The present document describes end-to-end use cases and signalling flows based on the roaming architecture for voice over IMS with local breakout. It summarizes the contents of existing 3GPP technical specifications which are needed for roaming use cases. The scenarios used cover the following use cases:

• registration when roaming;
• routeing from originating visited network to originating home network;
• loopback routeing from originating home network to originating visited network;
• routeing when the originating and terminating user reside in the same home network;
• routeing from the originating home network to the terminating home network;
• routeing from the originating visited network to the terminating home network;
• routeing in terminating home network when user resides in this network;
• routeing from terminating home network to the terminating visited network;
• insertion of service related media in the originating home network;
• routeing through transit networks; and
• access transfer scenarios (SRVCC).