Chapter 20

Networks

Networks

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

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

Hardware

How the PC’s will be linked All cables in a network come together in a

box called a hub data is moved from one PC to another in

discreet chunks called packets or frames every network card(NIC) has a built in

identifier called a Media Access Control or MAC address

Hardware

Every NIC in the world has a unique MAC address - 48 bit binary address

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

Topology - the different configurations of cabling between computers

2 types of topologies are commonly used today, even though there are numerous:– Bus Topology– Ring Topology

Bus Topology

Bus topology means that all PCs are connected via a single cable that runs to all PCs. (page 1147)

Every device must first wait to see if someone is sending packets before they can send a packet.

Every NIC on the bus sees and reads each packet. Called CSMA/CD

Bus Topology

Sometimes 2 cards do talk at the same time. This is called a collision.

A terminator must be placed at the end of the bus so that there is no signal bounce (just like a SCSI chain)

If the line breaks than the termination is useless and data can’t be sent because of signal bounces

Ring Topology

Connects all PC’s together but instead of a straight line it is more like a ring

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

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

Star bus - shrinking a bus into a hub, so that networks don’t collapse unless the hub breaks

Hardware Protocols

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

Coaxial cable - oldest of all types of network cable– only cable used in bus topologies, with a few

exceptions

Thick Ethernet

Can hook up to 100 devices on one segment, segments can run up to 500 meters

Clearly marked every 2.5 m Connect to devices via a vampire connector The cable from the vampire to the device must

be no longer than 50 m Uses a DB15 connector Becoming obsolete because of high cost

ThinNet (Thin Ethernet)

Invented as a cheap alternative to Thicknet Uses a specific type of coax cable - RG-58, looks

like cable wires but different Supports only 30 devices per segment, segments

can be up to 185 m long 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

Most popular of all networks today runs on UTP (unshielded twisted pair), 8

strands twisted together - p.1159 UTP comes in categories which define

maximum speed, most networks use CAT5 which runs up to 100Mbps, but not that quick yet - p.1159

Uses RJ45 connectors

10BaseT

RJ45 uses only two pairs of wires, the other four are currently useless

Color code on p. 1162 Max. distance from hub to device is 100 m. 10BaseT hubs act as repeaters You can actually hook 2 10BaseT NICs

without a hub, just connect them with a crossover cable

Other Ethernet

Repeater - electronic device that amplifies the signal on a line.– Used to extend the useful length of a cable

segment beyond its specified maximum

Fast Ethernet - same as 10BaseT but 100Mbps

Fiber Optic Ethernet

Best type of cabling you can get– uses light instead of electricity, so it avoids any

electrical problems– travels much farther - 2000 m

Standard is called 10Base FL, or FX Why isn’t it used most often?

– Very expensive to install and upgrade– Mainly used for a backbone (connects the hubs)

Protocols

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)

Client/Server - dedicating one machine to act as a “server”. It’s only function is to serve up resources to the other machines

Peer-to-peer - every computer can act as both a server and a client– much cheaper than C/S, but security is problem

Domain-based - used for larger networks, provides a centralized security function– you need Windows NT or 2000

NICs

Make sure when installing that you use the disk that comes with it, most are PnP

If using a legacy card, you must go to setup

Networks– LAN - Local area network– WAN - Wide area network– MAN - Metropolitan area network

Other things to know

Router - redirects data from one network to another, a smart device

Default gateway - Basically one computer to which data is sent in a LAN in order to communicate with the Internet