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Unit-
OSI -ISO Reference Model
o OSI stands for Open System Interconnection is a reference model that describes how information from a software application in one computer moves through a physical medium to the software application in another computer. o OSI consists of seven layers, and each layer performs a particular network function. o OSI model was developed by the International Organization for Standardization (ISO) in 1984, and it is now considered as an architectural model for the inter-computer communications. o OSI model divides the whole task into seven smaller and manageable tasks. Each layer is assigned a particular task. o Each layer is self-contained, so that task assigned to each layer can be performed independently.
Characteristics of OSI Model:
o The OSI model is divided into two layers: upper layers and lower layers. o The upper layer of the OSI model mainly deals with the application related issues, and they are implemented only in the software. The application layer is closest to the end user. Both the end user and the application layer interact with the software applications. An upper layer refers to the layer just above another layer. o The lower layer of the OSI model deals with the data transport issues. The data link layer and the physical layer are implemented in hardware and software. The physical layer is the lowest layer of the OSI model and is closest to the physical medium. The physical layer is mainly responsible for placing the information on the physical medium.
7 Layers of OSI Model
There are the seven OSI layers. Each layer has different functions. A list of
seven layers are given below:
o Data Transmission: It defines the transmission mode whether it is simplex, half-duplex or full-duplex mode between the two devices on the network. o Topology: It defines the way how network devices are arranged. o Signals: It determines the type of the signal used for transmitting the information.
2) Data-Link Layer
o This layer is responsible for the error-free transfer of data frames. o It defines the format of the data on the network. o It provides a reliable and efficient communication between two or more devices. o It is mainly responsible for the unique identification of each device that resides on a local network. o It contains two sub-layers: o Logical Link Control Layer o It is responsible for transferring the packets to the Network layer of the receiver that is receiving. o It identifies the address of the network layer protocol from the header. o It also provides flow control. o Media Access Control Layer
o A Media access control layer is a link between the Logical Link Control layer and the network's physical layer. o It is used for transferring the packets over the network. Functions of the Data-link layer o Framing: The data link layer translates the physical's raw bit stream into packets known as Frames. The Data link layer adds the header and trailer to the frame. The header which is added to the frame contains the hardware destination and source address. o Physical Addressing: The Data link layer adds a header to the frame that contains a destination address. The frame is transmitted to the destination address mentioned in the header. o Flow Control: Flow control is the main functionality of the Data-link layer. It is the technique through which the constant data rate is maintained on both the sides so that no data get corrupted. It ensures that the transmitting station such as a server with higher processing speed does not exceed the receiving station, with lower processing speed. o Error Control: Error control is achieved by adding a calculated value CRC (Cyclic Redundancy Check) that is placed to the Data link layer's trailer which is added to the message frame before it is sent to the physical layer. If any error seems to occurr, then the receiver sends the acknowledgment for the retransmission of the corrupted frames. o Access Control: When two or more devices are connected to the same communication channel, then the data link layer protocols are used to determine which device has control over the link at a given time.
o Packetizing: A Network Layer receives the packets from the upper layer and converts them into packets. This process is known as Packetizing. It is achieved by internet protocol (IP).
4) Transport Layer
o The Transport layer is a Layer 4 ensures that messages are transmitted in the order in which they are sent and there is no duplication of data. o The main responsibility of the transport layer is to transfer the data completely. o It receives the data from the upper layer and converts them into smaller units known as segments. o This layer can be termed as an end-to-end layer as it provides a point-to- point connection between source and destination to deliver the data reliably.
