When a large regional Bell operating carrier wants to offer wireless service to millions of
customers, its network architecture is one of the most important choices it will make,
especially if the two networks must come together to offer integrated services. US West
offers wireline service in 14 states to 25 million customers and wireless service in Arizona,
Colorado, Minnesota, Oregon, Utah and Washington. Network architecture especially
came into play when the company wanted to offer both its wireline and wireless customers
a wireless extension of their home and business phone numbers through its One Number
Service. This service allows customers to use their wireless phones as extensions of their
existing home and/or business so that calls made to their homes or businesses will ring on
their wireless phones. One Number Service allows the customer to turn the service off and
on from the phone and allows him to use the extension as a second home or office line.
IP for Mobility
When it comes to its One Number Service, optimizing resources and minimizing latency is
paramount for US West.
“Basically, it is a new rendition of mobility in the sense that a customer can take his local
call- delivery service wherever he wants,” said Angus Dougherty, US West Wireless
director of PCS integration.
In order to make it transparent to callers whether a US West customer is on his wireless or
wireline phone, the carrier had to minimize network-signaling latency. It did so by moving
from SS7 to IP.
“A wireless extension of a home number is a derivative of US West's Wireless Intelligent
Network,” Dougherty said. “We had to build a network that would beat switch and service
application event interval time-outs in order to give the appearance to incoming callers that
a customer who has a wireless extension is still at home or in the office with our additional
call setup delays.”
In essence, when the customer is roaming in Seattle and someone calls his home or office
number, the phone will ring in Seattle, with no noticeable delay, and he will be able to talk.
If the customer goes out of US West Wireless' coverage area, the transaction rate must be
quick enough to compensate for non-conforming signaling delays. For those cases where
signal latency exceeds US West quality metrics, incoming calls are immediately sent to the
customer's home or office. By migration to IP network signaling, US West Wireless has
been able to reduce authentication, call setup and call delivery of a One Number Service
subscriber significantly, providing him local-call service quality when roaming outside of
his home or office service area.
“And if you time out, the fallback is to always deliver the phone call to your home or office.
The intent is to get the call from the network to the wireless extension transparently,”
Dougherty said.
“A lot of that has to do with the fact that we have to take SS7 signaling through a
hierarchy of steps with dominant link interface signaling speeds in kilobits per second and
transition it to Internet processor interface signaling speeds at the megabits-per-second
rate,” Dougherty said. “Translation and routing requirements of STPs adds a tremendous
amount of latency and overhead to message processing. SS7 protocol is a product of the
'80s, and it is now time to step up to the next millenium. IP promises to get us there.”
Although SS7 continues to play a critical support role at US West, its engineering remains
focused on preserving the integrity of call delivery to its customer base, and the transition
to IP is systematic, Dougherty said. Unlike start-up local and wireless companies that can
niche out a customer group with the latest in time-to-market technology for local or
wireless services, US West must engineer technology transitions that maintain the
demands of its total subscriber base. Marketing and sales departments expect engineering
to deliver technology that enables quality services ubiquitously across the entire US West
market.
“When you understand the concepts of integration within an embedded system
architecture that has evolved over the last 80 years, the challenge of introducing a mobile
handset as an extension of the local service is one of timing and location management,”
Dougherty explained. “The objective behind the incorporation of mobility to an embedded
local carrier network is to deliver incoming and outgoing call activities from the customer's
home or business service area to the local exchange service area in which the handset
happens to be. The amount of overhead to maintain the movement, registration and service
delivery of that handset can only be managed using high-speed protocols, such as those
evolving within IP. Whoever can master mobile IP will master the integrated feature
transparency, call-delivery and service-delivery scenarios that everybody is trying to get
to.”
Interim ATM
Although many carriers are looking forward to adding IP, Dougherty said they also need a
lower network layer — frame relay, transmission control protocol (TCP) or ATM.
“To say that IP is going to provide telco-grade switching and voice services within the
Internet is an over generalization,” he said. He added that it may be feasible to do so when
the digital signal processing (DSP) technology and application protocol can be fast
enough and reliable enough to perform distributed call processing and connection control
for such services as digit collection, route determination, multiparty conference bridging
and intercept treatments.
“Some people would like to believe it is out there today on a mass-market level,”
Dougherty said. “If you are a small company starting from ground zero, you might be able
to get something going. But for a massive regional operating company that has to figure
out how to transition switching technology and still meet its quality assurance deliverables
to a mega-customer base, you have to take it step by step.”
For US West Wireless, that step is ATM, the transport medium that will deliver the
high-speed route signaling and quality of service (QoS) needed to facilitate the
introduction of IP for connection control, mobility and service integration of wireless
extension of local services. As the company moves into delivering content and services, it
will move more toward IP to do so. In the meantime, it is implementing ATM as its core
packet-switching infrastructure. As the carrier migrates toward voice over ATM,
Dougherty said, voice over IP (VoIP) doesn't have the QoS mechanisms that are necessary
to deliver a mass-market product. US West Wireless is taking a transitional step by relying
on voice over ATM, which Dougherty said does have QoS and is amenable to moving
from time-division multiplexing to ATM.
