Cisco expanded the reach of Rakuten Mobile’s nascent 4G LTE network in Japan with an inter-network roaming service that allows Rakuten Mobile customers to roam on rival KDDI’s network across the country. The move also deepens Cisco’s support of Rakuten Mobile’s 5G ambitions.

The Cisco work is based on the S10 signaling interface standard that was established by the 3GPP telecommunications standards body. For Rakuten Mobile, Cisco is running that interface within its Virtual Ultra Packet Core platform to connect mobility management entities (MMEs) between Rakuten Mobile and KDDI’s networks. The MME’s track user data sessions to support the handover of those sessions between the carriers’ networks.

The data path is managed by connecting KDDI’s network with Cisco’s System Architecture Evolution Gateway (SAEGW) virtual network function (VNF), which supports a control and user plane separation (CUPS) architecture. CUPS allows operators to separate the evolved packet core (EPC) into a control plane that can sit in a centralized location, for example the middle of the country, and for the user plane to be placed closer to the application it is supporting. It’s seen as essential to 5G networks and can also be deployed in 4G LTE networks.

Rakuten Mobile and KDDI are already linked through a 3GPP-based S8 interface that is used for connecting the SAEGW VNFs that are located in the core network and is used for transferring user data.

Kishen Mangat, head of Cisco’s Service Provider Mobility Business, noted in an interview with SDxCentral that the work showed that the “devil is in the details for providing a true production service.”

“They're using the S10 integration with KDDI’s network to provide a true production-grade service,” Mangat said. “That's really the significance of this announcement, the realization of a macro-scale network given all the assets that are required with Rakuten's architecture to make that happen.”

Cisco also has been working with KDDI on its 5G and network virtualization efforts. This includes a recently completed proof-of-concept (PoC) that demonstrated cloud-native software with Cisco’s Ultra Packet Core platform.

Mangat said that Cisco is focused on getting both Rakuten Mobile and KDDI into a similar network architecture space that it has done with T-Mobile US and its 5G standalone (SA) network.

“That’s where we intend to get them,” he explained. “To where their 4G and 5G networks can reside on a common platform and interact seamlessly.”

Rakuten Mobile’s 5G journey

Rakuten Mobile launched its fully virtualized greenfield network last week. That network runs on cloud-native infrastructure like containers and uses open radio access network technology. CTO Tareq Amin said the network architecture costs 40% less than traditional telecommunication infrastructure and saves more on opex.

The operator is working with a number of vendors, including Airspan, Altiostar, Cisco, Intel, Mavenir, NEC, Nokia, Red Hat, and Qualcomm. It planned to have 4,400 base stations deployed throughout Japan by the end of March and at least 8,600 base stations installed within the next year. It plans to turn on its 5G service by mid-year.

Japan’s already established mobile operators – NTT DoCoMo, KDDI, and SoftBank – have all begun to turn on their 5G networks. Those operators have pledged to invest a combined $14.4 billion in their networks through 2024. DoCoMo, which is the country’s largest operator, is carrying the largest burden of a promised $7.1 billion in investments. KDDI said it would invest at least $4.16 billion, while SoftBank pledged $1.84 billion in investments, and Rakuten has planned $1.73 billion in spending.