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An Ethernet crossover cable is a type of Ethernet cable used to connect computing devices together directly where they would normally be connected via a network switch, hub or router, such as directly connecting two personal computers via their network adapters.
Overview

The 10BASE-T and 100BASE-TX Ethernet standards use one wire pair for transmission in each direction. The Tx+ line from each device connects to the tip conductor, and the Tx- line is connected to the ring. This requires that the transmit pair of each device be connected to the receive pair of the device on the other end. When a terminal device is connected to a switch or hub, this crossover is done internally in the switch or hub. A standard straight through cable is used for this purpose where each pin of the connector on one end is connected to the corresponding pin on the other connector.

One terminal device may be connected directly to another without the use of a switch or hub, but in that case the crossover must be done externally in the cable. Since 10BASE-T and 100BASE-TX use pairs 2 and 3, these two pairs must be swapped in the cable. This is a crossover cable. A crossover cable must also be used to connect two internally crossed devices (e.g., two hubs) as the internal crossovers cancel each other out. This can also be accomplished by using a straight through cable in series with a modular crossover adapter.

Because the only difference between the T568A and T568B pin/pair assignments are that pairs 2 and 3 are swapped, a crossover cable may be envisioned as a cable with one connector following T568A and the other T568B. Such a cable will work for 10BASE-T or 100BASE-TX. 1000BASE-T4 (Gigabit crossover), which uses all four pairs, requires the other two pairs (1 and 4) to be swapped and also requires the solid/striped within each of those two pairs to be swapped.

[edit] Crossover cable pinouts
Two pairs crossed, two pairs uncrossed
10baseT/100baseTX crossover ( shown as T568A ) Pin Connection 1 pair Connection 2 pair Connection 1 Connection 2 Pins on plug face (jack is reversed)
1 2 3 Pair 2 Tip
white/orange stripe Pair 3 Tip
white/green stripe
2 2 3 Pair 2 Ring
orange solid Pair 3 Ring
green solid
3 3 2 Pair 3 Tip
white/green stripe Pair 2 Tip
white/orange stripe
4 1 1 Pair 1 Ring
blue solid Pair 1 Ring
blue solid
5 1 1 Pair 1 Tip
white/blue stripe Pair 1 Tip
white/blue stripe
6 3 2 Pair 3 Ring
green solid Pair 2 Ring
orange solid
7 4 4 Pair 4 Tip
white/brown stripe Pair 4 Tip
white/brown stripe
8 4 4 Pair 4 Ring
brown solid Pair 4 Ring
brown solid

Certain equipment or installations, including those in which phone and/or power are mixed with data in the same cable, may require that the "non-data" pairs 1 and 4 (pins 4, 5, 7 and 8) remain un-crossed.
Gigabit crossover
All four pairs crossed
10base-T/100base-TX/1000base-TX/T4 crossover (shown as T568B) Pin Connection 1 pair Connection 2 pair Connection 1 Connection 2 Pins on plug face (jack is reversed)
1 2 3 Pair 2 Tip
white/orange stripe Pair 3 Tip
white/green stripe
2 2 3 Pair 2 Ring
orange solid Pair 3 Ring
green solid
3 3 2 Pair 3 Tip
white/green stripe Pair 2 Tip
white/orange stripe
4 1 4 Pair 1 Ring
blue solid Pair 4 Tip
white/brown stripe
5 1 4 Pair 1 Tip
white/blue stripe Pair 4 Ring
brown solid
6 3 2 Pair 3 Ring
green solid Pair 2 Ring
orange solid
7 4 1 Pair 4 Tip
white/brown stripe Pair 1 Ring
blue solid
8 4 1 Pair 4 Ring
brown solid Pair 1 Tip
white/blue stripe

In practice, it does not matter if your Ethernet cables are wired as T568A or T568B, just so long as both ends follow the same wiring format. It is just as valid to make a four-pair crossover using T568A, or a two pair crossover using T568B, as it is to wire them the way shown here. Typical commercially available "pre-wired" cables can follow either format depending on who made them. What this means is that you may discover that one manufacturer's cables are wired one way and another's the other way, yet both are "correct" and will work. In either case, T568A or T568B, a normal (un-crossed) cable will have both ends wired according to the layout in the Connection 1 column.

[edit] Other networking technologies

Main article: Crossover cable

Other technologies use different pairs to transmit data, so crossover cables for them have different configurations to swap the transmit and receive pairs:

* Twisted pair Token ring uses T568B pairs 1 and 3 (the same as T568A pairs 1 and 2), so a crossover cable to connect two Token Ring interfaces must swap these pairs, connecting pins 4, 5, 3, and 6 to 3, 6, 4, and 5 respectively.
* A T1 cable uses T568B pairs 1 and 2, so to connect two T1 CSU/DSU devices back-to-back requires a crossover cable that swaps these pairs. Specifically, pins 1, 2, 4, and 5 are connected to 4, 5, 1, and 2 respectively.
* A 56K DDS cable uses T568B pairs 02 and 04, so a crossover cable for these devices swaps those pairs (pins 01, 02, 07, and 08 are connected to 07, 08, 01, and 02 respectively).

[edit] Automatic crossover

Automatic MDI/MDI-X Configuration is specified as an optional feature in the 1000BASE-T standard[1], meaning that straight-through cables will usually work between Gigabit capable interfaces. This feature eliminates the need for crossover cables, making obsolete the uplink/normal ports and manual selector switches found on many older hubs and switches and greatly reducing installation errors. Note that although Automatic MDI/MDI-X is generally implemented, a crossover cable would still be required in the occasional situation that neither of the connected devices has the feature implemented and enabled.

Even for legacy 10/100 devices, many NICs, switches and hubs automatically apply an internal crossover when necessary. Besides the eventually agreed upon Automatic MDI/MDI-X, this feature may also be referred to by various vendor-specific terms including: Auto uplink and trade, Universal Cable Recognition and Auto Sensing.

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Posted by waqasahmad

In short the difference is in signal electrical characteristics.

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Posted by HamidAliKhan

yes difference is signal electrical format & specifications

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Posted by Hash007

the main difference is in signalelectricalcharacteristics.

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Posted by waqqas1

The primary differences between an E1 (output) signal and a Ethernet Signal (output) signal are the format and electrical characteristics.

E1 is a bit stream (1s and 0s) that has a framing pattern associated with it so that the bit-stream can be broken down into frames and octets within the frames correspond to channels, and so forth. Electrically, as it appears on the cable pair, an E1 signal comprises bipolar (i.e. +ve and -ve voltage polarity) pulses that are "return-to-zero". Generally speaking the presence of a pulse, of either polarity is considered a binary "1" and absence of a pluse interpreted as a binary "0". Also, the polarity of pulses used for sending a binary "1"s alternate as in Alternate Mark Inversion (AMI). However, if there is a (long) string of binary "0"s, there will be "silence" (lack of pulses) which in turn will affect clock recovery. To avoid this situation E1 uses a scheme called HDB3 in order to suppress the occurence of more than 2 absent pulses (which could occur if there were 3 three or more "0"s in the binary information bit-stream) whereby pulses are inserted for binary "0" data and a bipolar-rule-violation method used to identify where this substitution has taken place. Since it can carry actual information, an E1 stream can, if necessary, carry sync status messages (SSM). In an E1 input module special circuitry is required to extract the underlying clock signal from this bipolar voltage signal.

A 2048 kHz output signal is just that. It comprises a square wave of nominally 50% duty cycle and in most implementations a zero dc bias. There is no binary (data) information transferred, just the clock waveform. The notion of clock extraction does not arise since the waveform is the clock signal itself.

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Posted by sagitraz