The state of Category 6 in TIA TR-42
Many thanks to all of you who wrote, telephoned, and thanked me in person for the Category 6 information. In response to your "keep-me-in-the-loop" requests, I offer the following
Many thanks to all of you who wrote, telephoned, and thanked me in person for the Category 6 information. In response to your "keep-me-in-the-loop" requests, I offer the following:
On April 6, at exactly 8:00 AM, a group of telecommunications cable, connecting-hardware, and test-equipment manufacturing experts assembled in Englewood, CO. The sole purpose of this meeting was to create Category 6-the standard ...or at least, Draft 6 of PN-3727 Transmission Performance Specifications for 4-pair 100-ohm Category 6 Cabling, which could be circulated within TR-42 as a Committee Ballot.
This Category 6 project plan indicated strategic milestones, including insertion loss of both solid and stranded Category 6 cables, insertion-loss deviation (ILD) values, the permanent-link models, de-embedded far-end crosstalk (FEXT), and the patch-cord near-end crosstalk (NEXT) loss test method.
After two long days of proposals, discussions, and compromises, the group agreed to assign the remaining un resolved issues to the various task groups of experts as "homework" items. The group also charged document editors with assimilating these assignments into Draft 6 in time for the TR-42.7 Subcommittee meeting, which took place in May.
They even developed a solution for those problematic assignments like balance and patch-cord testing. Unresolved issues would be added to Category 6 later as addenda. If that sounds familiar, you must be remembering Category 5: The Miniseries.
But on May 17, in Tyson's Corner, VA, after a very brief review of Draft 6, the TR-42.7 Subcommittee voted to send the draft back to the task groups for additional work. At this point, the earliest a draft Category 6 standard can be circulated for a TR-42 Committee Ballot is next month.
Preview of the coming attraction
During my recent correspondence with many of you, I discovered that there is a lot of misunderstanding about exactly what to expect when the standard is finally published. To you, I offer a preview of Category 6: The Standard.
The transmission performance of any cabling system depends on the cable, connecting hardware, patch cords and crossconnect wiring, the total number of connections, and the care with which all previously mentioned components are installed and maintained.
In this sense, Category 6 is not different from previous standards; however, the list of transmission requirements is longer, and testing is specified to 250 MHz. Most of the transmission requirements in PN-3727 are expressed in equations, with tables provided for information only. So where do they stand on the "to-do" list?
- The equation for connecting hardware insertion loss has been provided; however, the equation for cable, permanent-link, and channel insertion loss are marked "to be determined" (TBD). All pairs of the cable, connecting hardware, permanent link, and channel will be measured for insertion loss.
- The equations for equal-level far-end crosstalk (ELFEXT), FEXT loss, and power-sum ELFEXT have been provided. ELFEXT will be measured for all pair combinations for cable, connecting hardware, permanent link, and channel. Power-sum ELFEXT is also specified for cable, permanent link, and channel.
- The equation for connecting-hardware return loss has been provided; however, the equations for cable, permanent-link, and channel return loss are marked TBD. All pair combinations for the cable, connecting hardware, permanent link, and channel will be measured for return loss.
- Requirements for propagation delay and delay skew have been provided. All pairs of the cable, permanent link, and channel will be measured for propagation delay and propagation delay skew.
- The equations for cable and connecting-hardware balance are marked TBD, and reference is made to an annex that says, "text is pending from balance task group." All pairs for the cable and connecting hardware will be measured for balance. But even the equations currently in the draft are subject to change during the balloting process.
For Category 6 permanent-link and channel test configurations, field-testers must measure up to 250 MHz for wiremap, including shield connection if there is a shield present; insertion loss; length; NEXT loss, pair-to-pair, measured from local end and far end; NEXT loss, power-sum, measured from local end and far end; ELFEXT, pair-to-pair; ELFEXT, power-sum; propagation delay; and delay skew. All these areas will require a Level III tester. However, the tables specifying minimum requirements for Level III field-measurement accuracy are riddled with "for further study" (FFS) statements, and while there are a number of very strong opinions as to what the values should be, I am unclear on whether there is actually "further study" planned.
So PN-3727 Transmission Performance Specifications for 4-pair 100-ohm Category 6 Cabling Draft 6 remains a work-in-progress.
And these terms mean what?
Insertion loss, often referred to as attenuation, is a measure of the signal loss resulting from the insertion of a cable, connecting hardware, permanent link, or channel between a transmitter and receiver. Insertion loss is expressed in decibels relative to the received signal level.
Near-end crosstalk (NEXT) loss is a measure of the unwanted signal coupling from a transmitter at the near end into neighboring pairs measured at the near end. NEXT loss is expressed in decibels relative to the received signal level.
Far-end crosstalk (FEXT) loss is a measure of the unwanted signal coupling from a transmitter to the far end into neighboring pairs measured at the near end. FEXT loss is expressed in decibels relative to the received signal level.
Return loss is a measure of the reflected energy caused by impedance mismatches in the cabling system and is especially important for applications that use simultaneous bidirectional transmission. Return loss is expressed in decibels relative to the reflected signal level.
Propagation delay is the time it takes for a signal to propagate from one end to the other. Propagation delay skew is a mea surement of the signaling delay difference from the fastest pair to the slowest pair. Propagation delay and propagation delay skew are expressed in nanoseconds. All pairs of the cable, permanent link, and channel will be measured for propagation delay and propagation delay skew.
Balance is a measure of a system's ability to propagate a differential signal without conversion to a common-mode signal, and vice versa. Balance ensures the appearance of undesired signal coupling modes is minimized and is related to the emission and susceptibility characteristics of the cabling. Longitudinal conversion loss (LCL) is a ratio of differential voltage induced on a conductor pair as a result of subjecting that pair to longitudinal voltage. Longitudinal conversion transfer loss (LCTL) is a ratio of differential voltage induced on a conductor pair as a result of subjecting an adjacent pair to longitudinal voltage. Balance is expressed in decibels relative to the converted signal level.
Second Annual Salary Survey
Cabling Installation & Main-tenance is conducting its second annual salary survey of the telecommunications industry. To participate, fill out the form on our Website (www.cable-install.com)-and pass the word. The more people who participate, the better information we can provide you. We will publish the survey results in Cabling Installation & Maintenance later this year.
Donna Ballast is a communications analyst at the University of Texas at Austin and a bicsi reg-istered communications distribution designer (rcdd). Questions can be sent to her at Cabling Installation & Maintenance or at PO Drawer 7580, the University of Texas, Austin, TX 78713; tel: (512) 471-0112, fax: (512) 471-8883, e-mail: firstname.lastname@example.org.