It\u2019s a good  idea to commit each utility to memory, as they are very useful for  maintaining, configuring, and troubleshooting networks. Listed below are  seven of the most used utilities.<\/p>\n<p><strong>Seven TCP Utilities Explained<\/strong><\/p>\n<ul>\n<hr \/>\n<li><strong>1. ARP &#8211;<\/strong> Arp stands for Address Resolution  Protocol. It is used to map an IP address to a physical address found on  your NIC card. Using this command can tell us what physical address  belongs to which IP address.<\/li>\n<li><strong>2. Netstat &#8211;<\/strong> Netstat is a handy tool that displays  local and remote connections to the computer. It displays IP addresses,  ports, protocol being used, and the status of the connection.<\/li>\n<li><strong>3. Ping &#8211;<\/strong> Ping is a simple diagnostic tool that can  check for connectivity between two points on a network. It is one of  the most used TCP\/IP utilities when setting up a network or changing  network settings.<\/li>\n<li><strong>4. TraceRT &#8211;<\/strong> Tracert, or traceroute, is a command  that will show the path that packets of data take while being sent. It\u2019s  handy for checking to see where a possible network failure lies, or  even for ensuring that data packets are taking the fastest route  possible on a network.<\/li>\n<li><strong>5. FTP \/ TFTP &#8211;<\/strong> FTP and TFTP are both used for  transferring files. It is important to note that FTP is a TCP utility,  while TFTP is a UDP utility. TFTP tends to be less secure than FTP, and  is generally only used for transferring non-confidential files over a  network when speed is concerned.<\/li>\n<li><strong>6. Hostname &#8211;<\/strong> Hostname is a simple command that displays the hostname of the current computer. Simple, yet effective.<\/li>\n<li><strong>7. Whois &#8211;<\/strong> Whois information is just like an online  phonebook. It shows the contact information for owners of a particular  domain. By using a Whois search, you will find that Google is based in  California.<\/li>\n<hr \/>\n<\/ul>\n<h3>Closing Comments<\/h3>\n<p>The Application Layer isn\u2019t as exciting as the others. We don\u2019t  really have much physical interaction with the Application layer, and  most of the fun applies to developers and geeks only.<\/p>\n<p>There is still much to learn- TCP\/IP is just the very beginning of  the networking world. But with this lesson on the final TCP\/IP layer  complete, you can now say that you have a much better understanding of  the TCP\/IP model. (And networking in general.)<\/p>\n","protected":false},"excerpt":{"rendered":"<p>In the previous section we reviewed several aspects of the Transport Layer. We learned a great deal of information; covering sockets, ports, TCP, UDP, segments, and datagrams. Now we will take a look at the fourth and final layer of the TCP\/IP stack: the Application Layer. What Does The Application Layer Do? A lot of [&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-517","post","type-post","status-publish","format-standard","hentry","category-networking-stuff"],"_links":{"self":[{"href":"https:\/\/microsoftgeek.com\/index.php?rest_route=\/wp\/v2\/posts\/517","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=517"}],"version-history":[{"count":1,"href":"https:\/\/microsoftgeek.com\/index.php?rest_route=\/wp\/v2\/posts\/517\/revisions"}],"predecessor-version":[{"id":518,"href":"https:\/\/microsoftgeek.com\/index.php?rest_route=\/wp\/v2\/posts\/517\/revisions\/518"}],"wp:attachment":[{"href":"https:\/\/microsoftgeek.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=517"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/microsoftgeek.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=517"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/microsoftgeek.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=517"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}