GPRS GRX

Global roaming promises to be an important feature of 3G networks, but U.S. carriers don't even have roaming solutions for impending 2.5G networks.

The traditional “flat” roaming model has several significant performance and cost limitations. For example, end-to-end capacity has to be dedicated to each link, and the network is difficult to maintain and troubleshoot.

With more than 400 GSM carriers in 155 countries, almost 80,000 individual links are needed to interconnect them, not to mention ISPs and ASPs. Setting up and maintaining IP routing to other carriers' networks and the Internet is vexing.

A new GPRS roaming model is needed — one with fewer links that makes better use of network capacity. A global IP backbone, or GPRS Roaming Exchange (GRX), can interconnect GPRS networks and enable global roaming coverage. The GRX, which is based on a roaming-exchange hierarchy, interconnects GPRS carriers and provides seamless wireless access to applications when subscribers roam. The GRX standard is meant to replace the jungle of infrastructure and leased-line connections that have grown up around GSM voice roaming services.

According to Mike Walters, Nokia Networks business development manager (www.nokia.com), the complicated situation will only get worse with GPRS.

“If all I want to do is check my Hotmail account, all I need is access to the Internet. I can do that on the local network, and they may charge me one tariff,” he said. “But say I'm roaming and want access to my intranet. We now have to connect through the roaming capabilities of GPRS back to my home network and then connect through the VPN (virtual private network) functionality out to my company intranet.”

However, Walters said GRX is a viable and important solution for the future of roaming.

Global GPRS IP Roaming

GRX, based on the GSM Association's (www.gsmworld.com) IR.34 Recommendation, is a centralized IP-routing network for interconnecting GPRS and UMTS networks. As traffic is aggregated at the GRX level, carriers only need a connection to a local point of presence to enable global roaming.

GRX networks will interconnect to create a tier of the Internet through which carriers can exchange IP traffic securely that is generated by roaming customers. Traffic is aggregated at the regional level, and GRXs connect to the GPRS roaming backbone. The design makes more efficient use of bandwidth and can handle traffic bursts more easily.

“GRX is good news for all IP-based roaming, as GPRS is an IP-based router network where all traffic passes through routers that enable detailed logging,” said Sam Ekblom, Sonera (www.sonera.fi) interoperator services sales director. “This facilitates maintenance and troubleshooting.”

Instead of building bilateral links between carriers, GRXs enable a hubbing function. Carriers can link up with several GRXs, which are interconnected to provide roaming between carriers. The most likely GRX-roaming scenario will be a few large international exchanges linked to others via gateways. The result is multiple connections to the global network via one supplier, said Ekblom.

According to Walters, the GRX idea includes a clearinghouse to make roaming connections. If a subscriber from Europe wants to use a U.S. carrier's network, he still can access applications on Europe's network.

However, U.S. carriers must be able to bill for roaming services properly.

“It gets a little more complicated in GPRS where we actually have the capability to bill by what application I use instead of just how many minutes I use and what long distance is included,” he said. “The billing information becomes a lot more critical and a lot more complicated. That's where the idea of a GRX comes in.”

For GPRS and 3G, data roaming will be done over an IP backbone network, and GRXs will aggregate traffic, minimizing the number of links.

GRX connects a roaming handset to the Internet or intranets via access points in the home GPRS network, Ekblom said. Connections are done via standard SS7 signaling, GRX-based domain name system and GPRS core functionalities.

GRX Trials

Last September, Sonera and Nokia completed the first GRX-based GPRS roaming implementation. The tests, conducted by combining Sonera's GRX and Nokia's packet core network, proved the GRX concept.

In June, the two verified the quality of GRX roaming in a 3G environment. The QoS tests conducted in Nokia's UMTS platform involved three types of IP data: video streaming, Internet radio and normal file transfer protocol traffic (FTP). Data in the form of live images, sound and text files was transmitted via simulated 3G networks interconnected by GRX. Bulk data from external sources was used to simulate the role of other carriers. Each packet of data was assigned a priority and QoS class.

In the tests, data packets given top priority were transmitted faultlessly through the Sonera GRX. This means delay-sensitive traffic can be given higher priority over GRX roaming connections, allowing new types of all-IP services, implemented end-to-end, worldwide.

Simultaneously, lower-priority data can use remaining bandwidth, maximizing interoperator GRX roaming capacity without disturbing top-priority traffic.

Last month, Sonera and Telenor (www.telenorglobal.com) signed a commercial agreement to offer roaming between their GRX networks, becoming the first to offer inter-GRX roaming. The two commercial GRX networks are interconnected using a common peering point in Amsterdam, offering GPRS customers the same roaming and wireless Internet access as GSM subscribers.

According to Walters, connections between GPRS networks are enabled via border gateways. For example, each carrier is an island, and each is a GPRS network. The border gateway allows one island to talk to another.

“For those connections between islands, the carriers are looking at each other and (asking), who's going to maintain these connections, and that's where GRX comes in,” he said.

How carriers will charge each other has yet to be determined, but whoever establishes the GRXs can request payment for service and maintaining the link between carriers, or between U.S. and European carriers.

“GRX will be a key solution for global roaming, though some carriers will use alternative means, such as point-to-point bilateral connections,” Ekblom said, adding that those may lead to a confusing web of agreements.

Walters said GRX will be a bridge to next-generation GPRS and 3G roaming, but there will be concerns.

“How do we bill for QoS, and how is GRX going to maintain a QoS pipeline or a pipeline with a given QoS between two different carriers?” he asked.

For example, one carrier's customer roaming in another carrier's area wants to use an application that requires a certain level of QoS. Within one network, maintaining QoS may be simple. But once the user connects through the border gateway to the other network, that pipeline or resources must maintain QoS throughout the entire connection.

Initially, QoS won't be a major hurdle, because most applications won't be real time.

Currently in the United States, there are no intercarrier roaming agreements, but they'll be required to make GRX roaming work.

“Are there going to be roaming agreements between the major players in the United States?” he said. “At this point, I don't know.