LAN - Yong Liu 1 Outline Last week framing error detection...

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Unformatted text preview: Yong Liu 03/01/2011 1 Outline Last week framing error detection: parity, CRC flow control: stop-and-wait, sliding window error control: stop-and-wait, go-back-N, selective repeat this week shared broadcast medium multiple access control Ethernet 2 Multiple Access Links and Protocols 3 Two types of “links”: point-to-point PPP for dial-up access point-to-point link between Ethernet switch and host broadcast (shared wire or medium) each station is attached to a transmitter/receiver which communicates over a medium shared by other stations transmission from any station is received by all other stations old-fashioned Ethernet/802.11 wireless LAN/Satellite shared wire (e.g., cabled Ethernet) shared RF (e.g., 802.11 WiFi) shared RF (satellite) humans at a cocktail party (shared air, acoustical) Multiple Access protocols single shared broadcast channel two or more simultaneous transmissions by nodes: interference collision if node receives two or more signals at the same time multiple access protocol distributed algorithm that determines how nodes share channel, i.e., determines when node can transmit communication about channel sharing must use channel itself! no out-of-band channel for coordination 4 LAN Topology Bus Tree Ring Star 5 Bus and Tree Multipoint medium Transmission propagates throughout medium Heard by all stations Need to identify target station • Each station has unique address Need to regulate transmission To avoid collisions To avoid hogging • Data in small blocks - frames Terminator absorbs frames at end of medium 6 Ring Topology Repeaters joined by point to point links in closed loop Receive data on one link and retransmit on another Directed links Stations attached to repeaters Data in frames Circulate past all stations Destination recognizes address and copies frame Frame circulates back to source where it is removed Media access control determines when station can insert frame 7 Star Topology All stations connected directly to a central node Usually via two point-to-point links Central node can broadcast Physical star, logical bus Only one station can transmit at a time Central node can act as frame switch 8 IEEE 802 Architecture The IEEE 802 Architecture is a family of standards for LANs and MANs (metropolitan area networks) 9 LAN Protocol Architecture Physical Layer Encoding/decoding Preamble generation/removal Bit transmission/reception Transmission medium and topology Logical Link Control Interface to higher levels Flow and error control Medium Access Control Assembly of data into frame with address and error detection fields Disassembly of frame • Address recognition • Error detection Govern access to transmission medium • Not found in traditional layer 2 data link control...
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LAN - Yong Liu 1 Outline Last week framing error detection...

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