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Mobile Infrastructure 101

Light Reading
LR Mobile News Analysis
Light Reading
8/20/2001

The mobile Internet promises interesting, easy-to-use, high-performance services that pull in new subscribers while making lots of money for mobile operators. Most of the news in the past year has focused on new mobile PDAs and handsets, corporate applications, and spectrum licenses, but in moving to a data-optimized network from a system that was built for voice, mobile operators and their network engineers will also have to deal with a whole new set of infrastructure technologies. Granted, infrastructure isn’t as sexy as a new Stinger phone, but none of the new phones will be worth anything unless wireless carriers make the right infrastructure choices. In the end, it’s the infrastructure that delivers the services and the revenue.

This article shows how the wireless infrastructure will evolve as carriers move to 2.5G and 3G networks, and it shows how infrastructure plays a crucial role in making the mobile Internet pay.

Wireless Infrastructure Today – Voice, CDPD, and SMS

Today’s 1G and 2G wireless networks deliver powerful mobile voice services along with a set of relatively limited data services. The networks are made up of the following key components:

- Base Transceiver Station (BTS) – Typically called a base station or a cell site, the BTS provides mobile terminals with access to radio resources by managing access to the air interface.

- Base Station Controller (BSC) –BSCs control the base stations and are responsible for critical radio resource management, including cell site switchovers and cell site power management.

- Mobile Switching Center (MSC) – The MSC is the nerve center of today’s mobile networks. It supports call setup, forwards calls to the right cell sites, provides the interface to the public telephone network, and monitors call traffic to support billing.

- Home Location Register/Visited Location Register (HLR/VLR) – These are databases that maintain subscriber subscription and location information.

Signaling Protocols

Each mobile device uses a signaling channel that allows the network to locate it and allows the device to request radio resources to make a call. Radio resources are provided using one of a three air interface technologies:

- Frequency Division Multiple Access (or FDMA, used in first generation analog networks).

- Time Division Multiple Access (or TDMA, used in GSM and PCS networks such as those operated by VoiceStream and ATT).

- Code Division Multiple Access (or CDMA, used in networks such as those operated by Sprint and Verizon).
These signaling protocols provide basic transport for voice traffic in 2G networks, but operators need to layer on additional data services on top of air interfaces.

Data Service Protocols

Today’s data services are limited in coverage and capacity, and they’re expensive to administer and use. The market for these services has been very slow to develop because they’re nowhere near what customers have come to expect (except in Japan, where few customers have wired broadband connections).

The most widely deployed data services on today’s 2G infrastructures are based on CDPD, SMS, and circuit switched data protocols.

- Cellular Digital Packet Data (CDPD) – CDPD is used over TDMA networks and offers connections of up to 19.2 kbps, although that bandwidth can be shared by up to 30 users at a time. CDPD is used by providers like Cingular and AT&T, and covers about 50 percent of the United States. However, the performance of CDPD varies throughout the day (based on the level of cellular and Internet traffic on the network), and most CDPD implementations require that the user establish a connection each time he accesses the network—they are not “always on.”

- Short Message Service (SMS) - SMS transmits messages of up to 160 characters over the mobile signaling channel, and the service has been rolled out by AT&T, Cingular, VoiceStream, and others. SMS capacities are obviously quite limited. In fact, a whole new abbreviated language is evolving to allow viable exchanges on tiny cell phone screens. Still, the service has become very successful—especially in Europe—because it provides the desirable “always-on” packet connection to the network.

- Circuit Switched Data (CSD) - Circuit switched data services use the traditional telephone network along with a modem to provide services very similar to the original dial-up services over fixed networks. Data rates range from 9.6 to 14.4 kbps, although some providers offer higher data rates at the expense of allocating more capacity to the connection. While easy to deploy, this service uses an entire voice “circuit” for transmission, and so is too expensive to deploy in volume. Circuit switched service also requires the user to set up a connection each time he wants access.

With today’s inefficient mobile data networks, it’s not possible to allocate reasonable levels of access bandwidth to all subscribers because it simply costs too much to provision the capacity. Additionally, most users are looking for an always-on network that provides fast response times on-demand – not for high aggregate data rates once they endure a long delay prior to moving to data mode and connecting to a service. For most, an SMS-like service with higher data rate would be considered ideal.

