TAILIEUCHUNG - Lecture Digital communication systems - Lecture 18

The learning objectives for this chapter include: recognize the global leaders in newspapers, radio, and television; distinguish among the four main theories of government-press relationships; categorize media systems by ownership patterns and degree of government control; understand how politics, culture, geography, history, and economics affect a country's media system. | 11 14 12 Shared Media Networks Fall 2012 Lecture 18 Shared medium Media access MAC protocol Time division multiplexing Contention protocols Aloha Individual images source unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information see http fairuse. Fall 2012 Lecture 18 Slide 1 Fall 2012 Lecture 18 Slide 2 Shared Communications Channels Shared channel . wireless or cable packet queues channel interface Basic idea in its simplest form avoid collisions between transmitters - collision occurs if transmissions are concurrent Wanted a communications protocol rules of engagement that ensures good performance Nodes may all hear each other perfectly or not at all or partially Fall 2012 Lecture 18 Slide 3 Good Performance What are the Metrics High utilization - Channel capacity is a limited resource use it efficiently - Ideal use 100 of channel capacity in transmitting packets - Waste idle periods collisions protocol overhead Fairness - Divide capacity equally among requesters - But not every node is requesting all the time. Bounded wait - An upper bound on the wait before successful transmission - Important for isochronous communications . voice video Dynamism and scalability - Accommodate changing number of nodes ideally without changing implementation of any given node Not all protocols do well on all these metrics Fall 2012 Lecture 18 Slide 4 1 11 14 12 Utilization Fairness Utilization measures the throughput of a channel Many plausible definitions. A standard recipe - Measure throughput of nodes Xi over a given time interval U _ total throughput over all nodes Ch maximum data rate of channel - Say that a distribution with lower standard deviation is fairer than a distribution with higher standard deviation. - Given number of nodes N fairness F is defined as Example 10 Mbps channel four nodes get throughputs of 1 2 2 and 3 Mbps. So utilization is 1 2 2 3 10 . 0 U 1. .

• Kĩ thuật Viễn thông
• Communication systems
• Digital communication systems
• Digital communication
• Multiuser communication
• Multicarrier system
• Adaptive equalization
• Filter channel
• communication systems research
• communication applications
• electronic media
• communication solutions
• systems management