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Frame Relay For Wider Reach

Today's competitive business markets continue to shape the very nature of how we communicate. As the computing environment changes from a host-centric model to a network-centric model, corporations are redistributing network processing and utilizing the increased intelligence of network endpoints. New protocols and communication methods are taking advantage of this competitive potential, creating new demands for faster and more effective networks. Frame Relay is here to meet these demands.

What Is 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.

Simply put, Frame Relay is a way of sending information over a Wide Area Network (WAN) by dividing the information into frames or packets. Each frame has an address that the network uses to determine the destination of the frame. The frames travel through a series of switches within the Frame Relay network and arrive at their destination.

Along with the definition is the explanation of its functionality. Frame Relay is simply a programmed software located at the telephone company designed to provide more efficient, digital connections from one point to another. It is an emerging technology, which will provide a faster, and cost-effective method for accomplishing your computer networking.

Frame Relay is an example of a packet-switched technology. Packet-switched networks enable end stations to dynamically share the network medium and the available bandwidth.

Why Frame Relay?
Let's explore the network trends that contributed to the development of Frame Relay.

Need For Increased Speed
Today, rapid storage and retrieval of images for interactive applications is as common as transmitting full screens of text was in the 1970s and 1980s. Early graphics applications users who were accustomed to rapid information transfer over their LANs expected similar response times when transmitting data over the wide area network. Since peak bandwidth requirements for graphics were substantially higher than for text transactions, increased bandwidth and throughput were clearly required if response time expectations were to be met.

Dynamic Bandwidth Requirements
A typical LAN user followed a certain pattern in functioning which varied from high bandwidth bursts to periods of idle time "Bursty" traffic, as we call it, which is well-suited for statistical sharing of bandwidth, a characteristic of the Frame Relay technology.

Smarter Attached Devices
Decreasing cost of processing power resulted in the proliferation of intelligent PCs and powerful workstations and servers, all connected by LANs. These new end-user devices also offered the possibility of performing protocol processing, such as error detection and correction. This meant that the Wide Area Network could be relieved of the burden of application layer protocol processing--another perfect fit for Frame Relay.

Higher Performance
More LANs in general and Internet Protocol (IP) LANs in specific fuelled the need to internetwork LANs across the Wide Area Network, another factor that drove the growth of public Frame Relay services.

Frame Relay standards
The Frame Relay Forum has been instrumental in developing implementation agreements between its members to drive forward the early adoption of the Frame Relay protocol. To enable successful operation with both private and public Frame Relay networks, routers must conform to all the core standards of the Frame Relay protocol. These standards define the structure of the LAPD frame used by the Frame Relay protocol and are a basis for the addressing structure between the router and the network. In addition, the router requires information about the virtual connections provisioned by the Frame Relay service. This is achieved by signaling the User to Network Interface (UNI). All the major standards bodies have implementations for the UNI standard

1. CCITT I.233.1 [ Replaces I.122 ] ( T1.606 )
Frame Mode Bearer Services--Architectural Framework
2. CCITT Q.922 (ANSI T1.618) ISDN Data link Layer Specification for Frame Mode Bearer Services--Core Aspects of Frame Protocol
3. CCITT Q.933 (T1.617) ISDN Frame Mode Bearer Services Signaling Description--Signaling Specification for FRBS

How does Frame Relay work?
Similar to X.25, Frame Relay uses the concept of Virtual Circuits (VCs) to provide maximum bandwidth utilization and connectivity flexibility. A physical Frame Relay port can have multiple Virtual Circuits, each connecting to a different destination port. Unlike TDM (Time Division Multiplexing), where each application is assigned its own channel, such that idle bandwidth cannot be used, Virtual Circuits belonging to the same physical port can share all the available bandwidth so that applications can borrow from the unused idle bandwidth for a short duration to accommodate traffic burst.

To further optimize efficiency, Frame Relay takes advantage of the improvements in quality of digital transmission facility by using only the bottom two OSI (Open Systems Interconnection) protocol layers, rather than three as in the case of the X.25 protocol. (OSI is the international standard that defines an open systems connection by standardizing the interface for each layer; this assures the compatibility of multi-vendor hardware and software systems). By restricting its use to Layers 1 and 2, Frame Relay performs error detection only, whereas X.25 performs both error detection and retransmission. Frame Relay leaves retransmission up to the intelligent devices at each end of the network.

