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Chapter 33
Overview of Virtual Private Networks

Nathan J. Muller

Virtual private networks — carrier-provided networks that function like private networks — are an increasingly attractive alternative for obtaining private network functionality without the overhead associated with acquiring and managing dedicated private lines. Understanding the features and business benefits of VPNs and their access options is the first step in implementing this cost-effective method of transporting voice and data traffic across regional, national, and international locations.

INTRODUCTION

Carrier-provided networks that function like private networks are referred to as VPNs. By relying more on VPNs, corporations minimize the operating costs and staffing requirements associated with private networks. In addition, they gain the advantages of dealing with a single carrier instead of with the multiple carriers and vendors required for a typical private network. This relieves organizations of the costs associated with staffing, maintenance, and inventory without sacrificing control, service quality, and configuration flexibility.

AT&T introduced the first VPN service in 1985. Its SDN was offered as an inexpensive alternative to private lines. Since then, VPNs have added more functionality and expanded globally. Today, the Big Three carriers — AT&T (SDN), MCI (Vnet), and Sprint (VPN Service) — each offer virtual private networks. In the case of AT&T, various services — including high-speed data and cellular calls — may be combined under one service umbrella, expanding opportunities for cost savings within a single discount plan.

THE VPN CONCEPT

VPNs let users create their own private networks by drawing on the intelligence embedded in the carrier’s network. This intelligence is actually derived from software programs residing in various switch points throughout the network. Services and features are defined in software, giving users greater flexibility in configuring their networks than is possible with hardware-based services. In fact, an entire network can be reconfigured by changing a few parameters in a network database.

The intelligence inherent in virtual private networks lets network managers control many operating parameters and features within their communications environments. For example, the flexible-routing feature allows the network manager to reroute calls to alternate locations when a node experiences an outage or peak-hour traffic congestion. This feature is also used to extend customer service business hours across multiple time zones. The location-screening feature lets network managers define a list of numbers that cannot be called from a given VPN location. This helps contain call costs by disallowing certain types of outbound calls.

Originating call screening is a feature that gives network managers the means to create caller groups and screening groups. Caller groups identify individual users who have similar call restrictions, and screening groups identify particular telephone numbers that are allowed or blocked for each caller. Time intervals are also used as a call-screening mechanism, allowing or blocking calls according to time-of-day and day-of-week parameters.

With a feature called NNX sharing, VPN customers reuse NNXs (i.e., exchange numbers) at different network locations to set up their seven-digit on-net numbering plans. This provides dialing consistency across multiple corporate locations. Another feature, partitioned database management, lets corporations add subsidiaries to the VPN network while providing for flexible, autonomous management when required by the subsidiaries to address local needs. The VPN can even transparently interface with the company’s private network or with the private network of a strategic partner. In this case, the VPN caller is not aware that the dialed number is a VPN or private network location, because the numbering plan is uniform across both networks.

VPNs provide several other useful features, including ANI data, which is matched to information in a database containing the computer and telecommunications assets assigned to each employee, for example. When a call comes through to the corporate help desk, the ANI data is sent to a host, where it is matched with the employee’s file. The help desk operator then has all relevant data available immediately to assist the caller in resolving the problem.

MAKING THE BUSINESS CASE FOR VPNs

An increasing number of companies are finding virtual private networks to be a practical alternative method for obtaining private network functionality without the overhead associated with acquiring and managing dedicated private lines. There are several other advantages to opting for a virtual private network, including:

  The ability to assign access codes and corresponding class-of-service restrictions to users; these codes are used for internal billing, to limit the potential for misuse of the telecommunications system, and to facilitate overall communications management.
  The ability to consolidate billing, resulting in only one bill for the entire network.
  The ability to tie small remote locations to the corporate network economically, instead of using expensive dial-up facilities.
  The ability to meet a variety of needs (e.g., switched voice and data, travel cards, toll-free service, and international and cellular calls) using a single carrier.
  The availability of a variety of access methods, including switched and dedicated access, 700 and 800 dial access, and remote calling card access.
  The availability of digit translation capabilities that permit corporations to build global networks using a single carrier. Digit translation services perform seven-to-10-digit, 10-to-seven-digit, and seven-to-seven-digit translations and convert domestic telephone numbers to IDDD numbers through 10-to-IDDD and seven-to-IDDD translation.
  The ability to have the carrier monitor network performance and reroute around failures and points of congestion.
  The ability to have the carrier control network maintenance and management, reducing the need for high-priced in-house technical personnel, diagnostic tools, and spares inventory.
  The ability to configure the network flexibly, through on-site management terminals that enable users to meet bandwidth application needs and control costs.
  The ability to access enhanced transmission facilities, with speeds ranging from 56K bps to 384K and 1.536M bps, and plan for emerging broadband services.
  The ability to combine network-services pricing typically based on distance and usage with pricing for other services to qualify for further volume discounts.
  The ability to customize dialing plans to streamline corporate operations. A dealership network, for example, assigns a unique four-digit code for the parts department. Then, to call any dealership across the country to find a part, a user simply dials the telephone-number prefix of that location.


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