A PERIODIC PUBLICATION BY THE ABR CONSULTING
CONTACT US AT WWW.ABRCONSULTING.COM
NO. 01 VOLUME 04 - SEPTEMBER 21, 2001
IN NEW YORK AND WASHINGTON,
Our hearts are greatly saddened by the events of
September 11, 2001. Our prayers and thoughts are for all those who have
lost loved ones as the result of the horrific acts of terrorism that have
occurred in New York and Washington, D.C. We must stand united in
this time of loss.
I begin this issue of the newsletter on a Greyhound bus traveling from Portland,
Oregon to the San Francisco area. Facing days of flight cancellations, I
chose the bus to get home on September 14. 15 hours on the road. I haven't been on a
Greyhound bus since 1963 when I was in the Army. Given the circumstances,
it wasn't bad. The drivers were great and the passengers were mostly plane
ERROR IN LAST NEWSLETTER
the 08-24-01 issue of the newsletter, we had difficulty including a graphic into
our document. What we have found is that the newsletter firm that we use
does not incorporate HTML files for its basic newsletter format to which we
subscribe. We are correcting the problem. To see the complete issue
in full format, its now on our website in the newsletter archives.
TELECOM ROOM - NOT "CLOSET"
IT'S "TR" - NOT "IDF"
for certain IT spaces are finally changing. The space where communications
cables enter the building and terminate is called the "MDF" and the
space on each of the floors where the voice and data cables terminate is called
the "IDF". Telecom spaces have been called
"closets". These terms are old AT&T telephone terms from the
1960s. MDF stands for "main distribution frame" and IDF stands
for "intermediate distribution frame". The terms no longer
describe what actually goes on in these spaces but they have been very
resilient. Even the most recent RFP that we produced uses these
terms. But things are changing.
For two years, the Building Industry Consulting Service International (BICSI)
has been defining the the MDF as the "Main Cross-Connect (MCC) and the IDF
as the "Telecommunications Room (TR). Old habits die hard but we've
begun the change. We're not thrilled with "MCC" but the rest is
great. We're still suffering from everybody referring to our TRs as
closets. It conveys the image that they must still be small and they are
not. So if you see "TR" in the remainder of this newsletter, you
know what it means.
TELECOM DESIGN CONCEPTS FOR VOICE
OVER IP (VoIP)
Voice over IP (VoIP) is coming. Avaya, Cisco, Nortel, NEC,
Alcatel and others are producing voice over IP systems. This calls for 3
basic changes in the traditional communications cabling design concept for
terminating user station cables in the telecommunications rooms (TRs).
The voice station cables are no longer terminated on the
backboard next to the voice riser. Instead, they terminate on the rack-mounted
patch panels along with the data station cables. This increases the
quantity of rack-mounted patch panels required to terminate the station
cables. This also increases the amount of relay racks.
No longer can the voice station cables be specified to meet
Category 3 specifications which is all that's really needed for voice.
The specifications for the voice cables will now match the specifications
for the data cables. This will increase the costs for cabling your
The size of the telecommunications room (TR) needs to
increase to accommodate the additional relay racks. Specifically, the
room needs to be wider or more rectangular with the long sides being
longer. Square shaped rooms are not satisfactory unless the room is large and multiple rows of racks are expected.
AMOUNT OF PATCH PANELS PER RACK
Or, just too many cables
With the discussion above on terminating all station cables on
the network racks, it seems timely and appropriate to discuss a problem that we
have observed with too many patch panels on a communications relay rack.
Correctly stated, the problem isn't the excessive patch panels, it's the quantity of station cables
connecting to these patch panels on both the front and rear.
We explain. On a typical 7 foot
EIA-compliant rack, there are 42 rack units (1 RU-1.75 inches). This
permits 10 48-port, 2U patch panels to be installed on the rack. It is
assumed that each 48-port patch panel will be partnered with a 2U wire
manager. The rack is now at maximum density. These 10 48-port patch
panels will now permit 480 station cables to drop down and terminate on this one
rack. With Cat 6 cables and cable diameters increasing to .25 inches, a
very large bundle is created on the backside. Even neatly assembled,
combed and tie-wrapped, this bundle has a diameter of about 7"-8" or said in
another way, this bundle can almost stuff 2 4-inch conduits. Installing
taller racks does not resolve the problem.
Now we move the the front of the racks were the data patch cables (and soon to
be voice patch cables with voice over IP) are cross-connected to the voice and data switches.
With 480 cables on the back, and given 4 ports per user, you can count on no
less that 240 patch cables being cross-connected (one for voice and one for
data). But, you and I know that at least 300-350 will be connected.
Now consider that the voice and data switch is not on the next rack. In
fact, its 2 racks over. Now you have about 600 patch cables
involved. Now, we finalize this problem with the realization that we don't
use correctly-sized patch cables. We use the 7' and 10' cords for a
3' cross-connect (because that's all we have) and double up the excess cable in
the wire managers. The Chatsworth 3.25" x 6" and Panduit
4.25" x 5" vertical wire managers are not suitable for this
density. Oh, you can get the cables in there but the managers will be
I apologize for stretching this problem to the extreme but if you think this
doesn't occur, it does -- a lot. And, we know why.