The two protocols used in this layer are:
o Transmission Control Protocol o It is a standard protocol that allows the systems to communicate over the internet. o It establishes and maintains a connection between hosts. o When data is sent over the TCP connection, then the TCP protocol divides the data into smaller units known as segments. Each segment travels over the internet using multiple routes, and they
arrive in different orders at the destination. The transmission control protocol reorders the packets in the correct order at the receiving end. o User Datagram Protocol o User Datagram Protocol is a transport layer protocol. o It is an unreliable transport protocol as in this case receiver does not send any acknowledgment when the packet is received, the sender does not wait for any acknowledgment. Therefore, this makes a protocol unreliable. Functions of Transport Layer: o Service-point addressing: Computers run several programs simultaneously due to this reason, the transmission of data from source to the destination not only from one computer to another computer but also from one process to another process. The transport layer adds the header that contains the address known as a service-point address or port address. The responsibility of the network layer is to transmit the data from one computer to another computer and the responsibility of the transport layer is to transmit the message to the correct process. o Segmentation and reassembly: When the transport layer receives the message from the upper layer, it divides the message into multiple segments, and each segment is assigned with a sequence number that uniquely identifies each segment. When the message has arrived at the destination, then the transport layer reassembles the message based on their sequence numbers. o Connection control: Transport layer provides two services Connection- oriented service and connectionless service. A connectionless service treats each segment as an individual packet, and they all travel in different routes to reach the destination. A connection-oriented service makes a connection with the transport layer at the destination machine before delivering the packets. In connection-oriented service, all the packets travel in the single route. o Flow control: The transport layer also responsible for flow control but it is performed end-to-end rather than across a single link. o Error control: The transport layer is also responsible for Error control. Error control is performed end-to-end rather than across the single link.
6) Presentation Layer
o A Presentation layer is mainly concerned with the syntax and semantics of the information exchanged between the two systems. o It acts as a data translator for a network. o This layer is a part of the operating system that converts the data from one presentation format to another format. o The Presentation layer is also known as the syntax layer. Functions of Presentation layer: o Translation: The processes in two systems exchange the information in the form of character strings, numbers and so on. Different computers use different encoding methods, the presentation layer handles the interoperability between the different encoding methods. It converts the data from sender-dependent format into a common format and changes the common format into receiver-dependent format at the receiving end. o Encryption: Encryption is needed to maintain privacy. Encryption is a process of converting the sender-transmitted information into another form and sends the resulting message over the network. o Compression: Data compression is a process of compressing the data, i.e., it reduces the number of bits to be transmitted. Data compression is very important in multimedia such as text, audio, video.
7) Application Layer
o An application layer serves as a window for users and application processes to access network service. o It handles issues such as network transparency, resource allocation, etc. o An application layer is not an application, but it performs the application layer functions. o This layer provides the network services to the end-users. Functions of Application layer: o File transfer, access, and management (FTAM): An application layer allows a user to access the files in a remote computer, to retrieve the files from a computer and to manage the files in a remote computer. o Mail services: An application layer provides the facility for email forwarding and storage. o Directory services: An application provides the distributed database sources and is used to provide that global information about various objects. INTERNET CONNECTIVITY:
Depending on direction of data transmission, modem can be of these types − Simplex − A simplex modem can transfer data in only one direction, from digital device to network (modulator) or network to digital device (demodulator). Half duplex − A half-duplex modem has the capacity to transfer data in both the directions but only one at a time. Full duplex − A full duplex modem can transmit data in both the directions simultaneously. RJ45 Connector RJ45 is the acronym for Registered Jack 45. RJ45 connector is an 8-pin jack used by devices to physically connect to Ethernet based local area networks (LANs). Ethernet is a technology that defines protocols for establishing a LAN. The cable used for Ethernet LANs are twisted pair ones and have RJ connector pins at both ends. These pins go into the corresponding socket on devices and connect the device to the network. Ethernet Card Ethernet card , also known as network interface card (NIC) , is a hardware component used by computers to connect to Ethernet LAN and communicate with other devices on the LAN. The earliest Ethernet cards were external to the system and needed to be installed manually. In modern computer systems, it is an internal hardware component. The NIC has RJ socket where network cable is physically plugged in.
