Annex A provides examples of LCLS negotiation in the CN and LCLS configuration in the BSS. The examples also illustrate optional isolation scenarios and the change of the initial set of preferences during LCLS negotiation.
If the oMSC server requires receiving UL data from the terminating UE and sending DL data to the originating UE then it shall perform one of the following:
send LCLS-Negotiation (request) set to "LCLS-Not-Allowed" or;
send LCLS-Negotiation (request) set to "Need_Receive Backward = Yes, Need_Send_Backward = Yes", set LCLS-Configuration IE to "connected both-way in the BSS and send access DL from the Core Network, block local DL" on the originating call leg (as shown in Figure X.1.1). If the BSS supports this configuration then LCLS will be allowed; otherwise LCLS will not be permitted.
If the oMSC server requires receiving UL data from the originating UE it shall either:
send LCLS-Negotiation (request) set to "Need_Receive Forward = Yes" and set LCLS-Configuration IE to "connected both-way in the BSS and bi-cast UL" on the originating call leg after confirmation (as shown in Figure X1.2). If the BSS supports this configuration then LCLS will be allowed; otherwise LCLS will not be permitted. The data in the forward direction is passed to the tBSS due to the result of LCLS negotiation process on the originating call leg.
In order to avoid the forwarding of the data in the forward direction to the tMGW the oMSC can send LCLS-Negotiation (request) to the succeeding node set to "Need_Receive_Forward = No" and if it does not receive "Need_Receive_Forward = Yes" in the LCLS-Negotiation (response) then it may configure its MGW to isolate the network side termination from the access side termination (as shown in Figure X.1.3).
If the initial setting "Need_Receive_Forward = No" is overwritten by a succeeding Core Network node and the oMSC server receives "Need_Receive_Forward = Yes" in the LCLS-Negotiation (response) then it shall configure its MGW to be bothway through-connected (as shown in Figure X.1.4).
If the oMSC server receives a LCLS-Negotiation (response) set to "Need_Send_Backward = Yes" and "Need_Receive_Backward = Yes" (succeeding node of the oMSC server requires to send data to the oUE and to receive data from the tUE) then it shall perform one of the following:
send an LCLS-Negotiation (request) set to "LCLS-Not-Allowed" or;
set the LCLS-Configuration IE to "connected both-way in the BSS and send access DL from the Core Network, block local DL" on the originating leg (as shown in Figure X.1.5).
If the BSS supports this configuration then LCLS will be allowed and the requested LCLS configuration will be confirmed; otherwise LCLS will not be permitted.