Copper Cables

Copper wires are used to transmit data as electric signals. Ethernet, Token Ring, Copper Distributed Data Interface (CDDI) networks all use copper cabling to transmit data.

Most modern Ethernet networks use copper unshielded twisted-pair (UTP) cables. These are inexpensive, easy to install and support speeds of up to 1Gbps but should be no more than 100 meters in length. UTP cables are segregated into different category ratings.

Minimum rating of Cat3 is required to achieve a data transmission of up to 10Mbps - known as 10BaseT Ethernet.

Minimum rating of Cat5 is required to achieve data of 100Mbps - known as Fast Ethernet or 10BaseTX Ethernet - or 1Gbps which is known as Gigabit Ethernet or 1000BaseT Ethernet.

Coaxial cables support longer segment runs than UTP but most modern networks no longer use it.

CONNECTING UTP WITH RJ-45

UTP cables contain 4 pairs of colour-coded wires:

white/green and green
white/blue and blue
white/orange and orange
white/brown and brown

The 8 wires must be crimped into the 8 pins within an RJ45 connector. The pins in the RJ-45 connector are arranged in order from left to right.

In a typical Ethernet or Fast Ethernet cabling scheme, the wires that are connected to Pins 1 & 2 transmit data and the wires connected to Pins 3 & 6 receive data.

GigabitEthernet transmits and receives data on all 4 pairs of wires.

There are 2 different wire termination standards for an RJ-45 connector - T568A and T568B.

T568A standard is compatible with Integrated Services Digital Network (ISDN) cabling standards.

T568B standard is compatible with a standard established by AT&T.

Wires used for transmit and received in one standard are reversed in the other.

The T568A Standard:

uses the white/green and green wires for Pins 1 & 2
uses the white/orange and orange wires for Pins 3 & 6

The T568B standard:

uses the white/orange and orange for Pins 1 & 2
uses the white/green and green wires for Pins 3 & 6

The blue and brown wire pairs are typically connected to the same pin regardless of standard.

UNDERSTANDING STRAIGHT-THROUGH AND CROSSOVER CABLES

There are times when you should use T568A on one side and T568B on the other. A crossover cable uses a different standard at each end - used to connect two workstations, two switches, two routers over the same cable or any of the same two devices.

Dissimilar Ethernet devices such as router and switch, switch and PC must be connected with a straight-through Ethernet cable - uses the same pinout standard at each end.

If two dissimilar devices are connected with a straight-through, the transmit pair on one end is connected to the receive pair on the other. If two similiar devices are connected with a straight through, the transmit pins on one end are connected to the transmit pins on the other end which means no communication.

Because Gigabit uses all 8 wires of a UTP cable, the crossover pinout for a cable that is to be used over a Gigabit connection is slightly more complex than an inverse T568-standard.

In addition to inverting the transmit/receive wires, the white/blue and blue wires on one end should be inverse to the white/brown and brown wires on the other end.

Serial Cables

Serial cables are also copper but are not commonly used anymore. Most service providers equipment has transitioned to Ethernet and fibre-optic cables.

Cisco devices offer 5 types of serial cables. Most commonly used serial cable is a 25-pin EIA/TIA-232 cable with a DB-25 connector at the end.

One end of a serial cable is the Data Communications Equipment (DCE) and the other is the Data Terminal Equipment (DTE) end. The DCE end provides clocking to the DTE end - if clock rate is not configured on the DTE end, physical connectivity cannot be established.

Fibre Optic Cables

There are 2 main types of Fibre-Optic cables:

Multimode Fibre (MMF)
Single-Mode Fibre (SMF)

MULTIMODE FIBRE

MMF can use a 62.5 micron core and wavelength of 805 nanometres. They are typically used for distances less than 2km.

When light is transmitted through a fibre-optic cable, light is only propagated by the fibre core at certain angles or modes. The light transmitted into the core of an MMF cable is typically in the 850-nm or 1300-nm frequency range.

Because MMF has a relatively large core that permits many different angles of light, the signal becomes dispersed over great distances - this dispersion effectively limits the usable distance of MMF to 2km.

MMF is typically used in campus design that require at least 1Gbps of bandwidth and network runs that are less than 2km.

SINGLE-MODE FIBRE

SMF typically uses a 9-micron core. Light transmitted into the core is typically in the 1310nm or 1350nm frequency range.

Because SMF has a small core that permits very few angles of light, the signal does not become very dispersed over great distances - enables network runs of 80km or more.

Typically used in campus designs that require at least 10Gbps of bandwidth and network runs that are greater than 2km.

Fibre Optic Cable Connections

Older cables use ST and SC connectors. Older ST connector is round, spring-loaded connector.

The SC connector is square-shaped that snaps into its receptacle. SC is available in both single and duplex variables:

Newer fibre optic cables can also use LC or MT-RJ connectors. LC connectors are small form factor connectors that are available in both single and duplex variables. They snap into their receptacle and are half the size of SC connectors:

MT-RJ connectors look like a miniature RJ-45 Ethernet copper connector. They provide duplex interface in a single connector:

PoE

PoE provides in-line power for connected IP phones and WAPs over the same cable that carries voice and data traffic. PoE eases VoIP and WLAN implementations because you are not limited to installing devices next to existing power sources - as long as there is a network jack, the device can draw power from the network cable.

A Cisco Catalyst switch can provide power to both Cisco and non-Cisco devices that support either IEEE 802.3af standard, the IEEE 802.3at standard or the Cisco prestandard method.

For a Catalyst switch to successfully provide power, both the switch and device must support the same PoE method. After a common PoE method is determine, CDP messages are sent between Catalyst switches and Cisco devices can further refine the amount of allocated power.

802.3af standard divides power requirements into the following classes:

Class 0: 0.44 - 12.94W
Class 1: 0.44 - 3.83W
Class 2: 3.84 - 6.49W
Class 3: 6.49 - 12.95W

Class 0 is the default PoE level - devices classified as such will draw as much power as they need.

The 802.3at PoE Plus standard adds a fourth class, Class 4, which is used for high power PoE devices - class 4 provides 12.95W to 25.50W of power.

Cisco Catalyst switches monitor and police PoE ports. If a device attempts to draw more power than a port is configured to provide, a syslog message is issued and port shutdown and enters the error-disabled state.

Interfaces and Cabling