So far we have learnt about the UTP
cables and the RJ45 connector. Now let us learn how we should connect the 4
pair of wires inside the UTP cable to the 8 pins on the RJ45 connector.
For
this the TIA/EIA has defined a standard called as TIA/EIA 568 which defines the
pin-out, or order of connections, for wires into the eight-pin modular
connector plug: RJ45.
In
TIA/EIA-568 standard two types of pin/pair assignments are defined one is T568A
method and T568B method.
Now let’s take a
look at wiring scheme T568A & T568B:
To emphasize, we know that the standard pair coloring
scheme is:
Pair1: Blue (Contains two wires: White-Blue and Blue)
Pair2: Orange (Contains two wires: White-Orange and
Orange)
Pair3: Green (Contains two wires: White-Green and Green)
Pair4: Brown (Contains two wires: White-Brown and Brown)
(I remember with the statement “Boss Of Google Browsing”)
The Striped wire always carries the (+)ve signal and the Solid wire carries the (-)ve signal. Originally the positive is called as Tip and the negative is called as Ring.
T568A
wiring scheme:
According
to the T568A wiring standard the pins are connected as shown below:
* Pair one (Blue) should be in the middle i.e. Solid Blue wire is connected to pin4
White
Blue wire is connected to pin5
* Pair two (Orange) will cover the Pair1 i.e. White-Orange is connected to pin3
Solid
Orange is connected to pin6
* Pair three (Green) will be on the top i.e. White-Green is connected to pin1
Solid
Green is connected to pin2
* Pair four (Brown) will be at the bottom i.e. White Brown is connected to pin7
Solid
Brown is connected to pin8
T568B
wiring scheme:
According
to the T568B wiring standard the pins are connected as shown below:
* Pair one (Blue) should be in the middle i.e. Solid Blue wire is connected to pin4
White
Blue wire is connected to pin5
* Pair three (Green) will cover the Pair1 i.e. White-Green is connected to pin3
Solid
Green is connected to pin6
* Pair two (Orange) will be on the top i.e. White-Orange is connected to pin1
Solid
Orange is connected to pin2
* Pair four (Brown) will be at the bottom i.e. White Brown is connected to pin7
Solid
Brown is connected to pin8
What is Difference
between T568A and T568B?
From the
order of connection point of view the only difference between T568A and T568B
is the pair2 and pair3 are swapped.
That is: In T568A, pair two pins are connected to Pin3
and Pin6.
In T568B,
pair three pins are connected to Pin3 and Pin6.
Remember that the 1st and 4th
pair remains same in both the assignments:
Pair1 (Blue) is always connected to Pin4 and
Pin5.
Pair4
(Brown) is always connected to Pin7 and Pin8.
Then what are the technical differences and its use.
Working
of 10BaseT (Ethernet) and 100Base-TX (Fast Ethernet) on Cat5e cable:
Out
of the 8wires/4pairs only 4wires/2pairs are used for the 10BaseT and
100Base-TX. The remaining two pairs are
unused.
The
pins: 1, 2, 3 and 6 are used and the pins: 4,5,7,8 are never used in 10BaseT
and 100Base-TX.
Transmitting:
In
both the standards T568A and T568B, the first two pins (Pin1 and Pin2) are used
for transmitting a signal. That is:
In T568A:
The first pin is Green-white it is
used for transmitting a (+ve) signal.
The
second pin is Solid Green it is used for transmitting a (-ve) signal.
In T568B:
The first pin is Orange-white it is
used for transmitting a (+ve) signal.
The
second pin is Solid Orange it is used for transmitting a (-ve) signal.
Receiving:
In
both the standards T568A and T568B, the third pin & the sixth pin are used
for receiving a signal. That is:
In
T568A:
The
third pin is Orange-white it is used for receiving a (+ve) signal.
The sixth
pin is Solid Orange it is used for receiving a (-ve) signal.
