Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 48Slide 49Slide 50Slide 51Slide 52Slide 53Slide 541Welcome to CS 334/5342“Fig 1.5” – An internet4 Ethernet LANs linked by a WANBHMNO ATLCHLNetwork of networks3Comer Figure 1.1 – Growth of the Internet4WORLD TOTALS► Population 2010: 6,845,609,960►Internet Users Dec 31 2000: 360,985,492►Internet Users June 30 2010: 1,966,514,816 (+444.8 %)►Penetration of population: 28.7 %August 2010: “ Sometime this month, the 5 billionth device will plug into the Internet”“Today, there are over 1 billion computers that regularly connect to the Internet.”“But cellular devices, such as Internet-connected smartphones, have outstripped that total and are growing at a much faster rate.”52.2 Two Approaches to Network Communication* circuit-switched networks (telephone)3 phases:establish connection between end pointsuse connection relinquish connectiondisadvantage: cost independent of use * packet-switched networks (post office)at source, data divided into packetspackets individually sent from source to destinationdata reassembled at destinationadvantage: can share transport facilities disadvantage: traffic spike may overload62.4 Ethernet TechnologyComer Figure 2.1 Ethernet using twisted pair wiring (with HUB)782.4.5 Properties of an EthernetEthernet was “designed to be”i.e. “classical” or “original” Ethernet■ shared bus ■ broadcast technology■ best-effort delivery■ distributed access control- shared bandwidth- only one station transmitting at a time- “half duplex” (station transmits XOR receives)- all stations receive all messages- CSMA/CD- Like Post Office92.4.8 Ethernet Hardware AddressesDestination address as filterAn Ethernet station receiving packet checks destination addressignores packet if not intended for this station6 bytes total - globally uniqueHigh-Order 3 bytes: assigned to manufacturer by IEEELow-Order 3 bytes: serial number assigned bymanufacturer10Ethernet Addresses – continuedTypes of Destination addressAn address can be used to specify■ a single, specific station on this network (“unicast address”)■ all stations on this network(“broadcast address”)■ a subset of stations on this network(“multicast address”)Interface Modes of Operation■ normal modeInterface processes only packets with destination * its own unicast address * the network broadcast address■ promiscuous modeInterface process all received packets (including those addressed to other stations)1112Figure 2.1 (with hub)Figure 2.2 Format of an Ethernet frame (packet)1314► Bridge is “store and Forward” device, operating at frame level►2 interfaces operting in promiscous mode, frame buffer for each interface►receives frame, checks for validity before forwarding – no “runts”15►” An (almost) arbitrary number of Ethernets can be connected together with bridges”►”A set of bridged segments acts like a single Ethernet” (“transparent”)► “Most bridges . . . Make intelligent decisions about which frames to forward” -- No “runts”► Special case when bridge first powered up -- “flooding”16switch17► No waiting to transmit► not CSMA/CD► If we upgrade switch with fast backplane, we can have multiple transmissions at same time► Special case – station can be transmitting and receiving at same time - Full Duplex182.4.5 Properties of an EthernetEthernet was “designed to be”i.e. “classical” or “original” Ethernet■ shared bus- shared bandwidth- only one station transmitting at a time- “half duplex” (station transmits XOR receives) ■ broadcast technology- all stations receive all messages■ best-effort delivery■ distributed access control- CSMA/CD19■ not shared bus - point-to-point connections - not shared bandwidth - “full duplex” (station can be transmitting and receiving)■ not broadcast technology - stations receive only their own messages■ best-effort delivery■ no access control needed - private frame buffer - no entrance collisions - not CSMA/CD - exit port collisionProperties of a “switched” EthernetMost new wired Ethernet installations are switched20IEEE 802.11 standards for wireless LANsSpeed Range Radio Frequency802.11b 11 Mbits/sec 100 meters 2.4 GHz802.11a 54 Mbits/sec 80 meters 5 Ghz802.11g 54 Mbits/sec 150 meters 2.4 GHz802.11n 248Mbits/sec70 meters 2.4 and 5 GHzWe have 802.11g in the labReturn to section 2.4.7 Wireless Networks and Ethernet21Figure 1Figure 2(Independent) Basic Service Set(ad-hoc network)Extended Service Set(infrastructure network)New components: Distribution System each BSS has an Access Point22Figure 3 – Hidden Station Problem23Figure 4 – CSMA/Collision Avoidance24Independent Basic Service Set (IBSS)Station Service (SS) must be provided by all stations:(a) Authentication(b) Deauthentication(c) Privacy(d) Data Unit DeliveryExtended Service Set (ESS)Additional services that must be provided by the access point/distribution system:(a) Association(c) Disassociation(b) Distribution(d) Reassociation25Figure 5AP acts like a bridge26Figure 627Network, BSS, and Station IdentificationIn the Network Lab:BSSID is 00:06:25:49:B3:B2(MAC address of Access Point)Each station identification is its MAC addressESSID is netlab_w28Figure 6 - 802.11 frame formatWired Ethernet Frame FormatWired: All frames are data framesWireless: Management, Control, and Data frames29Usage of Address Fields in 802.11Address 1 identifies the immediate receiver(the unit that will process the frame)Address 2 identifies the transmitter(the unit that transmits the frame and will receive the acknowledgment)Usage of other addresses is situation-dependent.30Example 1 – IBSSFor frames traveling within an IBSS:Address 1 is the destination addressAddress 2 is the source addressAddress 3 is the BSSID(used as a filter, since IBSSs may overlap)Another IBSS!3132Client requestAddr 1 - immediate destination - APAddr 2 – client addressAddr 3 – ultimate destination (DA) Example 2 – ESS with 802.3 (wired) DS,