Ethernet card speeds may vary depending upon the protocols it supports. Old Ethernet cards had maximum speed of 10 Mbps. However, modern cards support fast Ethernets up to a speed of 100 Mbps. Some cards even have capacity of 1 Gbps. Router A router is a network layer hardware device that transmits data from one LAN to another if both networks support the same set of protocols. So a router is typically connected to at least two LANs and the internet service provider (ISP). It receives its data in the form of packets , which are data frames with their destination address added. Router also strengthens the signals before transmitting them. That is why it is also called repeater.
maintains a list of network addresses of all the devices connected to it. On receiving a packet, it checks the destination address and transmits the packet to the correct port. Before forwarding, the packets are checked for collision and other network errors. The data is transmitted in full duplex mode Data transmission speed in switches can be double that of other network devices like hubs used for networking. This is because switch shares its maximum speed with all the devices connected to it. This helps in maintaining network speed even during high traffic. In fact, higher data speeds are achieved on networks through use of multiple switches. Gateway Gateway is a network device used to connect two or more dissimilar networks. In networking parlance, networks that use different protocols are dissimilar networks. A gateway usually is a computer with multiple NICs connected to different networks. A gateway can also be configured completely using software. As networks connect to a different network through gateways, these gateways are usually hosts or end points of the network.
Gateway uses packet switching technique to transmit data from one network to another. In this way it is similar to a router , the only difference being router can transmit data only over networks that use same protocols. Wi-Fi Card Wi-Fi is the acronym for wireless fidelity. Wi-Fi technology is used to achieve wireless connection to any network. Wi-Fi card is a card used to connect any device to the local network wirelessly. The physical area of the network which provides internet access through Wi-Fi is called Wi-Fi hotspot. Hotspots can be set up at home, office or any public space. Hotspots themselves are connected to the network through wires.
Wireless access point Getting Connected
Getting connected" in network connectivity involves establishing
communication links between devices within a network. This includes
configuring hardware, utilizing wired (Ethernet cables) or wireless (Wi-Fi)
connections, and implementing security measures such as encryption and
password updates. Troubleshooting is crucial for maintaining stability,
involving checks on physical connections, router placement, firmware
updates, and network diagnostics. Best practices include regular
maintenance, changing passwords, and implementing firewall settings.
Adherence to these principles ensures a reliable, secure network
environment for effective data transfer and communication.
Whether it's setting up a local network at home or connecting to the
internet, this concept involves several key components and steps.
Key Components:
Devices: Computers, routers, switches, and other network
hardware.
Cables/Wireless: Ethernet cables for wired connections, Wi-Fi for
wireless connectivity.
Protocols: Fundamental protocols like TCP/IP form the basis for
data transmission.
Steps for Setup:
1. Hardware Configuration:
Position routers centrally for optimal coverage.
Connect routers to modems for internet access.
2. Wired Connectivity:
Use Ethernet cables to connect devices.
Plug cables into numbered LAN ports on the router.
3. Wireless Connectivity:
Configure Wi-Fi settings in the router.
Set a unique SSID and a strong password for security.
4. Network Security:
Implement encryption (WPA3) for Wi-Fi security.
Regularly update Wi-Fi passwords.
Troubleshooting:
1. Check Physical Connections:
Ensure proper cable connections.
Restart router and modem if needed.
2. Signal Strength:
Optimize router placement for better Wi-Fi coverage.
Minimize interference from other devices.
3. Update Firmware:
Regularly update router firmware for improved performance.
4. Network Diagnostics:
Use built-in tools (Ping, Traceroute) to identify connectivity
issues.
Check for software/firewall issues on devices.
Best Practices:
1. Regular Maintenance:
Update router firmware periodically.
Change Wi-Fi passwords for security.
2. Backup Configuration:
Save router settings to facilitate easy restoration.
3. Security Measures:
Implement firewall settings for added protection.
Exercise caution with open network access.
ISP: Internet Service Provider
ISP stands for Internet Service Provider. It is a company that provides
access to the internet and similar services such as Website designing and
virtual hosting. For example, when you connect to the Internet, the
connection between your Internet-enabled device and the internet is
executed through a specific transmission technology that involves the
transfer of information packets through an Internet Protocol route.
