Repeaters
5.1.6 This page will discuss how a repeater is used on a network.
The term repeater comes from the early days of long distance communication. A repeater was a person on one hill who would repeat the signal that was just received from the person on the previous hill. The process would repeat until the message arrived at its destination. Telegraph, telephone, microwave, and optical communications use repeaters to strengthen signals sent over long distances.
A repeater receives a signal, regenerates it, and passes it on. It can regenerate and retime network signals at the bit level to allow them to travel a longer distance on the media. Ethernet and IEEE 802.3 implement a rule, known as the 5-4-3 rule, for the number of repeaters and segments on shared access Ethernet backbones in a tree topology. The 5-4-3 rule divides the network into two types of physical segments: populated (user) segments, and unpopulated (link) segments. User segments have users' systems connected to them. Link segments are used to connect the network repeaters together. The rule mandates that between any two nodes on the network, there can only be a maximum of five segments, connected through four repeaters, or concentrators, and only three of the five segments may contain user connections.
The Ethernet protocol requires that a signal sent out over the LAN reach every part of the network within a specified length of time. The 5-4-3 rule ensures this. Each repeater that a signal goes through adds a small amount of time to the process, so the rule is designed to minimize transmission times of the signals. Too much latency on the LAN increases the number of late collisions and makes the LAN less efficient.
The next page will discuss hubs.
Hub
5.1.7 This page will describe the three types of hubs.
Hubs are actually multiport repeaters. The difference between hubs and repeaters is usually the number of ports that each device provides. A typical repeater usually has two ports. A hub generally has from 4 to 24 ports. Hubs are most commonly used in Ethernet 10BASE-T or 100BASE-T networks.
The use of a hub changes the network from a linear bus with each device plugged directly into the wire to a star topology. Data that arrives over the cables to a hub port is electrically repeated on all the other ports connected to the network segment.
Hubs come in three basic types:
• Passive – A passive hub serves as a physical connection point only. It does not manipulate or view the traffic that crosses it. It does not boost or clean the signal. A passive hub is used only to share the physical media. A passive hub does not need electrical power.
• Active – An active hub must be plugged into an electrical outlet because it needs power to amplify a signal before it is sent to the other ports.
• Intelligent – Intelligent hubs are sometimes called smart hubs. They function like active hubs with microprocessor chips and diagnostic capabilities. Intelligent hubs are more expensive than active hubs. They are also more useful in troubleshooting situations.
Devices attached to a hub receive all traffic that travels through the hub. If many devices are attached to the hub, collisions are more likely to occur. A collision occurs when two or more workstations send data over the network wire at the same time. All data is corrupted when this occurs. All devices that are connected to the same network segment are members of the same collision domain.
The next page discusses wireless networks.
Wireless
5.1.8 This page will explain how a wireless network can be created with much less cabling than other networks.
Wireless signals are electromagnetic waves that travel through the air. Wireless networks use radio frequency (RF), laser, infrared (IR), satellite, or microwaves to carry signals between computers without a permanent cable connection. The only permanent cabling can be to the access points for the network. Workstations within the range of the wireless network can be moved easily without the need to connect and reconnect network cables.
A common application of wireless data communication is for mobile use. Some examples of mobile use include commuters, airplanes, satellites, remote space probes, space shuttles, and space stations.
At the core of wireless communication are devices called transmitters and receivers. The transmitter converts source data to electromagnetic waves that are sent to the receiver. The receiver then converts these electromagnetic waves back into data for the destination. For two-way communication, each device requires a transmitter and a receiver. Many networking device manufacturers build the transmitter and receiver into a single unit called a transceiver or wireless network card. All devices in a WLAN must have the correct wireless network card installed.
The two most common wireless technologies used for networking are IR and RF. IR technology has its weaknesses. Workstations and digital devices must be in the line of sight of the transmitter to work correctly. An infrared-based network can be used when all the digital devices that require network connectivity are in one room. IR networking technology can be installed quickly. However, the data signals can be weakened or obstructed by people who walk across the room or by moisture in the air. New IR technologies will be able to work out of sight.
RF technology allows devices to be in different rooms or buildings. The limited range of radio signals restricts the use of this kind of network. RF technology can be on single or multiple frequencies. A single radio frequency is subject to outside interference and geographic obstructions. It is also easily monitored by others, which makes the transmissions of data insecure. Spread spectrum uses multiple frequencies to increase the immunity to noise and to make it difficult for outsiders to intercept data transmissions.
Two approaches that are used to implement spread spectrum for WLAN transmissions are Frequency Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Spectrum (DSSS). The technical details of how these technologies work are beyond the scope of this course.
A large LAN can be broken into smaller segments. The next page will explain how bridges are used to accomplish this.
Tuesday, December 29, 2009
Ethernet media and connector requirements / Connection media
Ethernet media and connector requirements
5.1.3 This page provides important considerations for an Ethernet implementation. These include the media and connector requirements and the level of network performance.
The cables and connector specifications used to support Ethernet implementations are derived from the EIA/TIA standards. The categories of cabling defined for Ethernet are derived from the EIA/TIA-568 SP-2840 Commercial Building Telecommunications Wiring Standards.
Figure compares the cable and connector specifications for the most popular Ethernet implementations. It is important to note the difference in the media used for 10-Mbps Ethernet versus 100-Mbps Ethernet. Networks with a combination of 10- and 100-Mbps traffic use Category 5 UTP to support Fast Ethernet.
The next page will discuss the different connection types.
