UNIT 2 - Networking Reference Models & Networking Devices.pptx

Networking Reference Models & Networking Devices

1. UNIT-2: Network Models & Devices

2. Overview Slide 2

3. Learning Objectives Slide 3

4. Slide 4 Reference Model & Layering Architecture

5. OSI Network Model Open Systems Interconnection (OSI) is a standard reference model for communication between end users in a network. By the term open system, we mean a set of protocols using which a system can communicate with any other system irrespective of the differences in their underlying hardware and software. The OSI model consists of seven separate but related layers, namely, physical, data link, network, transport, session, presentation and application layers. When data is sent from one machine to another, it travels down sequentially from layer to layer on the source machine and as it reaches the destination machine, it moves up through the layers. While the data passes through layers on source machine, each layer adds header (and sometimes, trailer which is usually added at data link layer) to it and passes the whole unit to the layer directly below it. The header attached at each layer contains control information such as sequence numbers and size of data. Slide 5

6. Functions of Physical Layer Slide 6

7. Functions of Data Link Layer This layer is responsible for reliable delivery of data from node to node and for providing services to the network layer. At sender’s side, the data link layer divides the packets received from the network layer into manageable form known as frames. These data frames are then transmitted sequentially to the receiver. At the receiver’s end, data link layer detects and corrects any errors in the transmitted data, which it gets from the physical layer. Other functions of data link layer are error control and flow control. Error control ensures that all frames have finally been delivered to the destination network layer and in the proper order. Flow control manages the sender to send frames according to the receiving capability of the recipient. Slide 7

8. Functions of Network Layer This layer provides end-to-end communication and is responsible for transporting traffic between devices that are not locally attached. Data in the network layer is called packet (group of bits) which in addition to data contains source and destination address. Packets are sent from node to node with the help of any of two approaches , namely, virtual circuit (connection oriented) and datagram (connectionless). In virtual circuit method , route is decided while establishing connection between two users and the same path is followed for the transmission of all packets. In datagram method , there is no connection established; therefore, sequenced packets take different paths to reach destination. Therefore, virtual circuit method resembles telephone system and datagram method resembles postal system. Other functions of network layer include routing, deadlock prevention and congestion control. Network layer makes routing decisions with the help of routing algorithms to ensure the best route for packet from source to destination. Congestion control tries to reduce the traffic on the network, so that delay can be reduced, and overall performance can be increased. Slide 8

9. Functions of Transport Layer The basic function of this layer is to handle error recognition and recovery of the data packets. It provides end-to-end communication between processes which are executing on different machines. It establishes, maintains and terminates communications between the sender process and the receiver process. It splits the message at the sender’s end and passes each one onto the network layer. At the receiver’s end, transport layer rebuilds packets into the original message, And to ensure that the packets arrive correctly, the receiving transport layer sends acknowledgements to the sender’s end. Slide 9

10. Functions of Session Layer The session layer comes into play primarily at the beginning and end of transmission. At the beginning of the transmission, it lets the receiver know its intent to start transmission. At the end of the transmission, it determines whether the transmission was successful. This layer also manages errors that occur in the upper layers such as a shortage of memory or disk space necessary to complete an operation or printer errors. Some services provided by the session layer are dialog control , synchronization and token management . Dialog control service allows traffic to flow in both directions or in single direction at a time and keeps track of whose turn it is to transmit data. Synchronization helps to insert checkpoints in data streams, so that if connection breaks during a long transmission, then only the data which have not passed the checkpoint yet need to be retransmitted. Token management prevents two nodes to execute the same operation at the same time. Slide 10

11. Functions of Presentation Layer The function of this layer is to ensure that information sent from the application layer of one system would be readable by the application layer of another system. Therefore, presentation layer concerns with the syntax and semantics of the information transmitted. This is the place where application data is packed or unpacked and is made ready to use by the running application. This layer also manages security issues by providing services such as data encryption and compression, so that fewer bits need to be transferred on the network. Slide 11

12. Functions of Application Layer This layer is the entrance point that programs use to access the OSI model and utilize network resources. This layer represents the services that directly support applications. This OSI layer is closest to the end users. Application layer includes network software that directly serves the end users of the network by providing them user interface and application features such as electronic mail. Slide 12

