/mcp(unassigned) number include situations where the number is not present in the routing table, or when there is no available path through the ISDN network. cannot be reached because the number is unassigned. No route to a specified transit network (national use) Typical scenarios include: A wrong transit network code was dialed. • The transit network does not serve this equipment. • The transit network does not exist • 2 Indicates that the gateway is asked to route the call through an unrecognized intermediate network. Destination address resolution failure Typical scenarios include: Domain Name System (DNS) • Invalid session target in configuration • 3 CC_CAUSE_NO_ROUTE Indicates that the called party cannot be reached because the network that the call has been routed through does not serve the desired destination. Send special information tone The typical scenario includes the dialed number that has a special condition applied to it. 4 Indicates that the called party cannot be reached for reasons that are of a long-term nature and that the special information tone must be returned to the calling party. Misdialed trunk prefix (national use) The typical scenario includes the wrong trunk prefix was dialed. 5 Indicates the erroneous inclusion of a trunk prefix in a called party number. Channel Unacceptable The typical scenario is failed channel on the network. 6 Indicates that the channel most recently identified is not acceptable to the sending entity for use in this call.