Connection media
5.1.4 This page describes the different connection types used by each physical layer implementation, as shown in Figure . The RJ-45 connector and jack are the most common. RJ-45 connectors are discussed in more detail in the next section.
The connector on a NIC may not match the media to which it needs to connect. As shown in Figure , an interface may exist for the 15-pin attachment unit interface (AUI) connector. The AUI connector allows different media to connect when used with the appropriate transceiver. A transceiver is an adapter that converts one type of connection to another. A transceiver will usually convert an AUI to an RJ-45, a coax, or a fiber optic connector. On 10BASE5 Ethernet, or Thicknet, a short cable is used to connect the AUI with a transceiver on the main cable.
The next page will discuss UTP cables.
UTP implementation
5.1.5 This page provides detailed information for a UTP implementation.
EIA/TIA specifies an RJ-45 connector for UTP cable. The letters RJ stand for registered jack and the number 45 refers to a specific wiring sequence. The RJ-45 transparent end connector shows eight colored wires. Four of the wires, T1 through T4, carry the voltage and are called tip. The other four wires, R1 through R4, are grounded and are called ring. Tip and ring are terms that originated in the early days of the telephone. Today, these terms refer to the positive and the negative wire in a pair. The wires in the first pair in a cable or a connector are designated as T1 and R1. The second pair is T2 and R2, the third is T3 and R3, and the fourth is T4 and R4.
The RJ-45 connector is the male component, which is crimped on the end of the cable. When a male connector is viewed from the front, the pin locations are numbered from 8 on the left to 1 on the right as seen in Figure .
The jack is the female component in a network device, wall outlet, or patch panel as seen in Figure . Figure shows the punch-down connections at the back of the jack where the Ethernet UTP cable connects.
For electricity to run between the connector and the jack, the order of the wires must follow T568A or T568B color code found in the EIA/TIA-568-B.1 standard, as shown in Figure . To determine the EIA/TIA category of cable that should be used to connect a device, refer to the documentation for that device or look for a label on the device near the jack. If there are no labels or documentation available, use Category 5E or greater as higher categories can be used in place of lower ones. Then determine whether to use a straight-through cable or a crossover cable.
If the two RJ-45 connectors of a cable are held side by side in the same orientation, the colored wires will be seen in each. If the order of the colored wires is the same at each end, then the cable is a straight-through, as seen in Figure .
In a crossover cable, the RJ-45 connectors on both ends show that some of the wires are connected to different pins on each side of the cable. Figure shows that pins 1 and 2 on one connector connect to pins 3 and 6 on the other.
Figure shows the guidelines that are used to determine the type of cable that is required to connect Cisco devices.
Use straight-through cables for the following connections:
• Switch to router
• Switch to PC or server
• Hub to PC or server
Use crossover cables for the following connections:
• Switch to switch
• Switch to hub
• Hub to hub
• Router to router
• PC to PC
• Router to PC
The category of UTP cable required is based on the type of Ethernet that is chosen.
The next page explains how repeaters work.
5.1.3 This page provides important considerations for an Ethernet implementation. These include the media and connector requirements and the level of network performance.
The cables and connector specifications used to support Ethernet implementations are derived from the EIA/TIA standards. The categories of cabling defined for Ethernet are derived from the EIA/TIA-568 SP-2840 Commercial Building Telecommunications Wiring Standards.
Figure compares the cable and connector specifications for the most popular Ethernet implementations. It is important to note the difference in the media used for 10-Mbps Ethernet versus 100-Mbps Ethernet. Networks with a combination of 10- and 100-Mbps traffic use Category 5 UTP to support Fast Ethernet.
The next page will discuss the different connection types.
Connection media
5.1.4 This page describes the different connection types used by each physical layer implementation, as shown in Figure . The RJ-45 connector and jack are the most common. RJ-45 connectors are discussed in more detail in the next section.
The connector on a NIC may not match the media to which it needs to connect. As shown in Figure , an interface may exist for the 15-pin attachment unit interface (AUI) connector. The AUI connector allows different media to connect when used with the appropriate transceiver. A transceiver is an adapter that converts one type of connection to another. A transceiver will usually convert an AUI to an RJ-45, a coax, or a fiber optic connector. On 10BASE5 Ethernet, or Thicknet, a short cable is used to connect the AUI with a transceiver on the main cable.
The next page will discuss UTP cables.
UTP implementation
5.1.5 This page provides detailed information for a UTP implementation.
EIA/TIA specifies an RJ-45 connector for UTP cable. The letters RJ stand for registered jack and the number 45 refers to a specific wiring sequence. The RJ-45 transparent end connector shows eight colored wires. Four of the wires, T1 through T4, carry the voltage and are called tip. The other four wires, R1 through R4, are grounded and are called ring. Tip and ring are terms that originated in the early days of the telephone. Today, these terms refer to the positive and the negative wire in a pair. The wires in the first pair in a cable or a connector are designated as T1 and R1. The second pair is T2 and R2, the third is T3 and R3, and the fourth is T4 and R4.
The RJ-45 connector is the male component, which is crimped on the end of the cable. When a male connector is viewed from the front, the pin locations are numbered from 8 on the left to 1 on the right as seen in Figure .
The jack is the female component in a network device, wall outlet, or patch panel as seen in Figure . Figure shows the punch-down connections at the back of the jack where the Ethernet UTP cable connects.
