The Crossover connections

Now a day’s in almost every home, Educational Institute and office UTP cables are used mostly as transmission medium of LAN. There are different types of UTP cables available in the market. Normally it is recommended to use category#5 UTP cables. In every UTP cable there are 4 pairs of different color cable. 

TIA/EIA-568A and TIA/EIA-568B are the two standards for cabling telecoms product in commercial building. They define the UTP colored cable numbering. According to them the numbering system is as follow:

TIA/EIA-568A Standard		TIA/EIA-568B Standard
Cable no	Color code	Cable no	Color code
1	white and green	1	white and orange
2	green	2	orange
3	white and orange	3	white and green
4	blue	4	blue
5	white and blue	5	white and blue
6	orange	6	green
7	white and brown	7	white and brown
8	brown	8	brown

There are two cabling method available, straight through and cross cable connection. 

cross cable connection between Hub

cross cable connection between two single PC

From the picture we see that crossed cable is used in a LAN network to connect switch/Hub to switch/Hub or a single PC to PC connection. Normally two different types of cross cable connection are seen in a LAN network. The reasons for their differences are as follow:

We can divide the LAN connection standards in two categories. In one category, the standard that required only two pairs two transmit and receive and in another category standards that need all four cables for transmitting and receiving.

On first category the standards will be 10base-T, 100bast-TX etc as they need only two pairs of cable to transmit and receive. Their cable specifications are as follow:

10base-T and 100base-TX crossed connection
Connection:1   TIA/EIA-568A Standard				Connection:2       TIA/EIA-568B Standard
Pair	Pin no	Color code	Action	Pair	Pin no	Color code	Action
1	1	white and green	BI_DA+	1	1	white and orange	BI_DA+
	2	green	BI_DA-		2	orange	BI_DA-
2	3	white and orange	BI_DB+	2	3	white and green	BI_DB+
	4	blue			4	blue
3	5	white and blue		3	5	white and blue
	6	orange	BI_DB-		6	green	BI_DB-
4	7	white and brown		4	7	white and brown
	8	brown			8	brown

From the table we see that in only 4 cables are used and the others are unused. So it does not matter how we connect the unused cable. But according to standard they normally connected with same no of cable of other side.

Simply the cross connection then appears as follow:

cross cable connection for 10base-T and 100base-TX

On the other category we can found 100BASE-T4 or 1000BASE-T as they used all four cables for communication. So no cables remain unused. So in cross cable connection of these standards they need to cross too. But the most interesting thing is still this type of cross cable can be used for 10base-T and 100base-TX connection. Because it does not matter for these standards how the unused cables are connected. So this type of cross cable connection can be used for all standards. Hence this the most recommended cross cable connection. 

Crossed connection for TIA/EIA-568A

10base-T, 100base-TX, 100base-T4 and 1000base-T  crossed connection
Connection:1   TIA/EIA-568A			Connection:2    TIA/EIA-568A Crossed
Pin no	Color code	Action	Pin no	Color code	Action
1	white and green	BI_DA+	1	white and orange	BI_DB+
2	green	BI_DA-	2	orange	BI_DB-
3	white and orange	BI_DB+	3	white and green	BI_DA+
4	blue	BI_DC+	4	white and brown	BI_DD+
5	white and blue	BI_DC-	5	brown	BI_DD-
6	orange	BI_DB-	6	green	BI_DA-
7	white and brown	BI_DD+	7	blue	BI_DC+
8	brown	BI_DD-	8	white and blue	BI_DC-

Crossed connection for TIA/EIA-568B

10base-T, 100base-TX, 100base-T4 and 1000base-T  crossed connection
Connection:1   TIA/EIA-568B			Connection:2    TIA/EIA-568B Crossed
Pin no	Color code	Action	Pin no	Color code	Action
1	white and orange	BI_DA+	1	white and green	BI_DB+
2	orange	BI_DA-	2	green	BI_DB-
3	white and green	BI_DB+	3	white and orange	BI_DA+
4	blue	BI_DC+	4	white and brown	BI_DD+
5	white and blue	BI_DC-	5	brown	BI_DD-
6	green	BI_DB-	6	orange	BI_DA-
7	white and brown	BI_DD+	7	blue	BI_DC+
8	brown	BI_DD-	8	white and blue	BI_DC-