13. Entities, Interfaces, Services, & PDUs Each layer contains some active elements called entities , such as process. Between two adjacent layers is an interface which defines the operations and services of the lower layer that are available to its immediate upper layer. The set of operations provided by a layer to the layer above it is called service. For communication and information sharing, each layer makes use of packet data units (PDUs). Depending on the information provided in the header, each PDU is given a specific name. For example, at transport layer , data plus PDU is called a segment . At network layer , segment and PDU (added by network layer) is given the name packet or datagram . And at data link layer , packet with data link PDU is called a frame . Slide 13

14. TCP/IP Network Model Now that we know about the concept of protocol layering and the logical connections between layers in our second scenario, we can introduce the Transmission Control Protocol/Internet Protocol (TCP/IP). TCP/IP is a protocol suite (a set of protocols organized in different layers) used on the Internet today. It is a hierarchical protocol made up of interactive modules, each of which provides a specific functionality. The term hierarchical means that each upper-level protocol is supported by the services provided by one or more lower-level protocols. The TCP/IP protocol suite is defined as five layers as shown in Figure. Slide 14

15. TCP/IP Network Model - Brief Description of Layers Physical Layer: We can say that the physical layer is responsible for carrying individual bits in a frame across the link. The physical layer is the lowest level in the TCP/IP protocol suite. The communication between two devices at the physical layer is still a logical communication because there is another hidden layer, the transmission media, under the physical layer. Data-Link Layer: We have seen that an internet is made up of several links (LANs and WANs) connected by routers. When the next link to travel is determined by the router, the data-link layer is responsible for taking the datagram and moving it across the link. Network Layer: The network layer is responsible for creating a connection between the source computer and the destination computer. The communication at the network layer is host-to-host. However, because there can be several routers from the source to the destination, the routers in the path are responsible for choosing the best route for each packet. Slide 15

16. TCP/IP Network Model - Brief Description of Layers Transport Layer: The logical connection at the transport layer is also end-to-end. The transport layer at the source host gets the message from the application layer; encapsulates it in a transport-layer packet (called a segment or a user datagram in different protocols); and sends it, through the logical (imaginary) connection, to the transport layer at the destination host. In other words, the transport layer is responsible for giving services to the application layer: to get a message from an application program running on the source host and deliver it to the corresponding application program on the destination host. Application Layer: The logical connection between the two application layers is end-to-end. The two application layers exchange messages between each other as though there were a bridge between the two layers. However, we should know that the communication is done through all the layers. Communication at the application layer is between two processes (two programs running at this layer). To communicate, a process sends a request to the other process and receives a response. Process-to-process communication is the duty of the application layer. Slide 16

17. Types of Addresses Associated with Layers of TCP/IP Model Each layer in the TCP/IP model uses an address for the efficient delivery of data between communicating nodes. The host-to-network layer (physical plus data link layer) relates to physical address, network layer relates to logical address, transport layer concerns with port address and application layer defines specific address. The description of these addresses is as follows: Physical Address: It is the address assigned to a node by the network (LAN or WAN) in which it is connected. Physical address is also known by other names including link address, MAC address and hardware address. IP Address: A universal addressing system is used that assigns each host in the network a unique address called logical address (also referred to as IP address or software address) which is independent of the underlying physical network. Each host connected to the Internet is assigned a 32-bit IP address and no two hosts connected to the Internet can have the same IP address. Port Address: since multiple processes may be running simultaneously on the host machine, there should be some means to identify the process to which data is to be communicated. To enable this, each running process on the host machine is assigned with a label what is known as port address. Using the port address, the transport layer ensures process-to-process delivery. In TCP/IP architecture, port address is of 16 bits . Specific Address: Some applications such as e-mail and World Wide Web (WWW) provide user-friendly addresses designed for that specific address. Some examples of specific address include an e-mail address that helps to identify the recipient of that e-mail and URL of a website that helps to search a document on the web. Slide 17

