NETWORK CABLING

I. Types of network cables: a. Coaxial Coaxial cable is more resistant to interference and attenuation than twisted-pair cable. Attenuation is the loss of signal strength which begins to occur as the signal travels further along a copper cable. The stranded, protective sleeve can absorb stray electronic signals so that they do not affect data being sent over the inner copper cable. For this reason, coaxial is a good choice for longer distances and for reliably supporting higher data rates which less sophisticated equipment. There are two types of coaxial cables Thinnet and Thicknet.  Thinnet is very flexible with about 0.25 inch thick. It is commonly used in every network installation. Thinnet can carry signal up to 185 meters (607 feet) before the signal starts to suffer from attenuation.  Thicknet is a relatively rigid cable about 0.50 inch thick. It is sometimes referred to as Standard Ethernet because it was the first cable used with poupular ethernet architecture. Thicknet can carry signal up to 500 meters (about 1,640 feet). Because of this distance ability, thicknet is usually used as a Backbone to connect several smaller thinnet-based networks.  A device called a transceiver connects the thinnet coaxial to the larger thicknet coaxial cable. The transceiver includes aconnector known as a vampire tap or a piercing tapto make the actual physical connection to thicknet core. An AUI port connector on a network adapter card is known as DIX (Digital Intel Xerox) connecto or DB-15 connector.

Network Introduction   Network Cabling   Wireless Network   Network Interface Card   OSI Model   Protocols   Ethernet - Network architecture   Token Ring - Network architecture   AppleTalk and ArcNet - Network architectures   Repeaters, Bridges, Routers, and Gateways   E-mail Standards   Modem & Async Comm.   T1, T3, and Switched 56 Digital Connectivities   Packet-Switching Network,Frame Relay and ATM   ISDN & FDDI

b. Twisted-pair cables There are two types of twisted-pair cables: unshielded twisted-pair (UTP) and shielded twisted pair (STP).  UTP using 10BaseT specification is the most popular type twisted-pair cable and is fast becoming the most popular LAN cabling. The maximum cable length is 100 meters (328 feet). This type of cable is used in creating standards that apply to a variety of building and wiring situations and ensure consistency of products for customers.  These standards include:    Category 1 for traditional UTP Telephone cable which can carry voice but not data;  Category 2 (consists of four twisted-pairs) for data transmission up to 4 Mbps;  Category 3 (consists of four twisted-pairs with three twist per foot) for data transmission up to 10 Mbps; Category 4 (consists of four twisted-pairs) for data transmission up to 16 Mbps; and  Category 5 (consists of four twisted-pair of copper wire) for data transmission up to 100 Mbps). One potential problem with UTP is Crosstalk. Crosstalk is defined as signals from one line getting mixed with signals from another line. Shielding is used to reduce crosstalk.  STP has excellent shielding to protect transmitted data from outside interference. The connector for TP cables knows as RJ-45 connector. It look alike RJ-11 telephone connector, but there is difference between them. RJ-45 houses eight cable connections, while RJ-11 only houses four.  c. Fiber-Optic Cable In fiber-optic cable, optical fibers carry digital data signals in the form of modulated pulses of light. This is relatively safe way to send data because no electrical impulses are carried over the fiber-optic cable. This means that fiber-optic cable cannot be tapped and data stolen, which is possible with any copper-based cable carrying data in the form of electronic signals. We will use this type of cable if we need to transmit data at very high speeds over long distances in a very secure media. Pricing for fiber-optic cable is competative to high-end copper cabling. We should not use this cable if we do not have the expertise to properly install it and connect devices to it. The maximum cable length is 200 kilometers (6,562 feet).  II. Transmission techniques over cables There are two techniques that can be used to transmit signals over cable: Baseband and Broadband Transmission.  BASEBAND TRANSMISSION Baseband systems use digital signaling over a single frequency. Signals flow in the form of discrete pulses of electricity or light. With this system, the entire communication channel capacity is used to transmit a single data signal. The digital signal uses the complete bandwidth of the cable, which constitutes a single channel.  A cable?s total bandwidth is the different between the highest and lowest frequencies that are carried over the cable.  Each device on baseband network transmits bidirectionally, and some can transmit and receive at the same time.  As a safeguard, this systems sometimes use repeaters to receive an incoming signal and retransmit it at its original strength and definition to increase the practical length of a cable. BROADBAND TRANSMISSION Broadband systems use analog signaling and a range of frequencies. With analog transmission, the signals are continous and nondiscrete. The signals flow across the physical medium in the form of electromagnetic or optical waves. With this system, the signal flow is unidirectional.  While baseband system uses repeaters, broadband system uses amplifiers to regenerate analog signals at their original strength. Because broadband transmission signal flow is unidirectional, there must be two paths for data flow in order for a signal to reach all devices.    There are two common ways to do this: Mid-split broadband configuration. This configuration divides the bandwidth into two channels, each using a different frequency or range of frequencies. One channel is used to transmit signals, the other to receive them. Dual-cable configuration. In this configurations, each device is attached to two cables. One cable is used to send and the other is used to receive.

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