A leased line is defined as a dedicated high-performance circuit leased by a common carrier between a customer and a service provider’s network. It is rented on an annual basis and usually carries voice and data or both. It can be used for internet access or for a private connection between two customer sites. Compared to other internet connectivity options such as DSL products, leased lines are relatively expensive but are supported by a comprehensive Service-Level Agreement (SLA) with a guaranteed fix time and a compensation clause.
Large companies generally use leased lines to connect several geographically different networks within their organisation. Services available are available to them in 10MB, 100MB and 1000MB speeds with Ethernet presentation ideal for offices within a short distance of each other. In the UK, Internet leased lines
are available at speeds from 64Kb/s increasing in 64Kb/s increments to 2.048Mb/s over a channelised E1 tail circuit and at speeds between 2.048Mb/s to 34.368Mb/s via channelised E3 tail circuits.
One disadvantage of a leased line is its inflexibility. Though it offers an ‘always on’ connection to the user, it has a flat-rate charge which means users have to pay a fixed price irrespective of the rate at which they use their connections. Also leased lines are very expensive when compared to the alternative solutions available. The ‘always on’ connectivity does expose an organisation’s network to a variety of threats such as hacking and malicious software present in the Web and users are responsible for the security and maintenance of network elements.
In the UK, telecom provider BT offers wholesale leased line products and other operators buy wholesale leased lines from BT and use them to provide a wide range of dedicated telecoms services to their customers.
Nowadays leased lines are slowly being replaced by services such as DSL, metro Ethernet, EFM and SDSL.
There are plenty of competitors to BT’s leased lines, namely UK service providers of business networking solutions which include leased lines, bonded ADSL, SDSL and managed VPN connections. Some of these companies have stated their technology architecture has made the fully meshed high bandwidth network a reality. Users need not depend any more on BT leased lines to run latency dependant applications such as Voice over IP (VoIP) or Citrix. These service providers can often enable businesses to run data networks with high levels of reliability and control at prices more affordable than a BT leased line by bringing together MPLS core and advanced high performance networking.
The ‘National Ethernet’ solution has the ability to enable all of an organisation’s LANs to operate as a single Ethernet domain without any complex routing protocols or routing equipment. These Ethernet solutions are claimed to be a flexible and totally secure low cost high bandwidth alternative to leased lines and ATM & Frame Relay services: offering unbeatable Class of Service (CoS) and reporting options with flexible bandwidth increments.
Another notable alternative to leased line connection is Digital Subscriber Line (DSL), a family of technologies that provides digital data transmission over the wires of a local telephone network. In telecommunications marketing, the term Digital Subscriber Line is widely understood to mean Asymmetric Digital Subscriber Line (ADSL), the most commonly installed technical varieties of DSL. In ADSL the speed of data that is being downloaded is faster than the speed of data that is being uploaded so it is more suited for users who browse the internet frequently and use the upload feature minimally. It is unsuitable for companies that specialise in streaming data.
In the UK, providers offer ADSL broadband services at speeds of up to 8 Mbps and faster upstream speeds and real-time email retrieval which can help users increase productivity and efficiency.
Symmetric digital subscriber line or SDSL provides performance that compares with leased lines connectivity but at a lower cost. Unlike ADSL which has lower upstream speeds SDSL is a symmetric connection that offers the same upload and download speeds. It provides a reliable and advanced service, as connection to the internet is delivered though a dedicated copper pair into the office. UK based SDSL providers have claimed to offer cheap single SDSL connections up to 2Mbps and bonded SDSL solutions utilising up to 8 x 2Mbps connections delivering a blistering 16Mbps synchronous bandwidth. There are also other providers who offer a 2 Mb/s SDSL service that has eight times more upload bandwidth than traditional ADSL.
Though SDSL connections are more expensive than ADSL they are cheaper when compared to leased lines and are more suitable for small to medium-sized businesses.
On the other hand leased lines are now rigorously advertised as high quality and reliable internet connectivity options and are backed by a 100% service availability target at all times and money back SLA available for failing to hit this target. Since leased lines are more prone to security attack, prominent leased line providers have claimed that their leased line networks are under constant review to take into account new threats and vulnerabilities.