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!