World Library  
Flag as Inappropriate
Email this Article

Leased line

Article Id: WHEBN0000481814
Reproduction Date:

Title: Leased line  
Author: World Heritage Encyclopedia
Language: English
Subject: Tanzania Telecommunications Company Limited, Point-to-point (telecommunications), Frame Relay, Optus, Local area network
Collection: Communication Circuits, Local Loop
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Leased line

A leased line is a private bidirectional or symmetric telecommunications line between two or more locations provided in exchange for a monthly rent. Sometimes known as a private circuit or data line in the UK.

Unlike traditional PSTN lines it does not have a telephone number, each side of the line being permanently connected to the other. Leased lines can be used for telephone, data or Internet services. Some are ringdown services, and some connect to a Private branch exchange.

Typically, leased lines are used by businesses to connect geographically distant offices. Unlike dial-up connections, a leased line is always active. The fee for the connection is a fixed monthly rate. The primary factors affecting the monthly fee are distance between end points and the speed of the circuit. Because the connection does not carry anybody else's communications, the carrier can assure a given level of quality.

An Internet leased line is a premium internet connectivity product, delivered over fiber normally, which is dedicated and provides uncontended, symmetrical speeds, full-duplex. It is also known as an ethernet leased line, DIA line, data circuit or private circuit.

For example, a T-1 channel can be leased, and provides a maximum transmission speed of 1.544 Mbit/s. The user can divide the connection into different lines for multiplexing data and voice communication, or use the channel for one data circuit. Leased lines, as opposed to DSL, are being used by companies and individuals for Internet access because they afford faster data transfer rates and are cost-effective for heavy users of the Internet.

Contents

  • History 1
  • Applications 2
    • Site to site data connectivity 2.1
    • Site to site PBX connectivity 2.2
    • Site to network connectivity 2.3
    • International private leased circuit 2.4
  • Availability 3
    • In the United Kingdom 3.1
    • In the United States 3.2
    • In Hong Kong 3.3
    • In India 3.4
    • In Italy 3.5
  • Leased line alternatives 4
  • See also 5
  • References 6

History

Leased lines services (or private line services) became digital in the 1970s with the conversion of the Bell backbone network from analog to digital circuits. This allowed AT&T to offer Dataphone Digital Services (later re-branded digital data services) that started the deployment of ISDN and T1 lines to customer premises to connect.[1]

Leased lines were used to connect mainframe computers with terminals and remote sites, via IBM Systems Network Architecture (created in 1974) or DECnet (created in 1975).

With the extension of digital services in the 1980s leased lines were used to connect customer premises to Frame Relay or ATM networks. Access data rates increased from the original T1 option up to T3 circuits.

In the 1990s with the advances of the Internet, leased lines were also used to connect customer premises to ISP Point of Presence whilst the following decade saw a convergence of the aforementioned services (frame relay, ATM, Internet for businesses) with the MPLS integrated offerings.

Access data rates also evolved dramatically to speeds of up to 10Gbit/s in the early 21st century with the Internet boom and increased offering in long-haul optical networks or Metropolitan Area Networks.

Applications

Leased lines are used to build up private networks, private telephone networks (by interconnecting PBXs) or access the internet or a partner network (extranet).

Here is a review of the leased line applications in Network designs over time:

Site to site data connectivity

Terminating a leased line with two routers can extend network capabilities across sites. Leased lines were first used in the 1970s by enterprise with proprietary protocols such as IBM System Network Architecture and Digital Equipment DECnet, and with TCP/IP in University and Research networks before the Internet became widely available. Note that other Layer 3 protocols were used such as Novell IPX on enterprise networks until TCP/IP became ubiquitous in the 2000s. Today, point to point data circuits are typically provisioned as either TDM, Ethernet, or Layer 3 MPLS.

Site to site PBX connectivity

Terminating a leased line with two PBX allowed customers to by-pass PSTN for inter-site telephony. This allowed the customers to manage their own dial plan (and to use short extensions for internal telephone number) as well as to make significant savings if enough voice traffic was carried across the line (especially when the savings on the telephone bill exceeded the fixed cost of the leased line).

