Relocating HLRs

The HLR is the core of delivering personal communications. It is the subsystem that keeps track of subscribers, where they are and what services they are using. It provides information to the MSC on how to handle and route calls to or from a mobile phone. Historically, these functions were embedded within the switching platform. But the HLR is moving.

Today, many carriers are relocating the HLR from the mobile switch to an independent platform. This allows multiple switches across the network to share the same HLR. For some carriers, it is an economic way to deploy the network. For others, it is a fundamental requirement for providing advanced personal communications. Regardless of the reason, it strategically positions the network toward a shared distributed computing architecture, which is critical as carriers move forward.

"Separating HLR functions from the switch is one step in the natural progression of separating call-processing intelligence from switching," said Mona Johnson, IN Forum technical marketing services and executive director. "Stand-alone HLRs are a great example of distributed intelligence communicating with each other."

The success of the Internet and its associated IP technologies is having a forceful influence on the evolution of telecom networks. Carriers want to take advantage of emerging technologies, such as fast-packet switches and ATM. To support new technologies, bundled services and the associated network interoperability requirements, wireless networks are evolving toward distributed service architecture.

"Our vision is a highly distributed IP-based architecture where the switching matrix becomes one element in a high-speed network," said Bill Yung, Nortel director of wireless solutions for wireless networks. "The HLR is just one of the elements of a distributed architecture. It is critically important to move there."

NETWORK EFFICIENCYEarly MSC architectures weren't designed with tremendous growth in mind. According to Lynn Whittington, Motorola Cellular Infrastructure Group chief technologist, originally HLRs were coupled with the switching platform to provide a reliable and cost-effective solution. But this compromised capacity and access speed.

A separate HLR improves call-processing capacity because the MSC no longer has the burden of responding to subscriber-related queries. The capacity and performance gains are unique to each network. There are substantial benefits for large networks with high subscriber volume and high roaming traffic.

This is a critical issue as carriers overhaul traditional cellular pricing by eliminating roaming charges, package minutes of use and bring long-distance rates equivalent to wireline. These trends have a major influence on calling patterns. In Europe, where subscribers do not pay for incoming calls, the number of calls towireless phones is remarkably higher than in the United States. Recent first-incoming-minute-free offers also have increased the percentage of incoming calls. As these trends change roaming and calling patterns, separating the HLR may become a necessary network upgrade.

"If wireless replaces landline phones as the primary business phone, then carriers will need to gear up their networks to handle the associated incoming call volume," said Ed Crabill, Lucent Technologies product manager. "Separating the HLR from the MSC is a key part to gearing up the network."

As carriers continue to compete based on price and service bundling, they are looking to drive costs out of delivering services. According to Mike Buhrmann, Global Mobility Systems president & CEO, carriers need to "architect the network to provide services at the lowest cost."

The HLR is a mission-critical application. Any HLR failure means subscribers are unable to make and complete calls. Deploying a centralized HLR increases the magnitude of a failure from a localized region to the entire network. Therefore, the HLR usually is deployed as a mated pair on a fault-tolerant platform.

In contrast, subscriber services and features such as voice mail and short message services are not mission critical. These services require a high-availability computer, which costs substantially less. Hence, co-locating the HLR with other service applications results in a higher network-infrastructure cost.

Moving the HLR off the switch also simplifies the subscriber-provisioning process. To add a new subscriber or change a subscriber's service profile, you have to update every MSC in the network. Established carriers have developed sophisticated proprietary systems that automatically update every switch from a central service-provisioning system. A central HLR provisions subscriber services from one network location.

A separate HLR simplifies service provisioning for new entrants that do not have extensive provisioning systems or carriers looking to sell services in new venues that their in-house systems do not support. For example, Powertel sells services through its retail stores and mass merchants such as Best Buy, Circuit City and Office Max.

"Using GSM and one SIM card standard for microprocessing information, our separate and single HLR provides one consistent way of provisioning and distribution on the Powertel network," said M. V. Thomas, Powertel director of network subsystem engineering.

SWITCH PLATFORM OR SCPSome MSC vendors have separated the HLR application from the call-switching functions and provided an HLR that runs on the same platform but on a separate box. The major advantage of this approach is that the switch vendor's proprietary services and features are still available.

You also can implement the HLR application on a service control platform (SCP). The key advantage is that you can share the HLR/SCP across different vendor switches. However, the feature set generally is restricted to those defined in the IS-41/WIN standards. Kalervo Lahtela, who is part of Nokia's convergence team, said integrating the HLR and SCP is an interesting approach, but there aren't any real advantages in doing so right now.

"To keep them separate provides more flexibility, just like keeping the MSC and HLR separate," he said.

However, HLR/SCP vendors have seen increased demand. Compaq Computers reported that there are now more than 17.5 million U.S. subscribers on its IS-41 HLR/SCP platform, compared with 10 million in October 1997. Other major HLR/SCP vendors also reported increased sales, which indicates carriers are realizing the value in making this change.

In the early stages of wireless, a carrier's success was reliant on proprietary features and services MSC vendors provided. Over time, the industry has converged service offerings, and standards have taken an increasingly important role. The IS-41/WIN standards are evolving rapidly to provide essential features and services. Increasingly, vendors are incorporating IS-41/WIN standards in their products. This has enabled carriers to deploy independent HLRs with minimal custom-integration effort.

With standard advancements, carriers are focusing on interoperability and service ubiquity.

"We support an open network architecture as a means to achieve feature and service transparency for our customers," said Jun-Yin Tsao, AirTouch Communications principal engineer.

For various reasons, many carriers are using more than one switching technology. Moving the HLR to an independent SCP is key to enabling subscriber features and services to function consistently across diverse network technologies.

For carriers that have deployed multiple-switch technologies and face interoperability issues, an HLR/SCP may provide the preferred and possibly the only solution. Andy Baker, Compaq senior product manager, reported that "HLR/SCP have been primarily deployed by large carriers for network efficiency improvements. However, we are increasingly seeing smaller carriers deploying the HLR/SCP to support service ubiquity across their affiliated networks."

Subscriber-feature transparency is a critical marketing issue and can be expensive to resolve.

"We have an extensive lab in Kansas that includes two MSCs from each of our vendors, where we undergo extensive testing to ensure all features work equally across different switch-vendor equipment," said Tom Murphy, Sprint PCS director of media relations.

A HLR/SCP can be the glue that holds disparate networks together and the enabler for the networks to perform ubiquitously wherever the subscriber roams.

FINDING A NEW HOMEThere is a clear trend to separate the HLR from the switching fabric. Whether deploying a separate HLR on a switch platform or an SCP, the move provides increased network capacity, improved performance and simplified service provisioning.

But there are numerous dynamics and variables to consider before you implement a separate HLR. Many of these factors are unique to each carrier. You should carefully consider what is already in place in your network and your relationship with your switching vendor in terms of delivering features and services. Only then will you know if it is time to move your HLR to a better location.