By Donna Ballast
Since the publication of the article, “Why shielded twisted-pair matters for 10GBase-T” in the December 2006 issue of Cabling Installation & Maintenance, I have received several questions:
- Is there really a Cat 6A FTP?
- Is Cat 6A FTP the same as Cat 6 FTP?
- Is TIA writing another new standard for Cat 6A FTP?
- Can Cat 6A FTP and Cat 6 FTP be intermixed?
Given all the system designer/installer and end-user interest now focused on 10-Gigabit Ethernet and all the new “shielded-cabling-systems” chatter we are hearing from cabling manufacturers, there are many among us who are understandably confused.
Just for the record, in TIA speak, FTP (foil-shielded twisted-pair) is ScTP (screened twisted-pair).
According to TIA/EIA-568-B.2-1 Commercial Building Telecommunications Cabling Standard, Part 2: Balanced Twisted Pair Cabling Components, Addendum 1-Transmission Performance Specifications for 4-pair 100-Ω Category 6 Cabling, published in June 2002, the Category 6 designation applies to UTP and ScTP cables whose transmission characteristics are specified up to 250 MHz.
According to the latest draft of SP-3-4426-AD10-B, which will eventually be published as TIA/EIA-568-B.2-10 Addendum 1-Transmission Performance Specifications for 4-pair 100-Ω Augmented Category 6 Cabling, the Category 6A designation applies to UTP and ScTP cables whose transmission characteristics are specified up to 500 MHz.
- So yes, there really is going to be both a Cat 6 ScTP and Cat 6A ScTP standard published by TIA, but this will not require a separate document.
- No, Cat 6 ScTP and Cat 6A ScTP will not have the same specifications, although the cables may be identical components that are just verified to different sets of specifications by the testing lab.
- Yes, Cat 6 ScTP and Cat 6A ScTP components can be mixed. But according to TIA/EIA-568-B.1 Section 10.2.3 the result cannot exceed Cat 6 ScTP, regardless of what field-testing indicates. Remember, while those electrons running down the conductor rarely read those labels on the cabling components, end-users writing punchlists do.
I also received a question about the ever-popular issue of grounding a shielded cabling system-in particular, grounding through the patch cord to the equipment. An interesting topic to say the least. I am currently researching the issues and suspicions raised by the individual who sent me the question, and will report in detail next month. Hang on, because this shielded issue is not going away anytime soon.
TSB-155 a done deal
After a long development process, TSB-155 Guidelines for the Assessment of Category 6 Cabling in Support of 10-Gigabit Applications finally has been approved. Now we wait for the “other” 10-Gig-over-twisted-pair specification, ANSI/TIA/EIA-568-B.2-10.
For now, let’s take a look at what led to the recently approved TSB-155 and yet-to-be-approved 568-B.2-10. When ANSI/TIA/EIA-568-B.2-1 Transmission Performance Specifications for 4-pair 100-Ω Category 6 cabling was published in May 2002, it characterized Category 6 cabling over a frequency range spanning from 1 MHz to 250 MHz.
Later, the Institute of Electrical and Electronics Engineers (IEEE) 802.3an group began work on the 10GBase-T specifications, and asked for additional bandwidth characterization of the installed base. Originally, the IEEE 802.3an’s goal was to specify 625 MHz over some length of Category 5e and 100 meters of Category 6. TIA agreed to do the work IEEE requested and, when doing so, discovered the much-ballyhooed alien crosstalk characteristic. Much (but not all) of the rest, as the saying goes, is history.
Fast forward to June 2006. The IEEE 802.3an 10GBase-T standard was approved. That standard’s specifications include physical coding and sublayer interface for 10GBase-T applications over balanced twisted-pair copper cabling systems; established signaling and interference requirements for semiconductor chips that will support 10-Gbit/sec performance; and specified four-connector channel electrical requirements for Augmented Category 6/Class EA, Class F, and Category 6/Class E cabling systems over the frequency range from 1 to 500 MHz.
When TSB-155 was approved very recently, it provided a way to determine if a Category 6 permanent link or channel meets the requirements of ANSI/TIA/EIA-568-B.2-1 from 250 to 500 MHz, and is sufficiently immune to alien crosstalk.
Specifically, TIA defines alien crosstalk as “unwanted signal coupling from a disturbing pair of a 4-pair channel, permanent link, or component to a disturbed pair of another 4-pair channel, permanent link or component.”
In TSB-155, alien crosstalk is referred to as “crosstalk coupling between 4-pair Category 6 cabling in close proximity” to the disturbed or victim cable. The rationale behind this choice of words: Anything else would be impossible or, at the very least, extremely difficult to test in the field.
Dependent upon the alien-crosstalk environment, 10GBase-T should operate over channel lengths of 37 to 55 meters of Category 6 cabling. In links that are less than 37 meters, alien crosstalk should not be a problem; however, only testing can verify that with certainty. TSB-155 states that field-test equipment used for assessing Category 6 cabling to the TSB-155 specs should meet Level IIIe field accuracy requirements as described in ANSI/TIA/EIA-568-B.2-10 Annex I.
With that explanation out of the way…what happens if you test your Category 6 cabling and find it does not meet the requirements stated in TSB-155? That’s when you implement the mitigation procedures, which are also provided in TSB-155.
If the channel fails for any reason other than alien crosstalk, the user can follow the list of options in TSB-155 Annex B. After performing the procedures called out in each option, the user must re-test to see if the channel passes. If it does not, the user moves to the next option. The options listed in TSB-155 are as follows:
- Replace the work area, patch, and/or equipment cords with Category 6A cords.
- Reconfigure the cross-connect as an interconnect.
- Replace the consolidation point connector with a Category 6 consolidation point connector.
- Replace the work area outlet connector with a Category 6A work area outlet connector.
- Replace the interconnect or cross-connect with a Category 6A interconnect or cross-connect.
TSB-155 does not list a sixth option, but implies that if these five fail, the next step is to replace the horizontal cable with Category 6A cable.
If the failure is due to alien crosstalk, there is another set of procedures to follow-again, testing after each one to see if the next is necessary:
1. When selective deployments of 10GBase-T applications are possible, utilize non-adjacent patch panel positions (patch panel adjacency should also be checked at the rear of the patch panel), separate the equipment cords, and unbundle the horizontal cables.
2. When deploying 10GBase-T applications in adjacent patch panel positions, in the telecommunications room, testing is recommended; the number of disturbed channels to be tested should be determined using statistical sampling techniques based upon the intended confidence level.
a. Identify measured patch panel positions to be included in the power sum.
b. Select and test those channels with connectors adjacent to, or cable segments in the same bundle as, the disturbed channel. For these channels, test the alien crosstalk to be included in the power sum calculation following the procedures in clause A.9.
3. In the event that the alien crosstalk transmission parameters given in either 6.1 or 6.2 are not met in step 2, the alien crosstalk may be mitigated by the following procedure:
a. Reduce the alien crosstalk coupling by separating the equipment cords and the patch cords and unbundling the horizontal cabling.
b. An alternative to separating equipment cords is to utilize equipment cords sufficiently specified to mitigate the alien crosstalk coupling, such as Category 6 ScTP and Category 6A.
c. Reconfigure the cross-connect as an interconnect.
d. Replace connectors with Category 6A.
e. Replace the horizontal cable with Category 6A.
DONNA BALLAST is BICSI’s standards representative, and a BICSI registered communications distribution designer (RCDD). Send your question to Donna at: email@example.com