The simple answer is that there is not enough space in the telecommunications
room (TR) for the correct amount of communications racks necessary to thin out
the density of the patch panels. Several circumstances contribute to this problem. First,
on retrofits of existing buildings, the originally constructed
telecommunications rooms (originally called "closets") are too small
for today's needs. Often, in high-rise multi-tenant buildings, the
telecommunications rooms are constructed as part of the concrete core.
We've been on projects where we just can't get the building owners and
architects to increase the size of the rooms. The result is that tenants
have to build additional spaces on their floors that connect to the small
As an example of this problem, we recently worked on a retrofit project where we
had to design an upgraded TR for a 30,000 sq.ft. floor. The floor
previously had 200 outlets with 3 ports each. The existing TR was 60 sq.ft.
and all voice station cables were terminated on the backboard. The two
data cables were terminated on the rack-mounted patch panels for a total of 400
ports on nine 48-port patch panels. The room was quite adequate for the
design with 3 relay racks. We were charged with providing 260 outlets with
4 ports each. Additionally, the customer wanted to design the room for
voice over IP (VoIP). This meant 1,040 ports on rack-mounted patch
panels. We needed twenty-two patch panels just for the voice and data
cables. We also had to design space for eight 48-port patch panels to
cross-connect voice cables to the riser and another four 48-port patch panels
for a training room and lab. Guess how much extra space we were able to
get? Actually, we were able to obtain another 20 sq.ft but it wasn't
enough. We had to crowd 8 racks in the room and stuff them fully with
patch panels, wire managers and switches. The room met all design
expectations but you won't see any pictures in our "greatest examples"
library. It was really crowded. It is this room that inspired this
Second, on new construction, traditional views on the sizing of IT spaces still
dominates the architectural and facilities industries. We frequently join
projects where we immediately have to inform the design team that the IT spaces
are too small. A 7' x 10' room may be satisfactory for a 10,000 sq.ft.
floor and it may be satisfactory for twice that space if voice station cables
are still terminated on the backboard. But it is woefully inadequate for
anything larger where a Voice over IP (VoIP) design is required. For
example, a fully-occupied 20,000 sq.ft. floor (140 cubicles plus conference
rooms) now needs a telecommunications room of no less than 8' x 14' or 140 sq.ft.
That's almost double the size in the previous example.
A third, but less common problem, involves having labs or training rooms on the
floor which increases the outlet count for the floor which in turn, increases
the patch panels needed in the TR. We usually run backbone fiber to the
larger labs and build a mini-TR in the lab. This permits cross-connects
for systems within the lab and reduces the impact on the TR.
RECOMMENDED SOLUTION: We recommend that the following criteria be adopted
when designing telecommunications rooms:
Place no more than eight 48-port RJ-45 patch panels per
rack. This places a limit of 384 station cables that can be terminated
on the backside of the patch panels. This quantity is much more
Place your IT switches in every other rack or at least every
3rd rack. A Cisco 6509 on racks 2 and 6 are just fine. Don't
design a 7-rack system with two switches centralized on rack 4.
Running patch cords from racks 1 and 7 will be ugly. Running patch
cords from racks 2 and 6 will be slightly less ugly.
Use maximum-width and depth vertical wire managers. The Chatsworth or Damac 6"x6" (single or double-sided) or the Panduit 4.25"x9" vertical wire manager is most suitable.
Most importantly, make sure the rooms are large enough for
the racks needed to support the floor. Since floor space comes in
various sizes, it makes sense that the size of the TR will vary as
well. Here are our recommended guidelines for the size of the TR for
the following given floor spaces. The size includes considerations for
mounting all station cables (voice and data) on the relay racks.
8,000-12,000 sq.ft. TR
should be 8'x10' or 80 sq.ft.
12,000-25,000 sq.ft. TR should be 8'x14'
or 112 sq.ft.
25,000-35,000 sq.ft. TR should be
10'x18' or 12'x15' or 180 sq.ft.
If you have a floor that is larger than 35,000 sq.ft., you
need more than one TR per floor.
WHEN DO I USE CAT 6 INSTEAD OF CAT
Interestingly, Cat 6 isn't even a TIA/EIA standard (it's still
in draft), and we're prepared here to list here circumstances where you should
specify it over Cat 5e cable. The differences between Cat 6 and Cat 5e
cable are substantial. Cat 6 is for gigaspeed, Cat 5e is not.
Performance for Cat 6 is much better than Cat 5e. We are advising clients
to install Cat 6 cables in the following circumstances:
New buildings that you own or have a lease of no less than 5
Retrofit projects involving 50% or more of the occupied
space in buildings that you own or there is still more than 5 years
remaining on the lease. Or, if less than 5 years, you are certain that
there is no intention to relocate and that the current lease will be
The circumstances where Cat 6 cable is least cost-effective to
install are as follows:
Leased buildings where the lease is 5 years or less and
there is a strong possibility that you will not re-new.
Retrofit projects on leased buildings that involve less than
50% of the occupied space.
Normal move, add & change work in leased buildings with
short remaining leases.
Cat 6 cable is not cost-effective for move, add & change
work in owned buildings. Mixing it with Cat 5 or Cat 5e cable is more
costly and doesn't provide any benefits. Wait until a large
re-modeling or retrofit project.
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Contact us at www.abrconsulting.com
Phone: 925.872.5523 Fax: 916.478.2814