Protocol layer,OSI model & POP3
- 1. Northern University of Business and Technology Khulna Code title: Computer Networks Course Code: CSE 4105 Presentation Topic: Protocol Layer & Service model,POP3 Group member: Name ID Umme salma 1160320004 Rasheduz zaman 1160320011 Md Ashik 1160320002 Zakirul islam 1160320010 Presented to Soumendu Roy Soumo Lecturer,Department of CSE NUBTK
- 2. What is Protocol • A protocol is a set of rules and guidelines for communicating data. Rules are defined for each step and process during communication between two or more computers. Networks have to follow these rule • Most network protocol suites are viewed as structured in layers. The International Organization for Standardization (ISO) designed the Open Systems Interconnection (OSI) Reference Model that uses structured layers to successfully transmit data.
- 3. OSI Model: • OSI stands for Open Systems Interconnection. • It has been developed by ISO – ‘International Organization of Standardization‘, in the year 1974. • It is a 7 layer architecture with each layer having specific functionality to perform. • All these 7 layers work collaboratively to transmit the data from one person to another across the globe. • OSI model acts as a reference model and is not implemented in Internet because of its late invention. Current model being used is the TCP/IP model
- 5. Application Layer: • The application layer is the seventh layer of the OSI model and the only one that directly interacts with the end user. • At the very top of the OSI Reference Model stack of layers, we find Application layer which is implemented by the network applications. These applications produce the data, which has to be transferred over the network. • This layer also serves as a window for the application services to access the network and for displaying the received information to the user. • It consists of protocols that focus on process-to-process communication across an IP network and provides a firm communication interface and end-user services.
- 6. The application layer provides many services, including: • SMTP • File transfer • Web surfing • Web chat • Email clients • Network data sharing • Virtual terminals • Various file and data operations
- 7. Presentation layer: • Presentation layer is also called the translation layer. The data from the application layer is extracted here and manipulated as per the required format to transmit over the network. The functions of the presentation layer are : • Translation : For example, ASCII to EBCDIC. • Encryption/ Decryption : Data encryption translates the data into another form or code. The encrypted data is known as the cipher text and the decrypted data is known as plain text. A key value is used for encrypting as well as decrypting data. • Compression: Reduces the number of bits that need to be transmitted on the network.
- 9. Session Layer: This layer is responsible for establishment of connection, maintenance of sessions, authentication and also ensures security. The functions of the session layer are : • Session establishment, maintenance and termination: The layer allows the two processes to establish, use and terminate a connection. • Synchronization : This layer allows a process to add checkpoints which are considered as synchronization points into the data. These synchronization point help to identify the error so that the data is re-synchronized properly, and ends of the messages are not cut prematurely and data loss is avoided. • Dialog Controller : The session layer allows two systems to start communication with each other in half-duplex or full- duplex
- 10. • Sending a message through some Messenger application running in a browser. • The “Messenger” here acts as the application layer which provides the user with an interface to create the data. • This message or so-called Data is compressed, encrypted (if any secure data) and converted into bits (0’s and 1’s) so that it can be transmitted
- 11. Transport layer: It is responsible for the End to End delivery of the complete message. Transport layer receives the formatted data from the upper layers, performs and segmentation also implements flow error control to ensure proper data transmission. It also adds Source and Destination port number in its header and forwards the segmented data to the Network Layer.
- 12. The functions of the transport layer are : • Segmentation and Reassembly • Service Point Addressing The services provided by transport layer: Connection Oriented Service Connection less service Transport layer is operated by the Operating System. It is a part of the OS and communicates with the Application Layer by making system calls.
- 13. Network layer: • Network layer works for the transmission of data from one host to the other located in different networks. It also takes care of packet routing i.e. selection of the shortest path to transmit the packet, from the number of routes available. The sender & receiver’s IP address are placed in the header by network layer. Network layer is implemented by networking devices such as routers The functions of the Network layer are : • Routing: The network layer protocols determine which route is suitable from source to destination. This function of network layer is known as routing. • Logical Addressing: In order to identify each device on internetwork uniquely, network layer defines an addressing scheme. The sender & receiver’s IP address are placed in the header by network layer. Such an address distinguishes each device uniquely and universally.
