Download to read offline
NETWORK-PROTOCOLS COPY LECTURE NOTESSSS
- 1. NETWORK PROTOCOLS The OSIand TCP/IP Model
- 2. What is NetworkProtocol? Set of rules governing exchange of information in an easy, reliable and secure way. The most popular model used to establish open communication between two systems is the Open Systems Interface (OSI) model proposed by ISO.
- 3. OSI Model TheOSI Model (Open Systems Interconnection Model) is a conceptual framework used to describe the functions of a networking system. The OSI model characterizes computing functions into a universal set of rules and requirements in order to support interoperability between different products and software. In the OSI reference model, the communications between a computing system are split into seven different abstraction layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application.
- 4.
- 5. 7 – Applicationlayer The application layer is the top layer of the OSI model; therefore, the closest to the end-user. In short, the application layer establishes communication between the end-user and the application they use. For example, web browsers or email clients. Moreover, the application layer defines protocols for successful communication between the user and applications. Some of the most notable application layer protocols include Hypertext Transfer Protocol (HTTP), Simple Mail Transfer Protocol (SMTP) and File Transfer Protocol (FTP). These protocols enable the software to send and receive information and present it to the user.
- 6. 6 – Presentationlayer The presentation layer is the sixth layer in the OSI model. It is also known as the syntax layer or translation layer because it translates from the application to the network format. This layer formats the data so that the application can understand it. This data representation process also involves encrypting and decrypting data. Two devices may communicate over an encrypted network. In this case, the presentation layer encrypts the users’ incoming data received from the application and decrypts it to readable data at the receiving device. Essentially, encryption ensures the secure transmission of data. Moreover, the presentation layer compresses the data received from the application layer to send it over to the session layer. The compression ensures more efficient communication by minimizing the size of the data transferred.
- 7. 5 – Sessionlayer The fifth layer of the Open Systems Interconnection model is the session layer responsible for establishing a session between two devices. A session is a time passing between the opening and closing of communication. The session layer ensures that this time is long enough to transmit data efficiently. Also, it closes the session on time to avoid wasting resources. Moreover, this OSI layer performs data transfer synchronization to ensure that data flows smoothly. For example, if a system sends a lot of data at once, the session layer can add checkpoints and break the data up into smaller pieces.
- 8. 5 – Sessionlayer
- 9. 4 – Transportlayer The transport layer makes end-to-end communication between two devices possible. In other words, it ensures that the message safely travels from the source to its destination. The transport layer receives the data from the session layer and divides it into smaller pieces, known as segments. Then, the receiving device reassembles the data so that the session layer can read it. Furthermore, the transport layer is responsible for flow control and error control. Flow control optimizes the data transfer speed so that the device with a faster connection does not send data too quickly. Otherwise, the device with a slower connection might not be able to handle it. Error control, or error checking, ensures that the system sends all the data. If the data is incomplete, the transport layer requests the information again.
- 10. 4 – Transportlayer
- 11. 3 – Networklayer The network layer simplifies the communication between two different networks. In other words, the network layer takes the segments from the transport layer, breaks them into smaller packets, and puts them together again at the receiving device. Also, the network layer is responsible for routing. Routing is a process that handles the data transmission through the best possible physical path to connect devices on different networks efficiently. Most importantly, the network layer uses the Internet Protocol (IP), one of the most critical network layer protocols, to ensure smooth data delivery. IP is a standard protocol that helps transfer data packets across networks until they reach their final destination.
- 12. 2 – Datalink layer Layer 2 – data link layer – is responsible for node-to-node data transfer. In other words, the data link layer transmits data between two directly connected nodes or two devices on the same network architecture. Specifically, the data link layer accepts the data packets from the network layer and divides them into frames. Then, it sends the data to its destination. The data link layer has two sublayers: media access control (MAC) and logical link control (LLC). The media access control encapsulates the frames to transmit them through the physical medium (wires and cables). If data transmission fails, LLC manages the retransmission of packets.
