10BASE5, 10BASE2, and 10BASE-T Ethernet are considered Legacy Ethernet. The four common features of Legacy Ethernet are timing parameters, the frame format, transmission processes, and a basic design rule.

10-Mbps Ethernet and slower versions are asynchronous. Each receiving station uses eight octets of timing information to synchronize its receive circuit to the incoming data. 10BASE5, 10BASE2, and 10BASE-T all share the same timing parameters.

For example, 1 bit time at 10 Mbps = 100 nanoseconds (ns) = 0.1 microseconds = 1 10-millionth of a second. This means that on a 10-Mbps Ethernet network, 1 bit at the MAC sublayer requires 100 ns to transmit.

For all speeds of Ethernet transmission 1000 Mbps or slower, transmission can be no slower than the slot time.

10BASE5, 10BASE2, and 10BASE-T also have a common frame format.

The Legacy Ethernet transmission process is identical until the lower part of the OSI physical layer.

This form of encoding used in 10-Mbps systems is called Manchester encoding.

10-Mbps Ethernet operates within the timing limits for a series of up to five segments separated by up to four repeaters. This is known as the 5-4-3 rule. No more than four repeaters can be used in series between any two stations. There can also be no more than three populated segments between any two stations.

10BASE5 is important because it was the first medium used for Ethernet.

10BASE5 was part of the original 802.3 standard.

The primary benefit of 10BASE5 was length.

10BASE5 may be found in legacy installations. It is not recommended for new installations.

10BASE5 systems are inexpensive and require no configuration.

Two disadvantages are that basic components like NICs are very difficult to find and it is sensitive to signal reflections on the cable. 10BASE5 systems also represent a single point of failure.

10BASE5 uses Manchester encoding.

It has a solid central conductor. Each segment of thick coax may be up to 500 m (1640.4 ft) in length. The cable is large, heavy, and difficult to install.

When the medium is a single coaxial cable, only one station can transmit at a time or a collision will occur. Therefore, 10BASE5 only runs in half-duplex with a maximum transmission rate of 10 Mbps.

Remember that only three segments can have stations connected to them. The other two repeated segments are used to extend the network.

Installation was easier because of its smaller size, lighter weight, and greater flexibility.

10BASE2 still exists in legacy networks. Like 10BASE5, it is no longer recommended for network installations. It has a low cost and does not require hubs.

10BASE2 also uses Manchester encoding.

Computers on a 10BASE2 LAN are linked together by an unbroken series of coaxial cable lengths. These lengths are attached to a T-shaped connector on the NIC with BNC connectors.

10BASE2 has a stranded central conductor. Each of the maximum five segments of thin coaxial cable may be up to 185 m (607 ft) long and each station is connected directly to the BNC T-shaped connector on the coaxial cable.

Only one station can transmit at a time or a collision will occur. 10BASE2 also uses half-duplex.

The maximum transmission rate of 10BASE2 is 10 Mbps.

There may be up to 30 stations on a 10BASE2 segment. Only three out of five consecutive segments between any two stations can be populated.

10BASE-T used cheaper and easier to install Category 3 UTP copper cable instead of coax cable.

The cable plugged into a central connection device that contained the shared bus. This device was a hub. This is referred to as a star topology.

As additional stars were added and the cable distances grew, this formed an extended star topology.

Originally 10BASE-T was a half-duplex protocol, but full-duplex features were added later.

10BASE-T also uses Manchester encoding.

A 10BASE-T UTP cable has a solid conductor for each wire.

UTP cable uses eight-pin RJ-45 connectors.

Though Category 3 cable is adequate for 10BASE-T networks, new cable installations should be made with Category 5e or better.

Half duplex or full duplex is a configuration choice.

10BASE-T carries 10 Mbps of traffic in half-duplex mode and 20 Mbps in full-duplex mode.

Although hubs may be linked, it is best to avoid this arrangement. Multiple hubs should be arranged in hierarchical order like a tree structure. Performance is better if fewer repeaters are used between stations.

The most important aspect to consider is how to keep the delay between distant stations to a minimum. A shorter maximum delay will provide better overall performance.

