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WAN Technologies: Important Points of Interest, Part 3 of 3

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Concluding this three-part series on WAN technologies, Sean Wilkins, co-author of CCNA Routing and Switching 200-120 Network Simulator, Academic Edition, discusses how satellite, wireless data, and leased lines are used as part of a networking solution.
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Overview

Part 1 of this series focused on the original technologies for connecting to a wide area network (WAN) such as the Internet. Part 2 discussed the technologies that evolved next in the quest for faster access speed, both upstream and down. This article concludes this series by focusing on three additional connection technologies: satellite, wireless data, and leased lines.

Satellite

Satellite data connections are often used to replace other connection methods that are unavailable or very limited. Many individuals or organizations that would like to have a network connection are restricted by their lack of proximity to service offerings. In some cases, providers don't offer service to a specific location because of the lack of expected revenue. In other cases, physically connecting to the location is not feasible (financially or otherwise). In these situations, either a wireless (land-based) or satellite connection is the best alternative. These options have been available for decades, but the cost was prohibitive. This situation is slowly changing as more providers are getting into the business and offering service to rural or remote locations.

While point-to-point satellite offerings are still available at higher costs, what's becoming more popular is a satellite Internet connection. With an Internet connection, individuals or organizations can utilize virtual private networking (VPN) technologies to provide secure remote access to branch offices or locations that previously couldn't get access at all without a very high price tag.

Connection speeds on "typical" satellite Internet offerings, as of this writing, are limited to about 20 Mbps (max) downstream and about 2–7 Mbps upstream. This pricing is comparable to that of DSL or cable. The biggest thing to monitor is the amount of total traffic allowed per month without exceeding a designated cap. DSL and cable offerings don't usually have traffic caps. Satellite networks also introduce considerably more delay (>500 ms) into a connection than other alternatives experience. This lag may become an issue if delay-sensitive traffic is going to be transported over the connection.

Wireless Data

The spectrum of wireless data technologies is wide, as these technologies have been growing at an exponential rate along with wireless device adoption. Some of the most popular technologies:

  • Enhanced Data rates for GSM Evolution (EDGE)
  • Evolution-Data Optimized (EV-DO)
  • Universal Mobile Telecommunications System (UMTS)
  • Worldwide Interoperability for Microwave Access (WiMAX)
  • Evolved High-Speed Packet Access (HSPA+)
  • Long-Term Evolution (LTE)

As these technologies have evolved, they have been roughly classified into generations (2G, 3G, 4G, and so on). For example, some of the most common networks currently deployed in North America include EDGE (2G), EV-DO and HSPA+ (3G), and LTE (4G).

While these technologies are primarily used for mobile Internet access, they can also be used along with VPN technologies to connect remote offices securely. This type of configuration is gaining popularity as the prices of DSL and cable Internet technologies have stayed low. If these options are unavailable in a particular area, organizations are limited to wireless data or satellite options utilizing the same VPN technologies. However, these connections are limited by the traffic amount allowed and the speed of the connection.

Leased Lines

Leased lines have been around for decades, providing a dedicated circuit between two endpoints, but the bandwidth provided is static. The most common type of leased line is the T-carrier in North America and the E-carrier in Europe. Each of these circuit types can be ordered and configured in a number of different configurations.

The smallest of the T-carrier circuits is the T1, which offers 24–64 kbps channels (DS0), equaling 1.536 Mbps, plus 8 kbps of framing equals a 1.544 Mbps line rate. Circuits can be ordered either as full T1 or fractional T1. When a fractional T1 is selected, only a certain number of channels of the T1 are usable by the customer.

Another common T-carrier circuit is the T3, which delivers a line rate of 44.736 Mbps, equal to 28 different T1s or 672 DS0s (The difference is composed of various framing bits.)

Europe uses E-carrier circuits rather than T-carrier circuits. These are divided into E1 and E3, similar to the T1 and T3 in North America. The difference is the number of channels provided. The E1 provides 32 channels instead of 24, offering a total line rate of 2.048 Mbps. An E3 transports 16 E1s and offers a total of 512 channels (DS0), with a total line rate of 34.368 Mbps.

T1 and E1 lines are often used in combination with other technologies. For example, in North America it's common to order Frame Relay using a T1 as the access link (T1 is Layer 1 and Frame Relay is Layer 2). This can be delivered to a customer in a number of ways. It's possible for the whole T1 to be configured to the customer, but limited by the Frame Relay configuration. Another possibility is delivering a fractional T1, where the customer uses only a portion of the channels available in the T1. This type of configuration can be combined with a voice solution. When configured in this way, it's possible for data traffic to utilize a number of the channels while a voice service uses the others.

Summary

This article wraps up this three-part series on important WAN technologies. Now you're more familiar with wireless technologies that provide access for systems without other wired options, as well as the oldest of the WAN technologies, T- and E-carrier links. At this point, you should have a good general high-level understanding of these technologies, which can help you in your future understanding in the context of your specific environment.

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