Internet Offload Using A Packet-Based
BY MICHAEL KHALILIAN
Internet offload was one of the first applications to make the ï¿½softswitchï¿½
a staple in the telecom dictionary. It was a way that a service provider
could address the increasing demands of Internet dialup customers and
protect its investment in the Public Switched Telephone Network (PSTN).
The following is an excerpt from a paper titled ï¿½Internet Offload Using
Packet-based Communications,ï¿½ created by the International Softswitch
Consortium to assist the industry in understanding the various types of
offload that are used and the benefits service providers can derive.
Typical Dial-Up Configuration
In todayï¿½s typical telecom network, each circuit switch must be
connected to every other switch creating a meshed-trunk architecture. As
the network grows, it becomes increasingly expensive and cumbersome to add
new switches. Consider a network with fifteen switches.
ISPs typically connect to the TDM switches (5ESS or DMS-100) using ISDN
PRI lines. Problems occur when an incumbent local exchange carrier (ILEC),
using the three or six leading digits (NPA or NPA-NXX) of a dialed number,
routes calls to the CLECï¿½s TDM switch. Because the ILEC does not use the
final four digits of the dialed number (XXXX), the CLEC switch is unable
to offload ISP dialup traffic from the TDM switch directly onto an SS7
enabled network access server (NAS). Thus are problems created by the rise
in Internet dial up traffic. The Class 5 switches that serve the ISPs get
hit with all of the traffic destined for that ISP, causing severe
congestion and requiring expensive upgrades to that switch.
Egress Switch Offload
Introducing a softswitch in such a network optimizes port utilization
by aggregating traffic and significantly reducing the number of trunk
ports required. Installing a trunking gateway and a softswitch in front of
the Class 5 switch at the egress central office alleviates this problem.
The trunking gateway intercepts the Internet traffic, and through a leased
T1 or PRI line, sends the traffic directly to the ISPï¿½s Remote Access
As ISP PRI terminations grow, the CLEC switches become increasingly
congested while handling the typically long dialup calls. The result is a
degraded quality of service that forces the CLEC to move PRIs to other
parts of the switch to balance the traffic load, or to buy additional
switching capacity. Service Providers are solving this problem by placing
a high-density, low-cost TDM switching fabric (gateway) between the ILEC
and CLEC TDM switches on the interconnecting trunk group. The gateway
terminates ISDN PRI interfaces and Inter-Machine Trunks (IMTs) under the
control of an SS7 enabled call agent.
In the traditional ISDN PRI-offload scenario, the SS7-IP gateway or the
multi-service intelligent switch receives the modem-generated Internet
traffic destined for Remote Access Servers (RASs) from the SS7 network,
switches and converts the InterMachine Trunks (IMTs) to ISDN PRI, and
terminates the session at the RASs at the ISP network. The RAS once again
requires ISDN PRI to get the user over to the PSTN.
This solution can be extended to divert Internet dial-up traffic off of
Class 4 switches as well. Now the trunking gateway appears to the ingress
Class 5 switches as a Class 4 switch, but is capable of routing the
Internet calls directly to the RAS, avoiding Class 4 congestion.
Ingress Switch Offload
The previous two solutions do nothing to divert Internet dial-up
traffic from the ingress Class 5 switches. While there are certainly not
as many Internet calls on these ingress switches, there are two compelling
reasons why an Internet call-diversion solution would be implemented at
this point in the network:
ï¿½ The ingress switches are most likely owned by a different service
provider than the egress switches or the intermediate Class 4 switches;
ï¿½ ISPs are beginning to outsource the management of RAS devices and
By installing an Internet call diversion solution, the service provider
that owns the ingress switches can capture some of that ISP business while
reducing the load on its Class 5 switches. One further benefit of the
deployment of an ingress switch offload solution is that it positions
service providers to place voice in packets as it enters the network,
providing an easy transition toward an all-packet voice network.
The main challenge for todayï¿½s telecommunications companies is
determining how to identify and deliver a winning business strategy that
is capable of sustaining growth and profitability, while remaining agile
and responsive to unprecedented levels of technological and environmental
change. Where competitive pressures apply, the effect is to reduce profit
margins as companies seek to generate additional revenue from greater
market share. In a competitive market, companies must continue to seek
ways of differentiating their products and services. Being the first to
market with new technology, improving process efficiency, and being able
to respond quickly to change are essential to securing market share and
delivering continuous growth and profitability to shareholders.
A distributed, softswitch-based architecture helps carriers succeed in
this environment by reducing costs, streamlining their networks,
simplifying administration, and maximizing resource utilization. The
separation of service logic, call control, and media transport enables the
interoperability of multi-vendor networks with both legacy telecom and
legacy data resources. A function at any one layer is truly independent of
the technology and vendor solution that may already exist in other layers.
Keys to successful softswitch architecture include multi-vendor support,
granular scalability to avoid over-provisioning of capacity, and
utilization of technological advancements to enable new services. It is
these attributes that a circuit-switched solution simply cannot replicate
and which will fuel the transition to packet technology and its benefits.
The International Softswitch Consortium (ISC) is the premiere forum for
the worldwide advancement of the next generation networks through
products, services, applications, and solutions utilizing packet-based
voice, data and video communications technologies available today via any
transport medium including but not limited to copper, broadband and fiber
The ISC establishes a common terminology for the softswitch-based
architecture, and it promotes interoperability, conducts research, and
liaises with governmental and industry organizations to address industry
issues that service providers and vendors face. By providing a variety of
educational seminars and by fostering the Open Network and Standard
Interfaces, the Consortium accelerates the advancement and usage of
The ISC membership includes wireline and wireless service providers and
carriers, governmental agencies, standards bodies, and equipment and
software vendors representing all network elements involved in the
softswitch-based and next generation network.
Michael Khalilian is the Chairman and President of the International
Softswitch Consortium. Please visit www.softswitch.org.
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2003 Table Of Contents ]