The B-channel connection between the user and the AU shall be controlled using the D-channel signalling procedures for call establishment described in 5.1. The specific B-channel to be used as a switched connection is selected using the channel selection procedures described in 5.1.2 and summarized in Table 6-1.
User requested channel and network response,
Outgoing access to either an AU or PH
Channel indicated in the SETUP message user to network direction |
Allowable network response (network-user) |
||
Information channel selection |
Preferred or exclusive |
D-channel indicator (Note 1) |
|
Bi |
Exclusive |
No |
Bi |
Preferred |
No |
Bi, Bi' |
|
Any |
(Ignore) |
No |
Bi' |
(Absent) |
Bi' |
||
Bi The indicated (idle) B-channel Bi' Any (other) idle B-channel NOTES 1. D-channel indicator shall be encoded "0" to indicate No and "1" to indicate Yes. 2. All other encodings are invalid. 3. All columns under the heading "Channel indicated in the SETUP message" indicate possible user codings of the Channel identification information element contained in the SETUP message sent by the user to the network requesting a connection to an AU or PH (see 4.5.13). The column under "Allowable network response" refers to the allowable responses by the network to the user. |
|||
On the basis of the call set-up information (e.g. called party number identifying an AU, transit network selection, etc.) and/or a subscription time agreement, the network provides a connection to the appropriate AU. The Bearer capability information element included in the SETUP message shall be encoded with:
- information transfer capability set to either
a) unrestricted digital information;or
b) restricted digital information;
- transfer mode set to circuit mode;
- information rate set to 64 kbit/s.
The user may also specify the layer 1 (e.g. rate adaption), layer 2 (i.e. LAPB), and layer 3 (i.e. X.25) information transfer protocols in the Low layer compatibility information element in the SETUP message (see Annex I).