Reference models in Networks: OSI & TCP/IP

This ppt provides an overview of OSI reference model and TCP/IP Reference model

1. REFERENCE MODELS Mukesh Chinta Asst Prof CSE, VRSEC

2. Need for Standards Over the past couple of decades many of the networks that were built used different hardware and software implementations, as a result they were incompatible and it became difficult for networks using different specifications to communicate with each other. To address the problem of networks being incompatible and unable to communicate with each other, the International Organisation for Standardisation (ISO) researched various network schemes. The ISO recognised there was a need to create a NETWORK MODEL that would help vendors create interoperable network implementations.

3. What is a Reference Model A reference model is a conceptual layout that describes how communication between devices should occur. A reference model has many advantages such as it defines standards for building network components thereby permitting multiple-vendor development and also defines which functions should be performed at each layer of the model thereby promoting the standardization of network.

4. ISO-OSI In 1984 in order to aid network interconnection without necessarily requiring complete redesign, the Open Systems Interconnection (OSI) reference model was approved as an international standard for communications architecture. The Open Systems Interconnection (OSI) reference model is a descriptive network scheme. It ensures greater compatibility and interoperability between various types of network technologies. The OSI model describes how information or data makes its way from application programmes (such as spreadsheets) through a network medium (such as wire) to another application programme located on another network. The OSI reference model divides the problem of moving information between computers over a network medium into SEVEN smaller and more manageable problems.

5. Why 7 Layers?? In 1983, Day and Zimmerman laid down certain principles that were applied to arrive at the seven layers can be briefly summarized as follows: A layer should be created where a different abstraction is needed. Each layer should perform a well-defined function. The function of each layer should be chosen with an eye toward defining internationally standardized protocols. The layer boundaries should be chosen to minimize the information flow across the interfaces. The number of layers should be large enough that distinct functions need not be thrown together in the same layer out of necessity and small enough that the architecture does not become unwieldy

6. OSI Model

7. OSI Model Data Flow

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9. OSI Upper Layers Layer 5 Layer 6 Layer 7 Application Presentation Session Application DATA DATA Format When to start Signaling 9 Mukesh Chinta, Asst Prof, CSE

10. OSI Lower Layers Transport Network Data Link Physical Layer 1 Layer 2 Layer 3 Layer 4 Reliability 0101 0101 Data transmission at the node interval Routing Physical connection

11. 11 Physical Layer Provides physical interface for transmission of information. Defines rules by which bits are passed from one system to another on a physical communication medium. Covers all - mechanical, electrical, functional and procedural - aspects for physical communication. Such characteristics as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, physical connectors, and other similar attributes are defined by physical layer specifications.

12. The physical layer is responsible for movements of individual bits from one hop (node) to the next. 12

13. Data Link Layer Data link layer attempts to provide reliable communication over the physical layer interface. Breaks the outgoing data into frames and reassemble the received frames. Create and detect frame boundaries. Handle errors by implementing an acknowledgement and retransmission scheme. Implement flow control. Supports point-to-point as well as broadcast communication. A special sublayer Medium access control sublayer deals with the problem of access control of shared channel. 13

14. The data link layer is responsible for moving frames from one hop (node) to the next. 14

15. DLL Hop-to-Hop Delivery 15

16. Network Layer 16 Implements routing of frames (packets) through the network. Defines the most optimum path the packet should take from the source to the destination Defines logical addressing so that any endpoint can be identified. Handles congestion and Quality of service issues in the network. Facilitates interconnection between heterogeneous networks (Internetworking). The network layer also defines how to fragment a packet into smaller packets to accommodate different media. In broadcast networks, the network layer is thin(nonexistent)

17. The network layer is responsible for the delivery of individual packets from the source host to the destination host.

18. Network Layer Delivery

19. Transport Layer 19 Purpose of this layer is to provide a reliable mechanism for the exchange of data between two processes in different computers. Accepts data from above, split into smaller units in needed Ensures that the data units are delivered error free. Ensures that data units are delivered in sequence. Ensures that there is no loss or duplication of data units. Provides connectionless or connection oriented service. Provides for the connection management. Multiplex multiple connection over a single channel.

20. The transport layer is responsible for the delivery of a message from one process to another.

21. Reliable Process-to-Process message delivery

22. Session Layer 22 Session layer provides mechanism for controlling the dialogue between the two end systems. It defines how to start, control and end conversations (called sessions) between applications. This layer requests for a logical connection to be established on an end-user’s request. Responsible for maintenance and termination of sessions. Token Management: Prevents two parties from attempting the same critical operation simulatenously . This layer provides services like dialogue discipline which can be full duplex or half duplex: dialog control Session layer can also provide check-pointing mechanism such that if a failure of some sort occurs between checkpoints, all data can be retransmitted from the last checkpoint: Synchronization.

