The committee began working on a faster Ethernet, quickly dubbed gigabit Ethernet. The goal was to increase performance while maintaining all Ethernet standards. Gigabit Ethernet had to provide service with both unicast and broadcast using the same 48-bit address scheme and also maintaining the same frame format. All configurations of gigabit Ethernet must use point-to-point links. In fig.(a) two computers are directly attached to each other.
However, uses a switch or hub connected to multiple computers and possibly additional switches or hubs as shown in fig.(b). In both figures, the Ethernet cable has exactly two devices on it.
Features of Gigabit Ethernet :
- It supports two different modes i.e. full-duplex mode and half-duplex mode. Full-duplex mode allows traffic in two directions at the same time. When a central switch connected to computers on the periphery this mode is used.
- In this, all lines are buffered so each computer and switch is free to send frames whenever it wants to. In this mode, contention is not possible.
- The computer is the only possible sender to the switch, and transmission will succeed even if the switch is currently sending a frame to the computer.
- A half-duplex mode is used when computers are connected to a hub rather than a switch. A hub does not buffer incoming frames.
- All the lines are electrically connected internally, simulating the multi-drop cable used in classic Ethernet. Standard CSMA/CD protocol is required in this mode because collisions are possible. Because a 64-byte frame can now be transmitted 100 times faster than in classic Ethernet, the maximum cable length must be 100 times less or 25 meters.
Tables for different Ethernet :
- Gigabit Ethernet supports both copper and fiber cabling as shown in table 1. When sending signals at the speed of 1 Gbps then it requires encoding and at every nanosecond, a bit must be sent.
- This trick was initially accomplished with short, shielded copper cables and optical fibers. For the optical fibers, two wavelengths are permitted and result in two different versions: 0.85 microns and 1.3 microns.
Table-1: Gigabit Ethernet Cabling
|1000Base-SX||Fiber optics||550m||Multimode fiber (50, 62.5 microns)|
|1000Base-LX||Fiber optics||5000m||Single(10 µ) or multimode(50, 62.5 µ)|
|1000Base-CX||2 pairs of STP||25m||Shielded twisted pair|
|1000Base-T||4 pairs of UTP||100m||Standard category 5 UTP|
- With the help of cheaper LEDs signaling at a short wavelength can be achieved. As it can run up to 500m for 50-micron fiber, therefore, can be used for connections within a building and also used with multimode fiber. Expensive lasers are required for signaling at a longer wavelength.
- Along with Gigabit Ethernet one more extension was introduced. Jumbo frames allow for frames to be up to 9 KB. This extension is proprietary. If it is used then Ethernet is no longer compatible with earlier versions therefore it is not recognized by the standard. But it was supported by most of the vendors.
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