Transcript Day 1
IST 126 Computer Networks Spring, 2016 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) 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. 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 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 email 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 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. 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. 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) Some Network Utilities • Ping – Allows you to check connectivity between devices on a network • Tracert – 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. 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 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 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 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 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