Until Rakuten Mobile extends its new 4G/5G network across the whole of Japan, it is reliant on a roaming deal with larger Japanese MNO KDDI to fill the gaps. Users will not get the same low Rakuten tariffs when they move onto the KDDI system, but they will be able to get national coverage, including on the high speed trains. Roaming between the two networks will be enabled by Cisco, which is providing an inter-network service based on the 3GPP’s S10 signaling interface standard. Cisco is running that interface within its Virtual Ultra Packet Core platform to connect the mobility management entities (MMEs) in Rakuten’s and KDDI’s networks, respectively. The MMEs track user data sessions to support handover. The data…