E.2 Incoming call in the MSC

09.123GPPApplication of ISDN User Part (ISUP) Version 2 for the Integrated Services Digital Network (ISDN) - Public Land Mobile Network (PLMN) signalling interfacePart 1: Protocol specificationTS

1) If the nature of the connection indicators parameter indicates that an outgoing half echo control device is included, any outgoing half echo control device on the incoming circuit of the MSC is disabled.

If the MSC is a Visited Mobile-service Switching Centre (VMSC), the backward call indicators parameter sent in the ACM indicates that an incoming half echo control device is enabled.

If the MSC is a Gateway Mobile-service Switching Centre (GMSC) or in case of call forwarding, the incoming half echo control device of the outgoing circuit is "reserved" and the echo control device indicator sent in the IAM is passed on:

– if the backward call indicators parameter received in the ACM indicates that an incoming half echo control device is included the incoming half echo control device of the outgoing circuit of the MSC is disabled;

– if the backward call indicators parameter received in the ACM indicates that an incoming half echo control device is not included the incoming half echo control device of the MSC is enabled. The backward call indicators in ACM are changed accordingly.

2) If the nature of the connection indicators parameter indicates that an outgoing half echo control device is not included, the outgoing half echo control device on the incoming circuit of the MSC is reserved.

If the MSC is a VMSC, the outgoing half echo control device is enabled and the backward call indicators parameter sent in the ACM indicates that an incoming half echo control device is included.

If the MSC is a GMSC or if the call is to be forwarded and the MSC knows that an outgoing half echo control device is necessary (e.g. called MS, forwarding to an international destination):

– the outgoing half echo control device on the incoming circuit is enabled and the echo control parameter sent in the IAM indicates "outgoing half echo control device included";

– the incoming half echo control device of the outgoing circuit is "reserved";

– if the backward call indicators parameter received in the ACM indicates that an incoming half echo control device is included the incoming half echo control device of the outgoing circuit of the MSC is disabled. The backward call indicators in ACM are passed on unchanged;

– if the backward call indicators parameter received in the ACM indicates that an incoming half echo control device is not included the incoming half echo control device of the MSC is enabled. The backward call indicators in ACM are changed accordingly.

If the MSC is a GMSC or if the call is to be forwarded and the MSC knows that an outgoing half echo control device is not necessary:

– the outgoing half echo control device on the incoming circuit is disabled and the echo control parameter in the IAM is passed on;

– the incoming half echo control device on the outgoing circuit is disabled.