- 13. 1 – Physicallayer The lowest layer of the OSI model is the physical layer with all the other layers of the OSI on top. As the name implies, the physical layer handles the equipment transmitting the data, such as cables and switches. From the data perspective, the physical layer transmits raw data in bits (1s and 0s). That means that the layer takes bits from one device, encodes them into a physical signal, sends them over and decodes them on the other end. Without these signals, the physical layer would not transmit the data through the physical medium. Consequently, the network architecture cannot exist without the physical layer, as this layer defines the hardware necessary to transmit bits over a network.
- 14. TCP/IP Model TheTCP/IP model was developed prior to the OSI model. The TCP/IP model is not exactly similar to the OSI model. The TCP/IP model consists of five layers: the application layer, transport layer, network layer, data link layer and physical layer. The first four layers provide physical standards, network interface, internetworking, and transport functions that correspond to the first four layers of the OSI model and these four layers are represented in TCP/IP model by a single layer called the application layer. TCP/IP is a hierarchical protocol made up of interactive modules, and each of them provides specific functionality.
- 15.
- 16. Network Access Layer A network layer is the lowest layer of the TCP/IP model. A network layer is the combination of the Physical layer and Data Link layer defined in the OSI reference model. It defines how the data should be sent physically through the network. This layer is mainly responsible for the transmission of the data between two devices on the same network. The functions carried out by this layer are encapsulating the IP datagram into frames transmitted by the network and mapping of IP addresses into physical addresses. The protocols used by this layer are ethernet, token ring, FDDI, X.25, frame relay.
- 17. Internet Layer Aninternet layer is the second layer of the TCP/IP model. An internet layer is also known as the network layer. The main responsibility of the internet layer is to send the packets from any network, and they arrive at the destination irrespective of the route they take. Following are the protocols used in this layer are: IP Protocol ARP Protocol ICMP Protocol
- 18. Internet Layer (Continued) IP PROTOCOL IP protocol is used in this layer, and it is the most significant part of the entire TCP/IP suite. Following are the responsibilities of this protocol: IP Addressing: This protocol implements logical host addresses known as IP addresses. The IP addresses are used by the internet and higher layers to identify the device and to provide internetwork routing. Host-to-host communication: It determines the path through which the data is to be transmitted. Data Encapsulation and Formatting: An IP protocol accepts the data from the transport layer protocol. An IP protocol ensures that the data is sent and received securely, it encapsulates the data into message known as IP datagram. Fragmentation and Reassembly: The limit imposed on the size of the IP datagram by data link layer protocol is known as Maximum Transmission unit (MTU). If the size of IP datagram is greater than the MTU unit, then the IP protocol splits the datagram into smaller units so that they can travel over the local network. Fragmentation can be done by the sender or intermediate router. At the receiver side, all the fragments are reassembled to form an original message. Routing: When IP datagram is sent over the same local network such as LAN, MAN, WAN, it is known as direct delivery. When source and destination are on the distant network, then the IP datagram is sent indirectly. This can be accomplished by routing the IP datagram through various devices such as routers.
- 19. Internet Layer (Continued) ARP PROTOCOL ARP stands for Address Resolution Protocol. ARP is a network layer protocol which is used to find the physical address from the IP address. The two terms are mainly associated with the ARP Protocol: ARP request: When a sender wants to know the physical address of the device, it broadcasts the ARP request to the network. ARP reply: Every device attached to the network will accept the ARP request and process the request, but only recipient recognize the IP address and sends back its physical address in the form of ARP reply. The recipient adds the physical address both to its cache memory and to the datagram header
- 20. Internet Layer (Continued) ICMP PROTOCOL ICMP stands for Internet Control Message Protocol. It is a mechanism used by the hosts or routers to send notifications regarding datagram problems back to the sender. A datagram travels from router-to-router until it reaches its destination. If a router is unable to route the data because of some unusual conditions such as disabled links, a device is on fire or network congestion, then the ICMP protocol is used to inform the sender that the datagram is undeliverable. An ICMP protocol mainly uses two terms: ICMP Test: ICMP Test is used to test whether the destination is reachable or not. ICMP Reply: ICMP Reply is used to check whether the destination device is responding or not.
