Type II (i.e. bearer selection) information shall be included in the Bearer capability information element. Type III information, when used, is included in the Bearer capability information element. The network may use and modify the information (e.g. to provide interworking). The rationale for the user including some terminal related information in the type III information (interworking related) is shown by the following example.
Normally with UDI, the rate adaption technique chosen is related to the terminal. The specification of a particular rate adaption scheme with a UDI bearer service could allow a compatibility decision by the destination terminal in a purely ISDN situation. However, it could also conceivably be used to allow interworking with a PSTN, assuming that the appropriate functions (i.e. data extraction, modem pool) are available at the interworking unit.
If the rate adaption information is carried in the Low layer compatibility information element, and not in the Bearer capability information element, then interworking by the network providing the bearer capability would not be possible. However, if the rate adaption information is carried in the Bearer capability information element,interworking would be possible.
Hence, there is some terminal related information which may be considered interworking related. The consequence for the calling user of not including such terminal related information in the Bearer capability information element is that the call may not be completed if an interworking situation is encountered.
When type III information is included for any user protocol layer, the following network involvement is permitted within the indicated user protocol:
– layer 1: mapping of the user protocol to other protocols, and encapsulation of the user protocol within another protocol;
– layer 2: relaying of layer 2 PDUs across different layer 1 environments, and encapsulation of the user protocol within another protocol. Full termination of the user protocol is not provided, and in particular routing or destination identification information within the user protocol is not analysed until the entity addressed by the Called party number information element is reached;
– layer 3: relaying of layer 3 PDUs across different layer 2 environments, and encapsulation of the user protocol within another protocol. Full termination of the user protocol is not provided, and in particular routing or destination identification information within the user protocol is not analysed until the entity addressed by the Called party number information element is reached.
When type II information is included for any user protocol layer, and in addition to the identification of the telecommunication service requested by the user, the following network involvement is permitted within the indicated user protocol:
– layer 1: mapping of the user protocol to another protocol, and encapsulation of the user protocol within other protocols;
– layer 2: relaying of layer 2 PDUs across different layer 1 environments, and encapsulation of the user protocol within another protocol. Full termination of the user protocol can be provided, and in particular routing or destination identification information within the user protocol is analysed and utilised to reach the destination entity. When the user protocol is terminated, the Called party number information element (if included) is ignored at this point;
– layer 3: relaying of layer 3 PDUs across different layer 2 environments, and encapsulation of the user protocol within another protocol. Full termination of the user protocol can be provided, and in particular routing or destination identification information within the user protocol is analysed and utilised to reach the destination entity. When the user protocol is terminated, the Called party number information element (if included) is ignored at this point.
For both type II and type III information, if the network involvement modifies (interworks) the user protocols described by the bearer capability, the bearer capability relayed to the destination is modified appropriately. If no network involvement occurs, the bearer capability relayed to the destination is not modified.
The interworking arrangements with other appropriate bearer capabilities (e.g. packet mode, frame mode) or other networks (e.g. PSTN, B-ISDN) which may be accommodated by some networks are beyond the scope of this Recommendation.