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Networking

Networking Basic network components and layered architecture Internet and WWW basics IP, TCP, URL, HTTP Jean Walrand, Communication Networks, a first course, McGraw-Hill 1998 (2 nd edition). Types of computer networks: Point-to-point connection (link) between two computers

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Networking

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  1. Networking • Basic network components and layered architecture • Internet and WWW basics • IP, TCP, URL, HTTP Jean Walrand, Communication Networks, a first course, McGraw-Hill 1998 (2nd edition). ECMM 6000, Fall 2004

  2. Types of computer networks: • Point-to-point connection (link) between two computers • Store-and-forward transmission: packets • Datagram packet switching: destination address in packet • also, LAN, WAN, ATM (virtual circuit switching), wireless e.g. PPP, SLIP A B C e.g. token ring ECMM 6000, Fall 2004

  3. multiple access networks (e.g. ALOHA, Ethernet) ECMM 6000, Fall 2004

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  8. Review of components • Hosts • Considered a “node” or “end point” in the network (client/server/printer) • Processes all levels of the protocol stack • Hubs • acts as an “extender” - similar in effect to taking all incoming lines and twisting the wires together • Does not do any processing - acts only at the physical layer • Bridges • attaches two physically identical LANs together, physical layer processing • forwards only traffic which is destined for “the other side” • Switches • depending on level of switch complexity, anywhere from a hub to a router • Routers • Processing at the Network layer • Route packets between networks with potentially different lower level protocol stacks (i.e., different physical and data link layers) • Gateways • Processes all levels of the protocol stack • Used to connect networks with different protocol stacks ECMM 6000, Fall 2004

  9. Layered communication model Message received Message sent Layer n Layer 2 Layer 1 Communication Sender Recipient medium Coulouris, Dollimore, Kindberg, Distributed Systems, Addison Wesley 2001 (3rd ed) ECMM 6000, Fall 2004

  10. ISO-OSI layer model Open systems interconnection reference model A B communication services communication services, e.g. file transfer, email, … 7. 7. Application local syntax, secure, efficient connections e.g. compression, security, format conversion 6. 6. Presentation connections 5. 5. supervises connections between end systems Session delivery of messages 4. 4. supervises end-to-end transmission Transport 3. 3. guides the packet from source to destinations Network implements packet delivery service between two nodes on the same physical link 2. 2. Data Link 1. 1. Physical Implements digital communication link that delivers bits ECMM 6000, Fall 2004

  11. Layer Description Examples Application Protocols that are designed to meet the communication requirements of FTP HTTP, , SMTP, specific applications, often defining the interface to a service. CORBA IIOP Presentation Protocols at this level transmit data in a network representation that is Secure Sockets independent of the representations used in individual computers, which may ( SSL),CORBA Data differ. Encryption is also performed in this layer, if required. Rep. Session At this level reliability and adaptation are performed, such as detection of failures and automatic recovery. Transport This is the lowest level at which messages (rather than packets) are handled. TCP, UDP Messages are addressed to communication ports attached to processes, Protocols in this layer may be connection-oriented or connectionless. Network Transfers data packets between computers in a specific network. In a WAN IP, ATM virtual or an internetwork this involves the generation of a route passing through circuits routers. In a single LAN no routing is required. Data link Responsible for transmission of packets between nodes that are directly Ethernet MAC, connected by a physical link. In a WAN transmission is between pairs of ATM cell transfer, routers or between routers and hosts. In a LAN it is between any pair of hosts. PPP Physical The circuits and hardware that drive the network. It transmits sequences of Ethernet base- band binary data by analogue signalling, using amplitude or frequency modulation signalling, ISDN of electrical signals (on cable circuits), light signals (on fibre optic circuits) or other electromagnetic signals (on radio and microwave circuits). ECMM 6000, Fall 2004

  12. What is a protocol `A protocol is a set of rules governing message interchanges which occur between a number of computers in a distributed system; each of these messages implement functions of the system. A protocol is also used to establish a connection and allow entities to exchange data about themselves, for example the operating system they are using and the format of the data that they intend passing; this is known as a handshake. ‘ D. Ince ECMM 6000, Fall 2004