From SS7 to IP
“Our strategy right now is focused on how we can take connection control and service
control that is SS7-oriented and move it to IP,” Dougherty said. “We have implemented
some level of IP orientation around our connection service control for mobility and
wireless extension. We are moving that into the virtual circuit arena of ATM and applying
IP to it so that our connection and service controllers are all interfaced over TCP/IP, so it is
an IP orientation around service and connection control. In migrating our SS7 network to
our wireless private packet network, which is an ATM-based IP orientation, we integrated
Tekelec SS7/IP gateways into our network-migration strategy. These gateways take SS7,
TCAP and IS-41, and MPTL3 and encapsulate them into the IP realm through methods
co-developed with Tekelec. That gives us much faster connection and service control than
the SS7 could ever imagine.”
US West Wireless is relying on software-definable, multiservice programmable switches to
bring its network vision to reality. Dougherty said programmable switches are the future
because they operate on the premise of AETF and ITU standard open operating,
development and application program interfaces, giving the carrier the option to seek
product solutions within the open market and limiting the liabilities of traditional telephony
supplier solutions.
US West Wireless is working with the only supplier it could find in the country that makes
a programmable switch that can meet the RFC and NEBS requirements and can help it
gracefully transition its enhanced integration services from embedded legacy switching
and service infrastructure to one of multiser-vices. These particular switches are built on a
common buss-back-plain architecture that interleaves TDM, ATM and IP packet switching
under the control of an independent connection and service controllers using open
application interfaces and service control protocols.
“These switches do not classify as ‘soft switches,' which are based on switched virtual
circuit logic,” Dougherty said. These programmable switches have DSP qualities and NEBS
reliability characteristics of the time/space mechanical switches of the past. Although they
are oriented around the DSP technologies, call connections can be set up with path
integrity and redundancy in the DSP fabric where a logic or transaction failure will drop a
call in progress.
“Common buss back plains in a multiservice programmable switching platform will provide
what it takes to deliver the abstraction techniques needed to deliver a VoIP call origination
to a traditional TDM switching infrastructure,” Dougherty added.
Comments? Write to rhonda_wickham@intertec.com.
IP-Based GSM Solution
Are programmable switches the wave of the future?
Steve Chen, Tecore vice president of marketing, said current switches are designed for a
particular function: landline, wireless, data, etc. In the not-too-distant future, the industry
will see one generic type of switch that will switch packet-based traffic, whether it is voice,
data, video or wireless, regardless of the application or protocol. (Tecore is not US West's
vendor.)
“The difference would be the type of software that is running on it,” he said. “It will
happen sooner than we think.”
Next-generation switching architecture is ideally suited for new companies because they
can minimize capital investment and get the most flexibility out of it, he added.
Tecore recently unveiled its AirCore Mobility Server and AirCore Mobility Gateway for
IP-based GSM applications in corporate networks. The switching solution provides
integration between IP-based corporate GSM networks and traditional circuit-switched
GSM networks. This multi-service switching platform is driven by software applications
and is built on top of a standard hardware platform.
The mobility server includes software applications for standard network elements, such as
MSC, HLR, VLR, authentication center, equipment identity register, and the operation and
maintenance center. The server provides an interface to base-station subsystem equipment
and allows end users to access and modify their service profiles through Internet access.
The gateway provides interface to multiple servers via an IP interface for voice and SS7
traffic. The gateway converts IP traffic into traditional circuit-switched interfaces including
C7 ISUP and ISDN PRI (Primary Rate Interface in ISDN), as well as GSM MAP for seamless
integration with existing GSM networks and public-switched telephone networks.
“The gateway takes all the voice traffic and signaling traffic over IP and converts it to the
traditional circuit-switched traffic,” Chen said. “So the gateway on the one end will
connect through IP to our servers, and the other end will connect via circuit-switched
signaling traffic to the existing PSTN network and the GSM network.”
Chen said there is a big push for corporate in-building types of applications for two
reasons: One is the move toward 3G; the other is the convergence of telecommunications
and computer networks.
“The application and the product will all be broadband-based, which of course is ideally
suited for the corporate environment,” he said.
The AirCore platform is designed to simultaneously support multiple wireless protocols
including GSM, CDMA, TDMA and AMPS, as well as an integrated prepaid solution.
“At some point in the future, all of these technologies will converge with 3G,” he said.
“The challenge right now is how do we get there from here? We see this as one of the
stepping stones toward that direction.”
Intelligent Network Honored
US West Wireless' work in IN applications was honored with a 2-part award at Telecom 99
in Geneva.
The company was cited for innovation in its total service portfolio, designed to simplify
the customer experience, which includes its One Number Service as well as one mailbox,
one bill, and the same look and feel as traditional wireline service. The Financial Times
Global Telecoms Award also noted the company's “best use of enhanced integrated
network solutions.”
“Our customers have told us they enjoy the freedom and mobility of wireless,” said Peter
Mannetti, US West Wireless president. “But they also want the convenience and
simplicity of having it all with one number — the same number as their home or office
phone. So our engineers made it happen.” Mannetti also acknowledged the involvement of
vendors Alcatel, Ericsson and Tekelec.
Wireless Reivew |
