Adopting Open Systems And SS7 In Remote Access Environments.

It' s doubtful if even one forecaster in 1996 correctly foretold the incredible growth of the Internet. Every day, 8 billion email messages are sent. Traffic on the Internet doubles every 100 days. There are now 830 million pages on the Web. Underlying this enormous growth in demand is equally impressive growth in the telecommunications infrastructure and equipment required to support ISPs, the enterprise, and other carriers.

Today, ISPs must deliver optimum service with a system that can be rapidly scaled at the lowest possible cost per port. The newest Point-of-Presence (POP) offerings utilize "smart," open system platforms that leverage the equipment buyers' existing software, hardware, and human skill sets. The ISP's POP provides the dial-up interface between businesses, home subscribers and the Internet.

POPs consist of eight major components (Figure 1): the RAS application, the base network software, system utilities, the operating system, PSTN (public switched telephone system)/modem pools, network and I/O subsystems, CPU subsystem and a hardware platform. In the "proprietary" POPs offered by legacy RAS suppliers, these components are designed from the ground up, utilizing proprietary hardware and software that make them expensive to build, maintain and support.

The newer "smart" POPs, by contrast, utilize Linux and Windows NT PCs, which provide most of the baseline hardware and software functionality needed to configure a POP, including the CPU, operating system, utilities, network software, remote access services, and basic I/O. In fact, the POP designer need only provide the RAS application software and PSTN interface. Turning an existing Linux or Windows NT server into a "smart" dial-up 56K/ISDN POP can be as simple as plugging in a high-density PCI card.

Because "smart" POPs utilize off-the-shelf components, they leverage economies of scale and industry familiarity that make them less expensive to build, operate and maintain. Smart POPs also reduce cost by providing added intelligence that can be used to integrate functions like authentication, DNS, and caching, functions that require dedicated servers in networks based on "dumb" POPs.

Processing Calls: Proprietary vs. Open Systems

Apart from reducing costs, the added intelligence provided by smart POPs can be used to enhance network efficiency, improve responsiveness, and reduce operating cost. When a subscriber request is received by a proprietary POP, the call is routed via backhaul lines to the ISP's Network Operations Center (the NOC) which performs the other classic technical functions of an ISP (Figure 2); domain name server, authentication, security, accounting, web cache, email, and ultimately connection to the Internet. Once processed at the NOC, the system signals back through the POP to the user's computer, satisfying the subscriber's request.

Smart POPs boost performance and enhance efficiency by handling subscriber authentication, DNS, and caching locally, thereby reducing communications between each POP and the NOC (Figure 3). According to studies performed by IC2000, a Florida ISP, this smart architecture improved initial customer connect times by as much as 2-3 seconds as compared to proprietary POP solutions.

Leveraging Software

In support of open system POP solutions, Microsoft has aggressively worked to enhance network functionality and lower overall network configuration cost. For example, the company has added powerful Routing and Remote Access Services (RRAS) functionality to the Windows NT server environment. NT and Linux systems also provide a plug-and-play platform for a host of other integrated and third party network access and ISP services, including client/server DNS and authentication, Multilink Point-to-Point protocol, automatic callback (to reduce subscriber toll charges), Virtual Private Network support, FTP, email, and web hosting support. All told, NT- and Linux-based network access platform provide savings at every step of purchase, installation, and operations cycle that can reduce total cost of ownership by as much as 50 percent.

When polled, ISPs who have implemented open system NT- or Linux-based RAS solutions cited the ability to avoid ongoing training costs as their number one cost-saving benefit. They also cited the fact that necessary skill sets in the labor pool were much more useable and affordable than trying to find staff suitably skilled in narrow proprietary systems. With an open systems approach, an ISP also avoids the ongoing staff training and certification necessary with proprietary systems.

Technical staff members can perform all installation, configuration, administration, troubleshooting, and ongoing maintenance procedures with familiar NT or Linux tools that they are already using. In fact, setting up a new open system is so simple that most new installations are up and the network administrator is set to run on the first day.

With ISPs seeking to meet escalating subscriber demands for connectivity, they must also consider ways to leverage existing hardware, especially PCs running either NT or Linux. With new open systems technology, an ISP can add up to 120 56K or ISDN ports to an existing NT or Linux server with a single PCI card. Moreover, the ISP can implement this system using even a low-end PC as a remote access server. Studies have shown that Windows NT RAS software utilizes less than 3 percent of a 90MHz Pentium processor when a PC card containing 24 modems and ISDN terminal adapters is plugged directly into the PC server. The number drops to just 2 percent for a 133 MHz Pentium server and drops even further for higher-speed processors.

An enterprising ISP could thus take an older PC server that has become inefficient for handling larger network database applications, insert network access card, and turn the PC into a smart POP that can handle up to 120 remote access sessions per server. To handle burgeoning demand, an ISP with a proprietary stand-alone POP solution doesn't have much flexibility in terms of adding capacity or functionality. However, the open systems approach provides an excellent roadmap to growth. For example, by combining seven RAS servers with a master server and an M1/3 multiplexer with DSX-1 and DS3 redundancy, ISPs can deploy 672 ports and upgrade to a T3 line.

