first of all this is my first post on this forum however I got quite a lot of very helpful information from here in the past.

My company is operating in travel business and the at the moment we really struggle to meet our guests internet demands. We upgraded our connections to bonded DSL to gain more bandwidth however it is still not enough.

As fibre is not available in the areas of our estate at the moment, we are looking into installing Leased Lines.

Our current supplier was unable to provide us with impartial info if it is going to take major improvement on the speed( they just want to sale more...). Since there is a massive hike in pricing costs I need to understand if it is going to improve speed of connection. Selling points like SLA are great but in the past we did not have downtime issues so it is hard to justify the costs.

Any input or experience in difference of speed between bonded DSL and Leased Lines greatly appreciated.

  • Can you provide more details on what they are offering (speed, etc) vs. your DSL lines?
    – Ron Trunk
    Sep 5, 2014 at 12:03
  • We have 2 bonded DSL, each 3 lines around 8 Mbits per line. So around ca.40 Mbits. Leased lines offers we considering are 40 or 50 Mbits over 100 bearer. Additionally Sep 5, 2014 at 12:31
  • 2
    You really need to add more detail. To start with, how many guests? What needs are you trying to meet? How do you expect those needs to change over the next [insert length of contract]? Balancing across multiple internet connections can be more complex and often one link becomes much more congested than the other; would a single leased line simplify and improve this? Are you using any sort of traffic shaping device (whether this is built into your router/firewall or a separate device)?
    – YLearn
    Sep 5, 2014 at 14:56

6 Answers 6


You need to check a few things;

  1. DSL is an aggregation technology which is normally on 'shared' media (you will be sharing with other, both the media to the point of presence and aggregation devices such as DSLAM, LNS so there is always potential for oversubscription.

  2. It will also depend on latency, you need to ask the carrier for latency numbers for the leased line and test this against your DSL links. (Leased line should be better) however remember if latency is high no matter how much Mb (bandwidth) you purchase your download speeds will be limited;

    Bandwidth-in-bits-per-second * Round-trip-latency-in-seconds = TCP window size in bits / 8 = TCP window size in bytes example below;

    RTT is 20 ms, and connection speed is 10Mbps.

    2 x (10Mbps/8 * .020s) = 50Kbytes (using standard window size of 64K)

  3. Maybe you should look at using QoS effectively to limit wasting bandwidth


I don't know where you are based, but I'm in the UK. Here ADSL is "contended" in other words you are potentially sharing your connection with a number of other users this can hammer performance at peak times http://en.wikipedia.org/wiki/Contention_ratio

A leased line isn't shared (1:1 contention ratio) so you get all the bandwidth all the time so can be quite a bit quicker than the numbers would suggest.

I've also found that the leased line we have is far more reliable than any ADSL connection we have.


"With the advent of ADSL2+ ("up to" 20Mbit/s service), FTTC (Fibre to the Cabinet) offering 40Mbit/s services and even FTTP (Fibre to the Premises) offering 100Mbit/s, BT no longer work on "contention ratio" as a planning rule."

So your milage may vary depending on what you've got.


Do you have any visibility into what is using the majority of your bandwidth? It is possible that you have a few of your users hogging all of the bandwidth.

In this case you would need to start limiting the amount of bandwidth a single user can use. This approach might be more cost effective than adding more bandwidth.

Some potential solutions to accomplish that are from Sonicwall, Ubiquiti, or even using iptables. Here are some ideas from a different question about this. Very high latency for HTTPS websites (except Google and some others), good latency for the HTTP


If the bandwidth is greater, then it is going to improve the speed of the connection... however, that's not your real question, is it? It seems you really want to know if it will improve the perceived speed for your clients.

