Determining if CIR is for you, part 1

We're sure most of you have been approached by salespeople from different service providers. One salesperson tells you how stupid it is to order a CIR-based service; the other tells you how risky it is to order a zero CIR service. You must be wondering, Who is right? Although this issue and the next won't give you answers for your particular situation, they will tell you what you need to know to make an educated decision.

Let's first examine the pros and cons of zero CIR frame relay services. By definition, a zero CIR service is any frame relay service where a PVC has a CIR of zero. The primary benefit of this service is that, generally, zero CIR PVCs are less expensive than CIR PVCs. Also, because carriers oversubscribe their backbone by at least 200% (maybe as much as 1,000%), you are never guaranteed of getting your CIR all the time, so why pay for it? If you order all zero CIR PVCs, you can have an infinite amount of PVCs and never oversubscribe your port. Finally, zero CIR frame relay service makes it easy to design your network; no PVC sizing is necessary.

But there are a few drawbacks to zero CIR service. For one, all packets are marked discard eligible (DE). During times of serious network congestion, DE packets are the first to be discarded. Second, if all PVCs are zero CIR, there is no way to determine which PVCs are "more important"; all are treated equally. If you have certain connections or applications that are "critical" and others that aren't, the network won't be able to distinguish between them.

Part 2: The pros and cons of CIR-based frame relay services

TeleChoice is one of the leading telecommunications consultancies worldwide for the design, development, implementation, and migration of new and leading edge telecommunications hardware, software and services. Our focus is on public networking and value-added services for the telecommunications industry. You can contact TeleChoice at its corporate headquarters at (973) 239-0700 or visit our Web site for more information.

Tips and tales from the frame relay trenches
Network World, 9/1/97.

Ten frame-relay design do's and don'ts
Network World, 9/1/97.

Steer clear of Frame Relay traffic snarls
Plan alternate routes to avoid congestion caused by burgeoning growth. Network World, 6/23/97.

Efficiencies of Frame Relay Networks
White paper that includes some cost comparsions (caveat: data is two years' old).

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