Tài liệu KRONE - White Paper - TrueNet - Do standards go far enough ppt

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Do the Standards go far enough?Do the Standards go far enough?

Current position and focus of Standards versusCurrent position and focus of Standards versus
what we now know regarding component matching.what we now know regarding component matching.
For some time now we have had ratified standards throughout the world relating to
generic, or structured cabling. We have seen progress from the initial Category 3
cable and connectors, to Category 4 albeit very briefly, to Category 5 where we are
today. We have also seen a shift of emphasis from component specifications to link
and channel specifications which is somewhat more meaningful to the end user.
In more recent times we have seen many drafts of Category 5 Enhanced, or Cat 5E,
and Category 6 and 7. All of these specifications focus heavily on bandwidth, with
progression from 16 MHz for Cat 3, to 20 MHz for Cat 4 and 100MHz for Cat 5.
Category 5 Enhanced still focuses on 100MHz of bandwidth, with some parameters
tightened and some new parameters added. Category 6 doubles this bandwidth to
200 MHz, so it is a quantum leap over Cat 5/ Cat 5E. Category 7, if it ever comes to
fruition, takes a further giant leap to 600MHz, however it will be a heavily screened
solution with possibly non-RJ45 connecting hardware.
As previously mentioned, we have seen many drafts of both Cat 5 Enhanced and
Cat 6, but the actual ratified published versions seem to be forever coming but
never arriving. In fact, as this paper is being written, we are up to draft 12 of Cat
5E! So why the delay? Well, a couple reasons come to mind. Firstly, and most
importantly, there is an ongoing problem with a relatively new parameter called
return loss. Return loss is a signal echo resulting from inconsistencies in the channel
structure, mainly due to poor component impedance matching. The other reason is
that it is no easy feat to produce a Category 6 jack that performs adequately at

200MHz and that remains backwards compatible with Cat 5 patch cords.




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Return Loss (RL)Return Loss (RL)
Let me come back to the issue of Return Loss (RL). For some time now the standards
bodies have been aware of the problem of poor performance of patch cords when
introduced to the basic link (which then becomes the channel). Now we have the
hard evidence to support this concern. Recently, KRONE and its cable partner
Prestolite Wire, have identified this problem and the effect on the channel,
particularly the data through-put, through the use of a new test instrument called
the Lacroy Newsline. This device has the ability to check both passive and active
channels, and when testing active channels has the ability to look at all seven layers
of the OSI model.
In looking specifically at the passive channel, the Newsline can show any impedance
anomalies throughout the cabling infrastructure, including the cable, connectors
and patch cords. Published standards specify components at 100Ω +/- 15 Ω, which
includes cable both solid and stranded, connectors and plug/socket assemblies. The
problem comes about from the fact that it appears this impedance spread is too
broad, resulting




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in excessive mismatches of components which affects data throughput on today’s
high speed networks. The diagrams below illustrate this point.
All components in the above diagrams are standards compliant, however the return

loss introduced by the signal reflections seriously distorts data signals leading to
excessive bit error rates (BER’s), resulting in re-transmission of data packets and an
insidious slowing down of your network.

This problem often manifests itself when a company upgrades its network from
10baseT to 100baseT, which uses more complex and less robust data protocols. The
MLT3 encoding used for 100baseT can very quickly degrade due to these
mismatches, resulting in receivers not being able to recognise the signal. CRC errors
become evident and the resultant retransmissions begin to mount. The two
diagrams below are actual traces of the data signal at the transmit end (left
diagram) and the receive end (right diagram). It’s hard to believe they are supposed
to be the same signal, although the right image would be attenuated somewhat in
normal circumstances.
Tuned Individual Pairs Within The CableTuned Individual Pairs Within The Cable
KRONE and Prestolite have solved this problem. We have truly matched the cable
and connectors, and Prestolite have also tuned the individual pairs within the cable
to ensure a much tighter impedance spread. The obvious resultant benefit is less
return




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loss therefore less signal degradation, significantly improving network performance.
Even the match of the Network Interface Card (NIC) to the cable plant is improved
by this tighter tolerance, often proving to be the saviour of a marginal NIC that may
otherwise be discarded and replaced.
Another excellent feature of the Lacroy Newsline is its ability to look at actual data
signals and transmission speed. Many dual speed cards have indicator LED’s
showing the transmission speed of the link, either 10Mb/s or 100Mb/s. The

Newsline has shown that these LED indicators are not accurate, often indicating
100Mb/s when in reality they are running at only 10Mb/s (sometimes even less!).
Many Network Administrators, when investigating complaints of slow networks,
look at these cards and see the “fast” light on and go off on a wild goose chase to
trouble-shoot their network.
Cabling, on many occasions, accounts for only about 5% of total network costs, yet
is often taken for granted. Money is regularly found for upgrading servers, software
and interface cards in a vain attempt to improve poor data throughput. Network
Administrators assume cable is cable and rarely look the cabling infrastructure when
diagnosing network problems. Similarly, cable experts have a “blind faith” in the
active electronics and rarely give any consideration to the compatibility of the active
equipment to the passive cable plant. The Lecroy evidence strongly suggests that we
should be looking at the whole network concurrently, as this is the only way we can
address the compatibility issue adequately.
Further detailed informationFurther detailed information on this issue can be obtained on the KRONE and
Prestolite web sites at www.krone.com.au or www.prestolitewire.com.