lte data roaming

8/13/2019 LTE Data Roaming

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Worldwide LTE Data Roaming

To establish LTE data roaming worldwide, two architectural issues should be addressed.

First, it's not easy for an LTE operator by itself to complete interconnectivity with its global roaming destinations. Instead of

current GRX and bilateral TDM links, roaming between LTE/EPC networks will require an efficient international exchangemechanism to integrate all the IP-based services originated in EPC/IMS and to interconnect them among numerous LTEoperators worldwide. Besides, although the existing GRX defines only best-effort IP transport, a QoS guarantee schemebetween visited and home networks is required to let LTE subscribers enjoy international services with the same quality asdomestic services.

Second, instead of the legacy SS7 MAP in GPRS roaming, roaming signaling in LTE/EPC uses Diameter on IP to exchangesubscribers' authentication and location update between visited and home networks. Diameter is an Authentication, Authorization and Accounting (AAA) protocol succeeding to RADIUS. Unfortunately, interoperability of Diameter technologyhasn't yet reached maturity. Actually, different vendors' EPC nodes sometimes can't successfully communicate to each otherdue to different implementations of Diameter signaling despite 3GPP standards.

Besides, interdomain routing by this new protocol is quite different from the traditional SS7 routing. For example, Diameter isbased on hop-by-hop routing, whereas SS7 is built on network-wide management. In addition, Diameter request-and-answer(response) uses the same path symmetrically while SS7 may not. LTE operators haven't ever experienced such interdomain

routing by Diameter. Consequently, it might be costly for each LTE operator by itself to create a new design of Diameter-based roaming signaling network and maintain it by connecting to multiple roaming destinations with SS7 reliability levels.

To solve the first issue, Figure 1 shows LTE roaming architecture, standardized by GSMA where IPX works as a hub thatprovides IP-level transport and service-aware gateways to ensure interoperability of any IP-based services with end-to-endQoS guarantee between LTE operators. Each LTE operator can connect the services to IPX through just one IP pipe. Then,roaming signaling (eg location update of a terminal by Diameter) and roaming data (eg IP-based application packetsencapsulated by GTP) are exchanged between LTE operator A (home network) and B (visited network) via IPX Provider 1. An IPX provider makes use of its international MPLS backbone for IPX and prioritizes the packets of the roaming signalingand roaming data with DiffServ to provide end-to-end QoS between LTE operators across another IPX. Thus, IPX helps LTEoperators interconnect to their worldwide roaming destinations with guaranteed QoS.

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This year will see the most rapid increase of commercial Long Term Evolution networks since the world's first commercialLTE was launched in 2009. According to the Global Mobile Suppliers Association, there were 89 commercial LTE networksin 45 countries as of July. With the global spread of LTE networks, international roaming between them is about to start. IPeXchange (IPX) is poised to become an important architectural solution to efficiently exchange international traffic of IP-based services interworking among LTE networks.

International 3G roaming is already popular. If you subscribe to a 3G roaming service, you can enjoy mobile data servicessuch as email and Web browsing, provided by your mobile network operator (MNO) while you're traveling in a foreigncountry. You can make international voice calls as well.

With General Packet Radio Service (GPRS) roaming, Signaling System No.7 ( SS7) Mobile Application Part carries roamingsignaling for the purpose of authentication and location update when a roaming user's terminal attaches a visited network. After the successful signaling, roaming data (IP packets of applications) are encapsulated by GPRS Tunneling Protocol

(GTP) and routed back from the visited network via GPRS Roaming eXchange (GRX) to the home network where the datatraffic breakouts to the Internet.

On the other hand, international voice is delivered by circuit-switched, not IP-based networks. Thus, only roaming data areinterconnected via IP between 3G operators while roaming signaling and voice, both of which include circuit-switched-basedprotocols, are still interconnected via international carriers' Time Division Multiplexing (TDM) links between 3G operators.