10BASE-T links can have unrepeated distances of up to 100 m (328 ft).

This page will discuss 100-Mbps Ethernet, which is also known as Fast Ethernet.

The two technologies that have become important are 100BASE-TX, which is a copper UTP medium and 100BASE-FX, which is a multimode optical fiber medium.

Three characteristics common to 100BASE-TX and 100BASE-FX are the timing parameters, the frame format, and parts of the transmission process.

Note that one bit time at 100-Mbps = 10 ns = .01 microseconds = 1 100-millionth of a second.

The 100-Mbps frame format is the same as the 10-Mbps frame.

Fast Ethernet is ten times faster than 10BASE-T. 

These higher frequency signals are more susceptible to noise. In response to these issues, two separate encoding steps are used by 100-Mbps Ethernet. The first part of the encoding uses a technique called 4B/5B, the second part of the encoding is the actual line encoding specific to copper or fiber.

In 1995, 100BASE-TX was the standard, using Category 5 UTP cable, which became commercially successful.

 In 1997, Ethernet was expanded to include a full-duplex capability that allowed more than one PC on a network to transmit at the same time.

Switches replaced hubs in many networks. These switches had full-duplex capabilities and could handle Ethernet frames quickly.

100BASE-TX uses 4B/5B encoding, which is then scrambled and converted to Multi-Level Transmit (MLT-3) encoding. 

Figure shows the pinout for a 100BASE-TX connection. This is identical to the 10BASE-T configuration.

100BASE-TX carries 100 Mbps of traffic in half-duplex mode. In full-duplex mode, 100BASE-TX can exchange 200 Mbps of traffic.

A fiber version could be used for backbone applications, connections between floors, buildings where copper is less desirable, and also in high-noise environments. 100BASE-FX was introduced to satisfy this desire.

100BASE-FX was never adopted successfully. This was due to the introduction of Gigabit Ethernet copper and fiber standards.

Gigabit Ethernet standards are now the dominant technology for backbone installations, high-speed cross-connects, and general infrastructure needs.

Figure summarizes a 100BASE-FX link and pinouts. A fiber pair with either ST or SC connectors is most commonly used.

The separate Transmit (Tx) and Receive (Rx) paths in 100BASE-FX optical fiber allow for 200-Mbps transmission.

Fast Ethernet links generally consist of a connection between a station and a hub or switch.

These are subject to the 100-m (328 ft) UTP media distance limitation.

A Class I repeater may introduce up to 140 bit-times latency. Any repeater that changes between one Ethernet implementation and another is a Class I repeater.

A Class II repeater is restricted to smaller timing delays, 92 bit times, because it immediately repeats the incoming signal to all other ports without a translation process.

Modification of the architecture rules is strongly discouraged for 100BASE-TX.

100BASE-TX cable between Class II repeaters may not exceed 5 m (16 ft).

Links that operate in half duplex are not uncommon in Fast Ethernet. However, half duplex is undesirable because the signaling scheme is inherently full duplex.

100BASE-TX links can have unrepeated distances up to 100 m. Switches have made this distance limitation less important.

These 1000-Mbps Ethernet or Gigabit Ethernet standards specify both fiber and copper media for data transmissions.

The 1000BASE-T standard, IEEE 802.3ab, uses Category 5, or higher, balanced copper cabling.

The 1000BASE-X standard, IEEE 802.3z, specifies 1 Gbps full duplex over optical fiber.

1000BASE-TX, 1000BASE-SX, and 1000BASE-LX use the same timing parameters, as shown in Figure. They use a 1 ns, 0.000000001 of a second, or 1 billionth of a second bit time.

The Gigabit Ethernet frame has the same format as is used for 10 and 100-Mbps Ethernet.

The differences between standard Ethernet, Fast Ethernet and Gigabit Ethernet occur at the physical layer.

This high-speed transmission requires higher frequencies. This causes the bits to be more susceptible to noise on copper media.

These issues require Gigabit Ethernet to use two separate encoding steps. Data transmission is more efficient when codes are used to represent the binary bit stream.

At the physical layer, the bit patterns from the MAC layer are converted into symbols.

