The data transmission rate can be determined individually. Basically, the ASI signal is the end product of a video compression, (MPEG-2 or MPEG-4) for further transmission, for example via satellite or broadband cable. The ASI standard is maintained by CENELEC, the European Committee for Electro technical Standardization, and is part of the collection of standards known as Digital Video Broadcast, or DVB. ASI carries MPEG data serially as a continuous stream with a constant rate at or less than 270 megabits per second, depending on the application.
IRD's can come in many different forms, and recently they are being offered in high density rackmount systems. For example an IRD formerly was able to usually convert a single program stream at a time; however some conversions are now being done in bulk. This is certainly true in the case of RF to IP, and IP to RF. Some commonly refer to these as Gateways, but alas these are still essentially decoders that are manipulating one format of a stream to a different format of the same stream. In most cases ASI decoding is the number one staple in a telecom headend; it's how they transport an entire CATV channel lineup of their offerings from one headend to another in a compact, low bandwidth, transport stream.
Choosing the best decoder for your ASI platform can be an arduous task. Sometimes multiplexing ASI streams is necessary and then delivering the content to a headend is another issue you may come across. ASI decoding has been a promenant staple of Thor Broadcast which has a variety of IRD's and decoding platforms for conversions and gateways. What can be a somewhat easy task gets harder when you have to change protocols or need higher density options for headend conversions. It's always a good choice to reach out to a veteran professional in the DVB world to ask questions to determine the best course of action.