What Is An Ethernet Extender?

What is an Ethernet extender?

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On this page you will find definitions for common terms for Ethernet extenders and other networking equipment and the media they utilize. 

Networking Devices

Ethernet Extender

An Ethernet extender (also network extender or LAN extender) is any device used to extend an Ethernet or network segment beyond its inherent distance limitation which is approximately 100 metres (328 ft) for most common forms of twisted pair Ethernet. These devices employ a variety of transmission technologies and physical media (wireless, copper wire, fiber-optic cable, coaxial cable).

Ethernet extenders forward traffic between LANs transparent to higher network-layer protocols over distances that far exceed the limitations of standard Ethernet.

Ethernet extenders that use copper wire include 2-, 4-, and 8-wire variants using unconditioned copper wiring to extend a LAN. Network extenders use various methods (line encodings), such as TC-PAM, 2B1Q or DMT, to transmit information. While transmitting over copper wire does not allow for the speeds that fiber-optic transmission does, it allows the use of existing network-grade copper or CCTV coaxial cable wiring. Copper-based Ethernet extenders must be used on unconditioned wire (without load coils), such as unused twisted pairs and alarm circuits.

Connecting a private LAN between buildings or more distant locations is a challenge. Wi-Fi requires a clear line-of-sight, special antennas, and is subject to weather. If the buildings are within 328’ (100m), a normal Ethernet cable segment can be used, with due consideration of potential grounding problems between the locations. Up to 656’ (200m), it may be possible to set up an ordinary Ethernet bridge or router in the middle, if power and weather protection can be arranged.

Specialized equipment can inter-connect two LANs over a single twisted pair of wires using VDSL technology. Distances of 1,000’ (300m) at 100Mbps symmetrical or up to 5 miles or more at 128 kbps is possible. The equipment is mostly simple to operate, and the connection wire is common, cheap and maintainable, as opposed to fiber optic cable.

Ordinary ADSL modems cannot be connected back-to-back, because the ATU-R (ADSL Termination Unit - Remote) units that are used by customers require specialized ATU-C (Central Office) support provided by phone company equipment, usually by a complex and expensive DSLAM (DSL access multiplexer). However some symmetric digital subscriber line (SDSL) modems can be connected back-to-back, allowing upload and download speeds of about 2Mbps over substantial distances, using a simple twisted pair of wires. Back-to-back operation may also be possible with single-pair high-speed digital subscriber line (G.SHDSL) modems.

Ethernet extenders can be based on a wide variety of technologies and utilize various types of cabling to provide broadband network speeds over distances that exceed the range of standard network cable.  The low cost and low maintenance requirements make Ethernet extenders a favorable alternative to fiber optic cable.

Modem

A modem (modulator-demodulator) is a network hardware device that modulates one or more carrier wave signals to encode digital information for transmission and demodulates signals to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modems can be used with any means of transmitting analog signals, from light emitting diodes to radio. A common type of modem is one that turns the digital data of a computer into modulated electrical signal for transmission over telephone lines and demodulated by another modem at the receiver side to recover the digital data.

Modems are generally classified by the amount of data they can send in a given unit of time, usually expressed in bits per second (sometimes abbreviated "bps"). Modems can also be classified by their symbol rate, measured in baud. The baud unit denotes symbols per second, or the number of times per second the modem sends a new signal. For example, the ITU V.21 standard used audio frequency shift keying with two possible frequencies, corresponding to two distinct symbols (or one bit per symbol), to carry 300 bits per second using 300 baud. By contrast, the original ITU V.22 standard, which could transmit and receive four distinct symbols (two bits per symbol), transmitted 1,200 bits by sending 600 symbols per second (600 baud) using phase shift keying.

Router

A router is a networking device that forwards data packets between computer networks. Routers perform the traffic directing functions on the Internet. A data packet is typically forwarded from one router to another through the networks that constitute the internetwork until it reaches its destination node.

A router is connected to two or more data lines from different networks (as opposed to a network switch, which connects data lines from one single network). When a data packet comes in on one of the lines, the router reads the address information in the packet to determine its ultimate destination. Then, using information in its routing table or routing policy, it directs the packet to the next network on its journey.