23. The session layer is responsible for dialog control and synchronization.

24. Presentation Layer 24 Presentation layer defines the format in which the data is to be exchanged between the two communicating entities. It deals with syntax and semantics of the information transmitted. Also handles data compression and data encryption (cryptography). Responsible for protocol conversion, character conversions, data encryption / decryption , expanding graphics commands and data compression

25. Application Layer Used for applications specially written to run over the network Allows access to network services that support applications Directly represents the services that directly support user applications (e.g., file transfer and email ) What the user sees or does Contains a variety of protocols that are commonly needed by users 25

26. The application layer is responsible for providing services to the user.

27. End System Intermediate Systems

28. Peer-to-Peer Communication

29. 29 OSI Protocols

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32. TCP/IP Reference Model 32

33. Meet the Protocol Family in the Internet TCP UDP IP SNMP ping tracert IPsec Mobile IP ARP RARP PPP DNS telnet ftp IP QoS HTTP IP telephony IP multicast BSD socket Winsock Java socket ICMP IPv4 IPv6 SMTP NTCIP DHCP POP3 Ethernet WAP GPRS r-utility ATM MIB WinPcap SLIP SMS Internet internet intranet tester developer administrator OSPF BGP MPLS RTP WWW

34. History & Background TCP/IP originated out of the investigative research into networking protocols that the US Department of Defense ( DoD ) initiated in 1969. In 1968, the DoD Advanced Research Projects Agency (ARPA) began researching the network technology that is called packet switching. The network that was initially constructed as a result of this research to provide a communication that could function in wartime., then called ARPANET, gradually became known as the Internet. The TCP/IP protocols played an important role in the development of the Internet. In the early 1980s, the TCP/IP protocols were developed. In 1983, they became standard protocols for ARPANET. Because of the history of the TCP/IP protocol suite, it's often referred to as the DoD protocol suite or the Internet protocol suite 34

35. Introduction 35 The  Internet Protocol Suite  (commonly known as  TCP/IP ) is the set of communications protocols used for the Internet and other similar networks. It is named from two of the most important protocols in it: the Transmission Control Protocol (TCP) The Internet Protocol (IP), which were the first two networking protocols defined in this standard.

36. Layers 36

37. TCP/IP Network Architecture Application Layer Transport Layer Network Layer Link Layer operating-system/computer-architecture independent LAN/MAN/WAN applicable physical-medium independent host host network network media media process process client-server model

38. TCP/IP Protocol Suite Ethernet ARP RARP IPv4 IPv6 TCP UDP ICMP Telnet FTP ping SNMP TFTP Serial line PPP SMTP POP3 21 23 110 25 69 161 port number IP address

39. TCP\IP Protocol Suite 39

40. Internet Layer The internet layer is the linchpin that holds the whole architecture together. Its job is to permit hosts to inject packets into any network and have them travel independently to the destination (potentially on a different network). Internet Protocol (IP) is the most important protocol in this layer. It is a connectionless protocol and does not provide reliability, flow control, or error recovery. IP provides a routing function that attempts to deliver transmitted messages to their destination. A message unit in an IP network is called an IP datagram . This is the basic unit of information transmitted across TCP/IP networks. Other internetwork-layer protocols are ICMP {Internet Control Message Protocol}, IGMP {Internet Group Management Protocol}, ARP {Address Resolution Protocol}, and RARP {Reverse ARP}. 40

41. Transport Layer Transport layer (host-to-host) is designed to allow peer entities on the source and destination hosts to carry on a conversation, just as in the OSI transport layer. Two end-to-end transport protocols namely TCP {Transmission Control Protocol} and UDP {User Datagram Protocol} have been defined. TCP is a reliable connection-oriented protocol that permits a byte stream originating on one machine to be transported without error on any machine in the internet. It divides the incoming byte stream into discrete message and passes each one onto the internet layer. It reassembles these messages at the receiver. It also handles flow control. UDP is an unreliable, connectionless protocol for applications that do not want TCP's sequencing or flow control and wish to provide their own. It is also widely used for one-shot, client-server-type request-reply queries and applications in which prompt delivery is more important than accurate delivery, such as transmitting speech or video. 41

