1. IST 126 Computer Networks Spring, 2014

2. What is a Computer Network? A group of computers and other devices that are connected together in order to share resources The network consists of both special hardware (NIC card, transmission medium, etc.) and software (network operating system)

3. Classification of Computer Networks LAN – Local Area Network consists of computers in a single location that are connected for the purpose of sharing resources. Used to share resources within a building or campus for example WAN – Wide Area Network consists of the links over long distances that are used to connect LANs. The links may be made over leased telephone lines or through wireless transmission (microwave). WANs can grow without bound. The Internet is the largest WAN in the world.

4. What is Shared in a Network? Information –Inventory –Company letterheads –Company procedural manuals Hardware –Printer –Hard disk –Almost any device that can be attached to a computer Software –Software can be installed on a central networked machine and then accessed by all cmputers on the network

5. Advantages of a Network Allows for sharing of information, hardware and software Allows information to be backed up to a central location to preserve the information Provides an additional layer of security Allows people to communicate through e- mail

6. Three roles for a Computer in a Local Area Network Client – Uses network resources but does not provide network resources to other computers Peer – Both uses and provides network resources Server – Provides network resources

7. Classification of LANs Client-server: Contains clients and servers that support them. Peer-to-peer: There are no servers. The network is used to share resources among independent peers Hybrid: A client-server network that also has peers sharing resources. Most networks are actually hybrid networks.

8. Advantages of Server-Based Networks Strong central security Central file storage Can share expensive equipment such as laser printers Dedicated servers that provide fast service Users don’t have to manage resource sharing Large number of users easily managed through accounts on the network.

9. Advantages of Peer-to-Peer Network No extra investment in server hardware or software No network administrator needed Users control resource sharing Lower cost for small networks (usually limited to 10 or fewer computers)

10. Some Network Utilities Ping – Allows you to check connectivity between devices on a network Traceroute – Shows the path a packet takes between two devices on a network Ipconfig – Shows TCP/IP setup parameters Try the above commands from command prompt.

11. IST 126 Transmission Media

12. Characteristics of Transmission Media Cost Ease of installation Bandwidth capacity – the amount of data that can be sent in a given amount of time Node capacity – the maximum number of nodes per segment Attenuation – the decrease of a signal strength over a distance EMI – electromagnetic inteference

13. Network Media Types Coaxial – uses electrical signal to send data Twisted pair – uses electrical signals also Fiber optics – uses light signals Wireless –Infrared –Microwave –Radio

14. Coaxial Cable A solid copper core (or stranded) conductor runs down the center of cable This wire is surrounded by plastic foam insulation The foam is surrounded by a second conductor that may be a wire mesh or a metallic foil Plastic jacket covers the cable for protection

15. Commonly Used Coaxial Cables RG-8 and RG-11: used with Thick Ethernet RG-58: used with thin Ethernet RG-59: used with cable TV

16. Characteristics of Coaxial Cable Cost is relatively inexpensive Installation relatively simple Typical bandwidth of 10 Mbps Node capacity is 30 for thinnet; 100 for thicknet Attenuation much less that for twisted-pair Susceptible to EMI Plenum-grade must be used in ceilings and walls

17. Twisted Pair Cable One or more pairs of two twisted copper wires are used Wires are twisted to decrease the amount of crosstalk and outside EMI Twisting the wires causes the emitted signals from the two wires to cancel out each other and hence reduce crosstalk The pair are color-coded Used in telephone connections

18. Types of Twisted Pair Cable Unshielded – consists of a number of twisted pair with a simple plastic casing Shielded – contains an extra layer of shielding to reduce effect of EMI Category 1-5 –Cat 5 supports up to 100 Mbps Use RJ-45 connector

19. Twisted Pair Characteristics STP is fairly expensive UTP is very economical STP is rigid and bulky and can be difficult to install Typically a bandwidth of 10Mbps UTP normally restricted to length of 100 meters due to attenuation UTP very susceptible to EMI STP reduces the effect of EMI

20. Fiber Optic Cable Uses light signals to transmit data Each fiber has an inner core of glass or plastic that conducts light The inner core is covered with a layer of glass that reflects the light back into the core An outer plastic sheath surrounds the inner core The cable may contain one or more fibers

21. Infrared Wireless Infrared light is used to transmit signals These signals are in the terahertz range of the electromagnetic spectrum Remote controls for televisions, VCRs use infrared signals These signals cannot penetrate walls and are diluted by strong lights Can be either line-of-site or broadcast that reflect off walls and ceilings

22. Microwave Wireless Use the lower gigahertz frequencies of the electromagnetic spectrum Can be terrestrial or use satellites Signals are line-of-site Cannot penetrate structures, so clear path needs to be established between source and destination

23. Radio Wireless Uses radio waves for transmission May use unregulated or regulated frequencies You cannot be guaranteed a clear channel if you use unregulated frequency Propagates in all directions Will pass through structures