In T568B:
The
third pin is Green-white it is used for receiving a (+ve) signal.
The
sixth pin is Solid Green it is used for receiving a (-ve) signal.
Coming
to 1000Base-T (Gigabit Ethernet), uses all the four pairs inside the Cat5e or
Cat6 UTP cables. Every single wire is used for transmitting and receiving a
signal.
Connection
types for connecting the devices:
Now coming
to connecting the devices using the Cat5E unshielded twisted pair cable with an
RJ45 connector.
The connections can be made between the two types of
devices:
- Like devices
- Unlike devices
Like Devices:
Connecting
PC to PC, Server to Server, Switch to Switch, Router to Router, so on.
Unlike Devices:
Connecting
a PC to a Switch, Switch to a Server, Router to a Switch so on.
The TIA/EIA has defined some specific
methods for connecting the like devices and unlike devices. Because for the
proper communication between two devices, the transmit pin of device1 should be
connected to the receive pin of device2.
So
if we consider the like devices, for example a PC. Every PC will transmit and
receive on the same pins, so to enable communication between two PC’s, the
cable connecting should be arranged in such a way that the Transmit pin of one
PC is connected to Receive pin of the other end PC.
Based on this, the TIA/EIA has developed
two methods of cabling, they are:
- Straight Through
- Crossover
Straight
Through:
If
we connect the wires inside the UTP cable to RJ45 connector on both the ends
using either T568A pin assignment or T568B pin assignment, then that cable is referred
as Straight Through cable.
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This cable will be used to connect the
unlike devices. E.g.: PC to Hub, Hub to Switch, Router to Switch, and Switch to
PC etc.
To
be more formal: the straight through cable is used to connect the DTE (Date
Terminal Equipment) device to a DCE (Data Communication Equipment) device.
Let’s
see the operation:
Here
the assignment order followed on both the ends of the cable is T568A. And the cabling
method used is “Straight-Through”. Since a Straight through cable connects the
pin1 on one end to pin1 of the other side, pin2 of one end to pin2 of the other
end, pin3 of one end to pin3 of the other end, and so on.
It makes the Transmit pins of one device
to connect to the Receive pins of the other device and vice versa.
Cross
over:
If
we connect the wires inside the UTP cable to RJ45 connector, on end using T568A
pin assignment and the other end using T568B pin assignment, or vice versa then
that cable is referred as Cross-over cable.
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(Image source: Internet)
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This cable will be used to connect the
like devices. E.g.: PC to PC, Hub to Hub, Router to Router, and Switch to Switch
etc.
To
be more formal: the crossover cable is used to connect the DTE to DTE, and DCE
to DCE.
Let’s
see the operation:
Since both the DTE devices transmit and
receive on the same pin numbers, here we need to adjust the cable so that transmit
pin of one device connects to receive pin of the other device.
That
is the reason for using the “Crossover cable”. Here the assignment order
followed is one side T568A and the other side T568B.
What
is the difference between Straight through and Crossover cabling?
To
make a cross over cable we just swap the position of the pair2 (Orange) and
pair3 (Green) at the other end. Nothing but Pin1 in connected to Pin3, and Pin3
is connected to Pin6.
What
is the difference between T568A and T568B?
In
T568A standard the pin1 will be Green-White, pin2 will be Green.
In
T568B standard the pin1 will be Orange-White, pin2 will be Orange.
In
T568A standard the pin3 will be Orange-White, pin6 will be Orange.
In
T568B standard the pin3 will be Green-White, pin2 will be Green.
As far as I know the mail intention
for inventing the T568B standard is to match it with the AT&T’s old 258A
color code.
Now a days all the NIC’s can auto sense and adjust them
accordingly even if the wrong type of cables is used to connect the devices, in
the software they just swap the transmit and receive pins function.
Finally to show you practically, here is a topology (Observe
type of connections between the devices):
* The dotted are Crossover cables.
In the next post, let us learn about the number system
conversions.
