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Frame Relays unique characteristics offer some distinct advantages over X.25, Switched 56/64 Kbps, and DDS. Additionally, Frame Relay is widely available both domestically and internationally. The market is highly competitive, which puts it in an advantageous position relative to other fast packet technologies (i.e., SMDS and ATM.)
Frame Relay Advantages
Advantages include its excellent support for bandwidth-intensive data and image traffic. Even stream-oriented traffic such as realtime voice and video can be supported, although not particularly effectively. The absolute speed of Frame Relay, its improved congestion control, and reduced latency certainly are improvements over X.25 networks. As Frame Relay is protocol-insensitive, it can carry virtually any form of data, and in variable-size frames. Bandwidth-on-demand, within the limit of the access line, is provided, with costs being reasonable for high-speed bursts. Additionally, the network is highly redundant, providing improved network resiliency.
The elimination of dedicated circuits makes Frame Relay highly cost-effective when compared to dedicated services such as DDS and T-carrier. Frame Relay is reasonably priced. In fact, savings of 30% to 40% over leased lines are commonly reported. Frame Relay costs, also, are scalable, maintaining a graceful relationship with the needs of the user organization in terms of bandwidth and number of terminating locations. Mesh networking, therefore, can be accomplished at reasonable cost, even on an asymmetrical basis.
Disadvantages
Disadvantages include its latency. Although it is an improvment over X.25, it does not compare well with SMDS and ATM. The latency issue can be significant when the service is used in support of SNA traffic, and renders Frame Relay largely unsuitable for voice and video. Additionally, only a few IXCs (e.g., LDDS Worldcom and MCI) currently offer high-speed Frame Relay service. Finally, the carriers have not come to terms on interconnectivity, leaving the user typically bound to a single carrier [11-18] and [11-3].
Frame Relay was designed to fill the gap between packet-switched networks (X.25), circuit-switched networks (Switched 56/64 Kbps), and dedicated data networks (DDS, T/E-Carrier). It is intended for intensive data communications involving block-level communications of data and image information. Frame Relay will support voice and low-speed video, although the quality can be generally is poor due to intrinsic latency (delay) and discarded frames during periods of network congestion due to heavy usage.
Frame Relay applications primarily, therefore, are data or image in nature. LAN internetworking, of course, is the driving force behind Frame Relay, although, controller-to-host, terminal-to-host, and host-to-host applications abound. The recent availability of dialup access also makes the service cost-effective for bandwidth-intensive telecommuting application. Internet Service Providers (ISPs) recently have made significant use of Frame Relay, both for user access to the ISP and for backbone network applications. For instance, the CompuServe network is about 60% Frame Relay and 40% X.25 [11-19].
An excellent example of the application of Frame Relay is that of the airline reservation networks, all of which are in the process of transition. Apollo Travel Services is converting its reservation network to Frame Relay to connect approximately 15,000 travel agency workstations at 1,000 sites. Owned by United Airlines, USAir, and Air Canada, Apollo expects response time to improve to two seconds from the current four seconds. The network will run at 56 Kbps, as opposed to the current 2,400 to 4,800 bps. Using AT&Ts InterSpan Frame Relay Service, running over a TCP/IP network platform, the service also will offer mesh networking between travel agencies, without the need to go through the Apollo head-end for e-mail and other purposes [11-20].
Voice over Frame Relay, over both private and public networks, is an option that recently has created a lot of interest. Although the voice stream is subject to intrinsic Frame Relay delays and although the service is overhead-intensive for such an application, it does allow the user organization to take advantage of occasional excess bandwidth to connect voice for free. [11-21], [11-22], [11-23], [11-24], [11-25], [11-26], and [11-27]. Advanced compression techniques such as ACELP (Algebraic Code-Excited Linear Prediction) appear to offer the best quality voice at 16 Kbps, 8 Kbps, and even 4.8 Kbps [11-28].
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