New SS7 Signaling Technology

Open systems network access combined with newly-implemented SS7 capabilities have begun to open up new performance and cost advantages for carriers and ISPs. The new SS7 capabilities installed on an open server offer carriers the opportunity to handle more Internet traffic without tying up critical class 5 switches on the PSTN. Class 5 switches were originally designed to handle 3 minute holding time voice calls, not long-hold-time Internet calls. Until now, most carriers have delivered subscriber calls to ISPs via T1/PRI lines provisioned from the nearest class 5 switch. Deploying a class 5 switch in this way uses the PSTN inefficiently and requires large capital expenses.

Using these new SS7 capabilities, carriers and ISPs can redefine the way they provide dial-up Internet access. The SS7-enabled network access system bypasses the end office class 5 switch by enabling carriers to connect ISPs to the PSTN using SS7 signaling and Inter Machine Trunks (IMTs) rather than PRIs. This approach frees voice ports and enables carriers to expand their ISP business without purchasing new switches. The net result is substantial capital savings and better utilization of network infrastructure.

A class 5 switch connects to the PSTN via SS7 A-Links for signaling and call control and IMTs for receiving the actual voice information. The new generation remote access equipment consists of an SS7 signaling gateway (SSG) and a network access server. The combination of SSG and NAS provides a class 5-equivalent function. The NAS is a Linux PCI or CompactPCI chassis equipped with remote access controllers. The NAS supports V.90 and ISDN dial-up sessions received from the PSTN over Inter Machine Trunks (IMTs, lines with no signaling). The SSG interfaces with the SS7 network, terminates the call, and provides the required call control and signaling to the NAS to enable the use of IMTs.

On the telco side, implementation of new SS7 Signaling Gateways (SSG) provides an Internet connection alternative to class 5 switches that runs on a much lower cost telco grade server. The SSG can handle 115 calls per second or 414,000 BHCAs (Busy Hour Call Attempts), allowing it to support up to 10,752 ports. The SSG can also support multiple SSP (Service Switching Point) terminations defined in a compilable call database and a variety of physical interfaces including V.35, RS499, RS450, and T1/E1.

Using the SS7 route set capability allows an open RA solution to provide load balancing across multiple sites to eliminate busy signals and reduce capital and operational costs. Consider a service provider with multiple POPs dispersed over a wide geographical area. If all ports are occupied at one POP, additional user calls can be rerouted automatically to another POP with available ports. This is particularly attractive in situations where various POPs experience peak loads at different times. This provides better service to the end customer by providing a connection rather than a busy signal, and a capital savings for the provider since no single POP needs to be fully provisioned with ports for peak loads. Because the SSG communicates with the NAS over an IP-based LAN or WAN, this allows the ISP and the telco to either co-locate units at the same facility or distribute them over multiple locations. For example, carriers can now locate multiple NAS units in each central office (CO) controlled by a single SS G. In this configuration, carriers can pick up incoming calls at the originating switch and bypass not only the end office switch, but also the rest of the circuit switched network.

The ongoing explosive growth of the Internet initially spurred infrastructure equipment providers to develop proprietary stand-alone RAS boxes. As with other parts of the computer industry, forward thinking designers realized that many standard computer functions were being needlessly and expensively duplicated in proprietary solutions.

The newest POP platforms utilize standard Linux and NT servers equipped with PCI plug-in network access cards. Because network access support requires only a tiny fraction of CPUs' resources, ISPs can add intelligence to their POP and dramatically improve subscriber response times for such functions as authentication and DNS.

The open systems approach also provides dramatic cost savings, cutting per-port costs in half. Additional cost savings can be achieved in the NOC by consolidating functions like authentication, DNS, web caching, web serving, and email; functions that require multiple servers in NOCs that utilize dedicated remote access servers. And even greater cost savings can be achieved by combining open network access systems with SS7 gate-ways, which enable carrier and ISP/CLECs to offer Internet access without having to purchase Class 5 switches.

Nathan Guedalia is a senior product manager at Ariel Corp. (Cranbury, NJ).

Fig 1
RAS Components Open Systems vs. Proprietary
 Open Systems          RAS Component         Proprietary
 RAS Specific         RAS Application          CUSTOM
 Windows NT or     Base Network Software
   Linux or-          System Utilities
                      Operating System
 RAS Specific        PSTN & Modem Pools
  Completely     Network and I/O Subsystems
Standard PCI or       CPU subsystem(s)
  Compact PCI        Hardware Platform
    Servers
Open system RAS solutions only address the RAS specific components
of the system. This reduces costs, optimizes use of existing servers,
and leverages widely available employee skill sets. ISP also gains
flexibility to configure software and hardware to subscriber
requirements.