Fiber-based Gigabit Ethernet, or 1000BASE-X, uses 8B/10B encoding, which is similar to the 4B/5B concept.

The 1000BASE-T standard, which is IEEE 802.3ab, was developed to provide additional bandwidth.

It is important for the 1000BASE-T standard to be interoperable with 10BASE-T and 100BASE-TX.

The first step to accomplish 1000BASE-T is to use all four pairs of wires instead of the traditional two pairs of wires used by 10BASE-T and 100BASE-TX.

This provides 250 Mbps per pair. With all four-wire pairs, this provides the desired 1000 Mbps.

Since the information travels simultaneously across the four paths, the circuitry has to divide frames at the transmitter and reassemble them at the receiver.

The 1000BASE-T encoding with 4D-PAM5 line encoding is used on Category 5e, or better, UTP. That means the transmission and reception of data happens in both directions on the same wire at the same time.

With this large number of states and the effects of noise, the signal on the wire looks more analog than digital. Like analog, the system is more susceptible to noise due to cable and termination problems.

The data from the sending station is carefully divided into four parallel streams, encoded, transmitted and detected in parallel, and then reassembled into one received bit stream.

1000BASE-T supports both half-duplex as well as full-duplex operation. The use of full-duplex 1000BASE-T is widespread.

The IEEE 802.3 standard recommends that Gigabit Ethernet over fiber be the preferred backbone technology.

The timing, frame format, and transmission are common to all versions of 1000 Mbps.

Two signal-encoding schemes are defined at the physical layer. The 8B/10B scheme is used for optical fiber and shielded copper media.

1000BASE-X uses 8B/10B encoding converted to non-return to zero (NRZ) line encoding.

The NRZ signals are then pulsed into the fiber using either short-wavelength or long-wavelength light sources.

The short-wavelength uses an 850 nm laser or LED source in multimode optical fiber (1000BASE-SX). It is the lower-cost of the options but has shorter distances.

The long-wavelength 1310 nm laser source uses either single-mode or multimode optical fiber (1000BASE-LX).

Laser sources used with single-mode fiber can achieve distances of up to 5000 meters.

Because of the length of time to completely turn the LED or laser on and off each time, the light is pulsed using low and high power. A logic zero is represented by low power, and a logic one by high power.

The Media Access Control method treats the link as point-to-point. Since separate fibers are used for transmitting (Tx) and receiving (Rx) the connection is inherently full duplex.

Gigabit Ethernet permits only a single repeater between two stations.

Since most Gigabit Ethernet is switched, the values in Figures are the practical limits between devices. Star and extended star topologies are all allowed.

A 1000BASE-T UTP cable is the same as 10BASE-T and 100BASE-TX cable, except that link performance must meet the higher quality Category 5e or ISO Class D (2000) requirements.

At 100 meters, 1000BASE-T is operating close to the edge of the ability of the hardware to recover the transmitted signal.

It is recommended that all links between a station and a switch be configured for Auto-Negotiation to permit the highest common performance. This will avoid accidental misconfiguration of the other required parameters for proper Gigabit Ethernet operation.

IEEE 802.3ae was adapted to include 10 Gbps full-duplex transmission over fiber optic cable.

This 10-Gigabit Ethernet (10GbE) is evolving for not only LANs, but also MANs, and WANs.

10GbE can provide increased bandwidth needs that are interoperable with existing network infrastructure.

10GbE physical layer standards allow both an extension in distance to 40 km over single-mode fiber.

Operation at 40 km distance makes 10GbE a viable MAN technology.

Compatibility with SONET/SDH networks operating up to OC-192 speeds (9.584640 Gbps) make 10GbE a viable WAN technology.

To summarize, how does 10GbE compare to other varieties of Ethernet?

• Frame format is the same, allowing interoperability between all varieties of legacy, fast, gigabit, and 10 gigabit, with no reframing or protocol conversions.
• Bit time is now 0.1 nanoseconds. All other time variables scale accordingly.
• Since only full-duplex fiber connections are used, CSMA/CD is not necessary.
• The IEEE 802.3 sublayers within OSI Layers 1 and 2 are mostly preserved, with a few additions to accommodate 40 km fiber links and interoperability with SONET/SDH technologies.
• Flexible, efficient, reliable, relatively low cost end-to-end Ethernet networks become possible.
• TCP/IP can run over LANs, MANs, and WANs with one Layer 2 transport method.

