TAILIEUCHUNG - CCNA 1 and 2 Companion Guide, Revised (Cisco Networking Academy Program) part 24

Cisco Networking Academy Program CCNA 1 and 2 Companion Guide, Revised part 24 is the Cisco approved textbook to use alongside version of the Cisco Networking Academy Program CCNA 1 and CCNA 2 web-based courses. The topics covered provide you with the necessary knowledge to begin your preparation for the CCNA certification exam (640-801, or 640-821 and 640-811) and to enter the field of network administration. | Page 199 Tuesday May 27 2003 9 01 AM Signals and Noise on Networking Media 199 Figure 4-15 Power Sum Near-End Crosstalk PSNEXT Some Ethernet standards such as 10BASE-T and 100BASE-TX receive data from only one wire pair in each direction. However for newer technologies such as 1000BASE-T that receive data simultaneously from multiple pairs in the same direction power sum measurements are important tests. Cable Testing Standards The TIA EIA-568-B standard specifies ten tests that a copper cable must pass if it is to 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 primary test parameters that must be verified for a cable link to meet TIA EIA-568-B standards are as follows 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 has a particular purpose as shown in Figure 4-16. A network interface card 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 Page 200 Tuesday May 27 2003 9 01 AM 200 Chapter 4 Cable Testing and Cabling LANs and WANs that no open or short circuits exist in 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. Figure 4-16 Ethernet Standards for RJ-45 Connectors Pinouts 1 G W 2 Green 3 O W 4 Blue 5 Blue W 6 Orange 7 Brown W 8 Brown T568A Pinouts 1 O W 2 Orange 3 G W 4 Blue 5 Blue W 6 Green 7 Brown W 8 Brown T568B The wire map test also verifies that all eight wires are connected to the correct pins on both ends of the cable. The wire map test

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