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The domain name system dns is a global network of

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Maps host names to IP Addresses. The Domain Name System (DNS) is a global network of servers that provide this service. Data Networking Technologies: LAN Cabling Types: Twisted Pair Cable n Relatively slow speed n Two insulated wires can be shielded (STP) or unshielded (UTP) n UTP is a four-pair medium comes in several categories n UTP can be easily tapped by eavesdroppers than the other cable types. n Category based on how tightly wound the wires are, tighter the wind the higher the rating and resistance to interference. n Cat 1 UTP– was used for telephone lines not good for data. n Cat 2 UTP – up to 4 MBps n Cat 3 UTP – Used for 10BaseT networks up to 10 MBps n Cat 4 UTP – Used in Token Ring Networks up to 16 MBps n Cat 5 UTP - Current UTP standard for new installations up to 100 MBps n Cat 6 UTP – up to 155 MBps n Cat 7 UTP – up to 1 GBps Coaxial Cable n Hollow outer conductor surrounds inner wire conductor. Currently two types in LANs n 50-ohm Cable for digital signaling n 75-ohm Cable for analog signaling and high speed digital signaling n Coax is more expensive but is more resistant to Electromagnetic Interference (EMI). n Used rarely except in Broadband communications n Comes in two types: n Thinnet – (RG58) n Thicknet – (RG8 or RG11) n Two common types of coaxial transmission methods: n Baseband – The cable carries a single channel n Broadband – cable carries several channels such as data, voice, audio, and video Fiber Optic Cable n Conducts modulated light transmission n Light waves are faster and travel greater distances n Difficult to tap
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n Resistant to EMI n Usually connects backbones in larger networks n Can be used to connect workstations to the network. n Expensive to install and to terminate. LAN Transmission Protocols: n Rules for communication between computers on a LAN n Formatting of the data frame, the timing and sequencing of packet delivery, and resolution of error states. Carrier Sense Multiple Access (CSMA) n Foundation of Ethernet Protocol. n Workstation continuously monitors the line waiting until it thinks it is free. n If the workstation doesn’t receive an acknowledgement from the destination to which it sent the packet, it assumes a collision has occurred and it resends the packet. n Persistent Carrier Sense - Unless receives acknowledgement it will resend. n Nonpersistent Carrier Sense – waits random amount of time and resends. CSMA/CA - Carrier Sense Multiple Access Collision Avoidance – Workstations connected to two coax cables, one to send and one to receive data. CSMA/CD - Carrier Sense Multiple Access Collision Detection Ethernet If the host detects another signal while transmitting it will send a jam signal causing all nodes to stop sending data. Nodes wait to resend. Designed to avoid collisions.
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