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 4519-1Computer Networking19-2Goal of a Network•Network: A collection connected entities–Refer to each entity in the network by the name “node” •generic name given to any device in a network.–The goal of a network is to allow nodes in the network to communicate in some way•thinking concretely:–nodes  computers–communication  transfer of bits–If computers are networked, we can communicate anything that can be represented in binary•Text, Images, Sound, Video, Programs, etc...–to facilitate such a network in abstract terms we need...19-3The Internet Hourglass Model•The physical layer is how machines are physically connected to each other . . .FTPHTTP NV TFTPTCP UDPIPToken RingWi-fi (802.11)EthernetInterNetworkTransportApplicationPhysical19-4Sending data on the physical layer•To send a packet to another computer on the LAN (local area network)–I set the source and destination of the frame accordingly (the destination is the MAC address of the computer I want to reach)–I send the frame out on the wire (I send the bits to my network interface card which will turn those bits into voltage pulses for me and send them on the wire)AEB CD•All other connected network interfaces on my local network “see” the frame go across the wire–Because they each know the protocol they will be able to tell one packet from another–Only the node with the same MAC address as the destination will accept the frame–Other network interfaces will ignore the frame, because it is not addressed to them19-5Communication Basics of Networks•Computers can be connected physically or via wireless connections–a physical connection. •Physically connect computers together.–Use of wires or optical cables.•Three most common physical links:–Twisted pair –Coaxial cable–Fiber-optic cable•Twisted pair–Two wires twisted together.•Makes them less susceptible interference:–unwound cable will act like an antenna and picking up radio frequency information or appliance noise.–Telephone company uses twisted-pair copper wires to link telephones.19-6Communication Basics of Networks•Coaxial cable–Also two wires: •One of the wires is woven of fine strands of copper forming a tube. •The wire mesh surrounds a solid copper wire that runs down the center. •Space between has a non-conducting material.•Makes them less susceptible to outside noise.•Cable companies use coax19-7Communication Basics of Networks•Fiber-optic cable–Light is fast.–Light can travel faster than power can travel along a wire–Can transmit more information down a single strand. •It can send a wider set of frequencies.–Each cable can send several thousand phone conversations or computer communications.–Fiber tends to have distance limitations19-8Communication Basics of Networks•Wireless connections–The link is made using electromagnetic energy that travels over the air instead of along wires or cables.–Three types of wireless communications commonly used in networking…•Infrared (IR)–Commonly used in TV and VCR remote controls.–Use infrared frequencies of electromagnetic radiation that behave much like visible light.–line of sight required.–Often used to connect keyboards, mice, PDAs, etc19-9Communication Basics of Networks•Radio frequency (RF)–Uses radio frequencies to transmit data•Function even though line of sight is interrupted.–Interference is a problem with these technologies…most use 2.4Ghz radio band (as Microwaves, Cordless Phones)–Used in Apple Airport/WiFi (802.11b), Airport Extreme (802.11g), and Bluetooth•Microwave–Often used to communicate with distant locations.–Must be line of sight.–Satellite communications use microwaves.19-10The Internet Hourglass Model•The physical layer is how machines are physically connected to each other . . .FTPHTTP NV TFTPTCP UDPIPToken RingWi-fi (802.11)EthernetInterNetworkTransportApplicationPhysical19-11The Internet is growing. . .•Seeds of Networking–1966: ARPA (Advanced Research Projects Agency) State Defense Department’s research organization. •Focused major development effort on computer networking.•ARPA’s Goal: To promote research in advanced future technologies by funding university and industry research proposals.•Result: Thousands of databases became available to the public.–1969 ARPAnet connects four universities – this will eventually grow into the Internet19-12Motivating the Inter-Network Layer•The physical layer does a lot, but it leaves a lot to be desired:–A mechanism to send packets off the LAN, to a computer on a different LAN•Can we just do the LAN thing (broadcast) across all computers?–would it make sense to broadcast every message to the entire Internet?–A new addressing convention that indicates something about hierarchy (even though we have no idea where physical machines are)•Some programs that allow discovering the addresses of computers you’d like to communicate with–Protocols that can be supported by any kind of computer, regardless of your LAN's protocol–Fundamentally, bridge different LANs.•IP: The Internet Protocol19-13The inter-network layer•The inter-network layer is what allows all machines on the Internet to communicate with each other–(Notice that many different protocols exist above/below IP, but they all converge to IP – this is how all computers can communicate over the Internet!)FTPHTTP NV TFTPTCP UDPIPToken RingWi-fi (802.11)EthernetInterNetworkTransportApplicationPhysical19-14Sending data across LANsLAN “1”LAN “2”cDcomputer connected to more than one LANA BCabcomputerscomputers19-15measuring speed•A given physical connection technology has a bandwidth: maximum bits per second on a link–Bandwidths are usually in bits per second (or Kbits per second, or Mbits per second), unless otherwise specified.–Think of it as “the maximum data rate you could possibly receive if you were the only person using the link”–In practice, you won’t see that maximum bandwidth at all times•Why? Other users.–The effective bandwidth is actually the bandwidth that you