ATM Applications
ATM is a strong contender for multimedia, voice, data and video networks. These technologies require timing-dependent transfer methods. ATM can accommodate all these various forms of user applications. Any given network could be any combination of technologies and ATM is sufficient to carry the payload.
Timing-dependent transfer is becoming more and more of a concern today. Many applications that were once segmented fairly obviously as data, voice, video or multimedia are becoming blurred in today's marketplace. For example, a simple word processor today can include a mixed array of information presentation in other than a text format only. However, some fifteen or so years ago word processors were only that a word processor. Believe it or not, long ago, word processors were evaluated on their respective ability to do things like move a block of text (cut and paste) and other things considered rudimentary today. Many word processors today have the ability not only to import graphics but manipulate them. Some can even accommodate multimedia presentations.
Another reason for the use of ATM is the ability to accommodate a wide variety of implementations. For example, an ATM backbone could be the right fit for a company where heavy video and multimedia traffic occurs. In this type of environments,
some users probably need only minimum network support such as printing and e-mail. For network users who need only network printing and e-mail, use of ATM is overkill. But, on the flip side, users in a network where heavy video traffic is used might consume large capability of bandwidth. Hence, utilization of the network can be measured on a per person, per use basis. It might initially seem to cost too much to implement ATM for a complete enterprise wide network, but analyzing it from another perspective could easily tell a different story. For example, the requirements for 70 per cent of the network to function adequately might require ATM technology. The remaining 30 per cent might not come near this in requirement. The bottom line is this: If ATM is implemented enterprise wide, all users benefit. Hence, in accommodating all user's averages the price per person, per use goes down rather than up. The net effect is a well designed ATM network implementation that yields room to grow while accommodating immediate needs as well. Another strong reason for ATM use is the expandability in provider. If designed approximately, ATM can be scaled upward to accommodate the growth needs of any organization.

  FRAME RELAY
Frame relay is a high performance WAN protocol that operates at the physical and data link layers of the OSI reference model. Frame relay originally was designed for use across Integrated Services Digital Network (ISDN) interfaces. Today, it is used over a variety of other network interfaces as well.
Frame relay is an example of a packet-switching technology. Packet-switched networks enable end stations to dynamically share the network medium and the available bandwidth. The following two techniques are used in packet-switching technology

. Variable-length packets . Statistical multiplexing
Variable-length packets are used for more efficient and flexible data transfers. These packets are switched between the various segments in the network until the destination is reached.
Statistical multiplexing techniques control network access in a packet-switched network. The advantage of this technique is that it accommodates more flexibility and more efficient use of bandwidth. Most of today's popular LANs, such as Ethernet and Token ring, are packet-switched networks.
Frame relay is often described as a streamlined version of X.25, offering fewer of the robust capabilities, such as windowing and retransmission of last data that are offered in X.25. This is because frame relay typically operates over WAN facilities
that offer more reliable connection services and a higher degree of reliability than the facilities available during the late 1970's and early 1980's that served as the common platforms for X.25 WANs. As mentioned earlier frame relay is strictly a Layer 2 protocol suite, whereas X.25 provides services at Layer 3 (the network layer) as well. This enables frame relay to offer higher performance and greater transmission efficiency than X.25, and makes frame relay suitable for current WAN applications such as LAN interconnection.
Frame relay, designed in the late 1980s and widely developed in the 1990s, is in many ways a second-generation X.25. Like X.25, it uses virtual circuits. However, because the fibre-based systems of the 1990s have much lower bit error rates than
the copper-based systems of the 1980s, frame relay was naturally designed for much lower error rates. The essence of frame relay is a VC-based packet switching service with no error recovery and no flow control. Whenever a frame relay switch detects an error in a packet, its only possible course of action is to discard the data. This results in a network with lower processing overheads and higher transmission rates than X.25, but requires intelligent end systems for data integrity. In most cases today, the frame relay network is owned by a public network service provider. Frame relay is extensively used today to allow LANs on different corporate campuses to send data to one another at reasonably high speeds.

Public frame relay network interconnecting two Ethernets through routers located on the Ethernets. The dotted line represents a virtual circuit..IP routes, with each IP router in a different corporate campus. Frame relay offers a corporation an alternative to sending its intercampus IP traffic over the public Internet, for which the corporation may have reliability and security concerns.
Frame relay is subdivided into two operating phases, control and user. Control phase establishes and terminates logical connection and translates protocols between user and the networks. Error and flow control are also addressed in this plane. The user plane end-to-end functions include delimiting frames, aligning packets, multiplexing frames, controlling size to assure that a particular frame is neither too big nor too small for a designated system that falls under this plane.
The format of a frame relay is similar to that of an HDLC data link frame. It begins and ends with delimiting flags. Following the beginning flag is the frame relay header field, which describes the frame, more or less the same way as HDLC control field describes an HDLC frame.
Frame relay is good for data traffic because of its lower overhead (less than 10 header bytes for hundreds or thousands of data bytes) and variable length for varying message sizes. It is a poor routing protocol for integrated services since it exhibits variable delays through the transmission path. These delays cause distortions in video and other type of traffic.
Advantages:
Frame relay has several advantages over comparable wide area networks such as X.25 and T-lines.
• Frame relay operatas at a higher speed (1.544 Mbps and recently 44.376 Mbps). This means that it can easily be used instead of mesh of T-1 or T-3 lines.
• Frame relay allows bursty data. Users do not have to adhere to a fixed data rate as in the case of X.25 or T-lines.
• Frame relay allows a frame size of 9000 bytes, which can accommodate all local area network frames.
• Frame relay is less expensive than other traditional WAN's. Disadvantages:
Frame relay is not perfect. Despite its low cost, there are some disadvantages: • Although some frame relay networks operate at 44.376 Mbps this is still not high enough for protocols with even higher data rates (such as B-ISDN).
• Frame relay allows variable length frames. This may create varying delays for different users. A frame relay switch handles a large frame from one user and a small frame from another user the same way. They are stored in the same queue if they are going out the same interference. The delay of a small frame following a large frame may be different than the delay of a small frame following another small frame; users of small frames are punished.
• Because of varying delays, which are not under user control, frame relay is not suitable for sending delay sensitive data such as real time voice or video. For example, frame relay is not suitable for teleconferencing.

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