White Paper: Shortlinks Structured Cabling - Data Center - R&M

White Paper 

Short Links in Structured Cabling – 

More Performance and Reliability with Cat. 6A

Short Links in Structured Cabling – 

More Performance and Reliability with Cat. 6A 

Contents 

1. The development of ISO/IEC 11801 ...........................................................................................................3 

2. The wish for shorter links and the question of headroom ...........................................................................4 

3. The advantage of additional headroom ......................................................................................................5 

4. How to measure short permanent links? ....................................................................................................6 

5. Conclusion: short and sweet.......................................................................................................................8 

Annex: The permanent link model of ISO/IEC 11801 Amendment 2.................................................................9 

© Copyright 2011 Reichle & De-Massari AG (R&M). All rights reserved. 

Dissemination and reproduction of this publication or parts hereof, for any purpose and in any form whatsoever, are prohibited 

without the express written approval of Reichle & De Massari AG. Information contained in this publication may be altered without 

prior notice. This document was produced with the greatest possible care; it presents the state of the art at the time of preparation. 

The right to make technical changes is reserved. 

White Paper | Short Links in Structured Cabling | v1.0 | ENG | Peter Fischer, Bruno Ritter 2

In the course of the development of Class EA, changes in 

cabling structure definitions were introduced in the 

standard ISO/IEC 11801 2010 Amendment 2. 

As a consequence, the standard no longer guaranteed 

the fulfilling of permanent link requirements with links 

below 15 meters in length. In various applications, 

however, lengths of below 15 m are regularly used, for 

example in data centers and office cabling. 

This white paper informs about the latest developments 

in standardized copper cabling solutions for short links. 

It aims to present new possibilities, provide information 

on the planning of high-performance data networks and 

decision support for product selection. 

1. The development of ISO/IEC 11801 

In 2006, the IEEE published the standard IEEE 802.3an, which defined the protocol for 10 Gigabit Ethernet 

(10GBase-T). After that the relevant standardization bodies set out to incorporate the requirements in the 

cabling standards. 

In 2008, the ISO/IEC 11801 Amendment 1 was released, defining the channel specifications – Class EA. The 

definition of the components, however, was not specified. 

The release of the ISO/IEC 11801 Amendment 2 in 2010 has closed this gap. The new standard defines the 

connecting hardware, i.e. cables and plug connectors of Cat. 6A (Table 1). 

Frequency IEEE EIA/TIA ISO/IEC 

Channel etc. Channel Components Channel Components 

1-500 MHz 10GBase-T 

IEEE 802.3an 

(2006) 

Cat. 6A 

EIA/TIA 568B.2-10 

(2008) 

Cat. 6A 

EIA/TIA 568B.2-10 

White Paper | Short Links in Structured Cabling | v1.0 | ENG | Peter Fischer, Bruno Ritter 3 

(2008) 

Application: Structured cabling, 

10 Gigabit Ethernet 

Class EA 

ISO/IEC 11801 

Amendment 1 

(2008) 

Table 1: Current cabling standards for typical requirements in data center and office cabling. 

Technology: Cat. 6A ISO connection modules, 

RJ45 plug connectors, 

twisted pair copper cabling 

Format: White Paper 

Topics: ISO/IEC 11801 Amendment 2, 

Channel Link and Permanent Link, 

NEXT headroom, planning of links 

and link lengths, benefits in 

efficiency, performance and cost 

thanks to high-grade components 

in short links 

Target: Inform about the use of short links 

in structured cabling, discuss 

planning and product selection, 

and R&M's quality positioning in 

Cat. 6A ISO/IEC 

Target group: Network managers, installers, data 

center planners 

Authors: Peter Fischer, Bruno Ritter 

Published: June 2011 

Cat. 6A 

ISO/IEC 11801 

Amendment 2 

See also the online available R&M white papers, published between 2006 and 2009, on the topics 10GBase- 

T and Cat. 6A. 

