Oversubscription - You knew it was too good to be true

Hey guys, I’m sure some of you out there are running off a T1 line and thinking you got a sweet deal with your T1 line. Do you know if you really have the full T1 line at your disposal? If not, is it a fractional T1 service?

Oversubscription Explained
Internet providers are measured in “Tiers.” A Tier 1 provider maintains their own national network and provides their customers with a 1:1 user to bandwidth ratio. Bandwidth ratio means if you order a 1000kbps connection, then that 1000kbps connection is strictly dedicated to you and not “shared” between multiple customers. The lower the ratio, the less your bandwidth is shared amongst other customers. ISPs that are connected to Tier 1s would begin the oversubscription process as they resell the bandwidth. This is why DSL sees the highest ratio of oversubscription, 100:1 for ADSL. Cable Internet also suffers from gross oversubscription, which explains why speeds can vary greatly during the day and at night.

Why do ISPs oversubscribe?
Oversubscription is a way for ISPs to optimize their resources. Most users will not be on at the same time, so what ISPs will do is subscribe multiple users to the same port. Oversubscription allows some carriers to collect more revenues than other carriers, by optimizing their pipeline usage. Based on a bandwidth ratio that ranges between 4:1 and 20:1 depending on the service being provided, oversubscription may actually occur several times before it reaches the end user. Though common practice, users should be careful because they may experience poor performance during high network usage.

It’s possible to have a dedicated line to yourself, but you’d have to pay a premium and negotiate service-level agreements (SLA) to ensure performance. For instance a 2mb/s (Megabits per second) DSL connection may cost $500 a month while a Fractional T3 with a committed bandwidth of 2mb/s will likely cost over $2000 a month. Even then, if all users of the ISP were to download all at once, there would be a connection slowdown, also referred to as the “Internet rush hour” aka “peak hours.”

Do not confuse a T1 Line with T1 Service
Remember, your ISP isn’t selling you a connection to the Internet; they are selling you a connection to their network that is connected to their own provider network, and so on. The networks connected lead up to the top Tier 1 networks, which, combined with servers and end users’ computers, make up the Internet.

Even T1 providers can be guilty of oversubscribing their pipeline to you. Make sure that you have exclusive use of your 1.544Mbps. Don’t be fooled by your ISP telling you they are selling you a Full T1 Line. Their line might be 1.544Mbps but that does not mean their service is. Remember, I’ve always said on this site that you get what you pay for. The cheaper you pay for T1, the more likely you’re getting shortchanged. Either there’s a fractional connection you don’t know about or it’s oversubscribed service. ISPs may advertise 1.544Mpbs for a T1 line, which would be true since that’s the maximum bandwidth, but you may never get to use it.
For example, T1 provider A might offer an oversubscribed T1 for $395 per month, while T1 provider B might offer a 1:1 ratio T1 for $495. Is it worth it to save $100 per month on the $395 T1 where you only average 384K speed most of the time? Or do you think it makes more sense to spend the extra $100 per month and be guaranteed to get 1544K speed all of the time, almost 5X the speed and guaranteed in writing? Which three year contract would you like to get stuck in? Remember, most providers will expect you to sign for two or three years and you will be stuck with poor performance, so do your homework!

At $395 per month for a oversubscribed T1 that operates at 384K most of the time, these providers are essentially selling you a very expensive cable modem, Why pay $395 for a T1 connection with performance you can get from a $50 cable modem? Isn’t the whole point of buying a T1 to have a guaranteed amount of upload and download at 1544K all the time? We think so! Make sure you research, and ask your ISP what their oversubscription ratio is and make them prove it in writing. Though we cannot guarantee complete accuracy, here is a list of ISPs under what we believe to be the known respective oversubscription ratios.

