| Welcome to Questy's Links and Lessons |
| Technology
study guides and tutorials. Physical Media |
|
|
|
|
Media
-- Provides
the electro-mechanical interface through which data moves among devices on the
network. Public
Switched Telephone Network (PSTN), often referred to as Plain Old Telephone Service
(POTS),
Modem - a device that allows one computer to communicate with another computer over a standard telephone line by modulating a digital signal into an analog signal that can travel through phone lines. Constructed from the words modulator and demodulator, it is a device that modulates a carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modem standards, or V dot modem standards, are defined by the ITU (International Telecommunications Union). Integrated Services Digital Network (ISDN) uses a single wire or fiber optic line to carry voice, data, and video signals. Basic
Rate Interface (BRI) is most commonly used in residential ISDN connections. It's
composed of two bearer (B) channels at 64 Kbps each for a total of 128 Kbps (used
for voice and data) and one delta (D) channel at Primary Rate Interface (PRI) is most commonly used between a PBX (Private Branch Exchange) at the customer's site and the central office of the phone company. It is composed of 23 B channels at 64 Kbps and one D channel at 64 Kbps. The total bandwidth is up to 1,536 Kbps. Digital Subscriber Line (DSL) - technologies use existing, regular copper phone lines to transmit data. DSL hardware can transmit data using three channels over the same wire. In a typical set up, a user connected through a DSL hookup can send data at 640 Kbps, receive data at 1.5 Mbps, and still carry on a standard phone conversion over one line. Cable Connection - access to the Internet through the same coaxial cable that brings cable TV into your home. A signal splitter installed by the cable company isolates the Internet signals from the TV signals. The two-way cable connection is always available and can be very fast. Speeds up to 30 Mbps are claimed to be possible, although speeds in the 1 to 2 Mbps range are more typical. T-Carrier Technology is a digital transmission service used to create point-to-point private networks and to establish direct connections to Internet Service Providers. It uses four wires, one pair to transmit and another to receive. T-1 lines support data transfer at rates of 1.544 megabits per second. Each T-1 line contains 24 channels. The E1 line is the European counterpart that transmits data at 2.048 Mbps. T-3, has 672 (64 Kbps) channels, for a total data rate of 44.736 Mbps. The E3 line is the European counterpart that transmits data at 34.368 Mbps. Twisted pair cabling is a common form of wiring in which two conductors are wound around each other for the purposes of canceling out electromagnetic interference which can cause crosstalk. The number of twists per meter make up part of the specification for a given type of cable. The two major types of twisted-pair cabling are unshielded twisted-pair (UTP) and shielded twisted-pair (STP). UTP - Unshielded Twisted Pair; uses RJ-45, RJ-11, RS-232, and RS-449 connectors, max length is 100 meters, speed is up to 100Mps. Cheap, easy to install, length becomes a problem. Can be CAT 2,3,4 or 5 quality grades. STP - In STP, the inner wires are encased in a sheath of foil or braided wire mesh. Shielded Twisted Pair uses RJ-45, RJ-11, RS-232, and RS-449 connectors, max length is 100 meters, speed is up to 500Mps. Not as inexpensive as UTP, easy to install, length becomes a problem. Can be CAT 2,3,4 or 5 quality grades. Category 1 Traditional UTP telephone cable. Category 1 can transmit voice signals but not data. Most telephone cable installed prior to 1983 is Category 1. Category 2 UTP cable made up of four twisted-pair wires, certified for transmitting data up to 4 Mbps (megabits per second). Category 3 UTP cable made up of four twisted-pair wires, each twisted three times per foot. Category 3 is certified to transmit data up to 10 Mbps. Category 4 UTP cable made up of four twisted-pair wires, certified to transmit data up to 16 Mbps. Category 5 UTP cable made up of four twisted-pair wires, certified to transmit data up to 100 Mbps. Fiber optic - (IEEE 802.8) Cable in which the center core, a glass cladding composed of varying layers of reflective glass, refracts light back into the core. Max length is 25 kilometers, speed is up to 2Gbps but very expensive. Best used for a backbone due to cost. Twisted-pair
Ethernet cable has the following specifications: Fast Ethernet Physical Specifications 100BASE-TX specification uses two pairs of Category 5 UTP or Category 1 STP cabling at a 100 Mbps data transmission speed. Each segment can be up to 100 meters long. 100BASE-T4 specification uses four pairs of Category 3, 4, or 5 UTP cabling at a 100 Mbps data transmission speed with standard RJ-45 connectors. Each segment can be up to 100 meters long. 100BASE-FX specification uses two-strand 62.5/125 micron multi- or single-mode fiber media. Half-duplex, multi-mode fiber media has a maximum segment length of 412 meters. Full-duplex, single-mode fiber media has a maximum segment length of 10,000 meters. Two techniques can be used to transmit signals over the data transmission media. A baseband transmission line provides only one channel per line, while a broadband transmission line provides multiple communication channels. Baseband systems use digital encoding techniques to carry digital data over a digital transmission line. In baseband transmission, all of the available frequencies in the transmission medium are used by one signal. Broadband systems use modulation techniques to transmit digital data over analog carrier waves. Broadband transmission lines can be much longer than baseband lines. coaxial cable: (coax) - commonly used for thick ethernet, thin ethernet, cable TV and ARCnet, coaxial cabling that uses BNC connectors; heavy shielding protects data, but expensive and hard to make connectors 10BASE5,
also called Thicknet or Thick Ethernet, uses thick, coaxial cable. a
50-ohm terminator on each end of the cable; 10BASE2
uses thin Ethernet cable. a
50-ohm terminator on each end of the cable; A British Naval Connector (BNC)- a.k.a. Bayonet Nut Connector - a.k.a. Bayonet Neill-Concelman (the inventors of the BNC connector) is usually used for thinnet coaxial cable. A terminator is a resistor attached to the end of the cable. Its purpose is to prevent signal reflections, effectively making the cable "look" infinitely long to the signals being sent across it. Unbounded media transmits data without the benefit of a conduit-it might transmit data through open air, water, or even a vacuum. Narrow band radio, laser, and microwave - transmission can not occur through steel or load bearing walls. Satellite - Has a transmission delay of 240 to 300 milliseconds Terrestrial microwave - Commonly used for long distance voice and video transmissions, and for short distance high speed links between buildings. Laser - Resistant to eavesdropping and capable of high transmission rates; susceptible to attenuation and interference. Spread spectrum radio - frequencies are divided into channel or hops. |
|
If you have used this section as a reference, please be aware that many pages have been updated, and some content of the individual pages has changed to better find the information. For more information on E- Commerce Check out: Questy.com/zen |
|
DISCLAIMER: Technology changes very rapidly. The information presented here as a study guide to illustrate concepts. No claim is made that this information is up to date, or that it represents the current technology used today. |
This area
is meant to be a study guide, not a comprehensive reference. |
| Support this website by checking out our Great Deals on Web Hosting and Domain Names: |
|
|
Welcome
to the World of Questy |