CPE Modem

Customer-premises equipment or customer-provided equipment (CPE) is any terminal and associated equipment located at a subscriber's premises and connected with a carrier's telecommunication channel at the demarcation point ("demarc"). The demarc is a point established in a building or complex to separate customer equipment from the equipment located in either the distribution infrastructure or central office of the communications service provider.

CPE generally refers to devices such as telephones, routers, switches, residential gateways (RG), set-top boxes, fixed mobile convergence products, home networking adapters and Internet access gateways that enable consumers to access communications service providers' services and distribute them around their house via a local area network (LAN).

A CPE can be an active piece of equipment, as the ones mentioned above or a passive equipment such as analogue-telephone-adapters or xDSL-splitters.

DSLAM (Concentrator)

A digital subscriber line access multiplexer (DSLAM, often pronounced dee-slam) is a network device, often located in telephone exchanges, that connect multiple customer digital subscriber line (DSL) interfaces to a high-speed digital communications channel using multiplexing techniques.

The DSLAM equipment collects the data from its many modem ports and aggregates their voice and data traffic into one complex composite "signal" via multiplexing. Depending on its device architecture and setup, a DSLAM aggregates the DSL lines over its Asynchronous Transfer Mode (ATM), frame relay, and/or Internet Protocol network (i.e., an IP-DSLAM using PTM-TC [Packet Transfer Mode - Transmission Convergence]) protocol(s) stack.

The aggregated traffic is then directed to a telco's backbone switch, via an access network (AN), also called a Network Service Provider (NSP), at up to 10 Gbit/s data rates.

The DSLAM acts like a network switch since its functionality is at Layer 2 of the OSI model. Therefore, it cannot re-route traffic between multiple IP networks, only between ISP devices and end-user connection points. The DSLAM traffic is switched to a Broadband Remote Access Server where the end-user traffic is then routed across the ISP network to the Internet. Customer-premises equipment that interfaces well with the DSLAM to which it is connected may take advantage of enhanced telephone voice and data line signaling features and the bandwidth monitoring and compensation capabilities it supports.

A DSLAM may or may not be located in the telephone exchange, and may also serve multiple data and voice customers within a neighborhood serving area interface, sometimes in conjunction with a digital loop carrier. DSLAMs are also used by hotels, lodges, residential neighborhoods, and other businesses operating their own private telephone exchange.

In addition to being a data switch and multiplexer, a DSLAM is also a large collection of modems. Each modem on the aggregation card communicates with a single subscriber's DSL modem. This modem functionality is integrated into the DSLAM itself instead of being done via an external device like a 20th-century voiceband modem.

Like traditional voice-band modems, a DSLAM's integrated DSL modems are usually able to probe the line and to adjust themselves to electronically or digitally compensate for forward echoes and other bandwidth-limiting factors in order to move data at the maximum possible connection rate.

This compensation capability also takes advantage of the better performance of "balanced line" DSL connections, providing capabilities for LAN segments longer than physically similar unshielded twisted pair (UTP) Ethernet connections, since the balanced line type is generally required for its hardware to function correctly. This is due to the nominal line impedance (measured in Ohms but comprising both resistance and inductance) of balanced lines being somewhat lower than that of UTP, thus supporting 'weaker' signals (however the solid-state electronics required to construct such digital interfaces are more costly).

Cable Media

Twisted Pair Cable

Twisted pair cabling is a type of wiring in which two conductors of a single circuit are twisted together for the purposes of canceling out electromagnetic interference (EMI) from external sources; for instance, electromagnetic radiation from unshielded twisted pair (UTP) cables, and crosstalk between neighboring pairs.

In balanced pair operation, the two wires carry equal and opposite signals, and the destination detects the difference between the two. This is known as differential mode transmission. Noise sources introduce signals into the wires by coupling of electric or magnetic fields and tend to couple to both wires equally. The noise thus produces a common-mode signal which is canceled at the receiver when the difference signal is taken.