For electricity to run between the connector and the jack, the order of the wires must follow T568A or T568B color code found in the EIA/TIA-568-B.1 standard, as shown in Figure . To determine the EIA/TIA category of cable that should be used to connect a device, refer to the documentation for that device or look for a label on the device near the jack. If there are no labels or documentation available, use Category 5E or greater as higher categories can be used in place of lower ones. Then determine whether to use a straight-through cable or a crossover cable.
If the two RJ-45 connectors of a cable are held side by side in the same orientation, the colored wires will be seen in each. If the order of the colored wires is the same at each end, then the cable is a straight-through, as seen in Figure .
In a crossover cable, the RJ-45 connectors on both ends show that some of the wires are connected to different pins on each side of the cable. Figure shows that pins 1 and 2 on one connector connect to pins 3 and 6 on the other.
Figure shows the guidelines that are used to determine the type of cable that is required to connect Cisco devices.
Use straight-through cables for the following connections:
• Switch to router
• Switch to PC or server
• Hub to PC or server
Use crossover cables for the following connections:
• Switch to switch
• Switch to hub
• Hub to hub
• Router to router
• PC to PC
• Router to PC
The category of UTP cable required is based on the type of Ethernet that is chosen.
The next page explains how repeaters work.
Cabling LANs / LAN physical layer / Ethernet in the campus
LAN physical layer
5.1.1 This page describes the LAN physical layer.
Various symbols are used to represent media types. Token Ring is represented by a circle. FDDI is represented by two concentric circles and the Ethernet symbol is represented by a straight line. Serial connections are represented by a lightning bolt.
Each computer network can be built with many different media types. The function of media is to carry a flow of information through a LAN. Wireless LANs use the atmosphere, or space, as the medium. Other networking media confine network signals to a wire, cable, or fiber. Networking media are considered Layer 1, or physical layer, components of LANs.
Each type of media has advantages and disadvantages. These are based on the following factors:
• Cable length
• Cost
• Ease of installation
• Susceptibility to interference
Coaxial cable, optical fiber, and space can carry network signals. This module will focus on Category 5 UTP, which includes the Category 5e family of cables.
Many topologies support LANs, as well as many different physical media. Figure shows a subset of physical layer implementations that can be deployed to support Ethernet.
The next page explains how Ethernet is implemented in a campus environment.
Ethernet in the campus
5.1.2 This page will discuss Ethernet.
Ethernet is the most widely used LAN technology. Ethernet was first implemented by the Digital, Intel, and Xerox group (DIX). DIX created and implemented the first Ethernet LAN specification, which was used as the basis for the Institute of Electrical and Electronics Engineers (IEEE) 802.3 specification, released in 1980. IEEE extended 802.3 to three new committees known as 802.3u for Fast Ethernet, 802.3z for Gigabit Ethernet over fiber, and 802.3ab for Gigabit Ethernet over UTP.
A network may require an upgrade to one of the faster Ethernet topologies. Most Ethernet networks support speeds of 10 Mbps and 100 Mbps.
The new generation of multimedia, imaging, and database products can easily overwhelm a network that operates at traditional Ethernet speeds of 10 and 100 Mbps. Network administrators may choose to provide Gigabit Ethernet from the backbone to the end user. Installation costs for new cables and adapters can make this prohibitive.
There are several ways that Ethernet technologies can be used in a campus network:
• An Ethernet speed of 10 Mbps can be used at the user level to provide good performance. Clients or servers that require more bandwidth can use 100-Mbps Ethernet.
• Fast Ethernet is used as the link between user and network devices. It can support the combination of all traffic from each Ethernet segment.
• Fast Ethernet can be used to connect enterprise servers. This will enhance client-server performance across the campus network and help prevent bottlenecks.
• Fast Ethernet or Gigabit Ethernet should be implemented between backbone devices, based on affordability.
The media and connector requirements for an Ethernet implementation are discussed on the next page.
5.1.1 This page describes the LAN physical layer.
Various symbols are used to represent media types. Token Ring is represented by a circle. FDDI is represented by two concentric circles and the Ethernet symbol is represented by a straight line. Serial connections are represented by a lightning bolt.
Each computer network can be built with many different media types. The function of media is to carry a flow of information through a LAN. Wireless LANs use the atmosphere, or space, as the medium. Other networking media confine network signals to a wire, cable, or fiber. Networking media are considered Layer 1, or physical layer, components of LANs.
Each type of media has advantages and disadvantages. These are based on the following factors:
• Cable length
• Cost
• Ease of installation
• Susceptibility to interference
Coaxial cable, optical fiber, and space can carry network signals. This module will focus on Category 5 UTP, which includes the Category 5e family of cables.
Many topologies support LANs, as well as many different physical media. Figure shows a subset of physical layer implementations that can be deployed to support Ethernet.
The next page explains how Ethernet is implemented in a campus environment.
Ethernet in the campus
5.1.2 This page will discuss Ethernet.
Ethernet is the most widely used LAN technology. Ethernet was first implemented by the Digital, Intel, and Xerox group (DIX). DIX created and implemented the first Ethernet LAN specification, which was used as the basis for the Institute of Electrical and Electronics Engineers (IEEE) 802.3 specification, released in 1980. IEEE extended 802.3 to three new committees known as 802.3u for Fast Ethernet, 802.3z for Gigabit Ethernet over fiber, and 802.3ab for Gigabit Ethernet over UTP.
A network may require an upgrade to one of the faster Ethernet topologies. Most Ethernet networks support speeds of 10 Mbps and 100 Mbps.
