The Frame Relay/ATM module covers all WAN technologies for permanent connectivity with remote locations.
Traditional Frame Relay and ATM are still used; however, despite the module's name, it also represents many modern technologies. The technologies in this module include the following:
■ Frame Relay is a connection-oriented, packet-switching technology designed to efficiently transmit data traffic at data rates of up to those used by E3 and T3 connections. Its capability to connect multiple remote sites across a single physical connection reduces the number of point-to-point physical connections required to link sites.
NOTE E3 is a European standard with a bandwidth of 34.368 megabits per second (Mbps). T3 is a North American standard with a bandwidth of 44.736 Mbps.
■ ATM is a higher-speed alternative to Frame Relay. It is a high-performance, cell-oriented, switching and multiplexing technology for carrying different types of traffic.
■ Leased lines provide the simplest permanent point-to-point connection between two remote locations. The carrier (service provider) reserves point-to-point links for the customer's private use. Because the connection does not carry anyone else's communications, the carrier can ensure a given level of quality. The fee for the connection is typically a fixed monthly rate.
■ SONET/SDH are standards for transmission over optical networks. Europe uses SDH, whereas North America uses SONET.
■ Cable technology uses existing coaxial cable TV cables. Coupled with cable modems, this technology provides much greater bandwidth than telephone lines and can be used to achieve extremely fast access to the Internet or enterprise network.
■ DSL uses existing twisted-pair telephone lines to transport high-bandwidth data, such as voice, data, and video. DSL is sometimes referred to as last-mile technology because it is used only for connections from a telephone switching station (at a service provider) to a home or office, not between switching stations. DSL is used by telecommuters to access enterprise networks; however, more and more companies are migrating from traditional Frame Relay to DSL technology using VPNs because of its cost efficiency.
■ Wireless bridging technology interconnects remote LANs using point-to-point signal transmissions that go through the air over a terrestrial radio or microwave platform, rather than through copper or fiber cables. Wireless bridging requires neither satellite feeds nor local phone service. One of the advantages of bridged wireless is its capability to connect users in remote areas without having to install new cables. However, this technology is limited to shorter distances, and weather conditions can degrade its performance.
■ MPLS combines the advantages of multilayer routing with the benefits of Layer 2 switching. With MPLS, labels are assigned to each packet at the edge of the network. Rather than examining the IP packet header information, MPLS nodes use this label to determine how to process the data, resulting in a faster, more scalable, and more flexible WAN solution.
NOTE Chapter 5, "Designing Remote Connectivity," discusses WANs in more detail.
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