The standard specifies that Class EA can only be fulfilled with Cat. EA components when the minimum length 

of 15 m for the permanent link (PL) is observed. The use of shorter PLs is allowed when the manufacturer 

guarantees that the PL requirements are met. 

(2010)

2. The wish for shorter links and the question of headroom 

Today, many users tend to shorten the links in order to save material, energy and costs. But what effect 

does this have on the performance and transmission reliability of the network? 

Shortening the distance between the two modules in a 2-connector permanent link results in a lower 

attenuation of the cable between the modules, which in turn increases the interfering effect of the further 

module. 

The standard, however, lists only one module in its calculation, which is problematic: Particularly, the limit 

values for NEXT and RL (return loss) can not be maintained any longer. This is why the standard defines a 

minimum link length of 15 m. 

What happens if a high quality module is paired with a high-quality cable? The result is a PL with much 

headroom in terms of length in the range between 15 m to 90 m. Using the R&M Advanced System for 

example, ensures a typical NEXT headroom of 6 dB with 15 m and 11 dB with 90 m (Figure 1). 

NEXT Headroom in dB 

Figure 1: NEXT headroom of permanent links, measured in an installation using the new Cat. 6A module of R&M. The 

zero line shows the limit value in acc. with ISO/IEC 11801 Amendment 2. 

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. 


3. The advantage of additional headroom 

Basically, it makes sense to lay permanent links that are exactly as long as is needed. However, that would 

mean that the links would often be shorter than the minimum length of 15 m. When components are used 

that only meet the standard requirements, the permanent links must be artificially extended with loops to 15 

m to make sure that the limit values are reached. This not only entails additional costs but these cable loops 

also take up space in the cable conduits and interfere with the ventilation, which results in an increase in 

infrastructure costs and energy consumption. 

Thanks to the large headroom with standard lengths, the use of R&M's Cat. 6A module allows a shortening of 

the minimum length as far as down to 2 m. This is sufficient to cover the customarily used lengths in data 

centers (Figure 2). 

On average, the cables between individual server cabinets and the network cabinet need to be 4 to 5 meters 

of length, if they are routed from above over a cable guidance system, or 7 to 8 meters if they are routed 

from below, through the raised floor. The loops to extend the cables to 15 m are not required when the Class 

EA / Cat. 6A solution developed by R&M is used. 


4. How to measure short permanent links? 

According to ISO/IEC 11801 Amendment 2 (Table A.5), less stringent requirements are applicable for short 

2-connector permanent links with an insertion loss of less than 12 dB, from 450 MHz on up. Even if the 

range in question is 450 MHz and 500 MHz, the field measuring device should always be set to "Low IL". 

The maximum lowering of the NEXT requirement is 1.4 dB. Figures 3 to 6 show an example of a measuring 

arrangement and the results. 

Figure 3: Testing of short permanent link (configuration 

PL2) with the Fluke DTX 1800 Cable Analyzer. 

Figure 4: Test result. The permanent link of 2.1 m in 

length meets all requirements of ISO/IEC 11801. 

((Für die englische Version müsste der Cable Analyzer auf Englisch eingestellt und abgebildet werden.)) 


Figure 5: NEXT 

measuring of a 

permanent link of 2 m 

in length, set up with 

R&M components. 

Figure 6: RL 

measurement of the 

same permanent link. 


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. 


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 ) 

⎞ 

⎟ 

⎠ 

[1] 

− [2] (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 ) 

− [3] (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 [2]: 

1. 4(( 

− 450) 

/ 50) 

f [4] (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.

Additional information 

[1] Cat. 6A vs. Kat. 6A – What's the Difference and Why Should I Care?, White Paper, R&M 06/2009 

[2] Cat. 6A and the new Re-embedded Test, Positioning Paper, R&M 05/2010 

[3] Re-embedded – new test procedure not just for Cat. 6A components, White Paper, R&M 2010 

For downloading go to www.rdm.com Home > Products & Solutions > Products in Focus > Cat. 6A > 

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