4. Cabling Overview

Twisted-Pair Cabling:

A regular twisted-pair cable consists of 4 pairs of copper wires, total of 8 wires. Each side of the cable is ended applying an RJ45 connector, RJ45 consists eight pins. When the connector is crimped to the cable, these pins make contact with each wire separately and it's necessary.

The wires comes with assigned color code to distinguish them and color code is dictated by the cabling standard - TIA/EIA-568B:

Color	Pin#
White-Orange	1
Orange	2
White-Green	3
Blue	4
White-Blue	5
Green	6
White-Brown	7
Brown	8

Each wire allotted for specific purpose. E.g., both Ethernet and Fast Ethernet uses 2 wires to transmit data , and 2 wires to receive data, while rest 4 wires remains inactive.

For communication to take place, transmit pins must connect to the receive pins of the remote host. This doesn't happen in a straight-through cabling configuration:

The crossover controlled either by the cable, or an intermediator device, such as a  switch.

Twisted-Pair Cabling - Cable and Interface Types:

The layout  of the wires in the RJ45 connector orders the routine of the cable. There are 3 types of twisted-pair cable:
• Straight-through
• Crossover
• Rollover

The network interface type decides when to use each cable:
• Medium Dependent Interface with Crossover (MDIX)

• Medium Dependent Interface (MDI)

Host interfaces are usually MDI, when hub or switch interfaces are usually MDIX.

Twisted-Pair Cabling - Straight-Through Cable:

A straight-through cable is applied in the following conditions:
• From a host to a hub - MDI to MDIX
• From a host to a switch - MDI to MDIX
• From a router to a hub - MDI to MDIX
• From a router to a switch - MDI to MDIX

Basically, a straight-through cable is used to connect any host device to a hub or switch, exclude for another hub or switch. The hub or switch supplies the crossover (or MDIX) function to link transmit pins to receive pins.

TIA/EIA-568B standard for a straight-through cable:

Pin#  Connector 1                                                   Connector 2         Pin#

1       White Orange     ------------------------   White Orange              1

2       Orange                 ------------------------   Orange                           2

3       White Green        ------------------------   White Green                3

4       Blue                        ------------------------   Blue                              4

5       White Blue           ------------------------   White Blue                   5

6       Green                     ------------------------   Green                           6

7       White Brown      ------------------------   White Brown               7

8       Brown                   ------------------------   Brown                           8

A straight-through cable also known as a patch cable/cord.

Twisted-Pair  – Crossover Cable:

A cross-over cable is applied in the following conditions:
• From same device to same device,
 Like: • host to a host – MDI to MDI

         • hub to a hub - MDIX to MDIX
         • switch to a switch - MDIX to MDIX
         • hub to a switch - MDIX to MDIX
         • router to a router - MDI to MDI

To make a cross-over cable, the transmit pins must be swapped with the

receive pins at one end of the cable:

•  1 & 3

•  2 & 6

Pin#  Connector 1                                                   Connector 2         Pin#

1       White Orange     ------------------------   White Green                 1

2       Orange                 ------------------------   Green                              2

3       White Green        ------------------------  White Orange                3

4       Blue                        ------------------------   Blue                               4

5       White Blue           ------------------------   White Blue                   5

6       Green                     ------------------------  Orange                          6

7       White Brown      ------------------------   White Brown               7

8       Brown                   ------------------------   Brown                           8

Make sure that the Orange and Green pins swapped on Connector 2.

The first connector standard is the TIA/EIA-568B, while the second

connector standard is the TIA/EIA-568A.

Twisted Pair – Rollover Cable:

A rollover cable is applied to link a workstation or laptop into a Cisco

device’s console or auxiliary port, for management functions. A rollover

cable is also known console cable, and its overlay is usually flat

and light-blue in colour.

To make a rollover cable, the pins are totally reversed on one end of the

cable:

Pin#  Connector 1                                                   Connector 2         Pin#

1       White Orange     ------------------------  Brown                               1

2       Orange                 ------------------------   White Brown                  2

3       White Green        ------------------------  Green                                3

4       Blue                        ------------------------ White Blue                       4

5       White Blue           ------------------------  Blue                                  5

6       Green                     ------------------------ White Green                    6

7       White Brown      ------------------------   Orange                             7

8       Brown                   ------------------------  White Orange                 8


It's used to configure Cisco's Router, Switches, and Firewalls.

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