Over the past few months, we've noticed YATLA (Yet Another Three-Letter Acronym) making its way into frame relay discussions. Now, in addition to having a committed information rate (CIR), it seems that folks want to talk about an "EIR"-or "excess information rate." To our knowledge, the EIR has never been formally defined, but, true to form for our industry, that doesn't seem to be slowing anybody down.
In our November 3 newsletter, we started a discussion of CIR. In particular, we talked about the two components that make up a CIR: the number of bits committed B(c) and the time T(c) over which those bits are measured. We also mentioned that there was another parameter, B(e), which is the number of excess bits that can "fly standby" if there's available bandwidth. However, any frames that contain bits that spill into B(e) will be marked as lower priority with the discard eligible (DE) bit.
There's also a third possibility: The bits received within the T(c) committed timeframe could, at least theoretically, exceed even the B(c)+B(e) quantity. In this case, the service provider may dump the bits on the floor without even attempting to transmit them.
It seems that the EIR is an attempt to quantify B(e) divided by T(c). The time over which B(e) is measured should be the same as the time T(c) over which B(c) is measured. This results in an EIR, analogous to the CIR.
So, as a user of frame relay services, have you been missing something by not asking for an EIR? Probably not. Virtually all service providers define the "EIR" such that the CIR plus the EIR equals the port speed. Information transport is at least attempted for everything offered to the network. But could an explicit EIR possibly be of use? Stay tuned.
To discuss this and other WAN issues with Steven Taylor, Joanie Wexler, and your fellow frame relay newsletter subscribers, please visit the Webtorials.Com Public Forum at www.webtorials.com/forum.htm.
Steven Taylor, consultant and broadband packet evangelist, and Joanie Wexler, an independent networking technology editor and writer, team up to bring you this analysis and commentary. Taylor specializes in education and market analysis, and Wexler adds incisive reporting and research. For more detailed information on most of the topics discussed in this newsletter, connect to www.webtorials.com, the first Web site dedicated exclusively to market studies and technology tutorials in the Broadband Packet areas of Frame Relay, ATM, and IP. Feedback and additional topic ideas are welcome. Please contact taylor@webtorials.com or joanie_wexler@mindspring.com.
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