General Design
Fast Ethernet is an extension of the existing Ethernet standard. It runs on UTP data or optical fiber cable and uses CSMA/CD in a star wired bus topology, similar to 10BASE-T where all cables are attached to a hub. And, it provides compatibility with existing 10BASE-T systems and thus enables plug-and-play upgrades from 10BASE-T. Fast Ethernet is sometimes referred to as 100BASE-X where X is a placeholder for the FX and TX variants.
The 100 in the media type designation refers to the transmission speed of 100 Mbit/s. The "BASE" refers to baseband signalling, which means that only Ethernet signals are carried on the medium. The TX, FX and T4 refer to the physical medium that carries the signal.
A Fast Ethernet adapter can be logically divided into a Media Access Controller (MAC) which deals with the higher level issues of medium availability and a Physical Layer Interface (PHY). The MAC may be linked to the PHY by a 4 bit 25 MHz synchronous parallel interface known as a Media Independent Interface (MII) or a 2 bit 50 MHz variant Reduced Media Independent Interface (RMII). Repeaters (hubs) are also allowed and connect to multiple PHYs for their different interfaces.
The MII may (rarely) be an external connection but is usually a connection between ICs in a network adapter or even within a single IC. The specs are written based on the assumption that the interface between MAC and PHY will be a MII but they do not require it.
The MII fixes the theoretical maximum data bit rate for all versions of Fast Ethernet to 100 Mbit/s. The data signaling rate actually observed on real networks is less than the theoretical maximum, due to the necessary header and trailer (addressing and error-detection bits) on every frame, the occasional "lost frame" due to noise, and time waiting after each sent frame for other devices on the network to finish transmitting.
Read more about this topic: Fast Ethernet
Famous quotes containing the words general design, general and/or design:
“Surely one of the peculiar habits of circumstances is the way they follow, in their eternal recurrence, a single course. If an event happens once in a life, it may be depended upon to repeat later its general design.”
—Ellen Glasgow (1873–1945)
“We raised a simple prayer
Before we left the spot,
That in the general mowing
That place might be forgot;
Or if not all so favored,
Obtain such grace of hours
That none should mow the grass there
While so confused with flowers.”
—Robert Frost (1874–1963)
“For I choose that my remembrances of him should be pleasing, affecting, religious. I will love him as a glorified friend, after the free way of friendship, and not pay him a stiff sign of respect, as men do to those whom they fear. A passage read from his discourses, a moving provocation to works like his, any act or meeting which tends to awaken a pure thought, a flow of love, an original design of virtue, I call a worthy, a true commemoration.”
—Ralph Waldo Emerson (1803–1882)