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This document is by no means a complete document on structured cabling. There are volumes of information written on this topic. This document is intended to highlight certain points, and assumes you have some knowledge of structured cabling.


Terms:

MDF Main Distribution Facility. Main or Central wiring closet, one per floor.
IDF Intermediate Distribution Facility. Secondary wiring closet, when needed, on each floor or in peripheral buildings.
Catchment Area Zone that falls within the area that can be served by an internetworking device such as a hub. Usually a circle 180 meters in diameter - for Ethernet CAT5 cabling.
Cut Sheet Cabling diagram
Horizontal Cabling The cabling from the workstation data outlet to the termination point in the IDF or MDF (patch panel or 110 block).
POP Point of Presence. The demarcation or entry point of the Phone Company's equipment and wiring in your building. (The point where the phone company's wiring ends and your wiring begins.)
Layer 1 Devices Network cabling, outlets, cable connectors, patch panels, hubs, repeaters
Layer 2 Devices Switches, bridges
Layer 3 Devices Routers
Collision Domains A collision domain is defined as a network segment that shares bandwidth with all other devices on the same network segment. When two hosts on the same network segment transmit at the same time, the resulting digital signals will fragment or collide, hence the term collision domain. It's important to know that a collision domain is found only in an Ethernet half-duplex network.
Broadcast Domain A broadcast domain is defined as all devices on a network segment that hear broadcasts sent on that segment.

Planning:    Top

When planning your network infrastructure think of it in the context of the OSI 7 layer model.
The layers you will be dealing with are layers 1 through 3. The Physical Layer, the Data Link Layer
and the Network Layer respectively.

Layer 1
Layer 1 deals with the network media (cabling) and the components that connect the
network devices to the media, e.g. cable connectors, transceivers, wall jacks, patch panels
and network cards (network cards can also be considered a layer 2 device).

Should your cabling be Unshielded Twisted Pair (UTP), Shielded Twisted Pair (STP) or COAX? If you are using UTP cabling should you use Category 3, 4, or 5 cabling?
For today's networks you should be using Category 5e (CAT5e) or higher data cabling. For your phone cabling you should use Category 3 cable.

Your LAN Technology and Physical Topology also have to be decided on. Will you be using Ethernet, Token-Ring, FDDI? For your physical topology will you use a star, extended star, bus, ring, etc.?

Hubs and Repeaters are also considered layer 1 devices so you will need to decide if you will be using Hubs to connect your network devices or perhaps a switch. Will you need repeaters to extend your network? Careful planning should obviate the need for repeaters, but there are times when you might need them.

Although not considered layer 1 devices, you should think about racks and or cabinets to house your networking equipment.

Layer 2

Layer 2 devices are Switches and Bridges. Bridges are layer 2 devices that are used to break up networks into segments. They are somewhat of an outdated technology and should be avoided. A switch or router can provide segmentation and are more intelligent devices.

In today's networking environment you should probably look at using switches as the central point of your network as opposed to hubs. Switches have become very affordable and have the benefit of breaking up collision domains and well as providing dedicated bandwidth for each device connected. Hubs are dumb, layer 1 devices that simply pass on signals. There is no filtering and bandwidth is shared by all devices connected to a hub. If you have a miniscule budget, then you might have to settle for hubs… but try to avoid them.

Layer 3
Layer 3 is where routing takes place. If you are going to be subnetting your network or connecting to other networks, either internal networks or external networks (like the Internet), you will need to add a Router(s) to your network. Routers are used to build scalable internetworks and will impose a logical structure to you network. Routers, unlike other networking devices (except VLAN capable switches), break up broadcast domains which is of concern in multi-network environments.

Other Considerations
Growth. Don't plan you network for just your current needs, plan for the future. What will your networking needs be in 3 years?
Documentation. Document your cabling, hardware and software. Label your cables! It is also a good idea to have a floor plan in each of your wiring closets showing the location of data outlets and their corresponding cable labels.


ANSI/TIA/EIA Standards:

Wiring Closets   Top

  • In the TIA/EIA-568-A cabling standard, a minimum of one wiring closet is required for each floor of your building. For every 1,000 square meters (10,000 square feet) or if any of your horizontal cables will exceed 90 meters (295 feet), you should have an additional wiring closet.

  • If your wiring closet is going to be a MDF, the floor should be able to bear 100 lbs/ft2. If your wiring closet is going to be a IDF, the floor should be able to bear 50 lbs/ft2.

  • Wiring closets should have raised floors when possible to route cabling. If raised floors aren't possible, you should use 30.5cm (12.1 inches) overhead ladder racks to route your cables. All cables should be tie wrapped.

  • Floor coverings should be tile or some other finished covering. No bare concrete or carpet should be used. At least two walls should be covered with 20mm (3/4inch) fire retardant plywood that is at least 2.4m (7.8 feet) high. If your wiring closet is also going to be the POP, then you should have 4.6 meters (15 feet) of plywood covered wall space for telephone wiring and equipment. Walls (including the plywood) should be painted with a fire retardant gray paint.

  • Ceilings should not be dropped or false ceilings. This is primarily a security concern.

  • Air conditioning should always be present in any wiring closet. A temperature of 21 degrees Celsius (69.8 degrees Fahrenheit) should be maintained when all equipment is running. No water pipes
    (unless required by fire codes for sprinklers) should be running above the wiring closets.