In the event of errors, Fame Relay simply drops bad frames to reduce overhead and enable greater throughput. Congestion is handled through vendor implementation of the congestion management techniques described in the Frame Relay standards. Standards-compliant congestion management means that, even during congestion, each end user device has guaranteed access to a defined amount of bandwidth.

Frame Relay also provides tremendous flexibility in terms of the types of devices that can be connected to the network. Because it is protocol transparent above Layer 2, the data link layer, most types of traffic can ride over a Fame Relay network without realizing that Fame Relay is being used. Because it is an access technique, Frame Relay is concerned only with the network interface; protocols determine the transfer of information on and off the WAN.

Virtual Circuits
Frame Relay technology is based on the concept of using Virtual Circuits (VCs). VCs are two-way, software-defined data paths between two ports that act as private line replacements in the network. While today there are two types of Frame Relay connections, Switched Virtual Circuits (SVCs) and Permanent Virtual Circuits (PVCs), PVCs were the original service offering. As a result, PVCs were more commonly used, but SVC products and services are growing in popularity.

Elements Of Frame Relay
Frame Relay networks are made up of Frame Relay access equipment, Frame Relay switching equipment, and public frame relay services.

Frame Relay access equipment is the customer premises equipment (CPE) that uses Frame Relay to send information across the wide area. Access equipment may be bridges, routers, hosts, packet switches, specialized Frame Relay "PADs" or any other similar devices.

Frame Relay switching equipment comprises devices that are responsible for transporting the Frame Relay compliant information offered by the access equipment. Switching equipment may be T1/E1multiplexers, packet switches, or any specialized Frame Relay switching equipment that implements the standard interface and is capable of switching and routing information received in Frame Relay format.

Public service providers (carriers) offer Frame Relay services by deploying Frame Relay switching equipment. Both Frame Relay access equipment and private Frame Relay switching equipment may be connected to services provided by a carrier. The service provider maintains access to the network via the standard Frame Relay interface and charges for the use of the service.

Benefits Of Frame Relay
Here are some of the benefits that Frame Relay offers.

Reduced Internetworking Costs
When using a private Frame Relay network, statistically multiplexed traffic from multiple sources over private backbone networks can reduce the number of circuits and corresponding cost of bandwidth in the wide area. Public Frame Relay services almost universally save money when compared with the equivalent service provided by dedicated leased lines.

Since Frame relay provides multiple logical connections within a single physical connection, access costs are also reduced. Equipment costs may be lowered by reducing the number of port connections required to access the network. For remote access devices, access line charges can be lowered by reducing the number of physical circuits needed to reach the networks.

Increased Performance With Reduced Network Complexity
Both by reducing the amount of processing (as compared to X.25) and by efficiently utilizing high-speed digital transmission lines, Frame Relay can improve performance and response times of applications.

Frame Relay reduces the complexity of the physical network without disrupting higher-level network functions. In fact, as discussed earlier, it actually utilizes the existence of these higher layer protocols to its advantage. It provides a common network transport for multiple traffic types while maintaining transparency to higher level protocols unique to the individual traffic types. The frames contain addressing information that enables the network to route them to the proper destination.

Interoperability With New Applications And Services
As compared with point-to-point leased lines, Frame Relay suits meshed networks and hub and spoke networks equally well. This means that Frame Relay easily accommodates new applications and future expansions of existing networks, for example, SNA migration to APPN.

In addition, Frame Relay standards have been developed to interwork with newly evolving services such as ATM. As new applications emerge and/or bandwidth requirements increase, networks can gracefully migrate to the appropriate technology without stranding existing network equipment.

Network Scalability, Flexibility And Disaster Recovery
To the end user, a Frame Relay network appears straightforward: one user simply connects directly to the Frame Relay cloud. A Frame Relay network is based on virtual circuits, which may be meshed, or point-to-point, and these links may be permanent or switched.

