OSI and TCP/IP Layering Models

1. OSI and TCP/IP Layering Models Presentation slides for the course CSE 323 – Computer Networks by Mohammad Mamun Elahi Assistant Professor Department of Computer Science and Engineering United International University mmelahi@uiu.ac.bd

2. services layer N layer N-1 layer N layer N-1 PDUs (protocol data unit) actual data flow on the lowest level The OSI Reference Model (contd.) In the late 1970s, to promote the compatibility of network designs, the International Organization for Standardization (ISO) proposed an architecture model called the open systems interconnection references model (OSI model). Layering Reference Models

3. The OSI Reference Model (contd.) Layering Reference Models

4. The OSI Reference Model (contd.) 7 application application network services (email, file transfer) 6 presentation formatting, encryption, and compression 5 session setup and management of end-to-end conversation transport end-to-end delivery of messages 4 3 network end-to-end transmission of packets data link transmission of packets on one given link 2 1 physical transmission of bits Layering Reference Models

5. The OSI Reference Model (contd.) Encapsulation data H: header T: trail Each may be empty. data AH 7 application application data AH PH 6 presentation data AH PH 5 session SH data AH TH PH transport SH 4 data AH TH PH NH 3 network SH data AH DT TH PH DH NH data link SH 2 1 physical bit streams Layering Reference Models

6. The TCP/IP Reference Model (Transmission Control Protocol/Internet Protocol) The TCP/IP Reference Model Layering Reference Models

7. The TCP/IP Reference Model (contd.) Layering Reference Models

8. Application Layer Layering Reference Models

9. Process A Process B Transport Layer • Five basic services • Segmenting upper-layer application data • Establishing end-to-end operations • Sending segments from one end host to another end host • Ensuring data reliability • Providing flow control Layering Reference Models

10. Internet Layer • The purpose of the Internet layer is to select the best path through the network for packets to travel. • IP performs the following operations: • Defines a packet and an addressing scheme • Transfers data between the Internet layer and network access layers • Routes packets to remote hosts Layering Reference Models

11. Network Access • The network access layer is also called the host-to-network layer. • Concerned with all of the issues that an IP packet requires to actually make a physical link to the network media. • Network access layer functions include mapping IP addresses to physical hardware addresses and encapsulation of IP packets into frames. Layering Reference Models

12. Comparison: OSI and TCP/IP Model • Similarities of the OSI and TCP/IP models: • Both have layers • Both have application layers, though they include different services • Both have comparable transport and network layers • Packet-switched, not circuit-switched, technology is assumed • Networking professionals need to know both models • Differences of the OSI and TCP/IP models: • TCP/IP combines the presentation and session layer into its application layer • TCP/IP combines the OSI data link and physical layers into 1 layer • TCP/IP appears simpler because it has fewer layers • TCP/IP transport layer using UDP does not always guarantee reliable delivery of packets as transport layer in the OSI model does Layering Reference Models

13. Comparison: OSI and TCP/IP Model (contd.) Layering Reference Models

14. Questions???? Layering Reference Models