The new generation of multimedia, imaging, and database products can easily overwhelm a network that operates at traditional Ethernet speeds of 10 and 100 Mbps. Network administrators may choose to provide Gigabit Ethernet from the backbone to the end user. Installation costs for new cables and adapters can make this prohibitive.
There are several ways that Ethernet technologies can be used in a campus network:
• An Ethernet speed of 10 Mbps can be used at the user level to provide good performance. Clients or servers that require more bandwidth can use 100-Mbps Ethernet.
• Fast Ethernet is used as the link between user and network devices. It can support the combination of all traffic from each Ethernet segment.
• Fast Ethernet can be used to connect enterprise servers. This will enhance client-server performance across the campus network and help prevent bottlenecks.
• Fast Ethernet or Gigabit Ethernet should be implemented between backbone devices, based on affordability.
The media and connector requirements for an Ethernet implementation are discussed on the next page.
Module 5 : Cabling LANs and WANs Overview
Cabling LANs and WANs
Overview
Even though each LAN is unique, there are many design aspects that are common to all LANs. For example, most LANs follow the same standards and use the same components. This module presents information on elements of Ethernet LANs and common LAN devices.
There are several types of WAN connections. They range from dial-up to broadband access and differ in bandwidth, cost, and required equipment. This module presents information on the various types of WAN connections.
This module covers some of the objectives for the CCNA 640-801, INTRO 640-821, and ICND 640-811 exams.
Students who complete this module should be able to perform the following tasks:
• Identify characteristics of Ethernet networks
• Identify straight-through, crossover, and rollover cables
• Describe the function, advantages, and disadvantages of repeaters, hubs, bridges, switches, and wireless network components
• Describe the function of peer-to-peer networks
• Describe the function, advantages, and disadvantages of client-server networks
• Describe and differentiate between serial, ISDN, DSL, and cable modem WAN connections
• Identify router serial ports, cables, and connectors
• Identify and describe the placement of equipment used in various WAN configurations
Overview
Even though each LAN is unique, there are many design aspects that are common to all LANs. For example, most LANs follow the same standards and use the same components. This module presents information on elements of Ethernet LANs and common LAN devices.
There are several types of WAN connections. They range from dial-up to broadband access and differ in bandwidth, cost, and required equipment. This module presents information on the various types of WAN connections.
This module covers some of the objectives for the CCNA 640-801, INTRO 640-821, and ICND 640-811 exams.
Students who complete this module should be able to perform the following tasks:
• Identify characteristics of Ethernet networks
• Identify straight-through, crossover, and rollover cables
• Describe the function, advantages, and disadvantages of repeaters, hubs, bridges, switches, and wireless network components
• Describe the function of peer-to-peer networks
• Describe the function, advantages, and disadvantages of client-server networks
• Describe and differentiate between serial, ISDN, DSL, and cable modem WAN connections
• Identify router serial ports, cables, and connectors
• Identify and describe the placement of equipment used in various WAN configurations
Thursday, December 24, 2009
Summary of Module 4
Summary
Data symbolizing characters, words, pictures, video, or music can be represented electrically by voltage patterns on wires and in electronic devices. The data represented by these voltage patterns can be converted to light waves or radio waves, and then back to voltage patterns. Waves are energy traveling from one place to another, and are created by disturbances. All waves have similar attributes such as amplitude, period, and frequency. Sine waves are periodic, continuously varying functions. Analog signals look like sine waves. Square waves are periodic functions whose values remain constant for a period of time and then change abruptly. Digital signals look like square waves.
Exponents are used to represent very large or very small numbers. The base of a number raised to a positive exponent is equal to the base multiplied by itself exponent times. For example, 103 = 10x10x10 = 1000. Logarithms are similar to exponents. A logarithm to the base of 10 of a number equals the exponent to which 10 would have to be raised in order to equal the number. For example, log10 1000 = 3 because 103 = 1000.
Decibels are measurements of a gain or loss in the power of a signal. Negative values represent losses and positive values represent gains. Time and frequency analysis can both be used to graph the voltage or power of a signal.
Undesirable signals in a communications system are called noise. Noise originates from other cables, radio frequency interference (RFI), and electromagnetic interference (EMI). Noise may affect all signal frequencies or a subset of frequencies.
Analog bandwidth is the frequency range that is associated with certain analog transmission, such as television or FM radio. Digital bandwidth measures how much information can flow from one place to another in a given amount of time. Its units are in various multiples of bits per second.
On copper cable, data signals are represented by voltage levels that correspond to binary ones and zeros. In order for the LAN to operate properly, the receiving device must be able to accurately interpret the bit signal. Proper cable installation according to standards increases LAN reliability and performance.
Signal degradation is due to various factors such as attenuation, impedance mismatch, noise, and several types of crosstalk. Attenuation is the decrease in signal amplitude over the length of a link. Impedance is a measurement of resistance to the electrical signal. Cables and the connectors used on them must have similar impedance values or some of the data signal may be reflected back from a connector. This is referred to as impedance mismatch or impedance discontinuity. Noise is any electrical energy on the transmission cable that makes it difficult for a receiver to interpret the data sent from the transmitter. Crosstalk involves the transmission of signals from one wire to a nearby wire. There are three distinct types of crosstalk: Near-end Crosstalk (NEXT), Far-end Crosstalk (FEXT), Power Sum Near-end Crosstalk (PSNEXT).
