In many network simulations and models the cost of processing a packet is considered negligible or overly simplified. The functionality of routers is steadily increasing and complex processing of packet payloads is being implemented (deep packet classification, encryption, content transcoding). We show two examples where processing cost can contribute to a significant portion of the overall packet delay. To enable a more precise consideration of processing delay, we present a tool called NPEST

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... Network Processing Estimator). NPEST is a framework on top of which packet processing functionality can be implemented and simulated using an actual processor simulator. NPEST can be programmed in C and greatly simplifies the implementation and simulation process as compared to using network processor simulators. The results derived from NPEST can either be used directly or be aggregated to processing statistics for network simulations. We present such results for two prototype applications: IP forwarding and IP security. We also show a comparison between the results obtained from NPEST and an Intel IXP1200 network processor.