Chapter 20 Networks

4 Questions that need to be answered concerning networks? –How will each computer be identified? –What kind of wire should you run in between them? –If more than one PC is accessing the same file, how can they be prevented from destroying each others changes to that file? –How can access to data and peripherals be controlled?

Networks 4 Networks can be broken down into four areas: –Hardware –Protocols –Network –Shared Resources

Hardware 4 How the PC’s will be linked 4 All cables in a network come together in a box called a hub 4 data is moved from one PC to another in discreet chunks called packets or frames 4 every network card(NIC) has a built in identifier called a Media Access Control or MAC address

Hardware 4 Every NIC in the world has a unique MAC address - 48 bit binary address 4 So when you send out a frame it contains not only the data that you intend to send, but also your MAC address and the MAC address of the person that you wish to send it to.

Hardware 4 Topology - the different configurations of cabling between computers 4 2 types of topologies are commonly used today, even though there are numerous: –Bus Topology –Ring Topology

Bus Topology 4 Bus topology means that all PCs are connected via a single cable that runs to all PCs. (page 1147) 4 Every device must first wait to see if someone is sending packets before they can send a packet. 4 Every NIC on the bus sees and reads each packet. Called CSMA/CD

Bus Topology 4 Sometimes 2 cards do talk at the same time. This is called a collision. 4 A terminator must be placed at the end of the bus so that there is no signal bounce (just like a SCSI chain) 4 If the line breaks than the termination is useless and data can’t be sent because of signal bounces

Ring Topology 4 Connects all PC’s together but instead of a straight line it is more like a ring 4 Use a transmission called token passing –a mini packet called a token constantly passes from one card to the next in one direction. If one PC wants to talk to another it must wait until it gets the token. Because of this you will hear the word token ring used when describing ring networks

Star Ring / Star Bus 4 Token Ring actually uses a topology called star ring. Instead of running a ring of cable all around the LAN, the ring is stored inside a special box called a Multi-Station Access Unit (MSAU) or a MAU 4 Star bus - shrinking a bus into a hub, so that networks don’t collapse unless the hub breaks

Hardware Protocols 4 A consortium of companies wrote a series of standards that defined everything necessary to get data from one computer to another. This series of standards was called Ethernet 4 Coaxial cable - oldest of all types of network cable –only cable used in bus topologies, with a few exceptions

Thick Ethernet 4 Can hook up to 100 devices on one segment, segments can run up to 500 meters 4 Clearly marked every 2.5 m 4 Connect to devices via a vampire connector 4 The cable from the vampire to the device must be no longer than 50 m 4 Uses a DB15 connector 4 Becoming obsolete because of high cost

ThinNet (Thin Ethernet) 4 Invented as a cheap alternative to Thicknet 4 Uses a specific type of coax cable - RG-58, looks like cable wires but different 4 Supports only 30 devices per segment, segments can be up to 185 m long 4 Plus side –much thinner, makes it easier to work with –the transceiver is built into the Thinnet card –has twist on connectors, called BNC connectors

10BaseT 4 Most popular of all networks today 4 runs on UTP (unshielded twisted pair), 8 strands twisted together - p UTP comes in categories which define maximum speed, most networks use CAT5 which runs up to 100Mbps, but not that quick yet - p Uses RJ45 connectors

10BaseT 4 RJ45 uses only two pairs of wires, the other four are currently useless 4 Color code on p Max. distance from hub to device is 100 m. 4 10BaseT hubs act as repeaters 4 You can actually hook 2 10BaseT NICs without a hub, just connect them with a crossover cable

Other Ethernet 4 Repeater - electronic device that amplifies the signal on a line. –Used to extend the useful length of a cable segment beyond its specified maximum 4 Fast Ethernet - same as 10BaseT but 100Mbps

Fiber Optic Ethernet 4 Best type of cabling you can get –uses light instead of electricity, so it avoids any electrical problems –travels much farther m 4 Standard is called 10Base FL, or FX 4 Why isn’t it used most often? –Very expensive to install and upgrade –Mainly used for a backbone (connects the hubs)

Protocols 4 Protocols - rules that networks follow when sending/receiving data –IPX/SPX - developed by Novell (first one) –NetBEUI - developed by IBM as the default for Windows –TCP/IP - developed by the government, default for NT as well as the Internet –AppleTalk - developed by Apple for use with Apple computers

Network Operating System (NOS) 4 Client/Server - dedicating one machine to act as a “server”. It’s only function is to serve up resources to the other machines 4 Peer-to-peer - every computer can act as both a server and a client –much cheaper than C/S, but security is problem 4 Domain-based - used for larger networks, provides a centralized security function –you need Windows NT or 2000

NICs 4 Make sure when installing that you use the disk that comes with it, most are PnP 4 If using a legacy card, you must go to setup 4 Networks –LAN - Local area network –WAN - Wide area network –MAN - Metropolitan area network

Other things to know 4 Router - redirects data from one network to another, a smart device 4 Default gateway - Basically one computer to which data is sent in a LAN in order to communicate with the Internet