Long-distance virtual private networks

Long-distance virtual private networks
Some businesses transmit data and voice calls across their own private networks such as on a college campus. Because all of the lines on campus are owned and maintained by the college, the college does not have to pay monthly phone bills for these calls. When someone at the college calls someone off campus, the public-switched network is used, and this usage is itemized on a phone bill.

Few organizations can afford to build their own private network, but they can still have some of the benefits of a private network by using a virtual private network (VPN). VPNs use public telecommunications infrastructure, but the carriers often provide more secure, private connections than a normal phone call would experience.

VPNs are used more for data than for voice calls. In today’s market, long-distance carriers will propose to a large client that the carrier be allowed to handle both voice and data traffic. Numerous technical issues must be clarified with the carrier if data traffic is to flow across the VPN. My objective is to explain how long-distance voice calls are affected by a VPN configuration.

VPNs connect all of a customer’s major locations through the long distance carrier’s lines. A location with dedicated T-1 service is an on-network site, while a location with switched service is an off-network site.

Save money with tie lines

Numerous businesses connect their locations with dedicated phone lines so that their computers can transmit data files back and forth. Without a private line, the business would have to send the data across normal phone lines using modems on both ends. If the locations are not in the same LATA, each call will be billed by the minute on the long-distance bill. If the call volume grows significantly, at some point it is more cost effective to pay for a dedicated connection. Private line pricing is based on bandwidth and mileage. To calculate the break-even point, simply compare the cost of a private line to the current cost of the dial-up calls.

A not-so-new trend in long distance is to migrate the voice long-distance calls across the same dedicated connection, as long as the connection can spare the extra bandwidth for the voice calls. In this scenario, the dedicated line is called a tie trunk because it connects two PBXs.

For example, a manufacturer in Maine made frequent long-distance calls to its office in Vermont. The company eventually automated its assembly line and had to share computer data between the two locations. Initially, the computers dialed each other and sent the data across normal phone lines. This became very expensive because the computers were calling each other throughout the day.

The telecom manager decided to install a T-1 line between the two locations to carry both voice and data long-distance calls (see Figure 1). This measure dramatically reduced the company’s costs, but it did not stop there. The Maine location made a large number of intrastate long-distance calls to customers and suppliers within the state. Maine intrastate rates are the highest in the country. In fact, some international rates are cheaper than Maine intrastate rates even though the actual distance is much greater

Figure 1: Tie lines.

To reduce the cost of the Maine intrastate calling, the telecom manager programmed his PBX to route all Maine intrastate calls through the Vermont office first. In doing so, these calls would be billed at the low interstate rate instead of the higher Maine intrastate rate. The call delay for the added mileage is undetected by the end user, for it happens in milliseconds.

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