Sargation university's open system interconnection
- 1. OSI Reference Model Unit II
- 2. OSI Model • Open Systems Interconnection (OSI) is a set of internationally recognized, non-proprietary standards for networking and for operating system involved in networking functions. • 7 Layers – 7. Application Layer – 6. Presentation Layer – 5. Session Layer – 4. Transport Layer – 3. Network Layer – 2. Data Link Layer – 1. Physical Layer
- 3. LAYER 7 – The APPLICATION Layer • The top layer of the OSI model • Provides a set of interfaces for sending and receiving applications and to use network services, such as: message handling and database query processing • Responsibility: The application layer is responsible for providing services to the user.
- 4. LAYER 6 – The PRESENTATION Layer • Manages data-format information for networked communications (the network’s translator) • For outgoing messages, it converts data into a generic format for network transmission; for incoming messages, it converts data from the generic network format to a format that the receiving application can understand • This layer is also responsible for certain protocol conversions, data encryption/decryption, or data compression/decompression • A special software facility called a “redirector” operates at this layer to determine if a request is network related on not and forward network-related requests to an appropriate network resource
- 5. LAYER 5 – The SESSION Layer • Enables two networked resources to hold ongoing communications (called a session) across a network • Applications on either end of the session are able to ex hange data for the duration of the session This layer is: • Responsible for initiating, maintaining and terminating sessions • Responsible for security and access control to session information (via session participant identification) • Responsible for synchronization services, and for checkpoint services
- 6. LAYER 4 – The TRANSPORT Layer • Manages the transmission of data across a network • Manages the flow of data between parties by segmenting long data streams into smaller data chunks (based on allowed “packet” size for a given transmission medium) • Reassembles chunks into their original sequence at the receiving end • Provides acknowledgements of successful transmissions and requests resends for packets which arrive with errors • The transport layer is responsible for the delivery of a message from one process to another.
- 7. LAYER 3 – The NETWORK Layer • Handles addressing messages for delivery, as well as translating logical network addresses and names into their physical counterparts • Responsible for deciding how to route transmissions between computers • This layer also handles the decisions needed to get data from one point to the next point along a network path • This layer also handles packet switching and network congestion control
- 8. LAYER 2 – The DATA LINK Layer • Handles special data frames (packets) between the Network layer and the Physical layer • At the receiving end, this layer packages raw data from the physical layer into data frames for delivery to the Network layer • At the sending end this layer handles conversion of data into raw formats that can be handled by the Physical Layer
- 9. LAYER 1 – The PHYSICAL Layer • Converts bits into electronic signals for outgoing messages • Converts electronic signals into bits for incoming messages • This layer manages the interface between the the computer and the network medium (coax, twisted pair, etc.) • This layer tells the driver software for the MAU (media attachment unit, ex. network interface cards (NICs, modems, etc.)) what needs to be sent across the medium • The bottom layer of the OSI model • The physical layer is responsible for movements of • individual bits from one hop (node) to the next.
- 10. Summary
- 11. 11 What is TCP/IP? • TCP/IP is a set of protocols developed to allow cooperating computers to share resources across a network • TCP stands for “Transmission Control Protocol” • IP stands for “Internet Protocol” • They are Transport layer and Network layer protocols respectively of the protocol suite • The most well known network that adopted TCP/IP is Internet – the biggest WAN in the world
- 12. 12 • A protocol is a collection of rules and procedures for two computers to exchange information • Protocol also defines the format of data that is being exchanged What is a protocol?
- 13. 13 Why TCP/IP is so popular? • TCP/IP was developed very early • Technologies were widely discussed and circulated in documents called “Request for Comments” (RFC) – free of charge • Supported by UNIX operating system
- 14. 14 TCP/IP Model • Because TCP/IP was developed earlier than the OSI 7- layer mode, it does not have 7 layers but only 4 layers TCP/IP Protocol Suite FTP, SMTP, Telnet, HTTP,… TCP, UDP IP, ARP, ICMP Network Interface
- 15. 15 Layer of Models Application Transport Network Network Interface TCP/IP 4-layers OSI 7-layers
- 16. 16 • Application layer protocols define the rules when implementing specific network applications • Rely on the underlying layers to provide accurate and efficient data delivery • Typical protocols: • FTP – File Transfer Protocol • For file transfer • Telnet – Remote terminal protocol • For remote login on any other computer on the network • SMTP – Simple Mail Transfer Protocol • For mail transfer • HTTP – Hypertext Transfer Protocol • For Web browsing Layer-1 Application Layer
- 17. 17 Layer-2 Transport Layer Application Transport Network Network Interface Message Segments h M h M h M
- 18. 18 TCP and UDP • TCP is a connection-oriented protocol • Does not mean it has a physical connection between sender and receiver • TCP provides the function to allow a connection virtually exists – also called virtual circuit • TCP provides the functions: • Dividing a chunk of data into segments • Reassembly segments into the original chunk • Provide further the functions such as reordering and data resend • Offering a reliable byte-stream delivery service TCP – Transmission Control Protocol
- 19. 19 Layer-3 Network Layer Application Transport Network Network Interface Message Segments h M h M h M h M h h M h h M h Datagrams / Packets
- 20. 20 Network Addresses and Subnets • A header is added to each segment in the Network layer IP 3 Total Length Time to Live Protocol Header CheckSum Source Address Destination Address Segment Segment
- 21. 21 Layer-4 Data Link and Physical Layers Application Transport Network Network Interface Message Segments h M h M h M h M h h M h h M h Packets h M h h M h h h Frames
- 22. Concept • OSI: Open Systems Interconnection. It was developed by ISO as a first step toward international standardization of the protocol used in various layers. It deals with connecting open system.. • TCP/IP: Transport Control Protocol/Internet Protocol. TCP is used in connection with IP and operates at the transport layer. IP is the set of convention used to pass packets from one host to another.
- 23. Difference • OSI makes the distinction between services, interfaces, and protocol. • The OSI model was devised before the protocols were invented. It can be made to work in diverse heterogeneous networks. • TCP/IP does not originally clearly distinguish between services, interface, and protocol. • TCP/IP model was just a description of the existing protocols. The model and the protocol fit perfectly.
- 24. Difference (continue) • The OSI model supports both connectionless and connection-oriented communication in the network layer, but only connection- oriented communication in the transport layer. • The TCP/IP model has only one mode in the network layer (connectionless) but supports both modes in the transport layer, giving the user choice.
- 25. Difference (continue) • OSI emphasis on providing a reliable data transfer service, Each layer of the OSI model detects and handles errors, all data transmitted includes checksums. The transport layer checks source- destination reliability. • TCP/IP treats reliability as an end to end Problem. The transport layer handles all error detection and recovery, it was checksums, acknowledgments, and timeouts to control transmissions and provides end-to-
- 26. Difference (continue) • Host on OSI implementations do not handle network operations. • TCP/IP hosts participate in most network protocols.