H3C SecPath U200 Series Installation Manual

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H3C SecPath U200 Series Installation Manual Manual pdf 77 page image

68Appendix E CablesEthernet twisted pair cableIntroductionAn Ethernet twisted pair cable consists of four pairs of insulated copper wires twisted together. Everywire uses a different color, and has a diameter of about 1 mm (0.04 in). A pair of twisted coppercables can cancel the electromagnetic radiation of each other, and reduce interference of externalsources. An Ethernet twisted pair cable mainly transmits analog signals and is advantageous intransmitting data over shorter distances. It is the commonly used transmission media of the Ethernet. Themaximum transmission distance of the Ethernet twisted pair cable is 100 m (328.08 ft). To extend thetransmission distance, you can connect two twisted pair cable segments with a repeater. At most fourrepeaters can be added, which means five segments can be joined together to provide a transmissiondistance of 500 m (1640.42 ft).Ethernet twisted pair cables can be classified into category 3, category 4, category 5, category 5e,category 6, and category 7 cables based on performance. In LANs, category 5, category 5e, andcategory 6 are commonly used.Table 31 Ethernet cable descriptionType DescriptionCategory 5 Transmits data at a maximum speed of 100 Mbps.Category 5e Transmits data at a maximum speed of 1000 Mbps.Category 6 Transmits data at a speed higher than 1 Gbps.Based on whether a metal shielding is used, Ethernet twisted pair cables can be classified into shieldedtwisted pair (STP) and unshielded twisted pair (UTP). An STP cable provides a metallic braid betweenthe twisted pairs and the outer jacket. This metallic braid helps reduce radiation, prevent informationfrom being listened, and eliminate external electromagnetic interference (EMI) of external sources. STPshave strict application requirements and are expensive although they provide better EMI preventionperformance than UTPs, so in most LANs, UTPs are commonly used.An Ethernet twisted pair cable connects network devices through the RJ-45 connectors at the twoends. Figure 55 shows the pinouts of an RJ-45 connector.