STP and UTP cable are designed to take advantage of the effects of crosstalk in order to minimize noise. Additionally, STP contains an outer conductive shield and inner foil shields that make it less susceptible to noise. UTP contains no shielding and is more susceptible to external noise but is the most frequently used because it is inexpensive and easier to install.
Fiber-optic cable is used to transmit data signals by increasing and decreasing the intensity of light to represent binary ones and zeros. The strength of a light signal does not diminish like the strength of an electrical signal does over an identical run length. Optical signals are not affected by electrical noise, and optical fiber does not need to be grounded. Therefore, optical fiber is often used between buildings and between floors within a building.
The TIA/EIA-568-B standard specifies ten tests that a copper cable must pass if it will be used for modern, high-speed Ethernet LANs. Optical fiber must also be tested according to networking standards. Category 6 cable must meet more rigorous frequency testing standards than Category 5 cable.
Data symbolizing characters, words, pictures, video, or music can be represented electrically by voltage patterns on wires and in electronic devices. The data represented by these voltage patterns can be converted to light waves or radio waves, and then back to voltage patterns. Waves are energy traveling from one place to another, and are created by disturbances. All waves have similar attributes such as amplitude, period, and frequency. Sine waves are periodic, continuously varying functions. Analog signals look like sine waves. Square waves are periodic functions whose values remain constant for a period of time and then change abruptly. Digital signals look like square waves.
Exponents are used to represent very large or very small numbers. The base of a number raised to a positive exponent is equal to the base multiplied by itself exponent times. For example, 103 = 10x10x10 = 1000. Logarithms are similar to exponents. A logarithm to the base of 10 of a number equals the exponent to which 10 would have to be raised in order to equal the number. For example, log10 1000 = 3 because 103 = 1000.
Decibels are measurements of a gain or loss in the power of a signal. Negative values represent losses and positive values represent gains. Time and frequency analysis can both be used to graph the voltage or power of a signal.
Undesirable signals in a communications system are called noise. Noise originates from other cables, radio frequency interference (RFI), and electromagnetic interference (EMI). Noise may affect all signal frequencies or a subset of frequencies.
Analog bandwidth is the frequency range that is associated with certain analog transmission, such as television or FM radio. Digital bandwidth measures how much information can flow from one place to another in a given amount of time. Its units are in various multiples of bits per second.
On copper cable, data signals are represented by voltage levels that correspond to binary ones and zeros. In order for the LAN to operate properly, the receiving device must be able to accurately interpret the bit signal. Proper cable installation according to standards increases LAN reliability and performance.
Signal degradation is due to various factors such as attenuation, impedance mismatch, noise, and several types of crosstalk. Attenuation is the decrease in signal amplitude over the length of a link. Impedance is a measurement of resistance to the electrical signal. Cables and the connectors used on them must have similar impedance values or some of the data signal may be reflected back from a connector. This is referred to as impedance mismatch or impedance discontinuity. Noise is any electrical energy on the transmission cable that makes it difficult for a receiver to interpret the data sent from the transmitter. Crosstalk involves the transmission of signals from one wire to a nearby wire. There are three distinct types of crosstalk: Near-end Crosstalk (NEXT), Far-end Crosstalk (FEXT), Power Sum Near-end Crosstalk (PSNEXT).
STP and UTP cable are designed to take advantage of the effects of crosstalk in order to minimize noise. Additionally, STP contains an outer conductive shield and inner foil shields that make it less susceptible to noise. UTP contains no shielding and is more susceptible to external noise but is the most frequently used because it is inexpensive and easier to install.
Fiber-optic cable is used to transmit data signals by increasing and decreasing the intensity of light to represent binary ones and zeros. The strength of a light signal does not diminish like the strength of an electrical signal does over an identical run length. Optical signals are not affected by electrical noise, and optical fiber does not need to be grounded. Therefore, optical fiber is often used between buildings and between floors within a building.
The TIA/EIA-568-B standard specifies ten tests that a copper cable must pass if it will be used for modern, high-speed Ethernet LANs. Optical fiber must also be tested according to networking standards. Category 6 cable must meet more rigorous frequency testing standards than Category 5 cable.
A new standard
A new standard (Optional)
4.2.9 This page discusses the new test standards for Category 6 cable.
On June 20, 2002, the Category 6 addition to the TIA-568 standard was published. The official title of the standard is ANSI/TIA/EIA-568-B.2-1. This new standard specifies the original set of performance parameters that need to be tested for Ethernet cabling as well as the passing scores for each of these tests. Cables certified as Category 6 cable must pass all ten tests.
Although the Category 6 tests are essentially the same as those specified by the Category 5 standard, Category 6 cable must pass the tests with higher scores to be certified. Category 6 cable must be capable of carrying frequencies up to 250 MHz and must have lower levels of crosstalk and return loss.
A quality cable tester similar to the Fluke DSP-4000 series or Fluke OMNIScanner2 can perform all the test measurements required for Category 5, Category 5e, and Category 6 cable certifications of both permanent links and channel links. Figure shows the Fluke DSP-4100 Cable Analyzer with a DSP-LIA013 Channel/Traffic Adapter for Category 5e.
The Lab Activities will teach students how to use a cable tester.
This page concludes this lesson. The next page will summarize the main points from the module.
4.2.9 This page discusses the new test standards for Category 6 cable.
On June 20, 2002, the Category 6 addition to the TIA-568 standard was published. The official title of the standard is ANSI/TIA/EIA-568-B.2-1. This new standard specifies the original set of performance parameters that need to be tested for Ethernet cabling as well as the passing scores for each of these tests. Cables certified as Category 6 cable must pass all ten tests.
