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Computer Science 335 Objectives and Main Areas of Coverage Communication is fundamentally complicated. transmitter MEDIUM I told you before! I didn’t understand. receiver Consider the Problems of Human Communication Computers Have Many of the Same Problems! • Receiver is unable to understand the message • Transmitter speaks when receiver not ready • Receiver doesn’t understand the message – not the type of message expected – not the right language – speaks too fast/slow • etc. Principles Apply At Many Levels On a computer motherboard Video Card CPU Memory (Main Bus) Sound Card Between Devices on a computer Between computers on a network Between Computers on Different Networks Distinguishing Problems 1. Direct Communication •Person to Person •Computer to Computer (serial cable) 2. Network Communication •Two Machines Interconnected with others 3. InterNetwork Communication •Networks Connected What are the problems to address? 1. 2. 3. 4. 5. 6. 7. Is the other computer ready? How does it know I’m sending data? How does it know the begin/end of my message? What if an error occurs? How does the other computer know? What if I send too fast? How do I know when the other computer recovers? NONE ARE NETWORKING PROBLEMS A B C How Does it Know Which One? A Network Concern! A B D C E F How Do We Know If It Is On THIS Network? An INTERNetworking Problem! Basic Principles • • • • • • • Synchronization (beginning and ending) Timing (rates of transmission / flow control) Encoding Error detection and correction Identification Routing Efficiency Principles Repeat • Many issues occur in a number of places • Understanding it once can be leveraged into the understanding of numerous features • Keep these issues at the forefront of learning • Many of your experiences will be similar but the wrong one. Be careful. Ask questions. • OSI model is not only a tool for design but a tool for organizing understanding What is the OSI model? • A framework for design presented by International Standards Organization (ISO) • A classical study of layered design • A framework for LEARNING how the process of computer communication works • Ultimate objective is to let any two PROGRAMS on any two COMPUTERS in the world talk to one another.