Evolving Wireless Data Nets To Support
BY RAVI RAVISHANKAR
This column, which looks at evolving the packet-switched domain to
deliver voice and multimedia services, is the second in a three-part series
that explores the evolution of the wireless network.
An inherent limitation of the circuit-switched, wireless network is its
inability to efficiently deliver high-speed data services. This limitation
has spurred the development of overlay packet-switched (PS) data networks
like general packet radio service (GPRS) to deliver data applications. The
PS overlays are best suited for ï¿½burstyï¿½ data services like e-mail and
mobile Internet browsing. However, they will require further evolution to
deliver fully integrated voice and multimedia services.
This evolution likely will occur in several phases. From a service
perspective, the first phase, known as 2.5G, will add support for wireless
data such as WAP and wireless Web browsing. The second phase will expand to
include voice support. From a network implementation perspective, 2.5G will
include the deployment of an overlay core network. This phase will require
minimum modification to the existing 2G radio access infrastructure and will
reuse the spectrum that is already available to 2G operators. The second
phase will require deploying a completely new 3G radio access network (RAN)
architecture, which moves packet-switched technology to the edge of the
network. The 3G RAN will also provide increased bandwidth to the edge
devices utilizing new spectrum. In all these cases, new handsets will be
required to access the wireless data service.
GETTING TO THE CORE
GPRS is the most popular core network technology being deployed to
support wireless data. GPRS serving nodes (GSN) are the heart of the
packet-switched fabric; they are comparable to the mobile switching center (MSC)/visitorsï¿½
location register (VLR) in todayï¿½s circuit-switched, wireless network.
Serving GSN (SGSN) nodes support mobility management functions such as
registration of the mobile devices to the network and roaming. A backbone IP
network known as the GPRS core provides packet transport between the GSN
nodes. The gateway GSN (GGSN) acts as a doorway between the GPRS core IP
network and external data networks such as the Internet or an intranet. The
overlay GPRS network uses SS7 signaling to interact with 2G GSM network
elements. The 2G GSM signaling network provides most of the signaling
required for GPRS.
The 2G radio access network interfaces to the SGSN using the
frame-relay-based gigabit interface, which is defined in GSM specifications.
As 3G RANs are deployed, a new interface defined by 3GPP, IU-PS, is required
from 3G RAN to the SGSN.
The wireless network is evolving along a path that is similar to that of
wireline networks. Like digital subscriber lines and cable in the wireline
world, GPRS provides ï¿½always onï¿½ access to the network with data rates
that are higher than those achievable with dial access services. Though the
initial driver for these alternate, high-speed access technologies is data,
it is clear that voice still remains the ï¿½killer app.ï¿½ The rate of
penetration of mobile phones in developed and developing countries is clear
proof of this. Providing traditional voice services using a GPRS data
backbone is as important as utilizing packet transmission in traditional GSM
GPRS provides a ï¿½content-neutral data pipeï¿½ between any two data
devices, where at least one is a wireless device. Supporting voice as
another form of data becomes a natural extension of the GPRS network.
However, there are real challenges in the actual implementation ï¿½
providing seamless roaming between 3G network and 2G networks, establishing
peering arrangements needed for GPRS roaming between carriers, and providing
service transparency between 2G and 3G voice. And, bridging the PSTN
paradigm to the Internet paradigm also presents challenges. It should be
possible for subscribers to make voice calls to a PSTN-like phone number,
URL address, or an e-mail-like address with total transparency. In some
cases, using a PSTN signaling protocol such as SS7 may be the appropriate
technology to provide service transparency with 2G. Other cases may require
using an Internet-based protocol such as session initiation protocol (SIP)
to take advantage of the Internet-style services. This requires a new
network entity ï¿½ a signaling router ï¿½ that can provide the protocol and
address mediation and find the service and route to the service with total
transparency to the bearer network.
ENHANCED SERVICE CREATION
Wireless operators have made a huge investment for 3G spectrum. Neither
voice or data services alone can guarantee a profitable return on this
investment. Operators are looking at developing a new breed of multimedia
services to drive revenues and profitability to offset the expenditure.
These services will emerge from the true convergence of voice and data with
enhancements from wireless-specific services such as location-based service.
True service revolution can only be achieved when a significant number of
third-party application providers and content providers can independently
develop services, which can then be delivered to the end subscriber using
carriers networks as a distribution channel. An open service creation
environment is critical to create this value chain of carriers, application
service providers, and the content providers. The 3GPP open service
architecture (OSA) is an attempt to migrate in this direction, though it is
too premature to call it a success.
It is a challenging time for the entire communications industry.
However, wireless carriers have an advantage ï¿½ they can benefit from the
experiences gained in the VoIP revolution that has already begun in the
wireline segment. The new breed of VoIP-based services deployed and proven
in the enterprise wireline segments will become the cornerstone for
next-generation wireless network services. c
Mr. Ravi Ravishankar is director, Advanced Technology Planning,
Tekelec. His focus is on defining signaling solutions and products for the
next-generation packet telephony and 3G wireless networks. Tekelec is a
leading developer of telecommunications signaling infrastructure,
softswitches, testing and diagnostic solutions, and service applications.
Please visit their Web site at www.tekelec.com.
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