1:1 bandwidth ratio:
· MCI/Uunet
· Sprint
· Abovenet
· Qwest
· Savvis
· Netifice
· Level 3
· New Edge Networks (upon request)

Below 1:1 (but not necessarily too bad):
· Global Crossing
· Neon
· AT&T
· XO
· Internap

Average to poor oversubscription:
· Megapath
· Speakeasy
· Covad
· Uslec
· Cogent
· Broadwing
· Focal
· ACC Business

Oversubscription is a good indicator of how to tell you are going to get what you pay for, and not get a misleading Internet connection. Remember that advertisements are tools to sell a product, so consumers have to sift through some of it to see that they are guaranteed what they expected at time of purchase. Sure, oversubscription help provide competitive prices, but no one wants to end up paying for an Internet service that’s only half the speed of what it’s capable of when someone can offer maximum speed for slightly more.

Committed Information Rate

Yes, something to make you feel better when paying your ISP bills.

Hey guys. It’s been a while, but I’m back. I don’t know if anyone still checks this page, but let’s move begin where we last left off… TELECOM! YAY!

Today I want to bring up committed information rates, or CIR. Simply put, it’s a written guarantee from an ISP to a customer stating the minimum bandwidth available at any given time on a frame relay network.

Derived from the term Committed Data Rate (CDR), CIR refers to voice and non-data packets, whereas CDRs deal with data. I may write a future article on CDRs, but in short, CIR provides end-to-end minimum bandwidth guarantees, while CDR provides such guarantees only from the user location to the service provider's backbone.

Usually above the CIR, an allowance of burstable bandwidth known as the Excess Information Rate (EIR) is given. The EIR rate is delivered when there is adequate bandwidth. Frame relay carriers define and package CIRs differently so check with your service provider for the package offered in your area.

A huge plus of CIR is that only packets sent above the CIR are marked discard eligible (DE) and are discarded first during times of high network traffic. All your packets within the CIR are safe from the early discarding. With CIR, your network traffic will closely match your actual traffic patterns without all the disposable data sent.

A problem with CIR is that it’s nearly impossible to measure precisely. In dealing with your service provider, make sure they specify the interval over which the CIR is measured. Your CIR may vary depending on how the provider measures the time interval. It may not be the provider’s fault, though. CIR adjustments can be based on a company’s experience with it. Once you know how your provider’s CIR is measured, though, you should have a good start in negotiating the CIR in your service level agreement.

CIR Guarantees. How does your ISP stack up? CIR is essentially what makes many T1 providers different. It is measured in % of the bandwidth or by a minimum guaranteed rate that you are guaranteed to receive with your service. A 90% CIR means you should receive 90% of your bandwidth speed at all times. Since a T1 is 1544K, with a 90% CIR you would be guaranteed to experience 1389.6K at all times, which is what you would expect for the money you will be spending on your Internet or Voice T1 line. Since many T1 providers are offering Frame Relay based T1 lines, the speed you experience and the price you pay will be determined by the CIR in your contract. For example, if you are paying for a 1544K frame relay T1 and your provider offers a 384K CIR, this means your ISP will guarantee only 384K Speed for your 1544K T1. YES this means you will be paying FULL PRICE for essentially what is a 384K T1 Line, that may or may never reach the full 1544K speeds you think you are paying for. Worse, most frame relay providers such as the local phone company will only guarantee 128K, or 64K, or even 0% CIR. You could wind up being stuck in a contract for 2 or 3 years paying close to $400 a month for a 64K dial-up speed T1 line. Sound impossible? Guess again! This kind of questionable business practice is very real and very common in telecom. It allows ISPs and Tel Co’s to maximize profit. So, if the price you are getting is too low, then you may be buying a frame relay T1. We advise you to investigate your ISP carefully or simply spend a little more for a Clear Channel T1 where you can be guaranteed a full T1. It is certainly worth the extra $50 to $100 per month to be assured you are getting what you expect out of your service. If your ISP is a frame relay T1 provider, then it is always necessary to verify the CIR with the company who you may be purchasing from. In short: be wary and READ YOUR CONTRACTS CAREFULLY!

For further reading on Frame Relay, check out my article on the subject.