Although the Category 6 tests are essentially the same as those specified by the Category 5 standard, Category 6 cable must pass the tests with higher scores to be certified. Category 6 cable must be capable of carrying frequencies up to 250 MHz and must have lower levels of crosstalk and return loss.
A quality cable tester similar to the Fluke DSP-4000 series or Fluke OMNIScanner2 can perform all the test measurements required for Category 5, Category 5e, and Category 6 cable certifications of both permanent links and channel links. Figure shows the Fluke DSP-4100 Cable Analyzer with a DSP-LIA013 Channel/Traffic Adapter for Category 5e.
The Lab Activities will teach students how to use a cable tester.
This page concludes this lesson. The next page will summarize the main points from the module.
Cable testing standards / Test parameters / Time base parameters / Testing Optical Fiber
Cable testing standards (Core)
4.2.5 This page will describe the TIA/EIA-568-B standard. This standard specifies ten tests that a copper cable must pass if it will be used for modern, high-speed Ethernet LANs.
All cable links should be tested to the maximum rating that applies for the category of cable being installed.
The ten primary test parameters that must be verified for a cable link to meet TIA/EIA standards are:
• Wire map
• Insertion loss
• Near-end crosstalk (NEXT)
• Power sum near-end crosstalk (PSNEXT)
• Equal-level far-end crosstalk (ELFEXT)
• Power sum equal-level far-end crosstalk (PSELFEXT)
• Return loss
• Propagation delay
• Cable length
• Delay skew
The Ethernet standard specifies that each of the pins on an RJ-45 connector have a particular purpose. A NIC transmits signals on pins 1 and 2, and it receives signals on pins 3 and 6. The wires in UTP cable must be connected to the proper pins at each end of a cable. The wire map test insures that no open or short circuits exist on the cable. An open circuit occurs if the wire does not attach properly at the connector. A short circuit occurs if two wires are connected to each other.
The wire map test also verifies that all eight wires are connected to the correct pins on both ends of the cable. There are several different wiring faults that the wire map test can detect. The reversed-pair fault occurs when a wire pair is correctly installed on one connector, but reversed on the other connector. If the white/orange wire is terminated on pin 1 and the orange wire is terminated on pin 2 at one end of a cable, but reversed at the other end, then the cable has a reversed-pair fault. This example is shown in the graphic.
A split-pair wiring fault occurs when one wire from one pair is switched with one wire from a different pair at both ends. Look carefully at the pin numbers in the graphic to detect the wiring fault. A split pair creates two transmit or receive pairs each with two wires that are not twisted together. This mixing hampers the cross-cancellation process and makes the cable more susceptible to crosstalk and interference. Contrast this with a reversed-pair, where the same pair of pins is used at both ends.
Other test parameters (Optional)
4.2.6 This page will explain how cables are tested for crosstalk and attenuation.
The combination of the effects of signal attenuation and impedance discontinuities on a communications link is called insertion loss. Insertion loss is measured in decibels at the far end of the cable. The TIA/EIA standard requires that a cable and its connectors pass an insertion loss test before the cable can be used as a communications link in a LAN.
Crosstalk is measured in four separate tests. A cable tester measures NEXT by applying a test signal to one cable pair and measuring the amplitude of the crosstalk signals received by the other cable pairs. The NEXT value, expressed in decibels, is computed as the difference in amplitude between the test signal and the crosstalk signal measured at the same end of the cable. Remember, because the number of decibels that the tester displays is a negative number, the larger the number, the lower the NEXT on the wire pair. As previously mentioned, the PSNEXT test is actually a calculation based on combined NEXT effects.
The equal-level far-end crosstalk (ELFEXT) test measures FEXT. Pair-to-pair ELFEXT is expressed in dB as the difference between the measured FEXT and the insertion loss of the wire pair whose signal is disturbed by the FEXT. ELFEXT is an important measurement in Ethernet networks using 1000BASE-T technologies. Power sum equal-level far-end crosstalk (PSELFEXT) is the combined effect of ELFEXT from all wire pairs.
Return loss is a measure in decibels of reflections that are caused by the impedance discontinuities at all locations along the link. Recall that the main impact of return loss is not on loss of signal strength. The significant problem is that signal echoes caused by the reflections from the impedance discontinuities will strike the receiver at different intervals causing signal jitter.
Time-based parameters (Optional)
4.2.7 This page will discuss propegation delay and how it is measured.
Propagation delay is a simple measurement of how long it takes for a signal to travel along the cable being tested. The delay in a wire pair depends on its length, twist rate, and electrical properties. Delays are measured in hundredths of nanoseconds. One nanosecond is one-billionth of a second, or 0.000000001 second. The TIA/EIA-568-B standard sets a limit for propagation delay for the various categories of UTP.
Propagation delay measurements are the basis of the cable length measurement. TIA/EIA-568-B.1 specifies that the physical length of the link shall be calculated using the wire pair with the shortest electrical delay. Testers measure the length of the wire based on the electrical delay as measured by a Time Domain Reflectometry (TDR) test, not by the physical length of the cable jacket. Since the wires inside the cable are twisted, signals actually travel farther than the physical length of the cable. When a cable tester makes a TDR measurement, it sends a pulse signal down a wire pair and measures the amount of time required for the pulse to return on the same wire pair.
