4. Wiring Standards and Specialised Cable

68A and 568B Standard

The Telecommunications Industry Association (TIA) and the Electronics Industry Association (EIA) have designed a wiring standard called 568A and 568B, which is used for the RJ-45 connectors on a UTP/STP cable. The number 568 refers to the order the wires within the Cat 5, Cat 3 and Cat 6 cables are terminated and attached to the connector. Both standards (568A and 568B) are the same in terms of the signal with a slight difference in the order the pins are terminated. They’re both used for patch cords in Ethernet networks. To be able to make these cables (in case you have to) you need to know which order to connect the wires to the connector. The following figure illustrates this, the pin numbers are read left to right while the connector tab facing down.

Image taken from Mike Harwood's Network+ Guide

Straight through vs. Crossover cable

When it comes to connecting devices to the network hubs, switches or routers there are two types of cables used a crossover and a straight-through UTP cables.

Crossover cables – in these cables two sets of wires are crossed over; these wires are wire 1 and 3 and wires 2 and 6. The meaning of crossover is that wire one at one end is crossed over to become wire 3 at the other end and wire 2 becomes wire 6 at the other end.

Straight-through – in a straight-through the wires at one end runs straight through to the other end. They’re not crossed.

Image from Mike Harwood's Network+ Guide

Both standards (568A and 568B) needs to be used when making these cables, one end wired according to the 568A and the other end wired according to the 568B standard.

Rollover and Loopback Cable

This cable is a cisco proprietary cable and can only be used to connect to cisco devices such as connecting a computer to the cisco router or firewall. The pin or wire structure of this cable are rolled over so pin 1 on one end become pin 8 on the other end and pin 2 becomes pin 7 and so on. This cable also uses 8 wires and an RJ-45 connector.

The loopback cable or sometimes called loopback plug uses a UTP cable and an RJ-45 connector. This cable is used as a cheap method of testing and troubleshooting network cable problems. When plugging the cable into a device it causes the devices light to come on and so indicates that it is working. Also when transmitting, the outgoing data is redirected (looped back) by the plug to the same sending device and thus the device believes it’s sending and receiving data.

Components of Wiring Distribution

In this section we’ll look at the wiring closet room or the as it is also called the telecommunications room. These rooms contain all the servers, routers, switches and patch cables.

Network Cross Connects

Cross connect is a term used to refer to the point at which the cables that runs throughout the network meet and connect.

These cables that run throughout the network can be divided into two sections Horizontal and Vertical (backbone) cables. Horizontal cables are those that connect client systems to the network, while vertical cables run between floors to connect different locations on the network. Both of these cables are joined and distributed from the wiring closet or telecoms room.

The distribution of cables can be done in three ways Horizontal cross connect, intermediate cross connect and vertical or main cross connect.

Horizontal cross connect – is the distribution point for horizontal cabling. It is the location where the vertical and horizontal connections meet.

The intermediate cross connects – used in large networks to provide an intermediate cross connect between the main and horizontal cross connect.

The main or vertical cross connect – is the location where cables coming from outside enter the building for distribution.

Horizontal Cabling

Horizontal cabling connects the telecoms room to the end user. It spreads from the telecoms outlet or network outlet with RJ-45 connectors, at the client end and includes all cables from that outlet to the telecoms room to the horizontal cross connect. The horizontal cross connect includes all connecting hardware, such as patch panels and patch cords. It is the termination point for all network horizontal cable. Horizontal cabling is also called permanent cabling because it runs through walls and ceilings. On the client side the length of cable between the horizontal connects and the telecoms outlet should not go over 90 meters and the patch cables not over 5 meters. This is to comply with twisted pair cable restriction limit of 100 meter per segment.

Image from Mike Harwood's Network+ Guide

Vertical Cabling

The vertical or as it is sometimes called the backbone cabling is the media used to connect the telecoms rooms, server rooms, and remote locations and offices. This type of cabling is usually fiber or high-speed UTP cable. It can connect locations outside of the LAN.

Image from Mike Harwood's Network+ Guide

Patch Panels

The patch panel is the distribution block, which provides connections between network equipment like hubs, switches, routers and the ports to the PCs connect; these PCs connects are spread throughout the building. Patch panels can be either wall mounted with RJ-45 ports or freestanding.

Image from Mike Harwood's Network+ Guide

Type 66 and Type 110 Punchdown Blocks

These blocks has a series of insulation displacement connectors (IDCs), these are metal tabs that the wires are placed. When the wire is punched down into these tabs using the punch-down tool it strips the wire insulation, which make a contact with the connector and sort of completes the circuit. The same telephony UTP wires are used.

There are two types of this block:

  • A type 66, which is old now and rarely used; usually it’s used to connect telephone systems and low speed networks. It has 50 rows of IDC contacts that houses 25 pairs. The type 66 block although mainly used for voice systems and low speed nets it is however approved for cat 5 cabling but not recommended to do so due to cross-talk and it is limited to 66MHz.
  • The type 110 block replaces the type 66 due to its support of higher frequency and low cross-talk tends to be suitable to use for networks. This type allows for 25, 50, 100, 200 and 300 wire pairs unlike the type 66, which only allows for 25 pairs. There are two components with the type 110 block: 110-IDC connectors, which are used to terminate the wires and the 110 wiring block, which the connectors are attached to. it has multiple 110 terminating connectors, one for each cable that must be terminated. The type 110 usually mounted on the wall.
Image From Mike Harwood's Network+ Guide

Main Distribution Frame (MDF) and Intermediate Distribution Frame (IDF)

The MDF and IDF define the type of wiring closets. The main wiring closet for a network holds most of the network equipment, including the routers, switches, wiring, servers, etc. This closet is also the closet where outside lines run into the network. This closet is known as the MDF. A key component of the MDF is the primary patch panel. The network connector jacks connected to this panel go out to the building for net connections.

Where there are multiple wiring closets, the MDF is used to connect these closets, which are known as secondary closets or IDFs via a backbone cable. This backbone cable can be fiber, UTP or even coaxial cables.

Image from Mike Harwood's Network+ Guide

Demarcation Point

This point marks the connections point of the ISP’s part of the network and the customer’s part of the network. For admins this point is important because it helps them isolate where the problem is and whether it is the responsibility of the customer or the ISP. Because the customer has no choice where this point is placed and because it could be in hard to reach places or inconvenient places on some occasions; a demarcation extension is used to extend this point to a more convenient place. The hardware used at the demarcation point is called a smart jack or a Network Interface Device (NID), which performs several primary functions:

  • Loopback feature ­– like the Ethernet loopback cable is used for testing purposes.
  • Signal amplification – it amplifies the signal; similar to a repeater.
  • Surge protection – protects from environmental situations such as a lighting.
  • Remote alarms – alerts the owner of any problems with the smart jack.

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