To answer this, review all the other answers. Also check if you're utilizing your upstream bandwidth or not. You say you have 3 DSL lines at 8 Mbits each... OK, that's nice, but what's the upload rate on those? If you're running 8Mb down but only 384kb up, that's 24 Mb downstream but barely over 1Mb upstream. While most users download more than they upload, every TCP connection sends SOMEthing upstream... and some, eg Skype calls, VOIP, BitTorrent, etc, send a HECK of a lot upstream! If you're utilizing all your upstream bandwidth, then even if you have plenty of downstream to spare your users aren't going to be able to use it til they can send their ACK packets, their requests, their half of the video call, etc.

Once you can identify your upstream and downstream bandwidth and utilization thereof, you can begin to tell what up/down bandwidth you'll need.

  • OK, so if I get this corrrectly with leased line 20 MBit/s my upload is not effecting download so I have clear 20 for download and the same for upload ? This is one of very valid points where even with the same type of connection speed leased line is technically faster than DSL equivalent. Sep 15, 2014 at 11:32
  • Most leased lines are symmetrical; most DSL is not (most DSL is ADSL, though there is SDSL available in some areas). So generally you're right, but I would get your provider to EXPLICITLY state 3 things: 1.) Upload Speed. 2.) Download Speed. 3.) Whether you can simultaneously upload and download at that rate. 3 is important to understand your bandwidth. I've seen (rarely, but seen it) providers give X upstream/downstream speed, but with a fine-print caveat that this is TOTAL bandwidth available, split between up and down.
    – Smithers
    Sep 15, 2014 at 14:59

You're either being quoted T1 (1.544 Mbps) or E1 (2 Mbps) lines. Those speeds are symmetrical, so you get 1.544 in each direction of a T1 simultaneously. The "A" in ADSL means it's asymmetric, and regardless of your ADSL speeds today, the upload of the circuit termination is a fraction of the download rate.

The problem to determine is- where do you need the speed? If the clients you service are needing to pull/download information to them to be happy, then bonding DSL is cheaper and can get you more than 1.544 Mbps of a T1. That's why ADSL technology is so popular in the residential Internet Access market- people send small amounts of internet requests that are fullfilled by webservers that send many multiples of data back (like video or web pages).

If they send you more information (for instance, they have to upload backups or reports on a frequent basis) than they typically download at a particular time, you might be tying one hand behind your back with DSL technology, even when bonded. There are so many speeds of DSL it doesn't help to ask here- just determine what your full upload capability is from the client location and compare that to 1.544 Mbps. If it's less, and they need to send you gobs of info versus receiving it, then you need a T1 at their location.

Also keep in mind that T1 lines can be bonded as well (in a former life I bonded 4 of them for roughly 6Mbps of bidirectional access).

If you are in a region of the world that has E1's, substitute 2Mbps for the 1.544 you see in this post.

  • 1
    Definitely good stuff. I'll just note that T1 lines can be so extremely expensive that you may be able to meet your required upload speed with bonded DSL at a fraction of the cost. Four 3M down x 368k up DSL circuits can approach a T1 line's upload speed at around 1/5th of the cost (depending on market of course). But yeah, once you need more than 1.5 M upload speed, look at T1 lines or, perhaps if available, Ethernet over Copper. Coax ("Cable") may work well too.
    – Smithers
    Sep 10, 2014 at 16:22

First you need to figure out what your problem is.

  1. Is the bonded DSL system failing to deliver it's headline speed due to either poor line conditions, congestion on the network (either the DSL backend network or the ISP network) or traffic shaping by the ISP?
  2. Do you have an unusual workload (maybe lots of creative types uploading data) that means you are being limited by upload rather than download bandwidth?
  3. Do you have a small proportion of users who are using an disproportionate amount of data and/or using aggressive protocols like bit torrent?
  4. Or do you simply need more downstream bandwidth than the headline speed of your current bonded DSL setup.

If your problem is 1 or 2 then moving to a leased-line at the same headline speed is likely to help. A leased line gives you an uncontended path to your ISP and typically gives symmetric up/down.

OTOH if you don't need too much upload and your DSL lines are managing to deliver their headline speeds then I don't think moving to a leased line at the same headline speed will help much.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.