Lecture 14: Internet Topology and Structure

ISDN Primary Rate

Basic Rate Access to an ISDN service (eg Telstra OnRamp2, last lecture) provides 2B+D channels. For large corporate (or other wealthy) users, the Primary Rate Access product (eg Telstra OnRamp30) gives 30 x B channels and a 64 kbps D channel, conceptually:

The number of B channels can be increased in multiples of 10.

The NT2 (typically a PABX) connects to a special OnRamp NT1, at a point called the T interface. An S interface can be provided on the customer side of the NT2.

Note that in the USA and Japan, the primary rate service is instead 20B+D over a 1.544 Mbps ( called a T1) bearer.

Where all of the available B channels are dedicated as a "leased line" point-to-point data service, users refer to an E1 (2Mbps) or T1 connection speed.

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