Giving the Signal SS7 Addresses Growth in IP
If you ask large Internet service provider (ISP)
network engineering managers or regional Bell
operating company (RBOC) network
provisioning managers to make a list of their
greatest short-term challenges, close to the top
will be two things: dealing with congestion on
the local exchange carrier (LEC) end-office
switches and the shortage of integrated services digital network (ISDN)
primary rate interface (PRI) ports on these same switches.
So with the red-hot growth of the Internet, ISPs and LECs are focusing
on how to evolve the circuit-switched-to-Internet protocol (IP) network
interconnects to better deal with the challenges of high volume. Traditional
interconnects to the Internet and to private IP networks are designed as
user-to-network interconnects, which use protocols such as PRI, basic
rate interface (BRI) and communications applications specification
(CAS), depending on their size and geographic location. These
user-to-network interconnects are restricted in their scale and functional
capabilities when compared to circuit-switched network-to-network
interconnects, which use signaling system 7 (SS7)/C7 protocols.
If you ask ISP and next-generation carriers about their mid- to
longer-term challenges, most will be focused on building new networks or
migrating their existing networks to full-service packet telephony to stay
ahead of the "convergence" curve. IP network operators already are
installing the first generation of voice over IP (VoIP) packet telephony
networks and planning for the migration to new world networks with a
goal of higher levels of voice quality, larger network scale and the
deployment of new-world services.
SS7 interfaces for IP network access servers improve network scale and
make it possible for IP networks to inter- connect with circuit-switched
networks on a peer-to-peer level for the first time. Moreover, the new
architectures enable the addition of next-generation services by giving IP
networks new levels of call control and service control.
All types of networks, including asynchronous transfer mode (ATM), time
division multiplexing (TDM) and IP, manage their interconnections using
large-scale devices that accommodate substantial volume. But the
interconnection of unlike networks, specifically IP and circuit-switched
networks, has evolved to user-to-network interconnect protocols such as
PRI, BRI and CAS. These protocols made sense for the smaller-scale
networks that have been developed, but they are inadequate for coping
with the larger-scale and multiservice networks of today.
An ideal way to increase the scalability of IP-to-circuit-switched network
interconnects and solve the congestion problem with end offices is to
migrate large IP points of presence (POPs) to an SS7 interconnect. SS7
interconnects allow IP networks to interconnect as either an end point or
in a fully meshed configuration. The IP POP then looks to the
circuit-switched network like a switch. This brings IP-to-circuit-switched
network connects up to a peer-to-peer level, matching the interconnect
architectures used in circuit-switched-to- circuit-switched networks
today.
Defining SS7
CCIT SS7 is known by this name in the United States; in most of the rest
of the world, it's called C7. SS7 is the large-scale signaling protocol used
in carrier networks to manage the core of the network and the
interconnects between today's carrier networks. SS7 is deployed in
varying configurations around the world, including fully associated and
quasi-associated configurations, as well as nonassociated configurations in
which the SS7 network physically is separated from the bearer networks.
The most important points to understand are that SS7 provides
substantially larger scales, thousands of DS-0s per link instead of the
24B+D T1 PRI and increased reliability through link set redundancy,
signaling route redundancy and other features. This increase in scale and
in reliability offers substantial benefits to the IP network operator.
SS7 interconnects have been protected heavily by carriers in the past. For
example, PTTs only would provide C7/SS7 interconnects on their
international interconnects. The opening of markets to competition in the
United States, Europe, Asia and the rest of the world has expanded the
SS7 interconnects, which now, in most cases, are fully regulated
interconnects.
This regulation has opened up market opportunities. Competitive LECs
(CLECs) in the United States can take advantage of SS7 interconnects
once they become licensed carriers. The cost of the interconnect is
regulated to ensure that new carriers can compete successfully. This
typically results in substantially lower costs for SS7 interconnects when
compared to PRIs.
For voice telephony, a critical component to being able to offer public
network services as opposed to private managed networks is to provide
switched access and egress to that network. This allows a user to call
from anywhere to anywhere--not just on-net. SS7 interconnects facilitate
equal access to the network from the public switched telephone network
(PSTN).
In 1998, several access-device manufacturers introduced the first
generation of SS7-enabled access ser vers. This technology is being
tested and deployed today by IP network operators worldwide. The
optimum configuration for SS7 access servers is to manage the SS7 on a
server that is physically separate from the access servers themselves. This
allows the SS7 server to manage the SS7 lin ks on the interconnect side
and the multiple access servers on the termination side.
Conservation and Revenue Creation
Without SS7, CLECs must install a full TDM switch (Class 5 for local
service in the United States) in every market before they can begin to
offer services. In markets where they would prefer to offer only IP
network services, but would like to take advantage of their SS7
interconnect rates, dial plans and the like, they traditionally had to install a
full switch and access servers. The high cost of switch deployment,
running into the millions of dollars, often makes new market entrance
cost-prohibitive.
