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A Bridge For SS7
Offload To IP: Optimizing SS7 Between Now And The
All-IP Future
BY REG CABLE
[Go right to SS7
Signaling In Smart Linux POPs]
As carriers and equipment manufacturers focus on
integrating traditional telephony and packet-based
networks, some may be tempted to leapfrog today's
networking signaling infrastructure to that of the
all-IP networking future. But this is impractical both
for technical and economic reasons. What's needed is a
bridge to efficiently optimize Signaling System 7
(SS7) capabilities between now and then. Offloading
long-haul SS7 links to IP is a logical first step.
As either a cost-savings avenue for major carriers,
a way for CLECs to trim the need to lease SS7 links
from incumbents, or a technology shortcut for
newcomers, it now is possible to shift necessarily
redundant, dedicated SS7 links from traditional
dedicated networks to packet-based Internet protocol
shared-use networking. Doing this transparently to the
SS7 network eliminates the need to consume
increasingly scarce point codes and the attendant need
for troublesome network reconfiguration. And the shift
can be especially efficient in accommodating the need
for the burgeoning SS7 links requirements for rapidly
growing wireless services.
In fact, emerging SS7/IP signaling gateway
technology can enable both wireline and wireless
operators to offload the growing volume of
long-distance signaling traffic -- now carried over
expensive, dedicated, traditional SS7 links -- to
lower-cost, shared-use IP networks. While particularly
cost-effective for long-haul carriers, it also can
extend SS7 capabilities to geographic locations where
SS7 links are simply unavailable or economically
infeasible.
The Bridge
Since the 1970s, SS7 has defined procedures and
protocols by which public switched telephone network (PSTN)
elements exchange information, out of band, over a
digital signaling network to handle call setup,
billing, routing, and control. Obviously, such
critical signaling capabilities must be available to
callers using both the PSTN and emerging IP networks.
Through the use of emerging next-gen signaling
protocols, converging networks can use new signaling
products that can configure SS7 over IP, frame relay,
or other packet-switched networks with reliability
comparable to the performance of the PSTN.
While industry innovators continue to work to bring
the quality of voice over IP (VoIP) up to par with the
PSTN's quality of service (QoS), there no longer
should be any practical reason why the multitude of
signaling functions can't take both technical and
economic advantage of riding the IP rails. The newly
created Stream Control Transmission Protocol (SCTP)
standard developed by the Internet Engineering Task
Force now ensures the reliability of SS7 messages
routed over IP.
The SCTP's standard means the traditional
double-link redundancy of SS7 signaling on
circuit-switched networks can be matched in the IP
world. Reliability is ensured because SCTP inherently
enables message acknowledgement and retransmission
schemes that ensure message delivery to the remote end
and head-of-the-line priority message transmission. It
also enables support for multiple network-interface
controllers to allow end points to dynamically choose
the most reliable IP network for message transmission.
Signaling gateways adhering to the SCTP standard can
deliver the IP equivalent by using dual Ethernet
capabilities for multi-homing. This IP route to
reliability allows for connections to transfer
signaling messages to completely independent networks
simultaneously.
These developments set the stage for all ranks of
carriers to take advantage of both the economics and
the technology of IP for SS7 signaling.
Taking Advantage
It's a common claim in the industry that there has
been some $3 trillion invested in the existing PSTN
infrastructure, and there's no argument that
packet-based networking is less costly than
circuit-switched. In the meantime, major carriers are
looking for ways to control costs as the need for
SS7/IP signaling is set to multiply, to deal with the
technical nature of wireless communications that
demand SS7 signals every step of the way. From simply
turning communications devices on, to verifying user
accounts, to dealing with roaming -- the demand for
SS7/IP signaling for wireless is perhaps 10 times the
need of wireline calls.
The largest SS7 providers today are the
inter-exchange carriers (AT&T, MCI, Sprint) and
the former regional Bell operating companies (RBOCs).
These major carriers with big investments in their
networking infrastructure can keep legacy equipment in
place while offloading long-haul signaling to IP to
absorb expanding demand. Offloading SS7 signaling to
IP can significantly reduce growth costs for
provisioning SS7 links as these carriers consider
their eventual migration to IP networks somewhere in
the future.
Moving down the food chain, smaller CLECs or small
independent telcos without national coverage -- or
wireless providers just starting to grow nationwide
networks -- are looking to ease the need to lease
expensive (and bandwidth-hogging) SS7 links from the
majors. SCTP-compliant SS7/IP gateways can
significantly ease this leasing obligation by
provisioning SS7 needs transparently -- without the
need for network addresses or point codes.
Meantime, such new age SS7/IP gateways can fill the
gap in geographic areas where dedicated SS7 links don't
exist. For example, GSM roaming service enabler
Comfone AG uses them to give customers in remote
countries access to databases in Switzerland. Routing
such SS7 queries over IP means the carrier can offer
roaming capabilities in places where SS7 links
otherwise would not have been provisioned because
traffic could not economically justify them.
Moving Forward
The need for and use of SS7 is by no means in decline.
Moreover, the creation of unprecedented wireless
applications will guarantee its expansion. Industry
analysts at CIR estimate carriers will spend $1.8
billion this year on Advanced Intelligent Networks (AIN
hardware and software, primarily SS7-related).
While packet telephony networks are expected to
generate about a billion dollars a year by 2002, those
numbers are dwarfed by the current $650 billion-plus
in revenues being generated on the circuit-switched
networks of the globe. And while much of that business
is built on networks supported by long-haul SS7 links,
we can expect a cautious but important trend to
rolling out of "bridging" technology that will
offload increasing portions of that traffic onto IP.
Reg Cable is vice president of the Signaling
Systems Group of Performance
Technologies.
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