White Paper 02. Juli 2002 Andreas Clauser Hauptsitz Binzstrasse 31 CH-8622 Wetzikon Tel +41 1 933 8375 Fax +41 1 930 49 41 Internet www.rdm.com Do you know if your Cat. 6 patch cord has been tested according to standards? Unfortunately, reality shows that many of the alleged Cat. 6 patch cords do not fulfil the values laid down in standards! It is common knowledge that today most of the installations are only measured as permanent links. But will your installations still yield the required performance, once the patch cords are connected? Is it enough when the stranded cable complies with the standard? How can you make sure yours is a good patch cord? This article will give you the answers to all these important questions when choosing patch cords. It also presents today s standards of patch cords and stranded cables and discusses their differences. Furthermore, it clearly describes how to proceedin order to find guaranteed top-grade patch cords. Summary Cat. 6 patch cords are specified in the standards PrEN 50173, ISO/IEC 11801 2 nd Edition and ANSI/TIA/EIA-568-B.2.1. They include defined minimum values for near-end crosstalk and return loss. Due to its consistent organisation the TIA/EIA-568-B.2.1, Draft 9 should be used as reference for the assessment of flex cables and patch cords. The draft of ISO/IEC 11801 2 nd Edition from April 2001 contains mistakes and should not serve as reference in the assessment of flex cables. CENELEC with PrEN 50173 has not yet defined a required near-end crosstalk value for Cat. 6 patch cords. There is only one way to make absolutely sure that your patch cord fulfils the standard, namely to ask the manufacturer for the test record from patch cord production. Detailed specifications The Cat. 6 patch cords are specified in the standards PrEN 50173, ISO/IEC 11801 2 nd Edition and ANSI/TIA/EIA-568-B.2.1. These standards issue identical required values for return loss. ISO/IEC White Paper/ Standards Seite 1 / 5
and TIA/EIA issue the same required values for near-end crosstalk, whereas CENELEC has not yet determined values required for Cat. 6 patch cord near-end crosstalk (as of April 2002). The new cabling standards specify patch cords of up to 20 metres. The frequency range is specified from 1 to 250 MHz. The near-end crosstalk values vary depending on the patch cord's length. By contrast the return loss values were specified independent of the patch cord's length.. Table 1: Standards for patch cords and flexible cables Document Name Title ANSI/TIA/EIA-568-B.2.1 Addendum No. 1 to TIA/EIA-568-B.2, "Transmission Performance Specifications for 4-Pair 100 Category 6 Cabling", November 2001 Draft 10 Preliminary ISO/IEC 11801 2 nd edition 2 nd CD, IT-Cabling for customer premises, April 2001 PrEN 50173 Information technology-generic cabling systems, August 2001 The standards give identical values for flex cables. There is, however, a small but significant difference: ISO/IEC 11801 specifies return loss between 4 and 250 MHz whereas ANSI/TIA/EIA set their frequency range at between 1 and 250 MHz. In reality, the return loss as specified in ISO/IEC 11801 2nd leads to the situation where the cable fulfils the standard for a flexible cable of 100 m, but the patch cords of between 5 and 10 m no longer fulfil the standard. Graph 1 Graph 2 RL S-STP flex cable 100m a RL S-STP flex cable 5m 7 7 6 6 Limit C6 flex cable 1,2 100m side a 3,6 100m side a 4,5 100m side a 7,8 100m side a Limite C6 Cord 1,2 5m 3,6 5m 4,5 5m 7,8 5m Limit C6 flex cable White Paper/ Standards Seite 2 / 5
Graph 1 shows the measurement of a 100 m flexible cable, which fulfils the specifications according to ISO/IEC. It only falls short of the limit below 4 MHz. Then, 20 metres of the cable were cut off and it was tested for the patch cords' limits as specified by ISO/IEC. To exclude any influence from the connector and the connector's termination the cable was measured separately. The result is shown below, in Graph 3: the patch cord fails. It is the same with patch cords of 10 metres (Graph 4). The patch cords of 5 metres only just about fulfil the ISO/IEC requirements again (Graph 2). Graph 3 Graph 4 RL S-STP flex cable 20m RL S-STP flex cable 10m 7 6 6 Magnitude [MHz] Limite Cord 1,2 20m 3,6 20m 4,5 20m 7,8 20m Limit (db) Limite C6 Cord 1,2 10m 3,6 m 4,5 m 7,8 m Limit flex cable The results are summarised in Table 2. They show that up to 3.7 db of reserve can be lost from a flexible cable to a patch cord of 20 metres due to the fact that ISO/IEC only start measuring cables from 4 MHz upward. Table 2: ISO/IEC 11801 2nd Edition Standard for 100 m flex cable Standard for patch cord up to 20 m Frequency range 4... 250 MHz 1... 250 MHz Length 100 m 20 m 10 m 5 m Frequency of smallest reserve 1.4 db 4.6 MHz -2.3 db 2.0 MHz -1.4 db 4.4 MHz 0.15 db 8.9 MHz Result PASS FAIL FAIL PASS The draft of ISO/IEC 11801 2 nd Edition from April 2001 contains mistakes and should not serve as reference in the assessment of flex cables. White Paper/ Standards Seite 3 / 5
In a second step the measuring results were compared with the specifications of ANSI/TIA/EIA 568- B2.-1 Draft 10 of November 2001. The results are summarised in Table 3. Table 3: ANSI/TIA/EIA 568-B.2-1 Draft 10 Standard for 100 m flex cable Standard for patch cord up to 20 m Frequency range 1... 250 MHz 1... 250 MHz Length 100 m 20 m 10 m 5 m Frequency of smallest reserve -2.0 db 1.5 MHz -2.3 db 2.0 MHz -1.4 db 4.4 0.15 db 8.9 Result FAIL FAIL FAIL PASS In TIA/EIA 568-B.2-1 Draft 10 the return loss specifications for flex cables are consistent with the limits for patch cords, both starting at 1 MHz. The reserves for the limits of a 100 m flex cable and of a 20 m patch cord also match. Furthermore, it is shown that the frequency of the worst value with reference to the limit is doubled when the patch cord's length is cut in half. This effect is caused by standing waves in the cable. Due to its consistent organisation the TIA/EIA-568-B.2.1, Draft 9 should be used as reference for the assessment of flex cables and patch cords. Reality has shown that only a few of the alleged Cat. 6 patch cords actually fulfil the values stipulated by the standards. How can you make absolutely sure that your patch cord complies with the TIA/EIA or ISO/IEC standards? It is only possible if the patch cord production is subject to a test system. The parameters near-end crosstalk and return loss must be fulfilled in compliance with ANSI/TIA/EIA-568- B.2.1 (as of Draft 9) or ISO/IEC 11801 2 nd Edition. How can a customer make sure such a test system was not only implemented by marketing but also in production? Here the only way is to ask for the manufacturer's test record of the patch cord production, which should list the measured values and the standards applied. Ask the manufacturer for the test record of the patch cord production. White Paper/ Standards Seite 4 / 5
White Paper/ Standards Seite 5 / 5