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Carriers must support legacy 2G/3G gear long after 4G networks go live

Even after most major carriers launch 4G networks based on Long-Term Evolution (LTE), service providers are still going to have to support subscribers on 2G/3G legacy networks for years to come.

Long after most major carriers finally launch next-generation 4G networks based on Long-Term Evolution (LTE), service providers will still have to support subscribers on  2G/3G legacy networks for years to come.

We just confused our customers because they walked into a store and we threw technologies at them, and they had to make a choice about which one ... to choose.


Mike Wright
Executive Director of Wireless Networks and Access TechnologiesTelstra Corp.

 "It's going to be tough for them to completely and rapidly get away from 3G or even 2.5G as well just because there [are] always going to be [customers] out there that have it," said Bill Rubino, principal analyst at ACG Research. "It's going to be a tough call for them to say we're no longer going to support 3G…. It really depends on the success they have with the proliferation of 4G clients."

Carriers cannot abruptly shut off service for subscribers on 2G/3G legacy networks, and overlaying 4G systems and platforms will add cost and complexity to network infrastructure and back-end system upgrades.

Supporting voice traffic over LTE is one example of the complications that legacy networks pose. Many mobile carriers are still struggling with how to manage voice handoff between LTE and 2G/3G legacy networks when LTE subscribers wander beyond the edge of the 4G network. The One Voice Initiative, which uses IP Multimedia Subsystem (IMS) architecture to carry voice over LTE, has won widespread approval from service providers, vendors and industry bodies. But carriers are still struggling with how to implement packet-switched voice over IP (VoIP) traffic alongside circuit-based 2G/3G legacy networks.

"The technology for voice over IP over 4G to work is not the stumbling block. It absolutely does work.… The real issue is legacy infrastructure," said Randy Fuller, director of business at Tekelec, a broadband data management vendor, speaking on a recent panel at 4G World in Chicago.

"How quickly people will flip over to doing voice over their LTE networks depends on how much legacy infrastructure they have and the cost of switching that service over -- the cost of the handsets, the amount of coverage in the network, the requirement that … it can fall back to a circuit network if you're not in LTE [range] or sufficient data coverage," Fuller added.

Easier 4G upgrade path from legacy 2G/3G core, RAN and back-end systems

Thanks to the responsiveness of vendors, not every piece of 2G/3G legacy networks will be difficult to support in a 4G upgrade.

Core network equipment vendors have succeeded with designing backwards compatibility into Evolved Packet Core (EPC) products, Rubino said. These modular EPC platforms enable operators to add, swap or remove blade servers in a single chassis to support 4G networks on top of legacy 2G/3G networks.

"The Cisco [Systems] platform from Starent [Networks], the ASR 5000, was really a purpose-built platform for the evolved packet core, and they have the functionality to handle the 3G aspects as well," Rubino said. "Ericsson is another case where they've taken a lot of their experience in what they've done to 2G and 3G and added it to the evolved packet core. Their experience in legacy protocols helped them to have that backwards compatibility as well."

Back-end systems such as network management tools, operational support systems (OSS) and billing support systems (BSS) will remain separate until the market matures, but vendors are making progress, Rubino added.

Radio access network (RAN) vendors such as Ericsson, Huawei and ZTE are also building modular network components to support multiple generations of technology, according to Mike Jude, program manager at Stratecast, a division of Frost & Sullivan.

"If you start replacing your network controllers or your cell site infrastructure with all this multimodal stuff, all of a sudden transit becomes easier.... Now you can support whatever you need to for as long as you need to do it because it's simply a card to go to the next generation," Jude said. "Technologically, transitioning shouldn't be a super big deal, but you still have to drag along the entire consumer marketplace with their instruments and at some point they'll just have to switch."

As a result, 4G networks are "not going to be completely separate networks [but] they are going to be an overlay" with some equipment able to handle all three generations of technology, Rubino said.

Not just technical challenges in sustaining 2G/3G during 4G network upgrade

Aside from the technical challenges, service providers will also have to make sure consumers aren't confused by the separate networks.

Australian telecom incumbent Telstra Corp. learned this the hard way in 2004 and 2005, when it launched two 2G networks -- code-division multiple access (CDMA) and global system for mobile communication (GSM) systems -- around the same time it deployed "the beginnings of a 3G network" and subsequently "lost our way," according to Mike Wright, executive director of wireless networks and access technologies at Telstra, speaking on an operator roundtable at 4G World.

"We just confused our customers because they walked into a store and we threw technologies at them, and they had to make a choice about which one of those flavors of technologies to choose," Wright said. "We undertook a major strategic review of our wireless business in 2005."

KT Corp., a South Korean telecom operator, will add an LTE network to its line-up after local regulatory bodies release the 900 Mhz band of spectrum KT has acquired, according to Hyun-Pyo Kim, director of mobile research and development at KT Corp., who also spoke on the roundtable.

KT's service portfolio also includes wideband code-division multiple access (W-CDMA) and WiMax, but KT Corp. is not focusing on teaching its 16 million mobile subscribers the ins and outs of 2G/3G versus 4G, Kim said. Instead, the service provider is marketing its new and legacy networks based by device or service -- cell phones on W-CDMA , mobile broadband services on WiMax and eventually LTE-capable smartphones on LTE .

"People don't care about what the technology is, but they care about price, performance and coverage," Kim said.

Let us know what you think about the story; email: Jessica Scarpati, News Writer

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