Application layer

undefined. *. Unit-5 : Application Layer. ‹#›. Application layer.

[Audio] The Application Layer is focused on how user interacts with the network. It provides services to the user, including sending emails, accessing and transferring files, accessing system resources, accessing the World Wide Web, and managing the network. Additionally, it offers user interfaces to enable interaction with the network. All necessary software applications for the network are based on this layer..

[Audio] The application layer of the Internet model is our focus today. It contains client/server programs, like email, which are directly accessible to users. Additionally, this layer has programs that support other applications, like the Domain Name System (DNS). This program translates URLs into IP addresses so that emails can be delivered to the right destination. An example of this process can be seen in figure 25.1. Emails are sent using Simple Mail Transfer Protocol (SMTP) and the DNS client locates the IP address of the recipient..

[Audio] Good morning everyone. Today I'll be talking about Application Layer. 25.1 talks about Name Space, specifically Flat Name Space and Hierarchical Name Space. As each address is unique, a name space must be organized in one of two ways: fiat or hierarchical. When names are created, each part of the name has a certain purpose. The first part can define the nature of the organization, the second part can define the name of the organization, and the third part can define departments within the organization..

To have a hierarchical name space, a domain name space was designed. In this design the names are defined in an inverted-tree structure with the root at the top. The tree can have only 128 levels: level 0 (root) to level 127 (see Figure 25.2)..

[Audio] We are discussing the Application Layer and its components. Labels are strings with a maximum of 63 characters and the root label is empty. Domain names are a sequence of labels, as shown in the image. Each node in the tree has its own domain name. The root domain name is 'edu' and below that is 'fhda.edu', followed by 'atc.fhda.edu' and finally 'challenger.atc.fhda.edu'..

[Audio] The application layer is the top layer of the TCP/IP reference model. At this layer, information is formatted into what is known as user datagrams or, more commonly, packets. The purpose of this layer is to provide an interface between the user and the network, allowing applications to use the network to send and receive data. In this unit, we will look at the protocols that make up the application layer, as well as how they are used to facilitate communication between different nodes on the network..

[Audio] The Domain Name Space is a hierarchical tree-like structure used to organize domains on the internet. It is divided into a number of zones and each zone is managed by a Root Server. To effectively manage such a vast amount of information, the Domain Name Space needs to be distributed across multiple computers. This not only reduces the workload of the Root Server but also ensures that the information is more reliable, as a single failure does not make the entire tree inaccessible..

[Audio] Inputs like mouse, keystrokes, and clicks are part of User Interface at the Application Layer. Outputs encompass text, video, images, and sound. The Domain Name System (DNS) is used to assign a logical address to the user. DNS helps to manage the size and complexity of the global network by disseminating the information among different computers, therefore making it easier for users to access the required services by using logical addresses..

[Audio] At the top of the OSI model is the Application layer, which acts as a bridge between the user and the network. It offers services such as e-mail, file transfer, and web-based applications, and allows users to access network resources and receive services from the network. Protocols used to provide these services include HTTP, FTP, and SMTP..

[Audio] In this slide, we will be looking at application layer and focusing on the concept of Primary and Secondary server. A primary server is a computer that sends data or services as requested by a client. A Secondary server, on the other hand, receives requests from a primary server. It loads all the information from the primary server. It should be noted that the primary server obtains all the information from the disk file. We will be discussing this further in the upcoming slides..

[Audio] The Domain Name System (DNS) is a protocol used to map domain names to IP addresses. The domain name space is divided into three sections: generic domains, country domains, and inverse domains. Inverse domains are set up in a hierarchical tree structure moving from the root up to the country domains and then to the generic domains. This structure allows for faster and more reliable service by allowing domains to be located more accurately..

[Audio] The application layer divides the domain name space into the top-level domains. At the top of the tree is the root domain. Moving down the tree there are the top-level domains divided into two categories: Generic domains and Country code domains. The generic domains define registered hosts according to their generic behavior. Each node in the tree defines a domain, which is an index to the domain name space database..

[Audio] At the Application Layer of the network model, applications interact directly with the network. This is where the Label Description Format (LDF) comes into play. LDF is an IP addressing system which assigns labels to organizations based on their type. The eight different categories of labels are 'com' for commercial, 'edu' for educational, 'gov' for government, 'int' for international, 'mil' for military, 'net' for network support, and 'org' for nonprofit organizations. This system allows for unique identification of organizations across the internet..

[Audio] The Application Layer of the OSI model is the layer that interacts directly with software applications that use the network. This layer contains information about the type of network services and protocols used. A table can be seen below that labels and describes common application layer protocols which includes Airlines and Aerospace companies, Businesses and Firms, Cooperatives, Information Service Providers, Museums and Nonprofits, Personal Names, and Professional Individual Organizations..

[Audio] The application layer of an address can be broken down into components to locate individual computers on the network. It starts with a root level, such as us.ca.cup.anza.fr, which can be divided into an index and country domain sections. The index is used to point to subdomains, like us.ca.cup that can be further subdivided into zw and anza. The country domain section uses two-character country abbreviations, like us for the United States. Second-level labels refer to organizations or more specific, national designations, like using abbreviations to subdivide the us designation..

