Networking+ Ch 5 Notes

  Networking + Chapter 5 Notes  Network Cabling ● TRANSMISSION BASICS ○ Bandwidth is the amount of data that could theoretically be transmitted during a given period of time, while throughput  is the measure of how much data is actually transmitted during a given period of time. ■ Bit rate - measurement of throughput and bandwidth ; expressed as bits transmitted per second ○ Three factors degrading network performance:  2  ■ Noise can degrade or distort a signal. Two common sources are: ● Electromagnetic Interference (EMI) - electrical activity ○ One type is radio frequency interference (RMI) ● Crosstalk - signal traveling on one wire/cable infringes on signal traveling over adjacent wire/cable. Three common types: ○ Alien crosstalk - occurring between two cables ○ Near end crosstalk (NEXT) - occurs between wire pairs near source of signal ○ Far end crosstalk (FEXT) - measured at far end of cable from signal source ■ Attenuation is the loss of a signal’s strength as it travels away from its source. ● Repeater - regenerates digital signal in its original form, operates at Layer 1 (Physical) ■ Latency is the brief delay between the time when data is transmitted and when it is received. ● Round trip time (RTT) - the length of time it takes for a packet to go from sender to receiver, then back from receiver to sender ● Jitter (also packet delay variation or PDV) - packets experiencing varying amounts of delay and arrive out of order ○ Duplex signals are free to travel in both directions over a medium simultaneously. Specifying a speed or duplex setting on a NIC that is not supported by a neighboring device results in a speed and duplex mismatch and, therefore, slow or failed transmissions.  3  ○ There are two settings, combined, to create different methods of communication: ■ Full-duplex, also called duplex  - signals may travel in both directions over a medium at the same time ■ Half-duplex - signals may travel in both directions, but only one direction at a time ■ Simplex - signals may travel in only one direction (one-way) or unidirectionally ● Multiplexing - a form of transmission that allows multiple signals to travel simultaneously over one medium ○ To carry multiple signals, a medium’s channel is logically separated into multiple smaller channels, or subchannels, by varying each signal: ○ Copper Line ■ time slot (TDM {time division multiplexing} ● Divides a channel into multiple intervals of time/time slots ■ STDM {statistical time division multiplexing} ) ● Assigns time slots to nodes but then adjusts these slots according to priority and need ■ frequency (FDM {frequency division multiplexing} ) ● Assigns different frequencies to create multiple frequency bands, each used by a subchannel, so that multiple signals can transmit on the line at the same time ○ Fiber-Optic Cable ■ WDM (wavelength division multiplexing) ● Works with any fiber-optic cable to carry multiple light signals simultaneously by dividing a light beam into different wavelengths, or colors, on a single fiber. ■ DWDM (dense wavelength division multiplexing or dense WDM)  4  ● Increases # of channels provided by normal WDM to between 80 and 320 channels ■ CWDM (coarse wavelength division multiplexing or coarse WDM) ● Lowers cost by spacing frequency bands wider apart to allow for cheaper transceiver equipment. Supports 4, 8, 16, or 18 channels per fiber ● COPPER CABLE  ○ ○ Coaxial cable (outdated now) “coax” - used to connect cable Internet and cable TV systems ○  ○ ○ F-connectors are used to terminate coaxial cable that transmits television and cable broadband signals. ○ The BNC  connector uses a turn-and-lock (or bayonet) style of coupling.   5  ○ Today’s networks might use RG-59 coaxial cable for short connections, such as distributing video signals to multiple monitors in a building, or RG-6 coaxial cable to deliver broadband cable Internet service and cable TV. ● Twisted-pair cable consists of color-coded pairs of insulated copper wires, each with a diameter of 0.4 to 0.8 mm. On Fast  Ethernet networks (which has a maximum speed of 100 Mbps), ● one pair sends data ● another pair receives data ● the other two pairs are not used for data transmission. ■ Networks using Gigabit Ethernet and higher standards (with a speed of at least 1,000 Mbps) use all  four pairs for both sending and receiving. ■ Twist ratio - the number of twists per meter or foot ○ STP (Shielded twisted pair) cable shielding acts as a barrier to external electromagnetic forces, thus preventing them from affecting the signals traveling over the wire inside the shielding. ■ The effectiveness