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UMD CMSC 132 - The Internet

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The InternetNetworking BackgroundNetworking ConceptsInternet Protocol (IP) AddressInternet (IP) AddressSlide 6PortsWays to communicateUDP is unreliableTCP is reliableWikipedia: Internet SocketsUser/Unreliable Datagram ProtocolTransmission Control ProtocolUDP / TCPUniform Resource Locators (URLs)Slide 16Protocols – Email DeliveryProtocol - HTTP GETNAT boxesMore terms and acronymsThe InternetNelson Padua-PerezWilliam PughDepartment of Computer ScienceUniversity of Maryland, College ParkNetworking BackgroundDefinitionSet of computers using common protocols to communicate over connecting mediaHistory1969 ARPANET1986 NSFnet1995 InternetNetworking ConceptsInternet addressesIPv4 vs IPv6PortsTCP vs. UDPReliabilityConnection vs. packet orientedSocketsURLsNAT boxesFirewallsInternet Protocol (IP) AddressUnique address for machine on internetGet from ISP when connecting to internetAllows network to find your machine32-bit unsigned integer  128.8.128.8Domain name service maps name to ip addressName and address for local machine localhost127.0.0.1Internet (IP) AddressDomain Name System (DNS)DNS servers on internet Can look up IP address associated with name DNS server may need to query other DNS serversedu DNS server queries umd.edu server to find cs.umd.eduMachine can have multiple IP addressesVirtual machinesInternet (IP) AddressProblemRunning out of 32-bit IP addressesExacerbated by initial address allocationStanford & MIT given more IP addresses than ChinaSwitching to 128-bit IP addresses in IPv61+ million addresses per square meter on EarthPortsAbstraction to identify (refine) destinationProvide multiple communications channels/services at single IP addressthink port # = extension #FormatUnsigned 16-bit integer (0 to 65,535)Ports 0 to 1023 are privileged portsMany ports pre-assigned to important services21 ftp (file transfer)23 telnet (remote terminal)25 SMTP (email)80 http (web)…Ways to communicateTCPtwo-way streaming connection between two machinesUDPsend of one packet of information from one machine to anotherUDP multicastsend of one packet of information from one machine to all machines on the local area networkUDP is unreliableUDP is build on top of the basic internet protocolSend a packet, hope it gets thereNo notification if it gets thereNo notification if it gets droppedPackets can arrive late or out of orderIntermediate routers wil l drop packets if the network is congested.TCP is reliableTCP is a reliable system built out of unreliable partsTwo way stream of bytesUses sequence numbers and acknowledgements and retransmissions to ensure that the packets do arrive and arrive in orderyou might have a failure, but you will be told that there was a communication failureWikipedia: Internet SocketsAsocket is a software abstraction, designed to provide a standard application programming interface (API) for sending and receiving data across a computer network. Sockets are designed to accommodate virtually any networking protocol, though in practice are used mostly for the internet suite of protocols (i.e. TCP/IP.) Sockets are implemented in many different computer languages and for most operating systems. In RFC documents relating to TCP or UDP, a socket on a certain host is defined as the combination of an IP address, a protocol, and a port number.The BSD operating system introduced network sockets in 1983.User/Unreliable Datagram ProtocolJust name the ip address and port you want to ship the data toProvide the datatypically < 512 bytes, but can be up to 65KbytesUDP packet contains a sending ip address and portcan be used to indicate where responses should be sentcan be spoofedTransmission Control ProtocolServer listens on a particular portonly one process can listen for TCP connections on each portClient says: Please connect to port 80 on www.cnn.coma whole bunch of packets get exchanged to establish a communication channeltemporary port numbers are generated on both ends and used for this communication channelAfter setup completes, server continues to listen for new requests to establish communication channelwhen channel no longer needed, closed and ports recycled.UDP / TCPUDP is lower overheadmuch more efficient for small msgsIs late data useful?many VOIP systems use UDP, missing packets are compensated fornoise/silenceUniform Resource Locators (URLs)Represent web resourcesWeb pagesArbitrary files…Exampleshttp://www.cs.umd.edu/index.htmlftp://www.cs.umd.edu/pub/doc/csd_policies.pdfhttps://login.yahoo.com/file://dir/my.txtUniform Resource Locators (URLs)Consists ofProtocolhttpftphttps (secure http)file…IP address (or domain name)Port (optional)http://www.cs.umd.edu:80/protocol specific informationProtocols – Email DeliveryProtocol - HTTP GET•Client connects to server on port 80GET /~pugh/index.html HTTP/1.0blank line•Server responses with HTTP headersHTTP/1.1 200 OKDate: Mon, 20 Feb 2006 03:47:44 GMTServer: ApacheLast-Modified: Wed, 15 Feb 2006 01:17:09 GMTETag: "9b2b1c-948-1222af40"Accept-Ranges: bytesContent-Length: 2376Connection: closeContent-Type: text/html; charset=ISO-8859-1•Followed by blank line, then contents of responseNAT boxesNetwork address translationUsed, for example, in your house, allows several different computers to all have their own internal IP address, and the NAT box mergers and manages these so that they appear to be one IP address on the Internetthe one assigned to you by your ISPComputers on the other side of the NAT box generally can’t initiate communication with youfor bad and goodMore terms and acronymsFirewallsystem that allows only certain communications to pass through part of a networkDHCPdynamic assignment of IP


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UMD CMSC 132 - The Internet

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Notes

Notes

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Recursion

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HTML

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Trees

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Lecture 1

Lecture 1

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Quiz #3

Quiz #3

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Hashing

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