01-Internet - Computer Networks with Internet Technology...

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Computer Networks with Internet Technology William Stallings Chapter 01 Data Networks and The Internet
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Data Networks Communication by transmitting data  intermediate switching nodes Switching nodes not concerned with content  End devices referred to as stations Computers, terminals, telephones, etc.  Nodes connected in some topology by  transmission links Station attaches to node Collection of nodes is a communications  network
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Figure 1.1 Simple Switching Network
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Circuit Switching Dedicated path between two stations Connected sequence of links between nodes E.g telephone network Communication involves three phases Circuit establishment Data transfer Circuit disconnect
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Circuit Establishment Station A to node 4 requesting connection to station E Circuit from A to 4 usually dedicated line Node 4 finds next leg to node 6 Based on routing information, availability, cost, node 4  selects circuit to node 5 Allocates a free channel TDM [time-division multiplexing] FDM [frequency-division multiplexing] Node 4 requests connection to E And so on
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Data Transfer Data may be digital (e.g., terminal to host) or  analog (e.g., voice) Signaling and transmission may each be digital  or analog Path is A-4 circuit, internal switching through 4,  4-5 channel, internal switching through 5, 5-6  channel, internal switching through 6, 6-E circuit Generally, full duplex (data in both directions)
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Circuit Disconnect Connection terminated Usually by one of the stations Signals to 4, 5, and 6 to de-allocate resources
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Circuit Switching - Notes Connection established before data transmission begins Channel capacity must be available and reserved.  Nodes must have capacity to handle connection Switches must have intelligence to make allocations and  devise route Can be inefficient Capacity dedicated for duration of connection Even if no data are being transferred For voice, utilization high, but still doesn’t approach 100% For terminal connection, may be idle most of the time Delay prior to data transfer for call establishment Once circuit established, network transparent to users Data transmitted at fixed rate  No delay other than propagation Delay at node negligible
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Packet Switching 1970 Evolved substantially since Basic technology fundamentally the same today One of few effective technologies for long-distance data  communications Frame relay and ATM (see later) variations Carries directly to Internet Advantages: flexibility, resource sharing, robustness,  responsiveness Cost: elaborate algorithms to cope with time delay and  overhead penalties of network operation
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This note was uploaded on 04/27/2010 for the course BAMU BSC taught by Professor Kmm during the Spring '10 term at University of New York in Prague.

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01-Internet - Computer Networks with Internet Technology...

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