- 14. • It translates logical network address into physical address. Concerned with circuit, message or packet switching. • Routers and gateways operate in the network layer. Mechanism is provided by Network Layer for routing the packets to final destination. • Connection services are provided including network layer flow control, network layer error control and packet sequence control. • Breaks larger packets into small packets
- 15. Data Link Layer: The data link layer is responsible for the node to node delivery of the message. The main function of this layer is to make sure data transfer is error free from one node to another, over the physical layer. When a packet arrives in a network, it is the responsibility of DLL to transmit it to the Host using its MAC address. Data Link Layer is divided into two sub layers : • Logical Link Control (LLC) • Media Access Control (MAC)
- 16. • The packet received from Network layer is further divided into frames depending on the frame size of NIC(Network Interface Card). DLL also encapsulates Sender and Receiver’s MAC address in the header. • The Receiver’s MAC address is obtained by placing an ARP(Address Resolution Protocol) request onto the wire asking “Who has that IP address?” and the destination host will reply with its MAC address
- 17. The functions of the data Link layer are: • Framing: It provides a way for a sender to transmit a set of bits that are meaningful to the receiver. This can be accomplished by attaching special bit patterns to the beginning and end of the frame. • Physical addressing: After creating frames, Data link layer adds physical addresses (MAC address) of sender and/or receiver in the header of each frame. • Error control: Data link layer provides the mechanism of error control in which it detects and retransmits damaged or lost frames. • Flow Control: The data rate must be constant on both sides else the data may get corrupted thus , flow control coordinates that amount of data that can be sent before receiving acknowledgement. • Access control: When a single communication channel is shared by multiple devices, MAC sub-layer of data link layer helps to determine which device has control over the channel at a given time.
- 18. Physical Layer: • It is responsible for the actual physical connection between the devices. The physical layer contains information in the form of bits. • When receiving data, this layer will get the signal received and convert it into 0s and 1s and send them to the Data Link layer.
- 19. The functions of the physical layer are : • Bit synchronization: The physical layer provides the synchronization of the bits by providing a clock. This clock controls both sender and receiver thus providing synchronization at bit level. • Bit rate control: The Physical layer also defines the transmission rate i.e. the number of bits sent per second. • Physical topologies: Physical layer specifies the way in which the different, devices/nodes are arranged in a network i.e. bus, star or mesh topology. • Transmission mode: Physical layer also defines the way in which the data flows between the two connected devices. The various transmission modes possible are: Simplex, half-duplex and full- duplex. • Hub, Repeater, Modem, Cables are Physical Layer devices.
- 20. • Post Office Protocol version 3 (POP3) is a standard mail protocol used to receive emails from a remote server to a local email client. • POP3 allows you to download email messages on your local computer and read them even when you are offline. • when you use POP3 to connect to your email account, messages are downloaded locally and removed from the email server. • This means that if you access your account from multiple locations, that may not be the best option for you. On the other hand, if you use POP3, your messages are stored on your local computer, which reduces the space your email account uses on your web server. What is POP3?
- 21. Advantages and Disadvantages: • POP3 accounts allow users to have mailboxes on a server with their domain name. Post Office Protocol Version 3 provides a simple, standardized way for users to access mailboxes and download messages to their computers. • The main advantage of this is that once the mail messages are delivered to the client PC, they can be read with or without connecting to the internet. • POP3 is the most popular protocol and is being supported by almost all email clients. Hence, it has become a standardized way for users to access and download messages to their computers.
- 22. • The main disadvantage of the POP3 protocol is that it is inadequate for the mobile user. • Since messages are downloaded to their mailboxes, the user will be able to access the messages from a PC only.
- 23. Mail Server Functionality • the protocol to "store" email on the server for a certain period of time, which would allow an individual to download it as many times as they wished within that given time frame. However, this method is not practical for the vast majority of email recipients. • While mail servers can use alternate protocol retrieval programs, such as IMAP, POP3 is extremely common among most mail servers because of its simplicity and high rate of success. Although the newer version of POP offers more "features," at its basic level, POP3 is preferred because it does the job with a minimum of errors.
- 24. Working With Email Applications • Many popular email programs, including Eudora and Microsoft Outlook, are automatically designed to work with POP3. • Each POP3 mail server has a different address, which is usually provided to an individual by their web hosting company. This address must be entered into the email program in order for the program to connect effectively with the protocol. • Generally, most email applications use the 110 port to connect to POP3. Those individuals who are configuring their email program to receive POP3 email will also need to input their username and password in order to successfully receive email.