18. Comparison B/W OSI, & TCP/IP Network Models Slide 18

19. Network Devices T o reduce complication, some network devices were developed. Network devices help nodes to get connected in a network for efficient communication. Network devices include NIC, repeater, hub, switch, router, bridge and gateway. Slide 19

20. Network Interface Card (NIC) It is a hardware device that connects clients, servers and peripherals to the network through a port. Most network interfaces come as small circuit board that can be inserted onto one of the computer motherboard’s slots. Alternatively, modern computers sometimes include the network interface as part of their main circuit boards (motherboards). Each network interface is associated with a unique address called its MAC address. The MAC address helps in sending information to the intended destination. NICs are the major factor in determining the speed and performance of a network . Slide 20

21. Repeater A repeater installed on the link receives signal, regenerates it and sends the refreshed copy back to the link. Repeaters are most used to extend a network. All network cable standards have maximum cable length specification. If the distance between two network devices is longer than this specification, a repeater is needed to regenerate the signal. T he repeaters have no in-built intelligence and they do not look at the contents of the packet while regenerating the signal . Slide 21

22. Hub It is a small box that connects individual devices on a network, so that they can communicate with one another. The hub operates by gathering the signals from individual network devices, optionally amplifying the signals, and then sending them onto all other connected devices. Amplification of the signal ensures that devices on the network receive reliable information. Slide 22

23. Bridge This device allows the division of a large network into two or more smaller and efficient networks. It monitors the information traffic on both sides of the network, so that it can pass packets of information to the correct location. A bridge examines each packet as it enters though one of the ports. It first looks at the MAC address of the sender and creates a mapping between the port and the sender’s MAC address. It then looks at the address of the recipient, comparing the MAC address to the list of all learned MAC addresses. If the address is in the list, the bridge looks up the port number and forwards the packet to the port where it thinks the recipient is connected. If the recipient’s MAC address is not in the list, the bridge then does a flood; it sends the signal to all the ports except the one from where it was received . Slide 23

24. Switch It is a multi-port bridge. It connects all the devices on a network, so that they can communicate with one another. The behavior of a switch is same as that of a bridge. It can inspect the data packets as they are received, determining the source and destination device of that packet, and forwarding that packet appropriately. The difference is that most switches implement these functions in hardware using a dedicated processor. This makes them much faster than traditional software-based bridges. Slide 24

25. Router It is an essential network device for interconnecting two or more networks. The router’s sole aim is to trace the best route for information to travel. A router creates and/or maintains a table, called a routing table that stores the best routes to certain network destinations. While bridges know the addresses of all computers on each side of the network, routers know the addresses of computers, bridges and other routers on the network. Routers can even ‘listen’ to the entire network to determine which sections are the busiest . Slide 25

26. Gateway It is an internetworking device, which joins networks operating on different protocols together. It is also known as protocol converter. A gateway accepts the packet formatted for one protocol and converts the formatted packet into another protocol. A gateway can be implemented completely in software, hardware, or as a combination of both. One can connect systems with different protocols, languages and architecture using a gateway . Slide 26

27. Difference B/W Bridge, Router, & Repeater Slide 27

28. Difference B/W Switch, & Hub Slide 28

29. Difference B/W Router, & Switch Slide 29

30. Review Questions Why we need a reference model and layering architecture? What is OSI network model? List down the layers of OSI network model. Discuss functions of physical, data link, and network layers concerning OSI model. Describe functions of transport, session, presentation, and application layers of OSI network model. State error control, and flow control. What are entities, interfaces, services, and PDUs? Explain TCP/IP network model & its layers. Describe protocols working at different layers of TCP/IP network model. Differentiate between TCP, UDP, SCMP, & SCTP transport layer protocols. Distinguish between, ARP, RARP, ICMP, IGMP, & IP network layer protocols. Compare OSI & TCP/IP network models. What are types of addresses associated with different layers of TCP/IP network model? Explain. Write a comprehensive note on networking devices like repeater, hub, switch, bridge, router, & gateways. What is network interface card (NIC)? What is difference between bridge, router, and repeater? Write down any five differences between hub, and switch. List down any five differences between switch, and router. Slide 30