This method starts to fail when the noise source is close to the signal wires; the closer wire will couple with the noise more strongly and the common-mode rejection of the receiver will fail to eliminate it. This problem is especially apparent in telecommunication cables where pairs in the same cable lie next to each other for many miles. One pair can induce crosstalk in another and it is additive along the length of the cable. Twisting the pairs counters this effect as on each half twist the wire nearest to the noise-source is exchanged.

Providing the interfering source remains uniform, or nearly so, over the distance of a single twist, the induced noise will remain common-mode. Differential signaling also reduces electromagnetic radiation from the cable, along with the associated attenuation allowing for greater distance between exchanges.

The twist rate (also called pitch of the twist, usually defined in twists per meter) makes up part of the specification for a given type of cable. When nearby pairs have equal twist rates, the same conductors of the different pairs may repeatedly lie next to each other, partially undoing the benefits of differential mode. For this reason it is commonly specified that, at least for cables containing small numbers of pairs, the twist rates must differ.

In contrast to shielded or foiled twisted pair (typically F/UTP or S/FTP cable shielding), UTP (unshielded twisted pair) cable is not surrounded by any shielding. UTP is the primary wire type for telephone usage and is very common for computer networking, especially as patch cables or temporary network connections due to the high flexibility of the cables.

Name	Typical construction	Bandwidth	Applications	Notes
Cat 3	UTP	16 MHz	10BASE-T & 100BASE-T4Ethernet	Described in EIA/TIA-568. Unsuitable for speeds above 16Mbps. Now mainly for telephone cables
Cat 4	UTP	20 MHz	16Mbps Token Ring	Not commonly used
Cat 5	UTP	100 MHz	100BASE-TX & 1000BASE-TEthernet	Common for current LANs. Superseded by Cat5e, but most Cat5 cable meets Cat5e standards.
Cat 5e	UTP	100 MHz	100BASE-TX & 1000BASE-TEthernet	Enhanced Cat5. Common for current LANs. Same construction as Cat5, but with better testing standards.
Cat 6	UTP	250 MHz	10GBASE-T Ethernet	ISO/IEC 11801 2nd Ed. (2002), ANSI/TIA 568-B.2-1. Most commonly installed cable in Finland according to the 2002 standard EN 50173-1.
Cat 6A	U/FTP, F/UTP	500 MHz	10GBASE-T Ethernet	Adds cable shielding. ISO/IEC 11801 2nd Ed. Am. 2. (2008), ANSI/TIA-568-C.1 (2009)

 

Fiber Optic Cable

An optical fiber cable is a cable containing one or more optical fibers that are used to carry light. The optical fiber elements are typically individually coated with plastic layers and contained in a protective tube suitable for the environment where the cable will be deployed. Different types of cable are used for different applications, for example long distance telecommunication, or providing a high-speed data connection between different parts of a building.

Coaxial Cable

Coaxial cable, or coax , is a type of cable that has an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield. Many coaxial cables also have an insulating outer sheath or jacket. The term coaxial comes from the inner conductor and the outer shield sharing a geometric axis. Coaxial cable was invented by English engineer and mathematician Oliver Heaviside, who patented the design in 1880.  Coaxial cable differs from other shielded cable used for carrying lower-frequency signals, in that the dimensions of the cable are controlled to give a precise, constant conductor spacing, which is needed for it to function efficiently as a transmission line.

Coaxial cable conducts electrical signal using an inner conductor (usually a solid copper, stranded copper or copper plated steel wire) surrounded by an insulating layer and all enclosed by a shield, typically one to four layers of woven metallic braid and metallic tape. The cable is protected by an outer insulating jacket. Normally, the shield is kept at ground potential and a signal carrying voltage is applied to the center conductor. The advantage of coaxial design is that electric and magnetic fields are confined to the dielectric with little leakage outside the shield. Conversely, electric and magnetic fields outside the cable are largely kept from interfering with signals inside the cable. Larger diameter cables and cables with multiple shields have less leakage. This property makes coaxial cable a good choice for carrying weak signals that cannot tolerate interference from the environment or for stronger electrical signals that must not be allowed to radiate or couple into adjacent structures or circuits.

Common applications of coaxial cable include video and CATV distribution, RF and microwave transmission, and computer and instrumentation data connections.