  13. ECMM 6000, Fall 2004

  14. Application message port TCP header TCP IP header Ethernet header IP Ethernet frame ECMM 6000, Fall 2004

  15. IP Header ECMM 6000, Fall 2004

  16. Around 4 billion IP addresses ECMM 6000, Fall 2004

  17. Transport layer protocols • TCP (Transmission Control Protocol): • connection-oriented • Reliable packet delivery in sequence • UDP (User Datagram Protocol): • connectionless (datagram) • Unreliable packet delivery • Packets may arrive out of sequence or duplicated • Less overhead • Simply adds port addressing to IP • Checksum is optional • Internet Control Message Protocol • Used by the nodes in the internet to implement IP ECMM 6000, Fall 2004

  18. TCP and UDP Header ECMM 6000, Fall 2004

  19. ECMM 6000, Fall 2004

  20. The Internet around 1990 Jean Walrand, Communication Networks, a first course, McGraw-Hill 1998 (2nd edition). The first three chapters give you a nice overview of the working of networks and the Internet. ECMM 6000, Fall 2004

  21. MCI backbone Retrieved from: http://global.mci.com/about/network/maps/?flash=1&theme=/, Sept 5/2003 See this site also for interesting network statistics (e.g. latencies) ECMM 6000, Fall 2004

  22. ISP ISP ISP ISP NAP NAP ISP ISP NAP NAP ISP Backbone ISP ISP ISP Network Service Provider Internet Service Provider Private Networks / hosts Internet network architecture Adapted from Electronic Commerce: A Managerial Perspective. Turban, Lee, King and Chung, 2000. Pg. 385 ECMM 6000, Fall 2004

  23. How big is the Internet today? • 171,638,297 connected computers (Jan 2003)“Source: Internet Software Consortium (http://www.isc.org/)” • 605.60 million people online Worldwide (Sep 2002) • Canada & USA 182.67 million • Europe 190.91 million • Asia/Pacific 187.24 million • Latin America 33.35 million • Africa 6.31 million • Middle East 5.12 million Source: Nua Internet Surveys; retrieved from: http://www.nua.ie/surveys/how_many_online/ Sept. 5/2003 ECMM 6000, Fall 2004

  24. b.atr.go.jp a.cs.dal.ca ECMM 6000, Fall 2004

  25. URL: A Global Address • Scheme • Server name • Path • File http://www.cs.dal.ca/cs1200/week1/x.html ECMM 6000, Fall 2004

  26. b.atr.go.jp a.cs.dal.ca 123.777.19.6 168.12.13.3 ECMM 6000, Fall 2004

  27. Routing and congestion control • Send information of nodes and links to each node of the network. This might include some physical properties such as maximal size of packets, typical time delays, … • Build map of network • Use routing algorithm to build routing tables for example: OSPF (Open Shortest Path First) if every router uses the same algorithm and maps they build consistent tables • Hierarchical Routing: `use local map to get to the highway, use highway map to get to your destination town, use local map to get to your friends house’. More sophisticated routing on `highway’ (BGP, Border Gateway Protocol) How is congestion controlled? ECMM 6000, Fall 2004

  28. How is congestion controlled? Flow control  TCP Destination publishes maximal acceptable window size in reply message Source destination discovers congestion from unusually long delay times of response  additive increase, multiplicative decrease ECMM 6000, Fall 2004

  29. Application layer:Programming example in Java The JAVA Socket class Socket oldSock = new Socket("penny.open.ac.uk", 1048); remote computer penny in the domain open.ac.uk with communication occurring via port 1048. InputStream ECMM 6000, Fall 2004

  30. Packet filtering firewalls • Packet filtering firewalls decide whether or not to forward packets based on their source and destination IP addresses and port numbers • Rules dictate whether or not packets should be forwarded • Typically once a connection through the firewall has been established, further packets are passed without scrutiny • Processes up to the network layer of the protocol stack (one notable exception is for FTP, which requires some application-level support) • Can perform IP Masquerading ECMM 6000, Fall 2004

  31. Proxy-based firewalls • Proxy-based firewalls operate at the application layer of the protocol stack • Every type of application for which a connection through the firewall is requested requires that a proxy server be running on the firewall for that specific application, or the request will be denied • Allows for logging of events at the application layer, much more detailed logging than a packet-filtering firewall allows • Requires that client machines inside the firewall be configured on an application by application basis to use the proxied services of the firewall ECMM 6000, Fall 2004

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