Remote concentrator
Encyclopedia
In modern telephony
Telephony
In telecommunications, telephony encompasses the general use of equipment to provide communication over distances, specifically by connecting telephones to each other....

 a remote concentrator, Remote Concentrator Unit (RCU), or Remote Line Concentrator (RLC) is the lowest level in the telephone switch hierarchy.

Subscribers' analogue telephone/PSTN
Public switched telephone network
The public switched telephone network is the network of the world's public circuit-switched telephone networks. It consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all inter-connected by...

 lines are terminated on concentrators. They have three main functions, namely:
  • Digitize, that is, turn voice, and sometimes data, from analogue into a digital form.
  • Connect off-hook lines through to the local exchange — the concentration function.
  • Multiplex, interleaving many calls together on a single wire or optical fiber.


Only a few hundred telephone lines attach to each remote concentrator. In North America, concentrators are located in an SAI
Serving area interface
The serving area interface or service area interface often called B-box, cross-connect box, cross box, ped , or access point is an outdoor telecommunications cabinet usually mounted on the ground on cable right-of-ways, but sometimes also on telephone poles...

 or other enclosure
Enclosure (electrical)
An electrical enclosure is a cabinet for electrical or electronic equipment to mount switches, knobs and displays and to prevent electrical shock to equipment users and protect the contents from the environment...

 in each neighborhood. In Europe, the buildings that once contained local Strowger switch
Strowger switch
The Strowger switch, also known as Step-by-Step or SXS, is an early electromechanical telephone switching system invented by Almon Brown Strowger...

 telephone exchanges are now usually empty except for a remote concentrator.
Only call packets from or destined to a phone serviced by the concentrator actually are processed by the concentrator — nonlocal phones' time slots just pass through the concentrator unchanged. If the concentrator malfunctions, a fail-safe relay connects the "in" wires to the "out" wires, and nonlocal phones detect no difference. The central switch periodically counts concentrators, and schedules maintenance, probably before users notice the failure. Concentrators for several hundred customers can be threaded on this loop like pearls.

The interface between remote concentrators and their parent telephone switches has been standardised by ETSI as the V5
V5 interface
V5 is a family of telephone network protocols defined by ETSI which allow communications between the telephone exchange, also known in the specifications as the local exchange , and the local loop...

 protocol.

When a user picks up the phone, the concentrator produces the dial tone
Dial tone
A dial tone is a telephony signal used to indicate that the telephone exchange is working, has recognized an off-hook, and is ready to accept a call. The tone stops when the first numeral is dialed...

. When the user dials, it reads the tones. Once the user has completed dialing, the concentrator's microcomputer sends the dialing data to the central switch, which allocates a time slot for the dialing phone on the wire pairs that pass through the concentrator and through the switch.

After the central switch tells the concentrator which time slot to use, the concentrator "opens" a time-slot on the loop to a local phone. The allocated time slot on the wiring into the concentrator is used to send data from the remote telephone's microphone to the local telephone's speaker. The allocated time slot on the wiring out of the concentrator (with the same time slot number) carries data from the local microphone to the remote speaker.

To arrange a connection, the switch just completes the circle between the user's phone and the remote phone. It interchanges the data from one to the other. In this limited sense, telephone "exchange" is exactly correct terminology.

Technology implications

Having a concentrator near a subscriber's telephone results in very low signal degradation before the analog signal is digitized. This provides reliably good voice quality.

Concentrators are often colocated with a Digital Subscriber Line Access Multiplexer
Digital subscriber line access multiplexer
A digital subscriber line access multiplexer is a network device, located in the telephone exchanges of the telecommunications operators. It connects multiple customer digital subscriber line interfaces to a high-speed digital communications channel using multiplexing techniques...

 (DSLAM). This can provide access to Asymmetric Digital Subscriber Line
Asymmetric Digital Subscriber Line
Asymmetric digital subscriber line is a type of digital subscriber line technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. It does this by utilizing frequencies that are not used by a voice...

 (ADSL) Internet service for subscribers who are beyond the normal 4 kilometre signaling limit on a copper wire loop. For example, a fiber optic cable might run up to 30 kilometres without a repeater from the telephone exchange to a concentrator site, and local subscriber wire local loop
Local loop
In telephony, the local loop is the physical link or circuit that connects from the demarcation point of the customer premises to the edge of the carrier or telecommunications service provider's network...

s can extend an additional 4 kilometres beyond the concentrator and its DSLAM. With repeaters in the fiber optic cable the distance from the telephone exchange can be extended much farther.

See also

  • Remote digital terminal
    Remote digital terminal
    In telecommunications, a Remote Digital Terminal typically accepts E1, T1 or OC-3 digital lines to communicate with a telephone Access network or telephone exchange on one side, and forms a Local Exchange on the other, which is connected to Plain Old Telephone Service lines....

  • Distributed switching
    Distributed switching
    Distributed switching is an architecture in which multiple processor-controlled switching units are distributed. There is often a hierarchy of switching elements, with a centralized host switch and with remote switches located close to concentrations of users....

  • Pair gain
    Pair gain
    In telephony, pair gain is a method of transmitting multiple POTS signals over the twisted pairs traditionally used for a single traditional subscriber line in telephone systems. Pair gain has the effect of creating additional subscriber lines...

  • Access network
    Access network
    An access network is that part of a telecommunications network which connects subscribers to their immediate service provider. It is contrasted with the core network, which connects local providers to each other...

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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