The Care and Feeding of ISDN4BSD
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2.2 Basic Rate ISDN 2.2 Basic Rate ISDN 2.3 The D-Channel

2.2.1 Frame format on the S0 bus

The (simplified) format of a transmit or receive frame on the S0 Bus looks like this:


A frame consists of four B-channel octetts (2 octetts for channel B1 and 2 octetts for channel B2) but only one half D-channel octet - this means it takes two frames to get a complete D-channel octet transmitted.

The layer 1 frame format and protocol is specified in [1]. It specifies:

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Hellmuth Michaelis 2000-08-30