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I understand the theory of having "dedicated bandwidth" but why would a small/medium business purchase a leased line for access to the internet? In today's day and age residential grade connections are more than sufficient in speed and reliability. Any cable or FIOS connection will blow a DS3 out of the water. These connections do not regularly go down and even "dedicated" lines still have issues. Dedicated line's aren't even dedicated as they are multiplexed on the same backhaul as everyone else. So what's the deal with a DS3? Why would a business pay thousands of dollars a month when they can get the fastest cable\FIOS connection for 1/10th the cost and many times the speed? Can anyone shed some light.

I understand the need for super high bandwidth OC grade lines. In this post I am referring to T1s and DS3s which are easily surpassed by shared connections.

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I believe an expensive leased line comes with a better SLA, and therefore an active monitoring of the circuit. – Adriano P Aug 17 '12 at 1:17
in a word yes. SLAs. The concrete promise is what you pay for. – Sirex Aug 17 '12 at 1:18
Yes but short of a piece of paper in all practicality the leased lines are near as likely to go down as the regular connections. Also you can get two different feeds from two different providers (say FIOS and cable) and still pay next to nothing compared to the DS3 with a more robust connection. The SLA doesn't seem to justify THAT much of an increase to where people pay upwards of $1000 for 1.544 Mbps. – user974896 Aug 17 '12 at 1:22
Well, a T1 can carry 24 voice lines, and are a common method of getting a bunch of analog lines into an office (especially if the T1 is delivered via copper, and not fibre). But apart from that, I'm all out of ideas – Mark Henderson Aug 17 '12 at 1:28
Consumer-grade services aren't generally provisioned over highly available infrastructure (i.e. SONET circuits with protection). As such the time to restoration will tend to be substantially higher. This absolutely costs more and - for a large number of enterprises - is often worth it... – rnxrx Aug 17 '12 at 1:28
up vote 10 down vote accepted

1.) Bandwidth != latency, and jitter matters. A dedicated leased line's latency is constant and is generally substantially lower than a DSL or FIOS connection. This can be a critical point for certain types of applications. The upstream bandwidth from a given POP is certainly a point of variability, but generally far less so than consumer-oriented concentrators which can suffer in non-intuitive ways under periods of congestion.

2.) Consistency of bandwidth - If you lease a DS-3 then you have that bandwidth available at all times and under all circumstances. Even business-grade DSL/cable/similar services are subject to variations in available bandwidth based on usage. There's more bandwidth available under most conditions, but potentially less under others.

3.) Availability - At least in the US, traditional leased lines can be had anywhere. If your facility happens to be in an industrial park or located somewhat remotely then cable/DSL/FIOS may simply not be available at all. This is especially true in many commercial settings where a SONET mux may already be present but other services aren't economically viable for SP's.

4.) Mixture of services - Many SP's will offer Internet transit bandwidth as well as private WAN service on the same physical pipe. While this can be accomplished on a shared medium, better results are often had on dedicated pipes. Also, as antiquated as it may sound there is still a lot of use of standard PRI's rather than SIP trunks for a lot of phone systems. These can be mapped into a timeslot along with other services.

5.) To your first point, ALL Internet service is multiplexed. That's kind of the point. Without oversubscription networks don't really make a lot of sense. Predictability of the behavior of oversubscription is the point - and this isn't something that has been a major design goal of transports dedicated to consumer transport.

In practice I'd generally rather see a straight Ethernet connection run natively or mapped over a SONET circuit for sites with substantial bandwidth requirements but there are plenty of instances where traditional SONET framing is really the only practical solution. For edge sites the consumer edge services (inclusive of so-called business grade) are generally both sufficient and attractively priced.

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Interesting points. I can see things like video conferencing\streaming being important considerations (for the upload and jitter you described above). For high bandwidth applications I can see the need for circuits on the SONET ring. For run of the mill internet access though I don't see the need. Hell I've seen call centers run off the cable co, VOIP and all. – user974896 Aug 17 '12 at 1:35
Yes - no question, the newer (cheaper) connection media types are increasingly appropriate. Availability is still a big sticking point for a lot of business locations, unfortunately. Add in international connectivity and things can really get odd. The other point is that when you go above a certain bandwidth requirement the options pretty much dwindle. – rnxrx Aug 17 '12 at 1:50
With regards to Bandwidth != latency, I can't speak for connections in the US, but in the UK the highest ADSL speed you can get is 24Mbps up and 1Mbps down (on ADSL2+) whereas a leased line starts at a minimum of 20Mbps both ways. Though these may be different from US-style leased lines, as ones in the UK all run on Ethernet Fibre from the local phone exchange. SLAs is the main bonus, if your ADSL goes down, it can take OpenReach a few months to fix it, whereas your leased line is contractually required to be back up within four hours. – CyberJacob Mar 14 '15 at 14:07

As a general rule, businesses don't install leased lines when there are cheaper, superior alternatives. However, not all of the world has access to cable and/or FIOS. I'm at a location right now that has a T1 that costs around $500/month. The alternatives were dial up, ISDN, satellite, or things even more expensive. We were told in 2001 that we'd have DSL available within 3 years. That kind of didn't happen.

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T1 is a type of ISDN.... – Chris S Aug 17 '12 at 2:32
By ISDN, I mean BRI. In fact, before the upgrade to T1, we had two 2B+D BRI lines for 128Kbps at something like $122/mo. – David Schwartz Aug 17 '12 at 2:45
Actually, it was 256Kbps. – David Schwartz Aug 17 '12 at 3:01
I pay $450 for a bonded 2xT1 too. Unless you're in the middle of nowhere, you're paying double. – Chris S Aug 17 '12 at 12:32

A few more things ...

1- MTTR, All Leased Lines have 24/7 dispatched service, your cable co is available in 3 to 5 days any time btw 8am and 5 pm maybe? but we will call you an hour before we show up!

2 - Dynamic re routing upon fail over cable modems do not run BGP

Bottom line is if you are running a big league business or ANY public co with inherent reputational risk where down time costs you $ every hour min sec there is NO choice, unless you want to get FIRED or put in jail (fiduciary duty, bank are required by law to maintain redundant connections to ensure you can get to your money when you want it) the first time it goes down!

PS But with all that said there are some amazingly cheap and sophisticated devices on the market with state of the art load balancing and fail over capabilities, which will take up to 4 diff WAN connects of any kind, however they themselves are a risk as they are not redundant and thus a single point of failure, bottom line is your still FIRED!

There is an OLD saying in the IT biz "No one ever got fired for buying IBM (than later Cisco) these are just some of the many reasons why.

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I love T1's because of the reduced latency and because gauranteed 3 mbs (if you have a double T1 OR T1-c like I have) is worlds better than a 10 mb maybe. To illustrate most cable users have experienced network lag while gaming or watching HD netflix streams, right? Well those activities use very little data so why is your cable connection choking on it? I mean an hour of HD netflix is like 2000 mbs or so and on my T1-c I get GAURANTEED 10800 Mbs per hour. So unless the netflix servers are having difficulty (very rare) 4 different HD netflixstreams can go on without any trouble. Gaming and other websurfing takes even less bandwidth so you get my point. Near Zero Latency and gauranteed bandwidth are way better than a cable company's high mb maybe you will get the bandwidth you need some of the time.

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This isn't adding much that the other answers haven't covered, and the question is more than a year old. Feedback such as this would probably work better in comment format when you have the reputation to post those. – Andrew B May 23 '14 at 0:55

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