42. Link Layer 42 The network interface layer, also called the link layer or the data-link layer, is the interface to the actual network hardware. This interface may or may not provide reliable delivery, and may be packet or stream oriented. In fact, TCP/IP does not specify any protocol here, but can use almost any network interface available, which illustrates the flexibility of the IP layer. Examples are IEEE 802.2, X.25, ATM, FDDI, and even SNA. It varies from implementation to implementation with vendors supplying their own version

43. Application Layer The Application layer is equivalent to the combined OSI session, presentation and Application Layers. All the functions handled by these 3 layers in the OSI model are handled by the Application layer in TCP/IP model. It provides a way for applications to have access to networked services.  The Application Layer has the responsibility for authentication, data compression, and end-user services such as terminal emulation, file transfer, e-mail, web browsing/serving, and other network control and management services. An application header and following data are packaged as a message Application layer is present on the top of the Transport layer. It includes all the higher-level protocols which are virtual terminal (TELNET), file transfer (FTP), electronic mail (SMTP) & HTTP (Hyper Text Transfer Protocol) 43

44. High Level Protocols IMAP4 - Internet Mail Access Protocol version 4 lets clients access an IMAP4 mail server to download their e-mail to a local computer program. It works using TCP as its transport protocol. FTP - File Transfer Protocol uses TCP as transport and allows the transfer of files between two computer systems with login required by the requester. Telnet – Sometimes incorrectly called Terminal Emulation across a network, it is used to remotely open a session on another computer acting as a server. It relies on TCP for transport. SMTP - Simple Mail Transfer Protocol is a TCP-transported application layer protocol used to send electronic mail. HTTP - Hypertext Transfer Protocol uses the TCP transport protocol to carry web browsing requests to a web server, and web pages from web servers to web browsers. POP3 - Post Office Protocol version 3 uses TCP as a way to offer clients access to a POP3 mail server to transfer their e-mail to a local program on their computer. BGP4 - Border Gateway Protocol version 4 is a routing protocol most often used between organizations. Two routers using BGP will establish a TCP connection to send each other their BGP routing tables. In that exchange is information about reachable networks including the full path to all BGP-known networks. 44

45. DNS3 - Domain Names System provides the ability to refer to IP devices using names instead of numerical IP addresses. It lets Domain Name Servers resolve these names to their corresponding IP addresses. DHCP - Dynamic Host Configuration Protocol uses UDP as its transport protocol to dynamically and automatically assign IP addresses and other networking configuration information to computers starting up on a given network. TFTP - Trivial File Transfer Protocol is a UDP-transported protocol that allows file transfer between two computers with no login or user required for its limited use. SNMP - Simple Network Management Protocol is used to manage all types of network elements based on various data sent and received using UDP as its transport protocol. RIP2 - Routing Information Protocol is an internal routing protocol used to dynamically update router tables on internal organization networks. It uses UDP as its transport protocol. 45 High Level Protocols

46. Internet Layer Protocols ARP - Address Resolution Protocol supports the packaging of IP data into Ethernet frames. It finds the local Ethernet (MAC) address that matches a specific local IP address. ICMP4 - Internet Control Message Protocol provides diagnostics and logical error reporting to help manage the sending of data between computers. Its best-known function is ping. IGMP - Internet Group Management Protocol supports multicasting by letting multicast routers track group memberships on each of its connected networks. IPsec - Internet Protocol Security is an end-to-end security scheme for securing Internet Protocol (IP) communications by authenticating and encrypting each IP packet of a communication session. 46

47. IP4 - Internet Protocol provides connectionless communication support for all protocols’ data, except ARP, by packaging that data into an IP datagram. OSPF - Open Shortest Path First is an internal routing protocol for use inside an organization. It checks the function of its link to each of its neighbor OSPF routers. Then, it sends the acquired routing information to those neighbor routers. EIGRP - Enhanced Interior Gateway Routing Protocol is a local routing protocol that is proprietary to Cisco. It is an advanced distance-vector routing protocol that shares internal organizational routing information found in three tables. 47 Internet Layer Protocols

48. Differences The application layer in TCP/IP handles the responsibilities of multiple layers in the OSI model. The OSI model numbers and names its layers, whereas the TCP/IP stack only names the layers. Unlike the transport layer in OSI, TCP/IP only guarantees reliable delivery of packets when TCP is the chosen protocol. OSI has much more complexity in its 7 layers than TCP/IP has in its 4 layers. In TCP/IP, protocols are deliberately designed to have more layer flexibility than the strict layers of the OSI model. TCP/IP functions are implemented, then standardized. OSI is standardized in concept only, though some functions work. OSI has more limited Network Management and Network Security. 48