Can you help me understand guaranteed CIR?

Can you help me understand guaranteed CIR?

In a Frame Relay Network implementing Voice/IP where the CIR is set for example at 512k -- what happens if there is network congestion sufficient enough for the carrier to discard packets not marked DE (discard eligible). I have been led to believe that carriers will in fact discard packets that are supposed to be "guaranteed." If carriers do in fact start discarding packets marked eligible/guaranteed then why pay more for a guaranteed CIR.

One major carrier (Sprint) does not provide a guaranteed CIR but rather uses zero CIR in all applications including voice/IP. They state that their port is guaranteed at 99.9% on whatever traffic is offered to it. Therefore, I am confused and hope you can clarify the CIR and packet eligible/discard eligible controversy.

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Different service providers offer different service level agreements. Many carriers offer a zero committed information rate (CIR) service because it is relatively inexpensive when compared with service level agreements involving a nonzero CIR. If Sprint guarantees 99.9% delivery, it may be sufficient for many users and meet with their expectations.

People wanting a lower likelihood of dropped packets will want to obtain a service level agreement for a specific CIR. If a business is sending important data or VoIP traffic across a Frame Relay interface, they will typically want to use a separate data link connection identifier (DLCI) which has its own CIR.

When the network becomes congested, the carrier will discard frames with the DE bit set before discarding those that do not. The carrier can discard frames without the DE bit set if the congestion level completely overwhelms their equipment. This, however, is a very unlikely event. That is why you would still pay more for a 'guaranteed' CIR.

This was first published in February 2004