The TDR test is used not only to determine length, but also to identify the distance to wiring faults such as shorts and opens. When the pulse encounters an open, short, or poor connection, all or part of the pulse energy is reflected back to the tester. This can be used to calculate the approximate distance to the wiring fault. The approximate distance can be helpful in locating a faulty connection point along a cable run, such as a wall jack.
The propagation delays of different wire pairs in a single cable can differ slightly because of differences in the number of twists and electrical properties of each wire pair. The delay difference between pairs is called delay skew. Delay skew is a critical parameter for high-speed networks in which data is simultaneously transmitted over multiple wire pairs, such as 1000BASE-T Ethernet. If the delay skew between the pairs is too great, the bits arrive at different times and the data cannot be properly reassembled. Even though a cable link may not be intended for this type of data transmission, testing for delay skew helps ensure that the link will support future upgrades to high-speed networks.
All cable links in a LAN must pass all of the tests previously mentioned as specified in the TIA/EIA-568-B standard in order to be considered standards compliant. A certification meter must be used to ensure that all of the tests are passed in order to be considered standards compliant. These tests ensure that the cable links will function reliably at high speeds and frequencies. Cable tests should be performed when the cable is installed and afterward on a regular basis to ensure that LAN cabling meets industry standards. High quality cable test instruments should be correctly used to ensure that the tests are accurate. Test results should also be carefully documented.
Testing optical fiber (Optional)
4.2.8 This page will explain how optical fiber is tested.
A fiber link consists of two separate glass fibers functioning as independent data pathways. One fiber carries transmitted signals in one direction, while the second carries signals in the opposite direction. Each glass fiber is surrounded by a sheath that light cannot pass through, so there are no crosstalk problems on fiber optic cable. External electromagnetic interference or noise has no affect on fiber cabling. Attenuation does occur on fiber links, but to a lesser extent than on copper cabling.
Fiber links are subject to the optical equivalent of UTP impedance discontinuities. When light encounters an optical discontinuity, like an impurity in the glass or a micro-fracture, some of the light signal is reflected back in the opposite direction. This means only a fraction of the original light signal will continue down the fiber towards the receiver. This results in a reduced amount of light energy arriving at the receiver, making signal recognition difficult. Just as with UTP cable, improperly installed connectors are the main cause of light reflection and signal strength loss in optical fiber.
Because noise is not an issue when transmitting on optical fiber, the main concern with a fiber link is the strength of the light signal that arrives at the receiver. If attenuation weakens the light signal at the receiver, then data errors will result. Testing fiber optic cable primarily involves shining a light down the fiber and measuring whether a sufficient amount of light reaches the receiver.
On a fiber optic link, the acceptable amount of signal power loss that can occur without dropping below the requirements of the receiver must be calculated. This calculation is referred to as the optical link loss budget. A fiber test instrument, known as a light source and power meter, checks whether the optical link loss budget has been exceeded. If the fiber fails the test, another cable test instrument can be used to indicate where the optical discontinuities occur along the length of the cable link. An optical TDR known as an OTDR is capable of locating these discontinuities. Usually, the problem is one or more improperly attached connectors. The OTDR will indicate the location of the faulty connections that must be replaced. When the faults are corrected, the cable must be retested.
The standards for testing are updated regularly. The next page will introduce a new standard.
4.2.5 This page will describe the TIA/EIA-568-B standard. This standard specifies ten tests that a copper cable must pass if it will be used for modern, high-speed Ethernet LANs.
All cable links should be tested to the maximum rating that applies for the category of cable being installed.
The ten primary test parameters that must be verified for a cable link to meet TIA/EIA standards are:
• Wire map
• Insertion loss
• Near-end crosstalk (NEXT)
• Power sum near-end crosstalk (PSNEXT)
• Equal-level far-end crosstalk (ELFEXT)
• Power sum equal-level far-end crosstalk (PSELFEXT)
• Return loss
• Propagation delay
• Cable length
• Delay skew
The Ethernet standard specifies that each of the pins on an RJ-45 connector have a particular purpose. A NIC transmits signals on pins 1 and 2, and it receives signals on pins 3 and 6. The wires in UTP cable must be connected to the proper pins at each end of a cable. The wire map test insures that no open or short circuits exist on the cable. An open circuit occurs if the wire does not attach properly at the connector. A short circuit occurs if two wires are connected to each other.
The wire map test also verifies that all eight wires are connected to the correct pins on both ends of the cable. There are several different wiring faults that the wire map test can detect. The reversed-pair fault occurs when a wire pair is correctly installed on one connector, but reversed on the other connector. If the white/orange wire is terminated on pin 1 and the orange wire is terminated on pin 2 at one end of a cable, but reversed at the other end, then the cable has a reversed-pair fault. This example is shown in the graphic.
A split-pair wiring fault occurs when one wire from one pair is switched with one wire from a different pair at both ends. Look carefully at the pin numbers in the graphic to detect the wiring fault. A split pair creates two transmit or receive pairs each with two wires that are not twisted together. This mixing hampers the cross-cancellation process and makes the cable more susceptible to crosstalk and interference. Contrast this with a reversed-pair, where the same pair of pins is used at both ends.
Other test parameters (Optional)
4.2.6 This page will explain how cables are tested for crosstalk and attenuation.
The combination of the effects of signal attenuation and impedance discontinuities on a communications link is called insertion loss. Insertion loss is measured in decibels at the far end of the cable. The TIA/EIA standard requires that a cable and its connectors pass an insertion loss test before the cable can be used as a communications link in a LAN.
