White Paper: Shortlinks Structured Cabling - Data Center - R&M
5. Conclusion: short and sweet Short links in structured cabling are not only possible but – combined with high-quality Cat. 6A components – they are even recommended. Cat. 6A modules and installation cables from R&M allow the setting up of permanent links with advantages that impact positively on the cost factor: • easier installation • no unnecessary cable loops • material savings of up to two thirds • improved ventilation, lower energy consumption • reduced costs of installation and operations The use of shorter PLs is allowed if the manufacturer guarantees the fulfilling of the PL requirements. In our R&Mfreenet warranty program, R&M guarantees a NEXT headroom of 4 dB for a permanent link of above 15 m, built with components from the R&M Advanced System. Alternatively, the high headroom provides customers with the possibility to set up very short PLs, which fulfill all the requirements of the standard ISO/IEC 11801 Amendment 2. White Paper | Short Links in Structured Cabling | v1.0 | ENG | Peter Fischer, Bruno Ritter 8
Annex: The permanent link model of ISO/IEC 11801 Amendment 2 ISO/IEC distinguishes between four configurations of the permanent link (Figure 7), relevant for network planning. The determining parameters for transmission quality are NEXT (near-end crosstalk) and RL (return loss). ISO/IEC calculates the limit values of NEXT of all four configurations [in dB] for the frequency range 1 ≤ f ≤ 300 [MHz] with this formula: ⎛ − 20lg⎜ ⎜ 10 ⎝ 74, 3−15 lg( f ) −20 + 10 94− 20 lg( f ) −20 The two terms in the bracket refer to the effect of the module at the near end and the effect of the cable. ISO/IEC specifically states that they should not be taken as individual limit values. This means that the overall limit value can be reached with very good cables and lower quality modules or with very good modules and lower quality cables. Different formulas are applicable to the frequency range 300 ≤ f ≤ 500 [MHz]. The ISO/IEC calculates the NEXT limit values for configuration PL2 [in dB] like this: 87. 46 21. 57 lg( f ) ⎞ ⎟ ⎠  −  (blue line in Figure 8) A moderate requirement applies to configuration PL3 with additional consolidation point and frequency range 300 ≤ f ≤ 500 [MHz]; it is calculated with this formula: 102. 22 27. 54 lg( f ) −  (violet line in Figure 8) Less stringent requirements are applicable to the configurations PL1, PL2 and CP2 in the frequency range above 450 MHz: If the insertion loss (IL) at 450 MHz is lower than 12 dB, the required NEXT curve can be lowered, calculated with the following formula : 1. 4(( − 450) / 50) f  (yellow line in Figure 8). Figure 7: Permanent link configurations acc. to ISO/IEC 11801 Amendment 2. 26 250 300 350 400 450 500 White Paper | Short Links in Structured Cabling | v1.0 | ENG | Peter Fischer, Bruno Ritter 9 NEXT [dB] 36 34 32 30 28 Frequency [MHz] PL2 PL3 Short Link Figure 8: NEXT limit values for the permanent link configurations 2 and 3 and for short links acc. to ISO/IEC 11801 Amendment 2.