Communication NetworksReview of TCP/IPNetworksSlide 4Slide 5HistoryKey IdeasPacket SwitchingEnd-to-End Error and Flow ControlInternetworkingMultiple AccessDNS: Domain Name ServiceP2P: Peer-to-peerVoIP: Voice over IPProtocols:Slide 16IP: Internet ProtocolTCP: Transmission Control ProtocolTCP Service:Congestion Control:TCP Algorithm: AIMDTCP: SummaryFlow ControlTCP Phases:UDP: User Datagram ProtocolFTP: File Transfer ProtocolHTTPARP: Address Resolution ProtocolTechnologyCommunication LinksSlide 31Telephone Switch RouterSwitchesCommunication NetworksA Second CourseJean WalrandDepartment of EECSUniversity of California at BerkeleyReview of TCP/IP•Networks•History•Key Ideas•Protocols•TechnologyNetworksWANMANNetworksWANMANLANWANLANNetworksHistory•1962 – L. Kleinrock proposes Packet Switching•1966 – L. Roberts proposes architecture to Darpa•1969 – First demonstration of packet switching: 4-node Arpanet•1969 – S. Croker introduces RFCs (managed by J. Postel) •1972 – R. Kahn proposes an open architecture: Inter-networking with stateless routers, best effort, no control plane•1973 – Kahn and V. Cerf propose early ideas of IP (32-bit address) and TCP (end-to-end ACKs with a window scheme)•1973 – R. Metcalfe invents Ethernet•1982 – IGP and EGP•Late 1970s, early 1980s – Berkeley develops BSD, a modified implementation of UNIX that includes TCP/IP•1983 – Arpanet switches to TCP/IP•1983 – P. Mockapetris invents DNS•1988 – Van Jacobson fixes TCP•1985 – 1995 – Internet supported by NSF and other agencies•1993? – T. Berners-Lee invents WWW•1995 – Internet is privatized•2000… - WiFi,VoIP, P2PSee http://www.isoc.org/internet/history/brief.shtmlKey Ideas•Packet Switching•End-to-End error and flow control•Internetworking•Multiple Access•DNS•P2P•VoIPPacket SwitchingABA | B | ….CA | B | ….A | B | ….A | C | ….A | C | ….A | C | ….End-to-End Error and Flow ControlABA | B | n | … | ECA | B | m | … | ECB | A| k | m | … | ECACKs all packets from A up to packet mError control fieldA can have up to N packets for B that have not been acknowledgedSelecting N adjusts the rate of transmissions: limit congestionIf ACK is late, A retransmits packetsInternetworking•Goal: Connect different networks1.1a1.2b1.0c2.0d2.1e2.2fa c|1.1 2.2 | Xd f |1.1 2.2 | Xa b|1.1 1.2 | YROUTERRouter looks at IP addresses (1.1, …)Each network uses local addresses (e.g., a, b, c, …)Multiple Access•Goal: Share one medium (e.g., WiFi)ABCtimeA | B |C | A |“Collision”Wait random time after collisionC | A |“Busy”A | B |Wait until idleDNS: Domain Name Service•Translate Name into IP address(e.g., google.com into 216.239.57.99)•Directory of DNS is distributed:.com, .edu, ….edu: berkeley.edu, stanford.edu, …•Mapping can depend on source address•Mapping can be done to multiple addressesP2P: Peer-to-peer•Goal: All peers become servers•Example: •Each peer knows the addresses of a set of peers: his “friends”•To find a file, peer A asks his friends who in turn ask their friends, and so on, until someone, B, says he has the file… (can limit search); A then asks B for the file.•Many variations are possible. The key idea is that there is no specialized server; every client becomes a server.VoIP: Voice over IP•Goal: Place phone calls over Internet(Should be cheaper because the Internet infrastructure is much lighter than that of the phone network.)•Steps: • Gateway converts phone signal into IP packets and vice-versa•Protocol to convert phone number into gateway IP address•Gateway converts usual control signals (dial tone, ringing, busy, …) into IP packets and vice-versaProtocols:•IP: Internet Protocol•TCP: Transmission Control Protocol•UDP: User Datagram Protocol•HTTP: Hypertext Transfer Protocol•FTP: File Transfer Protocol•ARP: Address Resolution ProtocolTCP UDPIPHTTP FTPProtocols:Fiber, Wires, WLEth.HTTP, FTP, …IPUDP - TCPPhysicalInterfacePhysicalInterfaceSynchronous unreliable bit pipeData LinkControlData LinkControlAsynchronous reliable bit pipePhysical LinkNetworkNetworkAsynchronous routed pathFH DataPhysicalInterfaceSynchronous unreliable bit pipeData LinkControlAsynchronous reliable bit pipePhysical LinkNetworkAsynchronous routed pathFH DataTransport TransportPH Data PH DataTH DataEnd Node Router End NodeApplication ApplicationDataIP: Internet Protocol•Delivers packets between any two hosts•Organizes address, manages routing tables•Addresses: 32 bits, arranged so that prefix determines next router toward destination•Routing algorithm: Essentially shortest path. Done in two levels: nodes are grouped; shortest path inside each group and across groups.•Tables updated periodically to adjust to changesTCP: Transmission Control Protocol•Implements reliable delivery of byte stream between hosts•Multiplexes multiple connections to and from a host: adds a “port” number•End-to-end retransmissions•Regulates flow to avoid congesting•Destination (flow control)•Routers (congestion control)•Method: ACKs, control number of unacknowledged packetsTCP Service:IPTransportA B C[A | B | p1 | p2 | …]p1 p2 p1 p2 p3 p1 p2portsApplicationHTTPDNSftpTCP: Byte Stream Ordered, reliable, well-pacedCongestion Control:• Flows share links:How to share the links bandwidth?TCP Algorithm: AIMDCxyA BxC D EyLimit rates:x = yTOC – Congestion Control - TCP Algorithm – AIMD •Try to be fairTCP: SummaryW164KBX0.5TO3DAX0.53DATOX0.5X0.5SS CASSCA33Flow Control•Objective: Avoid saturating destination•Algorithm: Receiver avertizes window RAWRAW window = min{RAW – OUT, W}where OUT = Oustanding = Last sent – last ACKed W = Cong. Window from AIMD + refinements[ACK | RAW | …]SYN kSYN n; ACK k+1DATA k+1; ACK n+1ACK k+n+1data exchangeFINFIN ACK½ closeFINFIN ACK½ closeTCP Phases:3-way handshakeUDP: User Datagram Protocol•Unreliable delivery of packets with error detection•Multiplexes multiple connections to and from a host: adds a “port” number•Adds error detection code for the packet•No retransmission, no flow controlFTP: File Transfer Protocol•Reliable delivery of file between hosts•Converts file into byte stream for TCPHTTP•Transfer of html files•Sets up TCP connections and FTP to transfer files•Closes connections after transferARP: Address Resolution Protocol•Discovers local address from IP address•Example: In
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