With SS7 interconnects on their access servers, IP networks now can be
extended into new markets, while using the advantages of their carrier
network interconnects, at a substantially lower cost. Lower-cost market
entrance expands an IP carrier's addressable market and increases its
opportunities to achieve high-revenue growth targets. SS7 interconnects
lower both capital and operating costs to a service provider.
An SS7-enabled access server installation is substantially less expensive
than using a circuit-switch and access-server combination to terminate dial
traffic. For each digital signal Level 0 (DS-0) terminated on an access
server via SS7, the carrier saves two DS-0 ports (originating and
terminating) on a switch. This reduces the capital cost of deploying or
extending network POPs. Regulated SS7 interconnects usually are less
expensive than the same-sized PRI connects. This translates into reduced
operating cost to the IP network operator.
SS7 enables IP network operators to mesh their IP and circuit-switch
networks, bypassing completely or adding new routes around the
congested end office. This achieves two key results: It removes a major
point of congestion from their network routing; and it adds multiple routes
to the IP network POP, providing greater flexibility in routing during
busy-hour or network- trouble conditions.
By relieving the end-office switch bottleneck, the service provider
experiences fewer cases of congestion and, as a result, returns fewer busy
signals to its customers. This increased quality of service (QoS) improves
customer retention and can be positioned as a key differentiator to the
market. This becomes increasingly important as the cost of Internet
access declines and ISPs begin to use QoS to pro- vide differentiated
service options to their customers.
SS7 trunk groups are substantially larger than PRI hunt groups, offering
larger resource options for call termination. Moreover, in virtual private
data network (VPDN) configurations, IP network operators can
configure geographically diverse POPs, further reducing the incidence of
congestion, increasing QoS and reducing net-work costs.
Tipping the Scales
SS7 interconnects dramatically increase the scalability of VoIP networks.
In today's evolving VoIP market, carriers are focused on three areas of
development: voice quality, network scalability and service rollout. The
migration to a network-to-network interconnect, and the scale that comes
with it, gives IP network operators the ability to manage the substantial
scale required for full-scale switched-access and egress interconnects
critical for full-service voice networks.
Moreover, the signaling server in the SS7 configuration provides basic
call-control functions for the gateway. The expansion of this call-control
capability means that IP network operators can manage services and
routing functions from the IP POP. By adding intelligent network
(IN)/advanced IN (AIN) interfaces, the signaling server/access server
combination permits intelligent network services to be applied at the
gateway. With the addition of LNP (local number portability), the IP
gateway is able to support LNP; this is key for local deployment of
packet telephony networks. This service capability enables the
development of next-generation services such as web-integrated 800,
unified messaging and others.
Speaking the Same Language
SS7 protocols vary in every country in the world and across equipment
manufacturers and carrier networks. Additionally, standards bodies such
as European Telecommunications Stand-ards Institute (ETSI) and
American National Standards Institute (ANSI) are constantly evolving
protocols to support new capability and to deliver new functionality. Any
carrier looking to provide international services needs an SS7 architecture
that easily can support worldwide protocol variants. Moreover, all IP
network operators need a system that can be modified easily to support
protocols in which the implementation differs from the documentation, and
to adapt to changes in the standards. Finding a single system that is
flexible and programmable, so that carriers can deploy the same system in
all of the markets in which they operate, will greatly reduce network
operations' complexity and cost.
SS7 support for data traffic only is the first step on the road to
multiservice packet telephony networks. CLECs and service providers
need to be certain that their equipment vendor has a clear development
path to add voice capability and manage large-scale network
interconnects for switched access and egress. The vendor should be able
to clearly articulate how it will evolve the current architecture to provide
full switching and network features.
The vendor must be able to mange small-scale as well as large-scale
installations affordably. A primary weakness with today's circuit-switched
environment is the high cost of the first port. Today's competitive carriers
must be able to track their capital investment to the realization of revenue,
and they need solutions that are as affordable for 100 DS-0 ports as they
are for 100,000 ports.
Another essential component for managing the total capital cost of a
network is to ensure that the vendor's SS7 products are compatible with
their full line of carrier-access servers and that their product plans will
continue to offer reverse compatibility. Flexibility, in terms of being able to
operate with the full line of access servers, will allow the IP network
operator to protect past investments, scale each POP correctly and
optimize the deployment of functionality and services.
Innovators in the service provider market space are moving rapidly down
the path toward full convergence of voice and data networks. Migration
from user-to-network level interconnects to network-to-network
interconnects is critical for the successful deployment of these networks.
The introduction of SS7 capability on access servers for data traffic today
is the first step in this evolution. The change is happening in Internet time,
and the addition of voice capability, expansion of scale and the migration
to full service switching point (SSP) replacement will be realized in a very
short period of time. |
