The OSI Model & the TCP/IP Protocol Suite

1. 3 The OSI Model &the TCP/IP Protocol Suite Tutun Juhana TelecommunicationEngineering School of ElectricalEngineering & Informatics InstitutTeknologi Bandung ET3003 Computer Networks

2. When Communication is simple Example 1 • The communication is so simple that it can occur in only one layer (sign language) Speak Spanish Speak English

3. When Communication is not simple Example 2 • Ann has to move to another town because of her job • We need three layers • It is hierarchical (the tasks must be done in the order given in the hierarchy) • Each layer uses the services of the layer immediately below it • Each layer gives the services to the layer immediately above it

4. Before 1990 everyone believed that the OSI model would become the ultimate standard for data communications - but this did not happen

5. The TCP/IP protocol suite became the dominant commercial architecture because it was used and tested extensively in the Internet • the OSI model was never fully implemented

6. THE OSI MODEL

7. 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

8. An open systemis a set of protocols that allows any two different systems to communicate regardless of their underlying architecture • The OSI model is not a protocol; it is a model for understanding and designing a network architecture that is flexible, robust, and interoperable • The OSI model was intended to be the basis for the creation of the protocols in the OSI stack

9. The OSI model The user support layers; they allow interoperability among unrelated software systems; They are almost always implemented in software the transport layer, links the two subgroups and ensures that what the lower layers have transmitted is in a form that the upper layers can use The network support layers; they deal with the physical aspects of moving data from one device to another (such as electrical specifications, physical connections, physical addressing, and transport timing and reliability); They are a combination of hardware and software, except for the physical layer, which is mostly hardware

10. Layered Architecture

11. An exchange using the OSI model Decapsulation Encapsulation

12. Physical Layer • Responsible for moving individual bits from one (node) to the next • It coordinates the functions required to carry a bit stream over a physical medium. • It deals with the mechanical and electrical specifications of the interface and transmission media • It defines the procedures and functions that physical devices and interfaces have to perform for transmission to occur

13. The physical layer is also concerned with the following • Physical characteristics of interfaces and media • Representation of bits • Data rate • Synchronization of bits • Line configuration • Physical topology • Transmission mode

14. Data Link Layer • The data link layer is responsible for moving frames from one hop (node) to the next • The data link layer transforms the physical layer, a raw transmission facility, to a reliable link • It makes the physical layer appear error-free to the upper layer (network layer)

16. Other responsibilities of the data link layer include the following • Framing • Physical addressing • Flow control • Error control • Access control

17. Network Interface Card Perform layer 1 and 2 protocols

18. Network Layer • The network layer is responsible for the source-to-destination delivery of a packet, possibly across multiple networks (links) • Whereas the data link layer oversees the delivery of the packet between two systems on the same network(link) • The network layer ensures that each packet gets from its point of origin to its final destination

21. Other responsibilities of the network layer include the following • Logical addressing • Routing

22. Transport Layer • The transport layer is responsible for the delivery of a message from one process to another • A process is an application program running on the host

23. Reliable process-to-process delivery of a message

24. Differences with Network Layer • Network layer oversees source-to-destination delivery of individual packets • It does not recognize any relationship between those packets • The transport layer ensures that the whole message arrivesintact and in order • Overseeing both error control and flow control at the source-to-destination level

25. Other responsibilities of the transport layer • Service-point addressing (port address) • Segmentation and reassembly • Connection control • The transport layer can be either connectionless or connection oriented • Flow control • Error control

26. Session Layer • Session layer establishes, maintains, and synchronizes the interaction between communicating systems • Responsibilities • Dialog control • Synchronization

28. Presentation Layer • The presentation layer is concerned with the syntax and semantics of the information exchanged between two systems • Translation • Encryption • Compression

30. Application Layer • The application layer enables the user, whether human or software, to access the network • It provides user interfaces and support for services (email, remote file access etc.) • Services provided : • Network virtual terminal • File transfer, access, and management (FTAM) • E-mail services • Directory services

32. Summary of OSI Layers

33. TCP/IP PROTOCOL SUITE

34. The TCP/IP protocol suite was developed prior to the OSI model

35. TCP/IP versus OSI model

36. Layers in the TCP/IP Protocol Suite • To discuss the purpose of each layer in the TCP/IP protocol suite, we will study a small private internet

38. Physical Layer • TCP/IP does not define any specific protocol for the physical layer • It supports all of the standard and proprietary protocols • The communication is between two hops or nodes, either a computer or router • The unit of communication is a single bit

39. We assume that the most efficient way to communicate with each other is via routers R1, R3, and R4 if a node is connected to n links, it needs n physical-layer protocols, one for each link because links may use different physical-layer protocols

40. Data Link Layer • TCP/IP does not define any specific protocol for the data link layer either • It supports all of the standard and proprietary protocols • The communication is also between two hops or nodes • The unit of communication however, is a packet called a frame

41. These frames may be different because link 1 and link 3 may be using different protocols and require frames of different formats

42. Network Layer • At the network layer (or, more accurately, the internetwork layer), TCP/IP supports the Internet Protocol (IP) • IP is the transmission mechanism used by the TCP/IP protocols • IP transports data in packets called datagrams, each of which is transported separately • Datagrams can travel along different routes and can arrive out of sequence or be duplicated • IP does not keep track of the routes and has no facility for reordering datagrams once they arrive at their destination

44. Transport Layer • Only the two end computers need to have the transport layer • The transport layer is responsible for delivering the whole message, which is called a segment from A to B • A segment may consist of a few or tens of datagrams • Where as the network layer is responsible for sending individual datagrams from computer A to computer B

45. The segments need to be broken into datagrams and each datagram has to be delivered to the network layer for transmission • Since the Internet defines a different route for each datagram, the datagrams may arrive out of order and may be lost • The transport layer at computer B needs to wait until all of these datagrams to arrive, assemble them and make a segment out of them

46. The transport layer was represented in the TCP/IP suite by two protocols: • User Datagram Protocol (UDP) • Transmission Control Protocol (TCP) • A new protocol called Stream Control Transmission Protocol (SCTP) has been introduced in the last few years

48. Application Layer • The application layer in TCP/IP is equivalent to the combined session, presentation, and application layers in the OSI model • The application layer allows a user to access the services of our private internet or the global Internet • electronic mail, file transfer, accessing the World Wide Web, etc. • The unit of communication at the application layer is a message

50. Addressing User-friendly addresses that are designed for specific application To enable communication between processes Needed in which each host can be identified uniquely, regardless of the underlying physical network • The address of a node as defined by its LAN or WAN • Have authority over the link