  • There should be at least 2 dedicated, non-switched AC duplex outlets, each on it's own circuit, in each wiring closet. There should also be one duplex outlet every 1.8m (5.9 feet) and they should be 150mm (5.9 inches) above the floor.

  • Fluorescent lighting should be avoided around cabling, but can be used when properly installed. A wall switch for the room's lighting should be just inside the door.

  • The door to the wiring closet should be .9m (3 feet) wide and swing open out of the room. There should be a lock on the door, but anyone in the room should be able to open the door.

  • If you are using distribution racks to mount your equipment they should have a minimum of
    15.2cm (6 inches) of wall clearance for the equipment plus another 30 to 45cm (1 to 1.5 feet) of space for access (figure at least 2.5 feet minimum).

  • A floor plate 55.9cm (22 inches) should be used to mount the rack to the floor for stability.

  • If using a cabinet there should be 76.2cm (30 inches) of clearance in the front for the door to swing open. Typical cabinets are 1.8m (6 feet) high x .74m (2.4 feet) wide x .66m (2.2 feet) deep.

  • Data and Phone cables running into IDFs and MDFs should be in 10.2cm (4 inch) conduit. Likewise, all horizontal cabling from workstations to wiring closets should be run through the same size conduit. Preferably, cabling from workstations should be run under a raised floor, but this is not always possible. An additional 2 sleeve cores or conduits should be installed in each wiring closet for future growth.
    Conduit should be kept within 15.2cm (6 inches) of the walls, and cabling coming into the wiring closets through conduit should be run directly onto a 30.5cm (12.1 inch) wide ladder rack.
    All holes or openings into wiring closets, that conduit runs through, must be sealed off with a smoke and fire retardant material.


Horizontal Cabling    Top
Horizontal cabling runs from the data outlet at the workstation to the patch panel or horizontal cross-connect in the wiring closet (IDF/MDF). It includes the outlet, horizontal cable, connectors, and patch cords/cables that comprise the horizontal cross-connect.

  • Grounding must conform to building codes as well as ANSI/TIA/EIA -697.

  • A minimum of 2 cables are required at each data outlet. Either 2 CAT5e cables or 2 Multi-mode fiber optic cables.

  • Hybrid bundled cables (multiple, single UTP cables bundled together) are allowed, but must meet TIA/EIA-568-A-3 standards.

  • One transition point is allowed between different forms of the same type of cable, but this should be avoided because transitions add another potential failure point.

  • 50 OHM COAX and 150 OHM STP cable should not be used for new installations. This is outdated cable.

  • Take into account the proximity of horizontal cabling to EMI (electromagnetic interference) sources.
    For example: motors, fluorescent lighting, power panels, surface to air missle guidance systems, etc.


Maximum Distances for Horizontal Cabling
(Using CAT5 UTP cabling in an Ethernet network)

3 Meters 90 Meters 6 Meters
3 Meters:

Work area patch cable.  From computer to wall

90 Meters:

What is considered the Horizontal Cabling. From wall outlet to the patch panel in the MDF or IDF (Server Room).

6 Meters:

The patch cable that cross connects a patch panel




Backbone Cabling    Top
Backbone cabling, also called vertical cabling, is wiring used to connect wiring closets to each other. Backbone cabling consists of backbone cabling runs, intermediate and main cross-connects, cable connectors, and patch cords used for backbone to backbone cross-connects.

Four types of network media are specified for backbone cabling
1.  100 ohm UTP 4 pair cable
2.  150 ohm STP 2 pair cable (outdated)
3.  62.5/125 -µm multimode fiber cable
4.  Single-mode fiber cable


Connecting Horizontal and Backbone Cabling
There are a variety of ways of connecting workstations, IDFs and MDFs. Below are some diagrams showing common methods of doing this. What you see is an extended star physical topology which is very common with Ethernet networks.

Some new terms are introduced, just to make things confusing. Main Cross-Connect, Horizontal
Cross-Connect, and Intermediate Cross-Connect - MCC, HCC, ICC.

MCC
- Main Cross-Connect. The same as the MDF. This is the main wiring closet.
See Figure A.

HCC - Horizontal Cross-Connect. The same as the IDF. This is an intermediate
wiring closet that sits between the workstations and the MDF.
See Figure A.







ICC - Intermediate Cross-Connect. This is another wiring closet that sits between
the IDF(s) and MDF.  See Figure B.







Note: When using ICCs in your network layout, ANSI/TIA/EIA-568-A states there can be only one ICC between the HCCs and the MCC.  Also, when using an ICC, no horizontal cabling (cabling from workstations) connects directly to the ICC. All horizontal cabling connects to the HCC or IDF.



Maximum Distances for Backbone Cabling   Top
The maximum distances for cable runs vary from one type of cabling to another. These distances can also be impacted by the way you design your wiring closet layouts. As an example, if single mode fiber optic cabling is to be used as a backbone media, and your network layout includes a MDF (MCC) and an IDF (HCC) then the maximum distance between the two wiring closets is 3000 meters.

If instead, you have a layout like Figure C below where you have an ICC between the MDF and IDFs, then the maximum distance of the backbone cable between the MCC and ICC is 2500 meters, and the maximum distance of the backbone cabling from the ICC to the IDFs or HCCs is 500 meters.

See Figure C.





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