Consolidate and conquer

Wireless telecommunications networks are in a constant state of flux. Whether existing cellular networks or new-build personal communication services systems, they are constantly being altered, expanded, tweaked and improved.

Recognizing this, wireless network operators will prefer to use the most economical, reliable and flexible methods of maintaining smooth operation. Digital cross-connect systems, boasting characteristics such as economic deployment, network redundancy and the ability to bundle traffic from various sites onto fewer-and therefore less expensive-facilities, can help wireless carriers achieve those requirements.

Cost-cutting The most immediate benefit of deploying DCSs in wireless networks is the money wireless carriers save. The majority of cellular and PCS providers rely heavily on leased-line facilities from their wireline counterparts for backhauling signals from base stations to switches and for connecting those switches to one another.

"The backhaul portion is a significant part of the PCS network," said Tom O'Boyle, director of marketing for network systems at Tadiran Telecommunications, which manufactures cross-connect equipment and markets to wireless and other types of carriers. "You want to reduce costs as much as possible.

Although the cost of those facilities varies from market to market-ranging from lower rates in rural areas to higher rates in traffic-heavy urban markets-leasing them is a major cost consideration for carriers.

"You need to get DS-1s and DS-3s as packed as possible," says Hubert Kostal, DACS 2 product and business manager at Lucent Technologies, another DCS equipment manufacturer. "You're paying for those leased lines, and your business returns are dependent on using them as efficiently as possible.

Given the cost of the mobile switching centers (MSCs)-the nerve centers of wireless networks that control all traffic-it clearly behooves carriers to get the most use out of each MSC in the network.

"They have to reduce the number of ports coming into the switch," says Jim Turwilliger, national PCS sales director for Alcatel Telecom, another DCS supplier that targets the wireless marketplace. "If they can concentrate the traffic, they have to spend a lot less money with the switch.

In addition, wireless providers pay the full rate for the transmission capability regardless of how much traffic a leased line hauls.

"You can't go to your local exchange carrier and buy a six DS-0 pipe," said Tadiran's O'Boyle. "You have to buy a full T-1.

Some wireless operators have begun building their own dedicated wireline facilities, but even those carriers must find ways to economize. Most accomplish that by consolidating traffic onto fewer lines. That's where DCSs come in (Figure 1).

"The primary application in cellular is to aggregate a bunch of DS-0s onto a T-1 to haul back to the MSC," says Jim Kliensmith, area vice president for wireless networks at Premisys Communications, which earlier this year introduced an adaptation of its wireline DCS to the wireless world.

Premisys primarily works in partnership with other infrastructure vendors, providing its technology to companies such as ADC Telecommunications, Tadiran, Alcatel and DSC Communications for use in their equipment, Kliensmith notes.

Another advantage of DCSs-and also a cost consideration-is the consolidation of underused leased-line facilities, a situation that is primarily encountered in lower- population rural regions.

"Cross-connects help to manage and economize the interconnection network," says Bob Hill, director of product marketing for transmission products at DSC. "You might have a DS-3 that is filled to only 50% capacity, but you're paying full rate. A cross-connect can peel off the unused bandwidth and groom the used bandwidth onto fewer facilities.

The systems can also centralize switching in low-traffic areas by aggregating it and hauling it back to a switch in a busier market, saving an operator the expense of deploying another switch until it becomes more economical to do so (Figure 2).

"When you're a startup PCS company, it's not necessarily economical to put a switch in every market," says Hill. "You don't have any subscribers or revenue coming in.

As those now-fledgling networks gain momentum, traffic may grow to the point at which it is no longer possible to aggregate for the sake of savings. But there will always be portions of the network where the advantages of DCSs are important, says one PCS provider.

"As we get more customers, the base stations become fuller and we won't be able to do it to the extent we're doing it now," says Dennis Kline, engineering manager at PrimeCo Personal Communications. "But as we start building out to the rural areas, we can still reduce T-1 costs quite substantially.

Reliable routing As effective as they are at reducing the money that wireless network operators have to shell out for facilities, DCSs can provide several additional advantages. First, because they monitor and control traffic flow, the systems provide network status monitoring capabilities and, in some cases, can help re-route traffic in the event of outages at base stations and other points in the network.

"[Carriers] use cross-connects to support restoration switching within the network," says Kostal of Lucent. "You can hard-wire in protection lines, but if you have a network that is growing, a cross- connect allows you to create an optimal protection scheme.

Using cross-connects for the sake of reliability may be more top-of-mind for cellular operators than it is for PCS carriers because higher-frequency PCS networks require cell sites to be closer together, Kostal notes. In that architecture scheme, even if one site fails, customers will never be too far from a working site, he says.

"Restoration in PCS could mean moving to the next cell," he says. "I've seen fewer restoration applications in PCS networks because the volume of traffic supported by each cell site tends to be less than that of a cellular [network]."

Still, at least one PCS provider stresses the importance of reliable backup systems and notes that DCSs will play a role in that application.

"Reliability is something we always look at," says Kline of PrimeCo. The PCS provider is banking on the functionality of the Alcatel DCS equipment it selected to provide network redundancy, he says. "We're trying to take cross-connects to the next level as far as reliability is concerned.

Network reliability is a particularly important issue in outlying, lower-traffic areas where avoiding excessive expenditures is pertinent, says Alcatel's Turwilliger.

"You have to have coverage out there, but you can't spend a lot of money on a microwave system," he says. Instead, carriers can maintain reliability by putting cross-connects on either end of fiber connecting to the switch as a backup, providing a dual purpose for the DCS.

"You're using it for grooming functions, but you're also backing up the traffic," Turwilliger says.

Many DCSs also provide remote troubleshooting capabilities, which helps warring operators slim down and compete more effectively with less, says Kliensmith of Premisys.

"They're looking at remote site management as their saving grace," he says.

That is particularly important for cellular operators that are battening down their networks in preparation for competition. But it rings true for PCS providers as well because those operators are looking to save money at every turn.

"They paid a premium for their licenses, so they may be very concerned about cash flow," says Hill of DSC.

Future proofing While DCS equipment provides wireless network operators with many immediate benefits, it also sets the stage not only for traffic capacity increases but also for advanced services that carriers may choose to deploy down the road (Figure 3).

For example, DCSs can be deployed to manage the flow of overlay transmissions over and above voice traffic, including SS7 transmission, cellular digital packet data and control channel transmissions such as RF fingerprinting for fraud control, says Stu Bennington, marketing manager for the digital systems division of DCS manufacturer Tellabs.

In addition, more and more bandwidth will be required as both PCS and cellular networks proliferate, he says, and DCS equipment can provide an economical way to provision more circuits to accommodate that.

"One advantage of cross-connects over other technologies is that they're a lot less labor-intensive," Bennington says. "You're automating your networks, which allows you to provision circuits more quickly and future-proof for capacity and service capability.

DCSs can also help link together disparate switches-in both single-vendor or multivendor environments-that may populate a large network by providing signaling interfaces for switch-to-switch functions that allow the different types of switches to communicate smoothly, says Kostal of Lucent.

"By putting traffic through the cross-connect, we gain some signal processing capabilities," he says.

Wireless network operators of all kinds are now scrambling to either finish building their networks or revamp them to be more capable and more competitive. By deploying DCSs, those carriers not only save costs at the front end but they also prepare for fluctuating traffic capacity, changes in infrastructure deployment and the introduction of new services.

"You're not only helping the economy of the networks," says Bennington, "you're also positioning them for future services.