Standards Watch : Hodgepodge of Technologies Slow Global Roaming Efforts

The ultimate goal in next-generation telecommunications is to make available all communications services to anyone, anytime, anywhere, through whatever type of mobile communications device a subscriber chooses.

As the industry moves toward 3G, however, true personal mobility, international roaming and international support for multiple services-such as data transfer, fax, short message service and supplementary services-have been slowed by the sheer number of incompatible systems that reside on multifarious networks.

Europe and Asia's GSM (Global System for Mobile Communications) standard and the U.S. standards of TDMA (Time Division Multiple Access) and CDMA (code division multiple access) must evolve so that registration, authentication, call routing and location updating are possible in 3G networks. "We have a hodgepodge right now, with companies like Singular and AT&T Wireless using TDMA, Sprint and Verizon using CDMA, and European and Asian companies using GSM," notes Dataquest analyst Tole Hart. "Because ANSI x.41 is used in the United States for intelligent networks, whereas CAMEL is used in Europe, GSM and ANSI standards will have to at some point communicate."

"There are things developing," notes Hart, pointing to Nextel's iDEN. But, he notes, for someone who roams from North America to Europe, there usually are flat fees that are quadruple what a domestic user pays.

Because roamers want to protect their investment when traveling from one market to another, whether within their service provider's area or not, major wireless players are looking for TDMA/GSM gateways.

While there currently exist international gateway standards, most globetrotters are out of luck when roaming unless they have dual-mode handsets, and unless their carriers have made agreements with other carriers in Europe or Asia. Without a special handset, it's difficult to go from TDMA to GSM and vice versa.

"There will be an increasing need for TDMA/GSM gateway deployments," says Ram Kumar, product manager for SHLR (standalone home location register), Lucent's subscriber database, which is central to wireless network operations.

Key, he believes, will be the HLRs (home location registers) and VLRs (visitor location registers). Together with the Mobile Switching Center (MSC), they provide the call routing, and possibly international roaming capabilities of GSM.

"GSM handles call routing through HLRs and VLRs," says Kumar.

To briefly explain: Through the Broadcast Control Channel, GSM services notice when the location area broadcast is not the same as the one previously stored in the mobile handset's memory. An update request and the international mobile subscriber identity (IMSI) are sent to the new VLR via the new MSC. A Mobile Station Roaming Number (MSRN) is allocated and sent to the handset's HLR (which always keeps the most current location) by the new VLR. The MSRN is a regular telephone number that routes the call to the new VLR and is subsequently translated to the TMSI of the mobile customer.

"Since HLRs contain all the administrative information of each subscriber registered in the corresponding GSM network, along with the current location of the mobile, all equipment vendors, including us, are looking closely at HLR and how it can be deployed in a GSM network," says Kumar. He notes there are extensions to ANSI x.41 for unified "super" HLR, which will support 2G and 3G networks. Although the GSM HLR is not a commercial product yet, Kumar expects it will be available next year. "We hope to penetrate those markets with equipment at both ends of the gateway next year," adds Kumar.

The Big Move

The communication efforts may come sooner than later. As evidenced by AT&T's big announcement Dec. 1 of its partnership with Japan's NTT DoCoMo, the United States has already begun moving more toward European and Asian standards. The two companies will work to deploy a network based on UMTS (Universal Mobile Telecommunications System), also known as WCDMA (Wideband Code Division Multiple Access) in the United States.

AT&T plans to accelerate the introduction of wireless data services by overlaying a GSM/GPRS platform to its existing nationwide network. The new network will not replace AT&T's networks that use TDMA and CDPD (Cellular Digital Packet Data), but will lay the foundation for deploying high-speed 3G EDGE (Enhanced Data rates for Global Evolution) technology. That deployment will begin late in 2001 and extend to most of its markets by the end of 2002, according to AT&T spokesperson, Ken Woo.

He notes that AT&T will be aggressive in making agreements with other carriers so that international roaming becomes a true reality. "We already have many service agreements," says Woo. "Singular is based on TDMA, so they are compatible with us, as is Verizon, which has analog roaming. Sprint, which has CDMA, also has roaming agreements with us."