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Exploding Signaling Demands? Move SS7 To IP
And Conserve STP Ports
BY REG CABLE
With bandwidth far less scarce than it once was, the networking world
now would be prudent to focus some attention on the ongoing explosion in
signaling obligations with a view to both reducing the number of SS7 links
needed and conserving scarce STP link ports. To accomplish this, SS7
signaling traffic can be efficiently shifted onto lower-cost IP-based
networks and concentrated onto fewer, highly utilized signaling links.
By doing so, intelligent new SS7 transport and routing products can
dramatically save network costs. Service providers leasing SS7 links can
virtually eliminate per-mile-per-link fees and reduce STP port charges for
SS7 connections. And carriers can avoid the curse of prematurely needing
to buy expensive new STP hardware to add link ports. Network designers can
even get new tools for architecting more efficient IP-based signaling
networks of the future.
Mushrooming SS7 applications --including call display, caller-ID,
wireless roaming, and short messaging service -- are contributing to an
overall double-digit annual growth for SS7 signaling needs. New SS7
technologies can provide a cost-effective (particularly for long-haul
traffic) option of offloading out-of-band signaling to more efficient and
lower-cost IP networks while retaining the high reliability that is
required in traditional SS7 networks. They can also free up STP connection
ports by concentrating traffic onto fewer SS7 links.
OFFLOADING TO IP
Signaling traffic for voice telephony is transported, routed, and
housed in the SS7 network on heavily utilized facilities generally owned
by inter-exchange carriers, RBOCs, and wireless carriers. SS7 links that
originate and terminate at the edge of the PSTN transport signaling
messages over dedicated 56 Kbps circuits with relatively low SS7 traffic
utilization. Using new SS7/IP network interworking technology, wireline
and wireless operators can offload volumes of long-distance signaling
traffic, now carried over redundant SS7 links, to shared-use IP networks
-- which are far less expensive to use.
This new transition technology -- bridging the PSTN's circuit-switched
world and the packet-switched IP realm -- is particularly efficient as an
SS7-link alternative for fast-growing worldwide wireless services.
Wireless networks can require up to 10 times the SS7 signaling traffic as
wireline networks because it is needed for activating communications
devices, verifying call accounts, and accommodating each roaming jump.
This new technology also can provide SS7 signaling in locations where SS7
links now are either nonexistent or economically prohibitive.
RELIABLE TRANSPORT
Such intelligent network devices ensure reliability of SS7 messages
routed over IP by employing the new Stream Control Transmission Protocol (SCTP)
which matches the double-link redundancy of SS7 signaling in the
circuit-switched network. SCTP insures message acknowledgement and
retransmission schemes, delivering messages to the remote end with
head-of-the-line priority transmission. SCTP provides network-level fault
tolerance through support of dual-Ethernet multi-homing and
multi-streaming capabilities that let connections simultaneously transfer
signaling messages to independent networks. This will route more reliably
than using standard TCP over IP. It also supports multiple network
interface controllers so that end points can dynamically pick the most
reliable IP network route for transmission.
The efficiency of an entire SS7 network declines and network management
becomes much more complex as more SS7 links are added because redundant
links in the traditional PSTN going to different locations add no
direct-link value. Reliably offloading SS7 signaling to IP, however, can
serve as a bridge for major carriers planning eventual migration to IP
networks, but committed to amortizing significant investments in their
circuit-based infrastructure. It can help absorb exploding demand for SS7
links -- the growth of which is becoming increasingly difficult to
forecast -- and cut the swelling cost of provisioning new links.
The typical service provider leasing SS7 circuits is probably paying
about one dollar per mile, per link, per month for SS7 links, which could
swell to $10 per mile for international coverage. Using an intelligent
signaling device at the edge to reliably run that traffic over IP can
eliminate these leasing costs. Such providers, of course, still will face
connection charges (anywhere from $300 to $1,000 per port, per month) for
a node on the carrier's STP. It is the finite capacity of those costly
STPs in the face of the mushrooming of SS7 traffic that haunts service
providers, carriers, and SS7-link wholesalers alike. Saving money on STP
ports is the second part of this equation.
CONCENTRATING LINKS
With growing numbers of SS7 links being terminated on the SS7 network,
core devices like STPs or HLRs (Home Location Registers) grow in size and
complexity. They also must support faster processing speeds simply to
manage the load. Because of the traditional, redundant architecture, they
also become increasingly less efficient because of the need to connect to
an array of other devices in the network, and each augmentation needs a
reconfiguration of the network with its attendant increased
network-management cost.
Because current network STPs are designed to only handle a finite (but
large) number of SS7 links, STP exhaust is the curse of the network
planner. Carriers always look to efficiently add STP ports, but the last
thing they want is to add a new multi-million dollar STP. The network
planner's dilemma stems from the need to buy a new STP because the last
port added broke the camel's back (it may not be "the weakest
link," but would certainly be the most expensive). Intelligent
switching products that concentrate SS7 traffic onto fewer but more highly
utilized links can optimize port capacity. Depending on the signaling
application and its inherent overhead load, this technology can
significantly reduce the number of SS7 links (and related ports) needed. A
typical SS7 call control application may see a five-to-one reduction in
links from, for example, 80 links at the edge down to 16 links in the
core. In this example, you've saved the expense associated with 64 SS7
links: through an elimination of long-haul, mileage-based costs, and a
reduced requirement for 64 ports on the STP itself.
Some new age link concentrators also have general STP-routing
functionality and can route SS7 traffic (in essence, serving as a
"baby" STP). They can look at a message, for instance, and
determine it was destined for a database application, such as an HLR.
Routing directly to an HLR rather than via an existing STP can offer
significant advantages to a carrier in terms of reducing costs and
simplifying network configurations.
CONCLUSION
SS7 message transport is far outstripping the growth in voice traffic,
particularly with the multiplying of popular new wireless applications. In
the meantime, most carriers are planning for IP while preserving legacy
equipment. An efficient and reliable transition technology can save
link-leasing costs for providers, conserve STP capacity for carriers, and
provide a practical signaling platform for architects of next-generation
all-IP networks.
No self-respecting carrier with a huge investment in SS7 -- the most
reliable piece of their networking architecture -- is going to risk moving
into such new territory unless they feel confident of the reliability of
signaling transport in IP land. But with new, highly reliable technology
standards for routing SS7 over IP, a credible economic and
management-simplicity case can be made for it. Progressive carriers should
be exploring this option.
Reg Cable is general manager of Signaling Systems for Performance
Technologies.
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