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Feature Article
February 2003

Internet Offload Using A Packet-Based Architecture


Internet offload was one of the first applications to make the �softswitch� 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 �Internet Offload Using Packet-based Communications,� 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 today�s 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 CLEC�s 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 ISP�s Remote Access Server (RAS).

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.

Tandem Offload

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:

� The ingress switches are most likely owned by a different service provider than the egress switches or the intermediate Class 4 switches; and

� ISPs are beginning to outsource the management of RAS devices and Internet traffic.

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 today�s 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 optics.

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 softswitch-based networks.

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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