16-HighSpeedLANs

16-HighSpeedLANs - William Stallings Data and Computer...

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Unformatted text preview: William Stallings Data and Computer Communications 8 th Edition Chapter 16 High Speed LANs Introduction Range of new technologies Fast and Gigabit Ethernet 100 Mbps up to 10Gbps for Gbps switched techniques are used Fibre Channel 100 Mbps up to 3.2 Gbps High Speed Wireless LANs 1 Mbps to 54 Mbps Why High Speed LANs? Office LANs used to provide basic connectivity Connecting PCs and terminals to mainframes and midrange systems that ran corporate applications Providing workgroup connectivity at departmental level Traffic patterns light Emphasis on file transfer and electronic mail Speed and power of PCs has risen Graphics-intensive applications and GUIs MIS organizations recognize LANs as essential Began with client/server computing Now dominant architecture in business environment Intranetworks Frequent transfer of large volumes of data Applications Requiring High Speed LANs Centralized server farms User needs to draw huge amounts of data from multiple centralized servers E.g. Color publishing Servers contain tens of gigabytes of image data Downloaded to imaging workstations Power workgroups Small number of cooperating users Draw massive data files across network E.g. Software development group testing new software version or computer-aided design (CAD) running simulations High-speed local backbone Processing demand grows LANs proliferate at site High-speed interconnection is necessary Ethernet (CSMA/CD) Carriers Sense Multiple Access with Collision Detection IEEE 802.3 IEEE802.3 Medium Access Control Random Access Stations access medium randomly Contention Stations contend for time on medium What were the precursors for CSMA/CD? ALOHA Packet Radio When station has frame, it sends Station listens (for max round trip time)plus small increment If ACK, fine. If not, retransmit If no ACK after repeated transmissions, give up Frame check sequence (as in HDLC) If frame OK and address matches receiver, send ACK Frame may be damaged by noise or by another station transmitting at the same time (collision) Any overlap of frames causes collision Max utilization 18% Slotted ALOHA Time in uniform slots equal to frame transmission time Need central clock (or other sync mechanism) Transmission begins at slot boundary Frames either miss or overlap totally Max utilization 37% CSMA Propagation time is much less than transmission time All stations know that a transmission has started almost immediately First listen for clear medium (carrier sense)...
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This note was uploaded on 02/10/2012 for the course CSC 411 taught by Professor Simmons during the Spring '08 term at S. Alabama.

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16-HighSpeedLANs - William Stallings Data and Computer...

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