Along with deployment of LTE, the circuit-switched domain in a core network is bound to be replaced with IP-basedtechnology in the future. Many MNOs are implementing all-IP infrastructure coupled with LTE by applying Evolved PacketCore (EPC) and IP Multimedia Subsystem(IMS) to reduce legacy cost and facilitate IP-based multimedia services. However,



only data services are currently available in LTE, while voice services are provided by circuit-switched fallback until Voiceover LTE (VoLTE) emerges in the market with the completion of LTE radio coverage and IMS deployment. From theviewpoint of roaming in LTE, although industry associations are standardizing VoLTE roaming architecture, its guideline isnot officially unveiled yet. Therefore, international LTE roaming can provide only data roaming service in the interim periodbefore VoLTE roaming architecture is released.

Worldwide LTE Data Roaming

To establish LTE data roaming worldwide, two architectural issues should be addressed.

First, it's not easy for an LTE operator by itself to complete interconnectivity with its global roaming destinations. Instead ofcurrent GRX and bilateral TDM links, roaming between LTE/EPC networks will require an efficient international exchangemechanism to integrate all the IP-based services originated in EPC/IMS and to interconnect them among numerous LTEoperators worldwide. Besides, although the existing GRX defines only best-effort IP transport, a QoS guarantee schemebetween visited and home networks is required to let LTE subscribers enjoy international services with the same quality asdomestic services.

Second, instead of the legacy SS7 MAP in GPRS roaming, roaming signaling in LTE/EPC uses Diameter on IP to exchangesubscribers' authentication and location update between visited and home networks. Diameter is an Authentication, Authorization and Accounting (AAA) protocol succeeding to RADIUS. Unfortunately, interoperability of Diameter technologyhasn't yet reached maturity. Actually, different vendors' EPC nodes sometimes can't successfully communicate to each other

due to different implementations of Diameter signaling despite 3GPP standards.

Besides, interdomain routing by this new protocol is quite different from the traditional SS7 routing. For example, Diameter isbased on hop-by-hop routing, whereas SS7 is built on network-wide management. In addition, Diameter request-and-answer(response) uses the same path symmetrically while SS7 may not. LTE operators haven't ever experienced such interdomainrouting by Diameter. Consequently, it might be costly for each LTE operator by itself to create a new design of Diameter-based roaming signaling network and maintain it by connecting to multiple roaming destinations with SS7 reliability levels.

To solve the first issue, Figure 1 shows LTE roaming architecture, standardized by GSMA where IPX works as a hub thatprovides IP-level transport and service-aware gateways to ensure interoperability of any IP-based services with end-to-endQoS guarantee between LTE operators. Each LTE operator can connect the services to IPX through just one IP pipe. Then,roaming signaling (eg location update of a terminal by Diameter) and roaming data (eg IP-based application packetsencapsulated by GTP) are exchanged between LTE operator A (home network) and B (visited network) via IPX Provider 1. An IPX provider makes use of its international MPLS backbone for IPX and prioritizes the packets of the roaming signalingand roaming data with DiffServ to provide end-to-end QoS between LTE operators across another IPX. Thus, IPX helps LTE



operators interconnect to their worldwide roaming destinations with guaranteed QoS.

Figure 1. International LTE Roaming on IPXRoaming data can be returned to the home network like 3G GPRS roaming, or alternatively LTE operators can apply localbreakout whereby data traffic can be directly routed from the visited network to the destination, e.g. to the Internet.

To solve the second issue, LTE operators can delegate Diameter routing management to IPX. In the LTE roamingarchitecture, roaming signaling applies Diameter Realm-based routing between home and visited networks via IPX(s).GSMA recommends that a Diameter Edge Agent (DEA), which corresponds to a Diameter Relay Agent or Diameter Proxy Agent defined in the basic Diameter specification (IETF RFC 3588), should be located at the edge of an LTE operator's core

network in order to make its internal nodes invisible from outside.

An IPX provider can also deploy a DEA, which may be also called Diameter Routing Agent (DRA), as a signaling-servicegateway. It aggregates Diameter routing management among multiple LTE operators to ensure interoperability of Diameterrouting. To reduce the cost of implementation and maintenance for Diameter routing, LTE operators may outsourceDiameter routing management of their DEAs to the DRA operated by IPX. The DRA in IPX may be also applied to mediationof Diameter parameters between LTE operators.

lte data roaming

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