Information about Ethernet Crossover Cable
)
Crossover cable suitable for use with 100BASE-T4 Fast Ethernet
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8P8C modular crossover adapter
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. For example, one would use a crossover cable to directly connect 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 latter. 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 TIA/EIA-568-B 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.
Crossover cable pinouts
| Pin | Connection 1 pair | Connection 2 pair | Connection 1 | Connection 2 | Pins on plug face (jack is reversed) |
|---|---|---|---|---|---|
| 1 | 3 | 2 | ){kind=small} white/green stripe | ){kind=small} white/orange stripe | |
| 2 | 3 | 2 | ){kind=small} green solid | ){kind=small} orange solid | |
| 3 | 2 | 3 | white/orange stripe | white/green stripe | |
| 4 | 1 | 1 | ){kind=small} blue solid | blue solid | |
| 5 | 1 | 1 | ){kind=small} white/blue stripe | white/blue stripe | |
| 6 | 2 | 3 | orange solid | green solid | |
| 7 | 4 | 4 | ){kind=small} white/brown stripe | white/brown stripe | |
| 8 | 4 | 4 | ){kind=small} brown solid | 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.
When a crossover cable is used to connect two routers or switches, some units, especially older ones, will work with two-pairs-crossed cables or four-pairs-crossed cables, but not both. Prudent technicians keep both kinds of crossover cables on hand.
| Pin | Connection 1 pair | Connection 2 pair | Connection 1 | Connection 2 | Pins on plug face (jack is reversed) |
|---|---|---|---|---|---|
| 1 | 2 | 3 | white/orange stripe | white/green stripe | |
| 2 | 2 | 3 | orange solid | green solid | |
| 3 | 3 | 2 | white/green stripe | white/orange stripe | |
| 4 | 1 | 4 | blue solid | white/brown stripe | |
| 5 | 1 | 4 | white/blue stripe | brown solid | |
| 6 | 3 | 2 | green solid | orange solid | |
| 7 | 4 | 1 | white/brown stripe | blue solid | |
| 8 | 4 | 1 | brown solid | white/blue stripe |
It really does not matter if your Ethernet cables are wired as T568A or T568B, just so long as both ends follow the same wiring format. In other words 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, (and often do), 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 first connections column.
Other networking technologies
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).
Automatic crossover NICs
Almost all newer Ethernet network interface cards (NICs), switches and hubs automatically apply an internal crossover when necessary. This feature is known by various vendor-specific terms, e.g., Netgear calls it Auto uplink and trade, and other common vendor terms include Auto-MDI/MDI-X, Universal Cable Recognition and Auto Sensing. This eliminates the need for crossover cables, obsoletes the uplink/normal ports and manual selector switches found on many older hubs and switches, and greatly reduces installation errors, especially by non-technical users.Automatic MDI/MDI-X capability is specified in the 1000BASE-T standard, so straight-through cables will work in almost all cases. But it is optional, so a crossover cable is needed if neither of the connected devices supports it, or the function has been disabled.
Networks created using crossover cables
| Machine 1 | Machine 2 | |
|---|---|---|
| IP | 192.168.1.2 | 192.168.1.3 |
| Subnet Mask | 255.255.255.0 | |
External links
- How to wire Ethernet Cables, with pinouts for 10-1000BASE-TX/T4 as well as general explanatory text on the various standards, POE (Power Over Ethernet), and other useful information.
- Crossover cable pinout (10/100base-TX)
- Pinouts For 100BASE-TX and 1000BASE-T
- Pinouts For 100BASE-TX and text on 1000BASE-T
- LAN Wiring on 10base-T, 100base-TX/T4, 1000base-T from Zytrax.com
- What are Straight and Crossover cable
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Low-end network switches appear nearly identical to network hubs, but a switch contains more "intelligence" (and a slightly higher price tag) than a network hub.
..... Click the link for more information.
Low-end network switches appear nearly identical to network hubs, but a switch contains more "intelligence" (and a slightly higher price tag) than a network hub.
..... Click the link for more information.
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Connects to:
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Connects to:
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NETGEAR
Public (NASDAQ: NTGR )
Founded 1996
Headquarters Santa Clara, California, United States
Key people Patrick Lo, CEO & Chairman
Industry Communications equipment
Products Hubs, Routers, Switches
Revenue $449.
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Public (NASDAQ: NTGR )
Founded 1996
Headquarters Santa Clara, California, United States
Key people Patrick Lo, CEO & Chairman
Industry Communications equipment
Products Hubs, Routers, Switches
Revenue $449.
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- The Internet protocol suite, a set of communications protocols that implement the protocol stack on which the Internet runs
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In homes, the gateway is usually the ISP-provided device that connects the user to the Internet.
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