The number of B channels can be increased in multiples of 10.
The NT2 (typically a PABX) connects to a special OnRamp 30 NT1, at a point called the T interface. An S interface can be provided on the customer side of the NT2. For a OnRamp2, the T and S interfaces are identical.
Note that in the US and Japan, the primary rate service is instead 20B+D over a 1.544 Mbps (T1) bearer.
Such links are called "semi permanent" because they are not a "fixed" physical link within the ISDN network but a permanent call set up by the ISDN terminal equipment.
In its more recent OnRamp products, Telstra currently offers its OnRamp Xpress service. This is similar to a SPC, but charging is much more complicated!
OnRamp Xpress charging is based on the idea of a monthly capped charge. Example:
A business purchases an OnRamp Xpress service to connect permanently to a local ISP at 64 kbps:
On Ramp 2 | $50 per month | Xpress 1 Plan Fee | $90 per month | Xpress 1 limited cap | $135 per month |