The basic standard governing CSMA/CD is IEEE 802.3. An IEEE 802.3 supplement, entitled 802.3ae, governs the 10GbE family. As is typical for new technologies, a variety of implementations are being considered, including:

• 10GBASE-SR – Intended for short distances over already-installed multimode fiber, supports a range between 26 m to 82 m
• 10GBASE-LX4 – Uses wavelength division multiplexing (WDM), supports 240 m to 300 m over already-installed multimode fiber and 10 km over single-mode fiber
• 10GBASE-LR and 10GBASE-ER – Support 10 km and 40 km over single-mode fiber
• 10GBASE-SW, 10GBASE-LW, and 10GBASE-EW – Known collectively as 10GBASE-W, intended to work with OC-192 synchronous transport module SONET/SDH WAN equipment

10-Gbps Ethernet (IEEE 802.3ae) was standardized in June 2002.

It is a full-duplex protocol that uses only optic fiber as a transmission medium.

The maximum transmission distances depend on the type of fiber being used.

When using single-mode fiber as the transmission medium, the maximum transmission distance is 40 kilometers (25 miles).

Some discussions between IEEE members have begun that suggest the possibility of standards for 40, 80, and even 100-Gbps Ethernet.

For 10 GbE transmissions, each data bit duration is 0.1 nanosecond.

Because of the short duration of the 10 GbE data bit, it is often difficult to separate a data bit from noise. 10 GbE data transmissions rely on exact bit timing to separate the data from the effects of noise on the physical layer. This is the purpose of synchronization.

In response to these issues of synchronization, bandwidth, and Signal-to-Noise Ratio, 10-Gigabit Ethernet uses two separate encoding steps. By using codes to represent the user data, transmission is made more efficient. The encoded data provides synchronization, efficient usage of bandwidth, and improved Signal-to-Noise Ratio characteristics. 

Currently, most 10GbE products are in the form of modules, or line cards, for addition to high-end switches and routers.

All 10GbE varieties use optical fiber media. Fiber types include 10µ single-mode Fiber, and 50µ and 62.5µ multimode fibers.

A range of fiber attenuation and dispersion characteristics is supported, but they limit operating distances.

No repeater is defined for 10-Gigabit Ethernet since half duplex is explicitly not supported.

Ethernet has gone through an evolution from Legacy —> Fast —> Gigabit —> MultiGigabit technologies.

While other LAN technologies are still in place (legacy installations), Ethernet dominates new LAN installations. So much so that some have referred to Ethernet as the LAN “dial tone”.

Ethernet is now the standard for horizontal, vertical, and inter-building connections. Recently developing versions of Ethernet are blurring the distinction between LANs, MANs, and WANs.

The IEEE and the 10-Gigabit Ethernet Alliance are working on 40, 100, or even 160 Gbps standards.

The future of networking media is three-fold:

1. Copper (up to 1000 Mbps, perhaps more)
2. Wireless (approaching 100 Mbps, perhaps more)
3. Optical fiber (currently at 10,000 Mbps and soon to be more)

Copper and wireless media have certain physical and practical limitations on the highest frequency signals that can be transmitted.

This is not a limiting factor for optical fiber in the foreseeable future. The bandwidth limitations on optical fiber are extremely large. In fiber systems, it is the electronics technology (such as emitters發射器 and detectors偵測器) and fiber manufacturing processes that most limit the speed.

Upcoming developments in Ethernet are likely to be heavily weighted towards Laser light sources and single-mode optical fiber.

When Ethernet was slower, half-duplex, subject to collisions, it was not considered to have the Quality of Service (QoS) capabilities required to handle certain types of traffic.

The full-duplex high-speed Ethernet technologies that now dominate the market are proving to be sufficient at supporting even QoS-intensive applications. This makes the potential applications of Ethernet even wider.