Lecture No_3,4 (OSI model).pptx

Reference Models Lecture -3-4 (Theory) Department of Computer Science and Engineering, Chitkara University, Punjab Prepared by Dr. Chetna (CSE)  Index Operating System Protocols and Models Refe...

Reference Models Lecture -3-4 (Theory) Department of Computer Science and Engineering, Chitkara University, Punjab Prepared by Dr. Chetna (CSE)  Index Operating System Protocols and Models Reference model Seven-Layers of OSI(Open System Interconnection) Concept of Layers Benefit of using layered Models Summary of layers Protocols used at each layer Protocol Data Unit (PDU)  Operating Systems (OS) All end devices and network devices require an operating system (OS). As shown in the figure 1, the portion of the OS that interacts directly with computer hardware is known as the kernel. The portion that interfaces with applications and the user is known as the shell. The user can interact with the shell using a command-line interface (CLI) or a graphical user interface (GUI). Figure 1 Operating system interacts with hardware, kernel, and Shell. Shell: The user interface that allows the user to request specific tasks from the computer. These requests can be made either through CLI or GUI interfaces. Kernel: Communication between hardware and software of a computer and manages how hardware resources are used to meet software requirements. Hardware: The physical part of a computer including underlying electronics. Note: The operating system on home routers is usually called firmware. The most common method for configuring a home router is by using a web browser-based GUI.  Protocols and Models How a network device operates within a network? A network device is a node in the wireless mesh network. It can transmit and receive wireless data and perform the basic functions necessary to support network formation and maintenance. Communications Fundamentals - Networks vary in size, shape, and function. For communication to occur, devices must know “how” to communicate, three elements in common: Message source (sender) - Message sources are people, or electronic devices, that need to send a message to other individuals or devices. Message Destination (receiver) - The destination receives the message and interprets it. Channel - This consists of the media that provides the pathway over which the message travels from source to destination. Sending a message, whether by face-to-face communication or over a network, is governed by rules called protocols. Protocols must account for the following requirements to successfully deliver a message that is understood by the receiver: An identified sender and receiver, Common language and grammar, Speed and timing of delivery, Confirmation or acknowledgment requirements.  Protocols and Models Network Protocol Requirements - Common computer protocols include the following requirements: Message encoding Message formatting and encapsulation Message size Message timing Message delivery options  Network Protocol Overview Protocols are implemented by end devices and intermediary devices in software, hardware, or both. Each network protocol has its function, format, and rules for communications. The table lists the various types of protocols that are needed to enable communications across one or more networks. Protocol Type Description Network Communications Protocols enable two or more devices to communicate over one or more networks. Protocols The Ethernet family of technologies involves a variety of protocols such as IP, Transmission Control Protocol (TCP), HyperText Transfer Protocol (HTTP), and many more. Network Security Protocols Protocols secure data to provide authentication, data integrity, and data encryption. Examples of secure protocols include Secure Shell (SSH), Secure Sockets Layer (SSL), and Transport Layer Security (TLS). Routing Protocols Protocols enable routers to exchange route information, compare path information, and then to select the best path to the destination network. Examples of routing protocols include Open Shortest Path First (OSPF) and Border Gateway Protocol (BGP). Service Discovery Protocols Protocols are used for the automatic detection of devices or services. Examples of service discovery protocols include Dynamic Host Configuration Protocol (DHCP) which discovers services for IP address allocation, and Domain Name System (DNS) which is used to perform name-to-IP address translation. The functions of these protocols are addressing, reliability, flow control, sequencing, error detection, and application interface. OSI Reference Model Figure 2 OSI Reference Model Benefit of using layered model These are the benefits of using a layered model to describe network protocols and operations as shown in Figure 3: Assisting in protocol design because protocols that operate at a specific layer have defined information that they act upon and a defined interface to the layers above and below Fostering competition because products from different vendors can work together Preventing technology or capability changes in one layer from affecting other layers above and below Providing a common language to describe networking functions and capabilities Two layered models used: Open System Interconnection (OSI) Reference Model and TCP/IP Reference Model Figure 3 Shows network protocols and operations of layered model  OSI Reference Model OSI Reference Model - Internationally Standardized Network Architecture. OSI = Open Systems Interconnection: deals with open systems, i.e. systems open for communications with other systems. Specified in ISO 7498. Model has 7 layers.  