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I hear the terms leased line and dedicated line and want to know what the difference is. For example, is DSL considered a lease line? or is T1 considered a lease line?

I hear all these terms being thrown around and I'm not sure I understand what constitutes a leased line?

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  • leased line costs in the UK have come down so much that they are now available to a lot more businesses than before
    – Paul Botham
    Feb 28, 2017 at 14:00
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The terms do get thrown about quite a bit and the definition is a bit of a murky issue as they can be used in several ways.

I would say that generally a leased line is a line you are paying someone else for use. For instance, you can string your own copper and establish your own T1/T3 service between buildings. However, you could also pay someone to provide and maintain that line. Often leased lines have a SLA associated with them.

A dedicated line would be a line that is dedicated to you/your company. For instance, in an office building, you may not have a dedicated line. You may have a PRI that comes into the building and provides service to multiple organizations. Often this is cheaper because the telecommunications company doesn't need as many lines going into the building and has fewer to maintain.

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They are not in my view strict well defined terms.

Generally people mean T/E, SDH/SONET as leased line, but DSL not.

When customers in RFQ request leased line from us, I interpret it as they feel DSL quality is inferior to 'legacy' solutions, and specifically want us to avoid using it. While technically there is no difference in the physical copper we order from incumbent, in both cases it's copper between customer site and our pop, we lease from the incumbent, it is just connected to different active device in our network.

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    I could be wrong, but I believe DSL is generally not considered to be a leased line because it often is carried over another existing line (typically a voice line). It is rather considered a service delivered over an existing leased line.
    – YLearn
    May 25, 2013 at 20:37
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    You do have dedicated pair in both DSL and E1 solution. Technically speaking that copper between those would be leased from the incumbent. But I guess what you're saying is that DSL may ride over your existing PSTN or ISDN line providing both services in same copper, this is true, then the DSL will have filters blocking it using those frequency bands. But in any case, it would be prudent to avoid using the terms due to their non-specific meaning and just talk about the actual technology and desired implementation.
    – ytti
    May 25, 2013 at 20:44
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Dedicated means not a shared medium. Dedicated Line @ Wikipedia

Leased means just that... you're leasing the line which could be using a shared services such as a MPLS VPN (or Frame Relay in the old days). Leased Line @ Wikipedia

A serial line is a type of interface using running HDLC or PPP. I wouldn't put this in the same category as dedicated or leased lines.

Dedicated Internet Access (DIA) is a common term used by ISPs and can be provided over leased or serial lines. You can't really have dedicated without leasing (i.e., a contract), unless you own the cable plant, but you could use something other than serial like Ethernet.

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A leased line typically refers to a point-to-point style link. A T1 /can/ be a leased line but isn't always.

Dedicated lines are a bit harder because that could mean anything. A point-to-point can be dedicated...an Internet connection can be advertised as being dedicated, but that's kind of a farse.Typically a dedicated line just means less oversubscription than a shared or non-dedicated line. Something like 10 or 20 to 1 instead of 100 or 200 to 1.

In all honesty these terms do not have a "standard" meaning. So they can be used in a lot of different contexts.

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At least from the point of view of a telecommunications carrier, when we say "leased line", we mean a physical, point-to-point connection billed per air mile. If you order a leased line from San Francisco to New York, we will obtain a leased circuit from the local telco to a long-distance inter-exchange carrier, and then another local loop as we call it, from the IXC to the New York telco destination. You pay for all it, at so many dollars per airmile. Note that the line by not always be a wire -- we may transform your "circuit" into a digital link along the way.

Serial lines are lower-speed leased lines, typically less than the standard 1.544Mb/2Mb/s lines. We don't use those much any more as few people want 128Kb/sec circuits.

A dedicated line is a leased line where your "line" may be virtualized along the way. You have a dedicated virtual pipe at a given capacity. Typically, you'd buy for example, a dedicated 10Mb and we'd create a local link to you, perhaps metro ethernet, turn that ethernet into a long-haul shared ethernet circuit (2-10Gb), and then back into ethernet at your end.

It comes down to this:

  1. If you need low-speed connectivity point-to-point, that's a serial line, but I'd recommend going straight to T-1 dedicated.
  2. If you need higher-speed dedicated links without any possibility of sharing the pipe along the way (perhaps for compliance reasons), that's a leased circuit.
  3. If you need high-bandwidth point-to-point, but you can tolerate "commingling the pipe", that's a dedicated connection.
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