NO. 01  VOLUME 04 - SEPTEMBER 21, 2001



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 people.  


In 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.  


Definitions 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.  


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).    

  1. 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.  

  2. 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 project.  

  3. 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.  

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 stuffed.  

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 closets.  

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 article.  

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:

  1. 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 manageable.  

  2. 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.  

  3. 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. 

  4. 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.  


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:

  1. New buildings that you own or have a lease of no less than 5 years.  

  2. 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 extended.  

The circumstances where Cat 6 cable is least cost-effective to install are as follows:

  1. Leased buildings where the lease is 5 years or less and there is a strong possibility that you will not re-new.  

  2. Retrofit projects on leased buildings that involve less than 50% of the occupied space.

  3. Normal move, add & change work in leased buildings with short remaining leases.  

  4. 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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