IT and facilities managers may not be fully aware of the
cabling systems performance journey from Plain Old Telephone Systems (POTS) cable to
currently available high performance copper and optical fiber systems. It is also
difficult to stay current on all the attempts to classify performance by
"levels", "categories", "classes", "bandwidths",
or "approved applications" by either manufacturers or standards committees.
align="right" border="0" hspace="4" vspace="4">Whether you are
an end user, consulting engineer, contractor, distributor, or manufacturer, it is critical
to consider the dynamics between application (network protocols), cabling system
performance, and cabling system life expectancy. As it would be an error to specify a
cabling system that does not satisfy the current and future performance requirements
essential to accommodate a corporate or institutional information systems strategy, it
would likewise be an error to over-specify a cabling system for an application due to a
misunderstanding of the requirements or issues surrounding the alternatives.
In an effort to alleviate any misunderstandings concerning
cabling system transmission performance classifications, this box describes the history of
the industry’s efforts to define twisted pair cabling system alternatives, provides
an account of current industry designations and expectations for twisted pair cabling
systems. Although there are many differences between the various specifications written
around premises cabling systems, this will focus on the issues related to performance.
EIA/TIA-568
In July 1991, the TR41.8.1 working group of the Electronic Industries
Association/Telecommunications Industry Association published ANSI/EIA/TIA-568,
"Commercial Building Telecommunications Wiring Standard", to formally define the
mechanical and electrical requirements for the cable and components that made up premises
cabling systems. This standard included specifications for 100 Ohm UTP (unshielded twisted
pair), 150 Ohm STP (shielded twisted pair), 50 ohm coax and 62.5/125 optical fiber.
Twisted pair cable and connecting hardware were specified electrically as components from
1 to 16 MHz. Although a cable levels program had been proposed to the industry, time did
not permit its inclusion in the standard.
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listed specifications by the designated standard. Although ACR is not specified by
ANSI/TIA/EIA-568-A or TIA TSB-67, the derived values based on NEXT and attenuation are
provided for comparison.
TSB 36:
However, shortly afterward in November 1991,TIA TR41.8.1 published Technical Systems Bulletin 36 (TSB 36), "Additional Cable
Specifications for Unshielded Twisted Pair Cables", which further defined UTP cable
performance by "categories". TSB 36 included definitions for cable Categories 1
through 5 and mechanical and electrical specifications for Categories 3, 4, and 5. TSB 36
also replaced the 150 Ohm STP Level 5 cable with 100 Ohm Category 5 cable, which had
extended performance requirements for near end crosstalk (NEXT) and attenuation up to 100
MHz.
TSB 40:
In order to provide a similar definition ofUTP connecting hardware and, more precisely, to specify connecting hardware to match the
performance of the cable categories, TIA TR41.8.1 published Technical Systems Bulletin 40
(TSB 40), "Additional Transmission Specifications for Unshielded Twisted Pair
Connecting Hardware". TSB 40 classified connecting hardware by Categories 3, 4 and 5
and listed NEXT and attenuation specifications up to 100 MHz. Recognizing that
installation practices could affect cable performance, TSB 40 also included
recommendations for specific handling procedures, such as pair untwist and jacket removal
when terminating Category 4 & 5 cable.
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definition)
ANSI/TIA/EIA-568-A
In October 1995, TSB 36, TSB 40 and TSB 40A were incorporated into ANSI/TIA/EIA-568
Revision A along with worst case electrical performance characteristics (Annex E
(informative)) for a UTP "channel" (see Figure 1). The channel at this time was
defined as everything from the NIC card to the LAN concentrator or hub. The components in
this channel definition included:
or patch panels
The equipment plugs were excluded since field test
equipment couldn’t separate them from the jacks on the equipment. This was the first
time that a published standard provided electrical performance parameters for something
more inclusive than cabling system components. Annex E specified NEXT and attenuation
performance for a channel constructed of Category 3, 4 or 5 components over a frequency
range of 1 to 100 MHz. This work acknowledged the importance of cabling system performance
and the fact that component specification alone did not assure that result.
ISO/IEC 11801
Also in 1995 the International Organization for Standardization (ISO) and the
International Electro-technical Commission (IEC) published the International Standard
ISO/IEC 11801, "Generic Cabling for Customer Premises". Like TIA/EIA-568-A,
ISO/IEC 11801 defined the channel as all the horizontal cabling including the patch cords
but less the equipment plugs. ISO also added a second definition called a link. The link
was everything from the equipment panel to the workstation outlet and was considered to be
what the contractor would leave in the wall. The link included patch cables (between two
halves of the cross connect) but not equipment cables.
The link model was used to determine minimum performance
(Figure 2). Four link performance classifications were also established (Class A, B, C and
D). Class D has the highest performance and is specified up to 100 MHz. Another difference
between ISO/IEC 11801 and TIA/EIA-568A was the inclusion of 120 ohm UTP and 100/120 ohm
FTPÂ .
Although not the first to be published, the International
Standard ISO/IEC 11801 provides a basis for global consistency and is now strongly
considered during the modification of all regional or national standards, including the
American National Standard ANSI/TIA/EIA-568-A, European Standard CENELEC EN 50173,
Canadian Standard CSA T 529, and Australian/New Zealand Standard AS/NZS 3080:1996.