Site to network connectivity

As demand grew on data network telcos started to build more advanced networks using packet switching on top of their infrastructure. Thus, a number of telecommunication companies added ATM, Frame-relay or ISDN offerings to their services portfolio. Leased lines were used to connect the customer site to the telco network access point.

International private leased circuit

An international private leased circuit (IPLC) functions as a point-to-point private line. IPLCs are usually time-division multiplexing (TDM) circuits that utilize the same circuit amongst many customers. The nature of TDM requires the use of a CSU/DSU and a router. Usually the router will include the CSU/DSU.

Then came the Internet (in the mid-1990s) and since then the most common application for leased line is to connect a customer to its ISP point of presence. With the changes that the Internet brought in the networking world other technologies were developed to propose alternatives to frame-relay or ATM networks such as VPNs (hardware and software) and MPLS networks (that are in effect an upgrade to TCP/IP of existing ATM/frame-relay infrastructures).

Availability

In the United Kingdom

In the U.K., leased lines are available at speeds from 64 kbit/s increasing in 64 kbit/s increments to 2.048 Mbit/s over a channelised E1 tail circuit and at speeds between 2.048 Mbit/s to 34.368 Mbit/s via channelised E3 tail circuits. The NTE will terminate the circuit and provide the requested presentation most frequently X.21 however higher speed interfaces are available such as G.703 or 10baseT. Some ISPs however use the term more loosely, defining a leased line as “any dedicated bandwidth service delivered over a leased fibre connection".

In the United States

In the U.S., low-speed leased lines (56 kbit/s and below) are usually provided using analog modems. Higher-speed leased lines are usually presented using FT1 (Fractional T1): a T1 bearer circuit with 1 to 24, 56k or 64k timeslots. Customers must manage their own network termination equipment—Channel Service Unit and Data Service Unit (CSU/DSU).

In Hong Kong

In Hong Kong, leased lines are usually available at speeds of 64k, 128k, 256k, 512k, T1 (channelized or not) or E1 (less common). Whatever the speed, telcos usually provide the CSU/DSU and present to the customer on V.35 interface.

Fibre circuits are slowly replacing the traditional circuits and are available at nearly any bandwidth.

In India

In India, leased lines are available at speeds of 64 kbit/s, 128 kbit/s, 256 kbit/s, 512 kbit/s, 1 Mbit/s, 2 Mbit/s, 4 Mbit/s, 8 Mbit/s, 16 Mbit/s T1(1.544 Mbit/s) or E1(2.048 Mbit/s). Customers are connected either through OFC, telephone lines ADSL, or through Wifi. Customers would have to manage their own network termination equipment, namely the Channel service unit and Data service unit.

In Italy

In Italy, leased lines are available at speeds of 64 kbit/s (terminated by DCE2 or DCE2plus modem) or multiple of 64 kbit/s from 128 kbit/s up to framed or unframed E1 (DCE3 modem) in digital form (PDH service, known as CDN, Circuito Diretto Numerico). Local Telephone companies also may provide CDA (Circuito Diretto Analogico), that are plain copper dry pair between two buildings, without any line termination: in the past (pre-2002) a full analog base band was provided, giving an option to customer to deploy xDSL technology between sites: nowadays everything is limited at 4 kHz of bearer channel, so the service is just a POTS connection without any setup channel.

For many purposes, leased lines are gradually being replaced by DSL and metro Ethernet.

Leased line alternatives

Leased lines are more expensive than alternative connectivity services including (ADSL, SDSL, etc.) because they are reserved exclusively to the leaseholder. Some internet service providers have therefore developed alternative products that aim to deliver leased-line type services (Carrier Ethernet-based, zero contention, guaranteed availability), with more moderate bandwidth, over the standard UK national broadband network. While a leased line is full-duplex, most leased line alternatives provide only half-duplex or in many cases asymmetrical service.

See also

References

  1. ^ Microsoft Encyclopedia of Networking, Second Edition. Microsoft Press. © 2002.
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 



Copyright © World Library Foundation. All rights reserved. eBooks from World eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.