Billing
In public networks, X.25 was typically billed as a flat monthly service fee depending on link speed, and then a price-per-segment on top of this. Link speeds varied, typically from 2400 bit/s up to 2 Mbit/s, although speeds above 64 kbit/s were uncommon in the public networks. A segment was 64 bytes of data (rounded up, with no carry-over between packets), charged to the caller (or callee in the case of reverse charged calls, where supported). Calls invoking the Fast Select facility (allowing 128 bytes of data in call request, call confirmation and call clearing phases) would generally attract an extra charge, as might use of some of the other X.25 facilities. PVCs would have a monthly rental charge and a lower price-per-segment than VCs, making them cheaper only where large volumes of data are passed.
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