TSB 67
Directly following TIA/EIA-568-A in 1995 was Technical Systems Bulletin 67,
"Transmission Performance Specifications for Field Testing of UTP Cabling
Systems". The purpose of TSB 67 was to more clearly define performance requirements
for premises cabling systems and how they should be measured in the field. This TSB
included separate definitions for the "Channel" and the "Basic Link"
(Figure 1) and specified different performance levels for each (Figure 2). The numbers
specified for basic link were more strict to allow for the addition of patch cables at a
later time and still maintain the channel performance requirements. TSB 67 also specified
the measuring accuracy of hand held testers in order to control the variation in results.
Industry Stability
At this time there appeared to be stability in the cabling system industry. Standards were
now established that specified performance requirements for components and completely
installed systems, providing guidelines to:
components or systems
Stability, however, is relative. As this brief summary of
the premises cabling systems business has already shown, performance requirements are
constantly changing. This first series of standards were written for cabling systems that
supported network protocols like 10BASE-T, 4 or 16 Mbps token ring, 100 Mbps FDDI, 100
Mbps Fast Ethernet and even 155 Mbps ATM. It would seem that these applications,
especially the latter, would be sufficient for most any application. Right? Guess again,
because it’s not unusual:
months after you purchased the fastest on the market.
workstation.
screens waiting for networks to respond when printing or saving files.
you to be more efficient at your work.
make you desirous.
that are "best in class".
don’t understand cabling system performance issues.
facilities, education providers, financial institutions or governments to want to install
the highest performance cabling infrastructure they can afford in order to accommodate the
things that are not unusual.
Based on the facts that hardware continues to get faster,
application software continues to use more memory and require more bandwidth and end users
continue to buy faster equipment, we know that network bandwidth requirements will
continue to increase. It would also be reasonable to presume that requirements for cabling
system performance will also change.
Cabling systems did begin to change. Terms like
"enhanced", "headroom", "margin", "high-end Cat
5", "Cat 5+", "Level 6" "Level 7", "Category
6", "Category 7" and phrases like "characterized to 350 MHz",
"able to transmit 622 Mbps to the workstation" and "able to transmit 1000
Mbps to the workstation" began to accompany premises cabling systems that were
designed with various amounts of added performance margin. To better explain these current
terms and phrases we need to look specifically at where they came from and what they were
describing.
E DIN-44312-5
Due to the anticipation of increasing network bandwidth requirements, and the uncertainty
that a Category 5 system would have high enough transmission and emissions performance for
an emerging 622 Mbps ATM application to operate properly, a need developed to generate a
specification to ensure that high speed data could run over copper cable systems. A
subcommittee of the Deutsches Instutut fur Normung (DIN), the German standards body,
generated it’s own standard for a 600 MHz cabling system. This draft specifies a
shielded cable which a handful of mostly European manufacturers are currently producing.
The only cable design that has met this standard is referred to as PiMF or Pairs in Metal
Foil which describes a 4-pair cable where each pair is enveloped in foil and then an
overall shield surrounds the 4-pair unit. The standard follows the requirements in EN
50173 but adds a link with performance specified up to 600 MHz, which in theory would
enable such a cabling system to support 622 Mbps ATM on two pairs using simple NRZ
encoding.
Additional Requirements for Category 5 and
Enhancements
In North America efforts are also occurring to put some boundaries around the numerous
"enhanced" Category 5 cables that are being marketed as "enhanced
performance" or "Cat 5+". One attempt to set boundaries comes from a
distributor of premises cabling components. They have published a document based on a
purchasing specification that requires their suppliers to qualify their high performance
unshielded twisted-pair cable by a series of "levels". Three levels of
performance are defined:
specifications of 10 dB pair-to-pair ACR at 100 MHz and 10 dB power sum ACR at 80 MHz.
pair-to-pair ACR at 155 MHz & 10 dB power sum ACR at 100 MHz.
10 dB pair-to-pair ACR at 200 MHz and 10 dB power sum ACR at 160 MHz.
The biggest concern with the effort just described is that
it only specifies cable performance. Applications run over a system of cable and
connecting hardware, hence the term cabling system. To cover this important issue the
ANSI/TIA/EIA UTP System Task Group is in the process of generating two addenda to
ANSI/TIA/EIA-568-A. One is titled, "Additional Transmission Performance
Specifications for 100W 4 -Pair Category 5 Cabling" and the second one is entitled,
"Additional Transmission Performance Specifications for 100W 4 -Pair Enhanced
Category 5 Cabling" These are summarized in figure 3
Category 6/Class E and Category 7/Class F
Additionally, the ISO/IEC Joint Technical Committee 1/SC 25 Working Group 3 (ISO/IEC JTC
1/SC 25/WG3) decided at the conclusion of the September 1997 meeting in Munich, Germany to
proceed with new cabling categories and classes that will provide significant improvement
over Category 5 and Class D. WG 3 will undertake simultaneous development of two new
balanced cabling categories and classes. Category 6/Class E will specify cabling system
channel performance to 200 MHz and Category 7/Class F will specify cabling system channel
performance to 600 MHz. Category 6/Class E also specifies that the modular jack interface
shall be maintained for all user interfaces at the TO (telecommunications outlet). The
Category 7/Class F interface connector at the TO will be capable of 4-pair termination and
performance. This interface connector will be internationally standardized. At this time
the modular jack interface is the default connector.
Extracts from a publication of AMP