How do I model bent-pipe satellite architecture with OPNET? How do I model cut-through devices with OPNET?

How do I model bent-pipe satellite architecture with OPNET? How do I model cut-through devices with OPNET?

The bent-pipe satellite architecture cannot use the current pipeline of the OPNET model. The reason is, in bent-pipe, the satellite node only transmits the signal from uplink to downlink. It doesn't check the C/N (Carrier-To-Noise Ratio) and make any correction -- all the works are left for the downlink receiver. In the OPNET model, the default is to check C/N and correct errors if possible in EACH link. To bypass this, there are a number of ways in which the concept of a cut-through device can be represented, as opposed to a store-and-forward device. Here are some suggestions:1) Before communicating the original packet to the satellite, do the following: - Obtain its total size (op_pk_total_size_get()) - Store the original size of the packet in a dummy field of the original packet - Create a dummy packet (op_pk_create ()) - Change the size of the original packet to 0 (op_pk_total_size_set ())Now you can send the original packet first and the immediately send the dummy packet. This will allow the original packet to experience propagation delay, but no transmission delay. The dummy packet will allow for the utilization of the channel for the period of time desired. When the satellite gets the original packet, it should do the following: - Obtain the original size from the dummy field - Set the packet back to its original size (op_pk_total_size_set()) - Send the packet immediately on the downlinkYou will not need to create a dummy packet at the satellite since the original packet will now contain its original size and will utilize the channel appropriately.2) You can also bypass the pipeline stages if desired. There is a routine called op_pk_deliver that delivers the packet at a specified receiver. You can also use a variation on this called op_pk_deliver_delayed if you want to take into account some additional latency.In the bent-pipe case, this can be used in the following fashion: - Compute the propagation delay for the packet - Deliver the packet to the satellite using op_pk_deliver_delayed - At the satellite, compute the propagation delay and transmission delay - Deliver the packet to the ground station using op_pk_deliver_delayed

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