Tài liệu KRONE - White paper - Limitation of RJ21 in Ethernet pptx

Use of RJ-21 Connectors in 100Base-T Active Connectivity KRONE, Inc. has performed numerous site surveys of end-user networks over the past year, and it has come to our attention that many users are upgrading to new 100Base-T switches that utilize the RJ-21 connector, also commonly known as a “Telco” connector, or “Amphenol” type. It consists of a 50 pin connector that accepts 25 pairs of cable simultaneously. KRONE has not been recommending this type of interface to our customers due to serious technical limitations of this connector, as described in this paper. All versions of the RJ-21 that we have seen do not conform to the impedance matching requirements of KRONE’s TrueNet TM system, and consequently can seriously effect network performance. Figure 1 shows a TrueNet impedance matched channel. All components are matched for optimum performance together, and the distance plot shows a clean trace centered around a nominal 100 ohms. Impedance matching of cabling and components is critical for efficient data transmission. Research conducted by KRONE and Anixter shows that mismatched systems can be standards-compliant, and still allow frame error rates approaching 25% of packets sent ! (source- Anixter). Figure 2 shows the frequency trace of the channel shown in Figure 1. The impedance stays tightly controlled across the entire range of 100Base-T operation, from approximately 1 to 125 Megahertz. These charts are displayed to show a baseline for the comparisons that we will make to the RJ-21 interfaces that we have seen in the field. Figure 1: A TrueNet Matched- Impedance Channel RJ-21 Figure 2: Frequency Trace of a TrueNet Channel KRONE, Inc. 6950 S. Tucson Way, Suite R Englewood, Colorado 80112 1-800-775-5766 www.kroneamericas.com www.truenet-system.com Figure 3 shows a close-up of an RJ21 harness that was connected to a switch at an actual user site. The impedance spike here is enormous—far greater than the 100 Ohms +/- 15 called out in the standard (notice the orange and brown pair actually fall to 60 ohms!) When viewed in the frequency domain in figure 4, we see wild oscillations in the orange and brown pair, as we might have predicted from the previous picture. It is these sorts of oscillations from mismatch that have the potential to cause such high frame error rates as previously noted. Figures 5 and 6 show the same type of problem with a different RJ-21 assembly at another site. The effects of the mismatch on the frequency trace are the same. The inherent problem with the RJ-21 connector is that it was never designed to run data. It is referred to as a “telco” connector for good reason—it’s typically used for telephone connections, not high frequency data signals. Several vendors claim to have upgraded these connectors to Category 5 performance, but no one has reported meeting the more stringent category 5e standard, which is now the de-facto minimum requirement for data (the TIA has dropped Category 5 from the standard). Furthermore, the 25 pair cables used in these assemblies is not category 5e compliant either, nor has the TIA established a standard for 25 pair cables above category 5. Tempting as it may be to install this type of infrastructure for its high density, KRONE believes that the performance degradation is not worth the convenience. The high error rates this sort of mismatch can cause contributes to increased troubleshooting, network drag, and possibly a shorter upgrade cycle, as a loss of bandwidth due to errors saps overall network capacity. KRONE recommends an impedance matched system using RJ-45 connectors instead. Figure 3: An RJ- 21 Assembly Figure 4: An RJ- 21 Assembly Figure 5: An RJ- 21 Assembly Figure 6: An RJ- 21 Assembly . Use of RJ-21 Connectors in 100Base-T Active Connectivity KRONE, Inc. has performed numerous site surveys of end-user networks over the. Frequency Trace of a TrueNet Channel KRONE, Inc. 6950 S. Tucson Way, Suite R Englewood, Colorado 80112 1-8 0 0-7 7 5-5 766 www.kroneamericas.com www.truenet-system.com