Crosstalk is measured in four separate tests. A cable tester measures NEXT by applying a test signal to one cable pair and measuring the amplitude of the crosstalk signals received by the other cable pairs. The NEXT value, expressed in decibels, is computed as the difference in amplitude between the test signal and the crosstalk signal measured at the same end of the cable. Remember, because the number of decibels that the tester displays is a negative number, the larger the number, the lower the NEXT on the wire pair. As previously mentioned, the PSNEXT test is actually a calculation based on combined NEXT effects.
The equal-level far-end crosstalk (ELFEXT) test measures FEXT. Pair-to-pair ELFEXT is expressed in dB as the difference between the measured FEXT and the insertion loss of the wire pair whose signal is disturbed by the FEXT. ELFEXT is an important measurement in Ethernet networks using 1000BASE-T technologies. Power sum equal-level far-end crosstalk (PSELFEXT) is the combined effect of ELFEXT from all wire pairs.
Return loss is a measure in decibels of reflections that are caused by the impedance discontinuities at all locations along the link. Recall that the main impact of return loss is not on loss of signal strength. The significant problem is that signal echoes caused by the reflections from the impedance discontinuities will strike the receiver at different intervals causing signal jitter.
Time-based parameters (Optional)
4.2.7 This page will discuss propegation delay and how it is measured.
Propagation delay is a simple measurement of how long it takes for a signal to travel along the cable being tested. The delay in a wire pair depends on its length, twist rate, and electrical properties. Delays are measured in hundredths of nanoseconds. One nanosecond is one-billionth of a second, or 0.000000001 second. The TIA/EIA-568-B standard sets a limit for propagation delay for the various categories of UTP.
Propagation delay measurements are the basis of the cable length measurement. TIA/EIA-568-B.1 specifies that the physical length of the link shall be calculated using the wire pair with the shortest electrical delay. Testers measure the length of the wire based on the electrical delay as measured by a Time Domain Reflectometry (TDR) test, not by the physical length of the cable jacket. Since the wires inside the cable are twisted, signals actually travel farther than the physical length of the cable. When a cable tester makes a TDR measurement, it sends a pulse signal down a wire pair and measures the amount of time required for the pulse to return on the same wire pair.
The TDR test is used not only to determine length, but also to identify the distance to wiring faults such as shorts and opens. When the pulse encounters an open, short, or poor connection, all or part of the pulse energy is reflected back to the tester. This can be used to calculate the approximate distance to the wiring fault. The approximate distance can be helpful in locating a faulty connection point along a cable run, such as a wall jack.
The propagation delays of different wire pairs in a single cable can differ slightly because of differences in the number of twists and electrical properties of each wire pair. The delay difference between pairs is called delay skew. Delay skew is a critical parameter for high-speed networks in which data is simultaneously transmitted over multiple wire pairs, such as 1000BASE-T Ethernet. If the delay skew between the pairs is too great, the bits arrive at different times and the data cannot be properly reassembled. Even though a cable link may not be intended for this type of data transmission, testing for delay skew helps ensure that the link will support future upgrades to high-speed networks.
All cable links in a LAN must pass all of the tests previously mentioned as specified in the TIA/EIA-568-B standard in order to be considered standards compliant. A certification meter must be used to ensure that all of the tests are passed in order to be considered standards compliant. These tests ensure that the cable links will function reliably at high speeds and frequencies. Cable tests should be performed when the cable is installed and afterward on a regular basis to ensure that LAN cabling meets industry standards. High quality cable test instruments should be correctly used to ensure that the tests are accurate. Test results should also be carefully documented.
Testing optical fiber (Optional)
4.2.8 This page will explain how optical fiber is tested.
A fiber link consists of two separate glass fibers functioning as independent data pathways. One fiber carries transmitted signals in one direction, while the second carries signals in the opposite direction. Each glass fiber is surrounded by a sheath that light cannot pass through, so there are no crosstalk problems on fiber optic cable. External electromagnetic interference or noise has no affect on fiber cabling. Attenuation does occur on fiber links, but to a lesser extent than on copper cabling.
Fiber links are subject to the optical equivalent of UTP impedance discontinuities. When light encounters an optical discontinuity, like an impurity in the glass or a micro-fracture, some of the light signal is reflected back in the opposite direction. This means only a fraction of the original light signal will continue down the fiber towards the receiver. This results in a reduced amount of light energy arriving at the receiver, making signal recognition difficult. Just as with UTP cable, improperly installed connectors are the main cause of light reflection and signal strength loss in optical fiber.
Because noise is not an issue when transmitting on optical fiber, the main concern with a fiber link is the strength of the light signal that arrives at the receiver. If attenuation weakens the light signal at the receiver, then data errors will result. Testing fiber optic cable primarily involves shining a light down the fiber and measuring whether a sufficient amount of light reaches the receiver.
On a fiber optic link, the acceptable amount of signal power loss that can occur without dropping below the requirements of the receiver must be calculated. This calculation is referred to as the optical link loss budget. A fiber test instrument, known as a light source and power meter, checks whether the optical link loss budget has been exceeded. If the fiber fails the test, another cable test instrument can be used to indicate where the optical discontinuities occur along the length of the cable link. An optical TDR known as an OTDR is capable of locating these discontinuities. Usually, the problem is one or more improperly attached connectors. The OTDR will indicate the location of the faulty connections that must be replaced. When the faults are corrected, the cable must be retested.
The standards for testing are updated regularly. The next page will introduce a new standard.
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