- 21. Transport Layer Thetransport layer is responsible for the reliability, flow control, and correction of data which is being sent over the network. The two protocols used in the transport layer are: User Datagram protocol Transmission control protocol.
- 22. Transport Layer (Continued) User Datagram Protocol (UDP) It provides connectionless service and end-to-end delivery of transmission. It is an unreliable protocol as it discovers the errors but not specify the error. User Datagram Protocol discovers the error, and ICMP protocol reports the error to the sender that user datagram has been damaged. UDP consists of the following fields: Source port address: The source port address is the address of the application program that has created the message. Destination port address: The destination port address is the address of the application program that receives the message. Total length: It defines the total number of bytes of the user datagram in bytes. Checksum: The checksum is a 16-bit field used in error detection. UDP does not specify which packet is lost. UDP contains only checksum; it does not contain any ID of a data segment.
- 23. Transport Layer (Continued) Transmission Control Protocol (TCP) It provides a full transport layer services to applications. It creates a virtual circuit between the sender and receiver, and it is active for the duration of the transmission. TCP is a reliable protocol as it detects the error and retransmits the damaged frames. Therefore, it ensures all the segments must be received and acknowledged before the transmission is considered to be completed and a virtual circuit is discarded. At the sending end, TCP divides the whole message into smaller units known as segment, and each segment contains a sequence number which is required for reordering the frames to form an original message. At the receiving end, TCP collects all the segments and reorders them based on sequence numbers.
- 24. Application Layer Anapplication layer is the topmost layer in the TCP/IP model. It is responsible for handling high-level protocols, issues of representation. This layer allows the user to interact with the application. When one application layer protocol wants to communicate with another application layer, it forwards its data to the transport layer. Following are the main protocols used in the application layer: HTTP SNMP SMTP DNS TELNET FTP
- 25. Application Layer (Continued) Hypertext transfer protocol or HTTP This protocol allows us to access the data over the world wide web. It transfers the data in the form of plain text, audio, video. It is known as a Hypertext transfer protocol as it has the efficiency to use in a hypertext environment where there are rapid jumps from one document to another. SNMP or Simple Network Management Protocol It is a framework used for managing the devices on the internet by using the TCP/IP protocol suite. SMTP or Simple Mail Transfer Protocol The TCP/IP protocol that supports the e-mail is known as a Simple mail transfer protocol. This protocol is used to send the data to another e-mail address.
- 26. Application Layer (Continued) DNS or Domain Name System An IP address is used to identify the connection of a host to the internet uniquely. But, people prefer to use the names instead of addresses. Therefore, the system that maps the name to the address is known as Domain Name System. TELNET or Terminal Network It establishes the connection between the local computer and remote computer in such a way that the local terminal appears to be a terminal at the remote system. FTP or File Transfer Protocol FTP is a standard internet protocol used for transmitting the files from one computer to another computer.
Editor's Notes
- #3 structure, a system of rules, or a foundation for development:
- #4 The International Organization for Standardization introduced the Open Systems Interconnection (OSI) model in 1984. The primary aim of the OSI was to help different hardware manufacturers to standardize the interworking of diverse communication systems. Ultimately, the OSI model emerged as a solution to challenges related to computer networking standards.
- #5 Hypertext Transfer Protocol (HTTP) is a set of rules for transmitting information between a client, such as a web browser, and a web server: How it works HTTP operates on a client-server model, where the client sends a request to the server, and the server responds with the requested data The Simple Mail Transfer Protocol (SMTP) is a technical standard for transmitting electronic mail (email) over a network. Like other networking protocols, SMTP allows computers and servers to exchange data regardless of their underlying hardware or software. File Transfer Protocol (FTP) is a network protocol that allows users to transfer files between computers over a network: How it works FTP uses a client-server model to open two connections between the computers. One connection is for commands and replies, and the other is for data transfer. Commands During an FTP transmission, computers, servers, or proxy servers use the commands "send," "get," "change directory," and "transfer".