of the shield depends on these characteristics: ● level and type of environmental noise ● thickness and material used for the shield ● grounding mechanism ● symmetry and consistency of the shielding ○ UTP (Unshielded twisted pair) cable is both less expensive and less resistant to noise than STP, and is more popular than STP, primarily because of its lower cost. UTP doesn’t have additional shielding. ○ STP and UTP both use RJ-45 modular connectors and data jacks, which look similar to analog telephone connectors and jacks. ○ STP and UTP have their differences and similarities:  6  ■ Throughput - both STP and UTP can transmit data at 10 Mbps, 1 Gbps, and 10 Gbps, depending on cabling and transmission method in use. ■ Cost - STP and UTP both vary in cost. UTP is generally cheaper. STP requires additional materials and more grounding. ■ Connector - STP and UTP both use RJ-45 (registered jack 45) modular connectors and data jackets. ● Telephone connections follow the RJ-11 (registered jack 11) standard. ■ Noise immunity - STP more resistant than UTP. Noise on UTP cable can be reduced with filtering and balancing techniques. ■ Size and scalability - The maximum segment length for both STP and UTP is 100 m, or 328 feet, on Ethernet networks that support data rates from 1 Mbps to 10 Gbps. ○ TIA/EIA has specified two different methods of inserting twisted-pair wires into RJ-45 plugs: TIA/EIA 568A and TIA/EIA 568B. Functionally, there is very little difference between these two standards; however, the same standard should be used throughout a network so data is transmitted and received correctly. ■ The TIA/EIA 568A is a standard pinout for RJ-45 plugs required by the federal government on all federal contracts. ■ The TIA/EIA 568B is a standard pinout for RJ-45 plugs commonly used in homes and businesses. ■ Pinouts - pin numbers and assignments ● Tx = transmit ● Rx = receive  7  ■ Straight-through cable (also “patch cable”) - a twisted-pair patch cable in which the wire terminations in both connectors follow the same scheme ; most common type of networking cable ■ Loopback adapter - A troubleshooting tool that plugs into a port and crosses the transmit line with the receive line, allowing outgoing signals to be redirected back into the computer for testing. ○ A crossover cable has the transmit and receive wires reversed and was used to connect a PC to a PC or a switch to a switch.  ○ ○ TX/RX reverse - a problem caused by mismatched pinout standards, resulting in near end crosstalk. ○ A router’s console port is used with a console cable, or rollover cable, to communicate with the router itself, such as when making configuration changes to the device. ■ Rollover cable - reverses all wires without regard to pairing. They have two different ports: ● Ethernet ports - allow for network communications ; are the type of port used to create LANs through the router ● Console port - used to communicate with the router itself ○ DB-9 and DB-25 connectors comply with the RS-232 standard.  8   ○ ○ A crimper pushes on the pins inside an RJ-45 connector so they pierce the wire’s insulation, thus creating contact between the two conductors. ○ IEEE’s 802.3af and 802.3at standards specify a method for supplying a small amount of power over twisted-pair Ethernet cables, a technology known as PoE (Power over Ethernet), requiring Cat 5 or better copper cable. ■ PoE+ - A method of delivering more current (up to 25.5 watts) than PoE does to devices using Ethernet connection cables. ■ PoE standard specifies two types of devices: ● PSE (power sourcing equipment) - device supplying the power ● PDs (powered devices) - devices that receive power from the PSE ○ A device’s NIC is rated for maximum network speeds defined by various Ethernet standards that operate at Layer 2 (Data link). However, the network must be wired with cabling that is capable of supporting those speeds.  9   ○  ○ ● FIBER-OPTIC CABLE ○ Fiber-optic cable (or “fiber”) contains one or several glass or plastic fibers at its center ○ Core - A cable’s central component that is designed to carry a signal, such as glass or plastic fibers in fiber-optic cable or strands of copper in twisted-pair cable. ○ Data is transmitted through the central fibers of fiber-optic cable via pulsing light sent from a laser or an LED source (a cool-burning, long-lasting technology used on shorter fiber-optic connections). ○ Cladding - The glass or plastic shield around the core of a fiber-optic cable. ○ Optical loss - The degradation of a light signal on a fiber-optic network as it travels away from its source. ○ SMF (single mode fiber) consists