Ethernet

Ethernet

Ethernet is a hardware and signaling specification developed by Xerox in 1970 for data networking. Ethernet is the defacto networking standard for LAN (local area network) communication and is standardized under the IEEE standard 802.3. Ethernet runs at 10Mb, 100Mb or 1Gb per second. It was originally developed by Xerox Corporation in cooperation with DEC and Intel in 1976. Ethernet uses a bus or star topology. Coaxial or twisted pair cable is used.
With over 50 million nodes installed, Ethernet is easily the most dominant data networking technology in use today.
Devices are connected to the network and access it using a 'Carrier Sense Multiple Access' with a Collision Detection (CSMA/CD) protocol (each computer checks to see if another computer is transmitting. If not it starts transmitting. If two computers accidentally transmit at the same time and their messages collide, they both wait and send again in turn. This is the reason that a Ethernet LAN never can work up to it full capacity.
Ethernet networks use unshielded twisted pair (UTP) Category 5 cable. CAT5 cable runs should not exceed 100 meters. Only two pairs of the Cat5 cable is acually used: pair 3 (green) on pins 1 and 2 of a standard RJ-45 connector, and pair 2 (orange) on pins 3 and 6.
EIA/TIA specifies RJ-45 connectors (ISO 8877) for UTP (unshielded twisted pair) cable.

To make sure that no two machines worldwide would end up with the same Ethernet address, each Ethernet controller comes with an address builtin from the factory. In order to make sure that they would never have to reuse addresses, the Ethernet designers allocated 48 bits for the Ethernet address. Ethernet equipment manufacturers have to register with a central authority, to make sure that the numbers don't overlap with any other manufacturer.

---

CAT5 Ethernet Cable: pair 1: blue pair: 2 orange pair: 3 green pair: 4 brown (twisted about 3 times per inch) See: Cat5 Cable

---

Straight Ethernet Cable

Cross-Cable

---

Ethernet Standard RJ45 Connection, Code EIA/TIA-568-B
PIN	ABBR	DESCRIPTION	PAIR	COLOR
1	TX+	Tranceive Data+	Pair 2	White/Orange
2	TX-	Tranceive Data-	Pair 2	Orange
3	RX+	Receive Data+	Pair 3	White/Green
4	n/c		Pair 1	Blue
5	n/c		Pair 1	White/Blue
6	RX-	Receive Data-	Pair 3	Green
7	n/c		Pair 4	White/Brown
8	n/c		Pair 4	Brown

CAT 5: 4 Twisted Pairs at 24 AWG
RJ 45:
(RJ xx: telephone connection interfaces, registered with the FCC, the U.S. Federal Communications Commission.)
Pins: looking at the wiring end of a plug with the latch down, pin 1 is on the left.


CAT 5 Cable Specifications:

Frequency	Max. Attenuation per 1000 ft/ 304 m	Resistance per 1000 ft/ 304 m	Capacitance	Impedance
4 MHz	13 dB	28,6 ohms	14 pF/ft	100 ohms
10 MHz	20 dB	28,6 ohms	14 pF/ft	100 ohms
20 MHz	28 dB	28,6 ohms	14 pF/ft	100 ohms
100 MHz	67 dB	28,6 ohms	14 pF/ft	100 ohms

CAT5 Connection Table, RJ 45, Code EIA/TIA-568-A and EIA/TIA-568-B

RJ 45	Pin	1	2	3	4	5	6	7	8
Code EIA/TIA-568-A	Pair	3 T	3 R	2 T	1 R	1 T	2 R	4 T	4 R
	Color	wt/gn	gn	wt/or	bl	wt/bl	or	wt/br	br
Code EIA/TIA-568-B	Pair	2 T	2 R	3 T	1 R	1 T	3 R	4 T	4 R
	Color	wt/or	or	wt/gn	bl	wt/bl	gn	wt/br	br

T568B is identical to T568A except that pairs 2 (orange) and 3 (green) are swapped.




ATTENTION !! The different USOC (Universal Service Order Code) Standard:

RJ 45 Pin		1	2	3	4	5	6	7	8
Pair		4 T	3 T	2 T	1 R	1 T	2 R	3 R	4 R
Color Code USOC		wt/br	wt/gn	wt/or	bl	wt/bl	or	gn	br

ISDN BRI RJ45 Standard (574616-MO97):

RJ 45 Pin		1	2	3	4	5	6	7	8
Pair				Tx+	Rx +	Rx -	Tx -

Category 5 Wiring Standards

Pin	EIA/TIA 568A	AT&T 258A, EIA/TIA 568B	10Base-T 10Mbps Cat3	100Base-TX 100Mbps Cat5	100Base-T4 100Mbps Cat3	100Base-T2 100Mbps Cat3	1000Base-T 1Gbps Cat5+
1	white/green	white/orange	TX+	TX+	TX D1+	BI DA+	BI DA+
2	green/white	orange/white	TX-	TX-	TX D1-	BI DA-	BI DA-
3	white/orange	white/green	RX+	RX+	RX D2+	BI DB+	BI DB+
4	blue/white	blue/white	na	na	BI D3+	na	BI DC+
5	white/blue	white/blue	na	na	BI D3-	na	BI DC-
6	orange/white	green/white	RX-	RX-	RX D2-	BI DB-	BI DB-
7	white/brown	white/brown	na	na	BI D4+	na	BI DD+
8	brown/white	brown/white	na	na	BI D4-	na	BI DD-
BI=BI directional data    RX=Receive Data    TX=Transmit Data

10BaseT and 100BaseT Cross Cable
Pin	Color Code	Color Code	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