[Audio] The Application layer of the TCP/IP protocol stack is responsible for the exchange of data between applications. Inverse domains can be used to map an IP address to its corresponding domain name. This process involves reversing the IP address, for example, the inverse of 132.45.34.121 is 121.34.45.132.in-addr.arpa, which is then used to identify the resources available and who provides them..

[Audio] The Application Layer is part of the OSI Model. It allows end-user software programs like web browsers, email clients, etc. access to network services. This unit covers the Domain Name System (DNS) and the messages it uses for communication. DNS is responsible for translating domain names to IP addresses at the network layer. There are two types of DNS messages: query and response. The format of both types of messages is the same - they consist of headers and question records. The response message includes additionally answer records, authoritative records, and additional records..

[Audio] The Application Layer of the TCP/IP Model is the topmost layer of the model and the network applications interact with this layer. In the header, the Identification is a 16-bit identifier assigned to the query which is echoed in the response. The flags and numbers of questions, answers, and additional records fields are also present in the header..

[Audio] DNS is the protocol used at the application layer to resolve host names to IP addresses. It can use either UDP or TCP, with a well-known port number of 53. Generally, DNS requests and answers are small, so the overhead from the higher layers is minimal..

[Audio] The Application Layer in the OSI model allows us to access data on the World Wide Web. The most widely used protocol in this layer is Hypertext Transfer Protocol (HTTP), which incorporates functionalities from both File Transfer Protocol (FTP) and Simple Mail Transfer Protocol (SMTP), making it more efficient. Whereas FTP requires multiple TCP connections, HTTP only requires one, thus making the communication faster. The data is transmitted in the form of SMTP messages, and the messages include headers similar to MIME, which are read and comprehended by both the browser and the server, enabling us to quickly access data over the internet..

[Audio] The figure illustrates how client and server communicate through the stateless protocol HTTP. The client initiates the process by sending a request message to the server, which is then answered by a response message from the server. This completes the exchange with both roles being fulfilled..

[Audio] At the Application Layer, requests from the user are formatted into messages which are sent to the Network Layer. The Network Layer forwards the messages to a remote application, and the response is returned from the Application Layer to the user. Request messages consist of a request line, header, and sometimes a body; response messages consist of a status line, header, and sometimes a body..

[Audio] Good morning everyone. In this slide, we will take a look at the application layer of a computer network and its components. In this layer, Request Type, or in other words the method, is used to initiate an action on the server, such as GET, POST, or PUT. After the Request Type is the Uniform Resource Locator URL, which is the address of the resource on the server. Following this is the HTTP version, which is used to tell the server what version of the HTTP protocol is being used. Finally, in the request and status lines, the common field is the HTTP version which is then followed by the status code and the status phrase..

[Audio] In this slide we discuss the application layer, the highest layer of the OSI reference model. It provides services to applications like web browsers and web servers. In this layer, a header exchange occurs to send and receive extra information about the document, such as the header name and its value. That is all for this slide..

[Audio] In this slide, the application layer is responsible for the communication between the applications that take the requests and the format of the information that is exchanged. To further illustrate this, let's look at the structure of a request and a response message. Both of them consist of headers, a blank line, and a body. The request message includes a request line, general headers, request headers, entity headers, and a body. On the other hand, the response message contains a status line, general headers, response headers, entity headers, and a body..

[Audio] In this section, we will go over the application layer and its use in retrieving a document. To demonstrate this, we will use the GET method to request for an image with the path /usr/bin/image1. The request line consists of the method, the URL, and the HTTP version. The header lines indicate that the client is able to accept images in GIF and JPEG format, and the response message contains the status line and header lines which define the date, server, MIME version, length of the document. The body of the document is at the end. This will help us understand how the application layer works and allows clients to access documents..

[Audio] The Application layer provides the interface between user applications and the transport layer. A client sends a request using the GET method to the server, which checks the requested resource. The server then sends the response using the HTTP/1.1 protocol including the content length and MIME-version, followed by the body of the requested document..

[Audio] An example of the HTTP protocol, part of the application layer, is looked at in this slide. The HEAD method is used to send a request to a web server to obtain information pertaining to an HTML document. This request consists of a status line and five lines of header. The date, server, MIME version, type of document, and length of the document are the return values. Pay attention that the response does not incorporate a body..

Figure 27.10 Example 2. [image] Server Client Request (HEAD method) HEAD /usr/user/filel.html HITP/I.I Accept: Response HTTP/I.1 200 0K Date: Tue, 08-Jan-02 GMT Server: Challenger MIME-version: 1.0 Content-type: text/html Content-length: 1020.

[Audio] We will discuss nonpersistent and persistent connections. Nonpersistent connection involves establishing a TCP connection for each request-response, while persistent connection lets the server keep the connection open after sending out response, thus avoiding the need for re-establishing the connection. Generally, the sender sends the length of the data with each response, unless the document is created dynamically or actively. In these cases, the server informs the client that the length is not known and closes the connection after sending the data..

END. *. ‹#›. Unit-5 : Application Layer.