1 Introduction to Transmission Data Sirak Kaewjamnong

2 An Introduction to the Mail System SomchaiSomsee PSU KU Post Office ์

3 Characteristics of the Mail System Each envelop is individually routed. No time guarantee for delivery. No guarantee of delivery in sequence. No guarantee of delivery : –lost –How can we acknowledge delivery?

4 Characteristics of the Mail System (Cont.) –Retransmission How to determine when to retransmit? –Timeout ? Need local copies of contents of each envelope. How long to keep each copy. What if an acknowledgement get lost?

5 An Introduction to the Mail System SomchaiSomsee PSU KU Post Office Application Layer Transport Layer Network Layer Link Layer

6 An Introduction to the Internet ksirakpu ratree.psu.ac.th prg.cpe.ku.ac.th Network Layer Link Layer Application Layer Transport Layer O.S. HD HD HD HDHD HD HeaderDataHeaderData

7 Characteristics of the Internet Each Packet is individually routed. No time guarantee for delivery. No guarantee of delivery : –Thing get lost –Acknowledgements

8 Characteristics of the Internet (Cont.) –Retransmission How to determine when to retransmit? –Timeout? Need local copies of contents of each packet. How long to keep each copy? What if an acknowledgement get lost?

9 Characteristics of the Internet (Cont.) No guarantee of integrity of data. Packets can be fragmented. Packets may be duplicated.

10 Layering in the Internet Transport Layer provides reliable, in sequence delivery of data from end-to- end on behalf of application Network Layer (Internet Layer) provides “best effort”, but unreliable, delivery of datagram Link layer (Host to Network Layer) Carries data over point to point links between hosts and router, or between router to router