of narrow core of 8 to 10 microns in diameter  10  ○ Laser-generated light travels over a single path inside SMF cables, reflecting very little. This continuity allows SMF to accommodate the highest bandwidths and longest distances of all network transmission media. ○ MMF (multimode fiber) contains a core with a larger diameter than SMF, usually 50 or 62.5 microns, over which many pulses of light generated by a laser or LED light source travel at various angles. ○ MMF contains a core with a larger diameter than SMF over which many pulses of light generated by a laser or LED light source travel at different angles. ○ FDP = fiber distribution cable - device on case on rack where fiber cables converge, connect with each other, and connect with fiber optic terminal equipment from the ISP.  ○ ○ Ferrule - extended tip of a connector that makes contact with the receptacle in the jack or other connector ○ Shapes and polishes currently used on SMF ferrules include: ■ UPC (Ultra Polished Connector) - allows the two internal fibers to meet and increases efficiency  11  ■ APC (Angle Polished Connector) - faces are placed at an angle to each other (industry standard = 8 degrees) ○ Older fiber networks might use ST or SC connectors. However, LC and MTRJ connectors are now more common because of their smaller sizes. ○ * You will need to memorize the above table for the exam! * ○ A media converter is hardware that enables networks or segments running on different media to interconnect and exchange signals. ○ Some switches and routers contain sockets where one of many types of modular interfaces, called transceivers, can be plugged in. Such transceivers are easily inserted into the sockets without disrupting operations and can be upgraded later as technology improves. ■ Hot-swappable - a hardware component that can be changed without disrupting operations ■ GBIC = Gigabit interface converter - standard type of transceiver designed for Gigabit Ethernet connections ■ Bidirectional - transmission method that allows each fiber cable to carry data in both directions  12  ■ BiDi transceivers (“bidirectional transceivers”) - new technology allowing bidirectional transmission on both ports ○ 1000Base-LX is the more common fiber version of Gigabit Ethernet and uses long wavelengths, while 1000Base-SX is also common, is less expensive to install, and uses shorter wavelengths. ○ * The exam requires knowledge of the two standards for Gigabit Ethernet ■ 1000Base-LX ● More common fiber version of Gigabit Ethernet ● Uses long wavelengths of 1,300 nanometers ● Used for long backbones connecting buildings in a MAN or for connecting ISP with its telecommunications carrier ■ 1000Base-SX ● Less expensive to install ● Uses shorter wavelengths of 850 nanometers ● Maximum segment length dependent on two things: ○ Diameter of the fiber ○ Modal bandwidth - measure of highest frequency of signal a multimode fiber can support over a specific distance, measured in MHz-km. Related to distortion occurring when multiple pulses of light arrive at end of fiber at slightly different times. The higher the modal bandwidth, the longer a multimode fiber can carry a signal reliably. ○ Cabling problems unique to fiber include: ■ fiber type mismatch ■ wavelength mismatch  13  ■ dirty connectors ● TROUBLESHOOTING TOOLS ○ Start troubleshooting a network connection problem by checking the network connection LED status indicator lights on the network ports of the devices involved. ○ A tone generator issues a signal on a wire (that can be detected by a tone locator) which emits an audible tone when the electrical signal is nearby. ○ A tone locator emits a tone when it detects electrical activity on a wire ○ A multimeter can measure many characteristics of an electric circuit, including its: ■ Resistance (opposition to electrical current) ■ Voltage ■ Impedance ○ Short circuit - unwanted connection ○ Open circuit - needed connections are missing ○ Continuity - whether it is carrying a signal to its destination ○ A cable continuity tester is battery operated and has two parts: ■ the base unit that connects to one end of the cable and generates a voltage ■ the remote unit that connects to the other end of the cable and detects the voltage to determine continuity of wired connections inside the cable ○ A sophisticated cable performance tester will include a TDR (time domain reflector) that issues a signal on a cable and then measures the way the signal bounces back, detecting types and locations of cable defects.  14  ○ An OPM (optical power meter) measures the amount of light power transmitted on a fiber-optic line.   