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Networks

Networks. Network Components. Learning Objectives. Describe different media for transmitting data and their carrying capabilities. Explain the different purposes of network components. Transmission Media (cables). Presented in order of performance

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Networks

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  1. Networks Network Components

  2. Learning Objectives • Describe different media for transmitting data and their carrying capabilities. • Explain the different purposes of network components.

  3. Transmission Media (cables) Presented in order of performance (increasing expense, speed of communication, level of traffic that can be managed, difficulty and usable length of installation and decreasing susceptibility to interference) http://members.tripod.com/barhoush_2/cabling.htm http://fcit.usf.edu/network/chap4/chap4.htm http://www.ecst.csuchico.edu/~sim/547/Old547/notes/NOTE4.htm

  4. UTP & Shielded TP • Unshielded Twisted Pair (UTP) • Two conductors, enclosed in a plastic sheath, twisted together. • Shielded Twisted Pair • Has a grounded screen around the conductors to shield the cable from extraneous electromagnetic radiation.

  5. Coaxial cable • A central conductor enclosed in a plastic sheath surrounded by a copper sheath which is surrounded by a plastic coating. Copper screen conductor • Baseband coaxial: • Single copper braid shield. • Broadband coaxial: • Two shields (1 - aluminium & 1 - copper). Central conductor Plastic insulators

  6. Optical Fiber- Used as backbones (fast route) for LANs or in WANs • Contains many optical fibers: • Glass or plastic fibers designed to guide light along them.

  7. Network Interface Cards (NIC) • Provides the hardware interface (circuit board) to connect a computer to a network. • Some NIC cards work with wired connections while others are wireless. http://en.wikipedia.org/wiki/Network_interface_controller

  8. Network Components

  9. Segment Repeater Repeater • Has only 2 ports and amplifies the signals between two networks or segments of a bus network that are too far apart. • Is not intelligent and simply amplifies all signals whether they are intended for the other segment or not. • Operate at the physical layer of OSI.

  10. Hubs Hub

  11. Hubs • All signals received by a hub are retransmitted down every other cable connected to it enabling a physical star network (but still theoretically a bus network as collisions are possible). • Multi-port repeaters. • Operate at the physical layer of OSI.

  12. Segment Bridge Bridges • Links only 2 LANs (which may or may not be similar) by controlling access from one part of the network to the other. • Could be thought of as an intelligent repeater.

  13. Bridges • Has the ability to learn the layouts of the networks. • Initially, all data the bridge receives is buffered and passed to both segments. • The bridge stores a table containing the addresses of sending nodes and the segment from which the data was sent. • Eventually, when all nodes have sent data, the bridge will know on which segment each node is. • Now it can use the address information in each packet to route data efficiently (either directing it back to the segment it came from or on to the other segment). • Is software based as it uses software to make its decisions. • Operate at the data layer of OSI.

  14. Bridge Algorithm • Data arrives at the bridge and is buffered. • Bridge checks destination address. • If destination is on same segment as sender then • discard the data • Else • pass data to other segment.

  15. Stations Stations Server Server Switch Switch Switch Switch Stations Stations Server Server Backbone

  16. Switch • An ‘intelligent’ hub which looks at the destination address of each packet it receives and delivers each packet to the correct destination (i.e. connects nodes in a circuit switching network). • Like a bridge but can link many LANs. • It allows many terminals all to use the same communications line (backbone – fast medium e.g. optical fibre) between network segments at different times. • If all stations want to access the main network, the switch has no affect on the speed of this link and it may be necessary to upgrade the link to the main network. • Operate at the data layer of OSI.

  17. Switch • Only stores physical addresses and can only deal with simple networks where there is only one possible path for any given packet. • If this is not the case ‘routers’ must be used (next). • Is hardware based as uses chips to make its decisions.

  18. Public network Router Router LAN LAN Routers

  19. Routers • Connect different types of network together. • Stores logical IP addresses and can deal with complex networks where there is more than one possible path to a destination by calculating the optimum route at the time. • i.e. Directs packets across a packet switched network. • Is software based as it uses its own operating system to make its decisions.

  20. Routers • Directs messages down different routes according to their desired destinations. • Use network addresses and addresses of other routers to create a route between two networks so must keep tables of addresses. • These tables are copied between routers using routing information protocol (RIP). • Often used to connects LANs & WANs e.g. connect a LAN to the internet using one IP address. • Operates at all layers up to the transport layer of OSI.

  21. Routing Algorithm • Router receives a network level packet. • Network destination address is checked. • Packet is sent to the appropriate network.

  22. Gateway • A gateway is a network point/router that acts as an entrance to another network. • On the Internet, a node/router or stopping point can be either a gateway node or a host (end-point) node/router. • Both the computers of Internet users and the computers that serve pages to users are host nodes. • The computers that control traffic within your company's network or at your local Internet service provider (ISP) are gateway nodes/routers. • In the network for an enterprise, a computer server acting as a gateway node is often also acting as a proxy server and a firewall server. • http://en.wikipedia.org/wiki/Default_gateway

  23. Modems • Necessary if communication link is analogue • e.g. To transmit and receive data on the internet. • Hardware which converts digital signals to analogue for transmission and vice versa for receiving.

  24. Firewall • Software (and possibly hardware) to control unauthorised outside access to a private network.

  25. Plenary • Explain the part played in network systems by: • Switches • Routers • Bridges • Modems

  26. Plenary • Switches • A device that allows many terminals all to use the same communications line at different times. • Routers • Connects different types of network together. • Software at a node (on the network). • Which directs messages down different routes. • According to their desired destination.

  27. Plenary • Bridges • Links two LANs (which may or may not be similar). • Uses address information in packets. • Has the ability to learn the layouts of the networks. • Can control access from one part of the network to the other. • Modems • Necessary if communication link is analogue. • Converts digital signals to analogue for transmission.

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