tokens: ['This', 'is', 'the', 'central', 'node', 'in', 'the', 'IMS', 'network', 'responsible', 'for', 'session', 'control', 'It', 'manages', 'session', 'establishment', 'modification', 'and', 'termination', 'handling', 'the', 'actual', 'service', 'invocation', 'It', 'is', 'closely', 'involved', 'in', 'authentication', 'and', 'registration', 'processes', 'of', 'the', 'UE', 'and', 'ensures', 'that', 'proper', 'services', 'are', 'routed']