Wireless Infrastructure Tomorrow – 2.5 and 3G

To overcome these limitations, the industry is now deploying 2.5G and 3G mobile network infrastructures capable of supporting more efficient packet switched data. Rather than being based on analog, circuit-switched networks, these new networks are based on IP as the underlying data transmission mechanism. These networks require new radio technologies that transmit data more efficiently, and they directly send data to packet switched core networks (as opposed to sending it through the circuit switched infrastructure that forms the core of 2G networks). The radio technology upgrades being deployed (GPRS, WCDMA, CDMA 1X and 3X, and so on) make it far easier for mobile operators to allocate bandwidth between voice and data services.

New infrastructure for new services

In order to support new data services, 2.5 and 3G networks include new core networking components.

- Micromobility Manager – In the new packet core network, the BSC will divert voice traffic to the MSC, but it will divert data traffic to a new micromobility manager that specifically supports data traffic. This node is called a PCF in CDMA networks and an SGSN in GSM (GPRS/UMTS) networks.

- Mobile Gateways – These gateways perform roaming management, are responsible for provisioning network-level services for the subscriber, and provide subscribers with access to third party networks, corporate network services, and Mobile Virtual Network Operator (or MVNO) services. These gateways are called GGSNs in GSM and TDMA networks, and they’re called PDSNs within CDMA networks.

The new mobile Internet infrastructure supports an efficient packet-switched access network with capacities ranging from 20 kbps to 80 kbps per subscriber in the near term, and several hundred kbps per subscriber within a few years as 3G radio technologies are rolled out. Although we typically think of 3G networks in terms of hundreds of kilobytes per second, 20-80 kbps is actually enough to provide very good service for the vast majority of mobile applications. The challenge isn’t bandwidth or transmission speed; it’s managing the connections.

Getting It Right and Making It Pay

With the infrastructure to support always-on 20-80 kbps transmission, mobile operators are on their way to value-added services, far larger subscriber bases, and much greater revenue per subscriber. But the transmission rate is only half the battle. The major challenges are outlined below.

- Always-on service. Mobile subscribers want the network to be available immediately at all times – they’re not interested in waiting for the equivalent to a dial-up connection to the network each time they use it. Data applications should appear as just another menu item on the mobile device. The infrastructure must maintain these connections for millions of subscribers.

- Multiple Classes of service. High paying and business users may want access to priority services with a guarantee of higher bandwidth or shorter delays for their critical applications. Mobile operators will need an infrastructure that supports various service classes.

- Service model flexibility. Mobile operators will want the flexibility to rapidly expand their subscriber bases by partnering with other service providers. Operators will want to be able to work with third parties that may have access to a specific market segment they are unable to acquire through direct marketing, or that is more expensive to acquire directly. For example, an operator might partner with an overseas MVNO who can supply local phone numbers, or with an application service provider who offers specific m-commerce applications.

- Security. Enterprise users must be able to securely access their networks via existing VPN and firewall equipment without the need to deploy mobile-specific components within the corporate backbone. The corporate office will often want to maintain control over the security of the connection (authentication, key exchange, and so on), and will want a guarantee that there are no security holes in any connection.

- Seamless roaming. Operators will need to support seamless roaming between wireless LANs and wireless WANs, so customers can obtain higher transmission speeds while sipping a latte at Starbuck’s without losing their connection when they walk back to the office. Seamless roaming makes it possible for subscribers to have single billing relationship that offers the best network connection available regardless of location, and it allows network operators to share in the revenues available through deployment of such high-speed hot-spot technologies.

Overcoming these challenges will be the key to 2.5 and 3G services that are both captivating for the user and profitable for the provider. While the technology being deployed in today’s early network rollouts may offer only a limited array of services (operators are focused on simply getting the bugs worked out of end-to-end delivery in the early days), core networks will rapidly get more sophisticated in order to deal with the scale required in a network delivering a successful packet service and to provide the network-level services desired by the user (and profitable for the operator). The infrastructure described here delivers more bandwidth, but more importantly it also ensures carrier profitability by enabling highly differentiated and “sticky” services that users will love.


Carol Politi is co-founder and vice president of marketing for Megisto.
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