ECE155ALecture8

ECE155ALecture8 - 1 Computer Networks Lecture 8 Professor...

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Unformatted text preview: 1 Computer Networks Lecture 8 Professor Louise E. Moser Winter 2010 2 Medium Access Control Sublayer IEEE 802 standards 802.3 Wired LAN - Ethernet 802.2 Logical link control where 802.3 and 802.11 converge 802.11 Wireless LAN (Wi-Fi) 802.15.1 Wireless PAN - Bluetooth 802.15.4 Wireless PAN - ZigBee 2 Medium Access Control Sublayer IEEE 802 standards 802.3 Wired LAN - Ethernet 802.2 Logical link control where 802.3 and 802.11 converge 802.11 Wireless LAN (Wi-Fi) 802.15.1 Wireless PAN - Bluetooth 802.15.4 Wireless PAN - ZigBee 802.16 Broadband Wireless (WiMAX) 3 802.3 Wired LAN - Ethernet Ethernet Cabling Manchester Encoding Ethernet MAC Sublayer Protocol Binary Exponential Backoff Algorithm Ethernet Performance Fast Ethernet Gigabit Ethernet Retrospective on Ethernet 4 Ethernet Cabling Three kinds of Ethernet cabling (a) 10Base5 (b) 10Base2 (c) 10Base-T & 100Base-T 5 Ethernet Devices Transceiver Handles carrier detection and collision detection When collision detected, puts special invalid signal on cable so other transceivers also know collision occurred Repeater Connects cables and receives, amplifies, retransmits signals in both directions 6 Manchester Encoding Binary encoding Hard to distinguish 0 bit (0-volt) from idle (0-volt) Requires that clocks of all stations are synchronized Manchester encoding what Ethernet uses Differential Manchester encoding 7 Ethernet MAC Sublayer Protocol Uses 1-persistent CSMA/CD Frame formats: (a) DIX (DEC, Intel, Xerox) Ethernet (b) IEEE 802.3 Preamble Allows receivers clock to synchronize with senders clock SoF Start of Frame Destination address Highest order bit 0 individual, 1 multicast, all 1s broadcast Type Tells receiver what to do with frame, which process to give it to Pad Used to produce valid frame >= 64 bytes Checksum 32-bit hash code of data, CRC 8 Ethernet MAC Sublayer Protocol Why impose a minimum frame length? To prevent a station from completing the transmission of a short frame before the first bit reaches the far end of the cable where it collides with another frame and, thus, to ensure that the sender can detect the collision All frames must take more than 2 to send so that the transmission is still taking place when the noise burst returns to the sender 9 Binary Exponential Backoff Time divided into slots Length of slot = 2 = worst-case round-trip propagation time Binary exponential backoff After 1st collision, station picks 0 or 1 at random, waits that number of slots and tries again After 2nd collision, station picks 0,1,2,3 at random, waits that number of slots and tries again...
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This note was uploaded on 05/20/2010 for the course ECE 155a taught by Professor Louisee.moser during the Winter '09 term at UCSB.

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ECE155ALecture8 - 1 Computer Networks Lecture 8 Professor...

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