Ethernet Flashcards
Network data transmission
Network data transfer works by modulating the properties of a transmission medium—electric current, infrared light, or radio waves—to encode a signal. One example of modulation is transitioning between low and high voltage states in an electrical circuit. These voltage pulses can encode symbols, which can be mapped to digital bits—ones and zeros.
Each media type supports a range of possible frequencies. Higher frequencies allow for more data to be transferred per second. The range of frequencies is referred to as the media bandwidth.
Bandwidth
bandwidth is a frequency range measured in cycles per second or Hertz (Hz), but the term is very widely used in data networking to mean the amount of data that can be transferred, measured in multiples of bits per second (bps). Encoding methods mean that, for instance, a signal with 100 MHz frequency bandwidth can transfer much more than 100 Mbps.
The Institute of Electrical and Electronics Engineers (IEEE) 802.3 Ethernet standards
The Institute of Electrical and Electronics Engineers (IEEE) 802.3 Ethernet standards (ieee802.org/3) are very widely used on both LANs and WANs. Ethernet standards provide assurance that network cabling will meet the bandwidth requirements of applications. These Ethernet media specifications are named using a three-part convention, which is often referred to as xBASE-y. This describes the following:
- The speed or bit rate in megabits per second (Mbps) or gigabits per second (Gbps).
- The signal mode (baseband or broadband). All mainstream types of Ethernet use baseband transmissions, so you will only see specifications of the form xBASE-y.
- A designator for the media type.
For example, 10BASE-T denotes an early implementation that works at 10 Mbps (10), uses a baseband signal (BASE), and runs over twisted pair copper cabling (-T).
Copper cable is used to transmit electrical signals. The cable between two nodes creates a low voltage electrical circuit between the interfaces on the nodes. There are two main types of copper cable: twisted pair and coaxial (coax). Copper cable suffers from high attenuation, meaning that the signal quickly loses strength over long links. Twisted pair cable is rated to Category (or “Cat”) standards that define what bandwidth it should support, up to a given distance.
collision domain
Each network node connected to the same media is in the same collision domain. When two nodes transmit at the same time, the signals are said to collide, and neither signal can reach its destination. This means that they must be resent, reducing available bandwidth. The collisions become more frequent as more nodes are added, and consequently the effective data rate is reduced.
Carrier Sense Multiple Access with Collision Detection (CSMA/CD).
The Ethernet protocol governing contention and media access is called Carrier Sense Multiple Access with Collision Detection (CSMA/CD).
A collision is the state when a signal is present on an interface’s transmit and receives lines simultaneously. On detecting a collision, the node broadcasts a jam signal. Each node that was attempting to use the media then waits for a random period (backoff) before attempting to transmit again.
The collision detection mechanism means that only half-duplex transmission is possible. This means that a node can transmit or receive, but it cannot do both at the same time.
100BASE-TX Fast Ethernet Standards
The Fast Ethernet standard uses the same CSMA/CD protocol as 10BASE-T but with higher frequency signaling and improved encoding methods, raising the bit rate from 10 Mbps to 100 Mbps. 100BASE-TX refers to Fast Ethernet working over Cat 5 (or better) twisted pair copper cable with a maximum supported link length of 100 meters (328 feet).
Gigabit Ethernet Standards
Gigabit Ethernet builds on the standards defined for Ethernet and Fast Ethernet to implement rates of 1,000 Mbps (1 Gbps). When installed using Cat 5e or better copper wire, Gigabit Ethernet is specified as 1000BASE-T. Gigabit Ethernet does not support hubs; it is implemented only using switches. The maximum distance of 100 meters (328 feet) applies to cabling between the node and a switch port, or between two switch ports.
Fiber Ethernet Standards
Fiber optic cable uses infrared light signals. The light signals are also not susceptible to interference or noise from other sources and less effected by attenuation. Consequently, fiber optic cable supports higher bandwidth over longer links than copper cable. Fiber optic cabling is divided into single mode (SMF) and multimode (MMF) types, and MMF is categorized by optical mode designations (OM1, OM2, OM3, and OM4).
Ethernet standards over fiber set out the use of different types of cable for 100 Mbps, 1 Gbps, 10 Gbps, and 40/100 Gbps operation. There are variants for long wavelength optics, required for long-distance transmission, and short wavelength optics. Some of the main standards for speeds up to 10 Gbps are listed in the table.