7-Layer OSI Model Figure 4 displays 7 layers of OSI model and overview of their specific task. Layer 7 Application Layer Layers 1-4 relate to communications Layer 6 Presentation Layer technology. Layer 5 Session Layer Layers 5-7 relate to user applications. Layer 4 Transport Layer Layer 3 Network Layer Layer 2 Data Link Layer Layer 1 Physical Layer Figure 4 Shows OSI model layers Communications subnet boundary  Reference model (OSI) OSI: Open Systems Interconnection Established in 1947, the International Standards Organization (ISO) is a multinational body dedicated to worldwide agreement on international standards. An ISO standard that covers all aspects of network communications is the Open Systems Interconnection (OSI) model. It was first introduced in the late 1970s. First adapted ISO certification given in year 1984. Layers of OSI model Figure 5 shows responsibilities of OSI model layers Figure 5 Shows responsibilities of OSI model layers Interaction between layers in OSI model Figure 6 shows interaction between layers in OSI model at each layer in detail. Figure 6 Shows interaction between layers in OSI model. An exchange using the OSI model Figure 7 shows the exchange of information using OSI model and transmission medium. Figure 7 Exchange of information using OSI model.  Layers in the OSI model In this section we briefly describe the functions of each layer in the OSI model. Physical Layer Data Link Layer Network Layer Transport Layer Session Layer Presentation Layer Application Layer Layer 1 :Physical Layer Figure 8 Shows the physical layer information transmitted in OSI model. Note The physical layer is responsible for movements of individual bits from one hop (node) to the next. Layer 2 : Data link layer Figure 9 Shows the data link layer information transmitted in OSI model. Note The data link layer is responsible for moving frames from one hop (node) to the next. Layer 3 : Network layer Figure 10 Shows the network layer information transmitted in OSI model. Note The network layer is responsible for the delivery of individual packets from the source host to the destination host. Source to destination delivery Figure 11 Shows the network layer detailed information transmitted in OSI model.  Layer 4: Transport Layer Manages transmission packets 1. Repackages long messages when necessary into small packets for transmission 2. Reassemble packets in the correct order to get the original message. Handles error recognition and recovery. 1. Transport layer at receiving acknowledges packet delivery. 2. Resends missing packets Transport Layer is responsible for end-to-end connectivity. It is also known as the heart of OSI Layers. Following tasks are performed at the Transport Layer : - Identifying Service Multiplexing & De-multiplexing Segmentation Sequencing & Reassembling Error Correction Flow Control Transport Transport layer Figure 12 Shows the transport layer information transmitted in OSI model. Note The transport layer is responsible for the delivery of a message from one process to another. Identify Service Figure 13 TCP Vs UDP Segmentation Figure 14 Segmentation process Sequence & Reassembling Figure 15 Sequence & Reassembly  Layer 5: Session Layer Allows two applications on different computers to establish, use, and end a session.e.g. file transfer, remote login Establishes dialog control -Regulates which side transmits, plus when and how long it transmits. Performs token management and synchronization. Session Layer is responsible for establishing, maintaining and terminating session. Session ID works at Session Layer. Examples : RPC - Remote Procedure Call SQL - Structured Query Language NFS - Network File System Session layer Figure 16 Shows the session layer information transmitted in OSI model. Note The session layer is responsible for dialog control and synchronization. Layer 6 -Presentation layer Figure 17 Shows the presentation layer information transmitted in OSI model. Note The presentation layer is responsible for translation, compression, and encryption. Layer 7 - Application layer Figure 18 Shows the application layer information transmitted in OSI model. Note The application layer is responsible for providing services to the user. Summary of layers Figure 19 Presents the summary of layers of OSI model. Protocol supported at various layers  Protocols at Application layer TELNET: Telnet stands for the TELetype NETwork. It helps in terminal emulation. It allows Telnet clients to access the resources of the Telnet server. It is used for managing files on the internet. It is used for the initial setup of devices like switches. The telnet command is a command that uses the Telnet protocol to communicate with a remote device or system. Port number of telnet is 23. FTP: FTP stands for file transfer protocol. It is the protocol that actually lets us transfer files. It can facilitate this between any two machines using it. But FTP is not just a protocol but it is also a program. FTP promotes sharing of files via remote computers with reliable and efficient data transfer. The Port number for FTP is 20 for data and 21 for control. TFTP: The Trivial File Transfer Protocol (TFTP) is the stripped-down, stock version of FTP, but it’s the protocol of choice if you know exactly what you want and where to find it. It’s a technology for transferring files between network devices and is a simplified version of FTP. The Port number for TFTP is 69.  Continued…. SMTP: It stands for Simple Mail Transfer Protocol. It is a part of the TCP/IP protocol. Using a process called “store and forward,” SMTP moves your email on and across networks. It works closely with something called the Mail Transfer Agent (MTA) to send your communication to the right computer and email inbox. The Port number for SMTP is 25. SNMP: It stands for Simple Network Management Protocol. It gathers data by polling the devices on the network from a management station at fixed or random intervals, requiring them to disclose certain information. It is a way that servers can share information about their current state, and also a channel through which an administrate can modify pre- defined values. The Port number of SNMP is 161(TCP) and 162(UDP). DNS: It stands for Domain Name System. Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address. For example, the domain name www.abc.com might translate to 198.105.232.4. The Port number for DNS is 53 Continued… DHCP: It stands for Dynamic Host Configuration Protocol (DHCP). It gives IP addresses to hosts. There is a lot of information a DHCP server can provide to a host when the host is registering for an IP address with the DHCP server. Port number for DHCP is 67, 68. Presentation layer protocols MPEG: The Moving Pictures Experts Group's standard for the compression and coding of motion video for CD's is very popular. QuickTime: This is for use with Machintosh or Power PC programs, it manages audio and video applications. SSL (Secure Socket Layer) and TLS (Transport Layer Security) are popular cryptographic protocols that are used to imbue web communications with integrity, security, and resilience against unauthorized tampering. Session layer protocols NetBIOS is a non-routable OSI Session Layer 5 Protocol and a service that allows applications on computers to communicate with one another over a local area network (LAN). NetBIOS was developed in 1983 by Sytek Inc. as an API for software communication over IBM PC Network LAN technology. SAP: The protocol used by SAP programs that communicate using the NI interface is called the SAP Protocol. This is an enhanced version of the TCP/IP protocol, which has been supplemented by one length field and some options for error information. Transport layer protocol Transmission Control Protocol (TCP) - is a transport protocol that is used on top of IP to ensure reliable transmission of packets. TCP includes mechanisms to solve many of the problems that arise from packet-based messaging, such as lost packets, out of order packets, duplicate packets, and corrupted packets. User Datagram Protocol (UDP) – a communications protocol that facilitates the exchange of messages between computing devices in a network. It's an alternative to the transmission control protocol (TCP). In a network that uses the Internet Protocol (IP), it is sometimes referred to as UDP/IP.  Internet protocol IPV6: Internet Protocol version 6 is the most recent version of the Internet Protocol, the communications protocol that provides an identification and location system for computers on networks and routes traffic across the Internet. ICMP: ICMP is a network level protocol. ICMP messages communicate information about network connectivity issues back to the source of the compromised transmission. It sends control messages such as destination network unreachable, source route failed, and source quench. MPLS: Multiprotocol Label Switching, or MPLS, is a networking technology that routes traffic using the shortest path based on “labels,” rather than network addresses, to handle forwarding over private wide area networks. ARP: ARP is the protocol used to associate the IP address to a MAC address. When a host wants to send a packet to another host, say IP address 10.5. 5.1, on its local area network (LAN), it first sends out (broadcasts) an ARP packet. Data Link Layer Protocols PPP: In computer networking, Point-to-Point Protocol is a data link layer communication protocol between two routers directly without any host or any other networking in between. It can provide connection authentication, transmission encryption, and data compression. ATM: ATM is a core protocol used in the SONET/SDH backbone of the public switched telephone network (PSTN) and in the Integrated Services Digital Network (ISDN), but has largely been superseded in favor of next- generation networks based on Internet Protocol (IP) technology Physical layer Protocols ISDN: ISDN or Integrated Services Digital Network is a circuit-switched telephone network system that transmits both data and voice over a digital line. You can also think of it as a set of communication standards to transmit data, voice, and signaling. These digital lines could be copper lines. 100Base-TX: 100Base-TX is an Ethernet networking standard (IEEE 802.3u standard.) that supports up to 100 Mbps transfer speed. 100Base- TX was also called as FastEthernet, because Ethernet was 10 Mbps that time and FastEthernet was faster than Ethernet. PDU (Protocol Data Unit) Questions 1.Which type of communication will send a message to a group of host destinations simultaneo unicast anycast multicast Broadcast 2.What process is used to receive transmitted data and convert it into a readable message? encapsulation access control decoding flow control 3.What is done to an IP packet before it is transmitted over the physical medium? It is segmented into smaller individual pieces. It is tagged with information guaranteeing reliable delivery. It is encapsulated in a Layer 2 frame. It is encapsulated into a TCP segment. Questions 4.What process is used to place one message inside another message for transfer from the source to the destination? decoding access control encapsulation flow control 5.A web client is sending a request for a webpage to a web server. From the perspective of the client, what is the correct order of the protocol stack that is used to prepare the request for transmission? Ethernet, IP, TCP, HTTP HTTP, TCP, IP, Ethernet HTTP, IP, TCP, Ethernet Ethernet, TCP, IP, HTTP References : Data Communications and Networking’ by Forouzan, 5th Edition, 2013 Netacad course Computer Networks Dr. Vidhu Baggan