Because of this structure, Frame Relay is more easily scalable than a fixed point-to-point network. This means that additions and changes in a network are transparent to end users, giving telecommunications managers the flexibility to modify network topologies easily and scale networks as applications grow and sites are added. This inherent flexibility lends itself equally well to the provision of alternate routes to disaster recovery sites, which are, in many cases, transparent to the end user.

Choosing The Frame Relay Service
Today, Frame Relay is available worldwide from a large number of domestic and international carriers. These carrier services vary according to the capabilities of the platform on which the network is provisioned. It is important to understand the issues of Frame Relay service provisioning before committing to one particular service.

Frame Relay is a frame switched statistical multiplexed technology that provisions more bandwidth at the access layer (i.e. Frame Relay ports to the end users routers) than in the backbone. Thus the carrier then relies upon the statistically bursty nature of LAN interconnect traffic not to have too many coincidental bursts and congest the backbone network. However, the ratio of carrier access bandwidth to backbone bandwidth or 'overbooking' dictates the ability of the service to handle LAN bursts without becoming congested. Some carriers leave as much as 20 per cent of the trunk capacity free for data bursts while others overbook by as much as thirty times in order to gain backbone trunk efficiency.

Therefore it is important to understand the carriers' overbooking strategy within their Frame Relay network in order to select the service with the best potential for carrying "bursty" LAN traffic.

Tariffing also varies depending upon the carrier. There are many different methods of tariffing a Frame Relay service, however, most services are tariffed on a flat rate or fixed CIR (Committed Information Rate) basis. The tariff for the CIR will depend on size (i.e. 256 Kbps and 512 Kbps) and geographical distance. In addition, there are port charges for each Frame Relay port provisioned. Most likely, tariff structures will eventually move away from fixed CIR billing towards a usage based system in line with the implementation of SVC services.

The performance of the service is extremely important. It is essential that a high performance router is matched with an appropriate service. Additionally, it is important to ensure that switching performance nodal delay information is available from any prospective carrier. Remember that performance is also affected by the overbooking and congestion susceptibility of the network.

Application of Frame Relay
Originally Frame Relay was used predominantly for LAN interconnection. However, recent developments in various standards bodies have broadened its use to support delay-sensitive applications such as Voice over Frame Relay.

Retail, manufacturing, bank and finance are only a few of the industries now benefiting from Frame Relay's ability to provide affordable and efficient connectivity between many sites. Besides, the bandwidth sharing qualities of Frame Relay make it an attractive alternative to leased lines. Service providers also benefit because the efficient use of bandwidth enables them to support a larger customer base.

The most popular Frame Relay application provides companies with LAN to LAN communication. This allows companies to integrate their information systems in order to have employees throughout the enterprise to access specific information residing on a LAN somewhere in the enterprise. The devices on the LANs can communicate over the Frame Relay network regardless of their native protocol.

For example, native protocols that can traverse Frame Relay networks include SNA, DECnet, IPX, TCP/IP, and AppleTalk. Therefore, Frame Relay has the ability to make the users perceive that the entire company is on one large LAN. Application software such as groupware, e-mail, document sharing, database and many other LAN applications can utilize Frame Relay technology.

Frame Relay is a technology that can create a robust wide area networking fabric that integrates information systems together to form an enterprise network. It is an affordable and capable service for supporting today's bandwidth intensive applications as well as those residing on legacy systems. Because logical connections are defined in software, it is easy to manage moves, changes, additions, and deletions of logical connections. Systems analysts should consider the use of Frame Relay for corporate applications that incorporate information systems at more than one location because of the technical, financial and logistical advantages of the technology.

Advantages of Frame Relay

  • Lower cost of ownership.
  • Well-established and widely adopted standards that allow open architecture and plug-n-play service implementation.
  • Low overhead combined with high reliability.

Disadvantages of Frame Relay

Frame Relay offers users the ability to improve performance (response time) and reduce transmission costs dramatically for a number of important network applications. However in order to be effective, Frame Relay requires that two conditions be met:

1. The end devices must be running an intelligent higher layer protocol.
2. The transmission lines must be virtually error-free.

Some of the major applications of frame relay:

  • Meshed LAN Peer to Peer Networking
  • Systems Network Architecture over Frame Relay
  • Voice over Frame Relay (VoFR)
  • Frame Relay to A


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